Cell injury, cell death & adaptations by Dr Nadeem (RMC)

CELL INJURY,
CELL DEATH
&
ADAPTATIONS

An Overview
Introduction to Pathology
Overview of Cellular Response to Stress
and Noxious Stimuli
Cellular Adaptations to Stress
Hypertrophy
Hyperplasia
Atrophy
Metaplasia
Overview of Cell Injury and Cell Death
Causes of Cell Injury

An Overview…. contd
The Morphology of Cell and Tissue Injury
Reversible Injury
Necrosis
Patterns of Tissue Necrosis
Sub cellular Response to Injury
Mechanisms of Cell Injury
Depletion of ATP
Damage to Mitochondria
Influx of Calcium
Accumulation of Oxygen- Derived Free Radicals
( Oxidative Stress)
Defects in Membrane Permeability
Damage to DNA and Proteins

An Overview….. contd
Examples of Cell Injury and Necrosis
Ischemic and Hypoxic Injury
Ischemia – Reperfusion Injury
Chemical (Toxic) Injury
Apoptosis
Causes of Apoptosis
Mechanisms of Apoptosis
Examples of Apoptosis
Intracellular Accumulations
Pathologic Calcification
Cellular Aging

• Pathology is the scientific study of disease
• Pathos means - suffering
Logos means – study
• Pathology is the bridging discipline involving both basic
science and clinical practice and is devoted to the study of
the structural and functional changes in cells, tissues, and organs
that underlie disease.
• By the use of different techniques pathology attempts to explain
the whys and wherefores of the signs and symptoms manifested
by the patient while providing a sound foundation for rational
clinical care and therapy
• The ultimate goal of pathology is the identification of the causes
of disease, a fundamental objective leading to successful therapy
and disease prevention
DEFINITION OF PATHOLOGY

AIM OF PATHOLOGY LAB
Aim of pathology lab is to deliver accurate
and timely data to assist in the diagnosis
of disease and to monitor response to
treatment.

LEARNIING PATHOLOGY
Pathology is best learnt in two ways:
I. GENERAL PATHOLOGY:
•General Pathology is concerned with the basic reactions of cells
and tissues to abnormal stimuli that underlie all diseases
•General Pathology is our current understanding of the causation,
mechanisms and characteristic of the principal types of disease
process.
II. SYTEMETIC OR SYSTEMIC PATHOLOGY:
•Systemic Pathology examines the specific responses of
specialized organs and tissues to more or less well defined
stimuli.
•Systemic Pathology is the description of specific diseases as they
effect individual organs or organ systems (e.g. appendicitis, lung
cancer etc)

FOUR ASPECTS OF A DISEASE PROCESS THAT
FORM THE CORE OF PATHOLOGY
The four aspects of a disease process that forms the core of
pathology are :
(i) Etiology or the cause of the disease
(ii) Pathogenesis or the mechanisms of disease
development
(iii) Morphologic Changes or the structural alterations
induced in the cells and organs of the body
(iv) Clinical Significance of the functional consequences
of morphologic changes in the form of symptoms
and signs of the disease.

SKIN ABSCESS LUNG CANCER CIRRHOSIS HYPERTENSION
Characteristic of disease: The relationship between etiology, pathogenesis, morphological and
functional manifestations

Pathology is the foundation of medical science and practice.
Without pathology the practice of medicine would be reduced to
myths and folklore.
Experimental Pathology : Scientific knowledge about human
diseases is obtained from experimental studies on animals
Clinical Pathology: Scientific knowledge is obtained about
human diseases from observations on patients.
SCOPE OF PATHOLOGY

SUBDIVISIONS OF CLINICAL PATHOLOGY
Pathology is a vast subject with many ramifications. In
practice it has following major subdivisions:
• HISTOPATHOLOGY: The branch of pathology deals with the
the investigation and diagnosis of disease form the examination of
tissues
• CYTOPATHOLOGY: The investigation and diagnosis of disease
from the examination of isolated cells.
• HAEMATOLOGY: The branch of pathology which deals with
disorders of the cellular and coagulable components of blood.
• MICROBIOLOGY: The branch of pathology which deals with the
study of infectious diseases and the organisms responsible for
them

5. IMMUNOLOGY: The study of the specific defense mechanisms of
the body.
6. CHEMICAL PATHOLOGY: The study and diagnosis of disease
form the chemical changes in tissues and fluids.
7. GENETICS: The study of abnormal chromosomes and genes.
8. TOXICOLOGY: The study of effects of known or suspected
poisons.
9. FORENSIC PATHOLOGY: The application of pathology to legal
purposes (e.g. investigation of death in suspicious circumstances)

OVERVIEW OF CELLULAR
RESPONSES
TO
STRESS AND NOXIOUS
STIMULI

Cells are active participants in their
environment,constantly adjusting structure and
function to accommodate changing demands and
extracellular stresses
Cells tend to preserve their immediate
environment and intracellular milieu within a
relatively normal range of physiologic parameters

CELL INJURY AND CELL DEATH
Stress on cell
Cell tends to preserve its intracellular milieu within a relatively
narrow range of physiologic parameters
Cell undergoes Adaptation (Hyperplasia, Hypertrophy, Metaplasia)
Adaptive capability fails: Cell Injury develops
Reversible Cell Injury
Severe & persistent stress: Irreversible Cell Injury
Ultimately Cell Death by two processes
NECROSIS APOPTOSIS

Relationship between normal, adapted,
Reversibly injured and dead myocardial
cells. The cellular adaptation depicted
here is hypertrophy , the type of
reversible injury is ischemic coagulative
necrosis

Stages in the cellular response to stress and injurious stimuli

Relationship between normal, adapted, reversibly injured and dead myocardial cells
Figure page 2 tobbins
The cellular adaptation depicted here is hypertrophy, the type of reversible injury is ischemia, and the irreversible
injury is ischemic coagulative necrosis . In the example of myocardial hypertrophy (lower left) , the left ventricular
wall is thicker than 2 cm (normal, 1- 1.5 cm). Reversibly injured myocardium shows functional effects without any gross
or light microscopic changes , or reversible changes like cellular swelling and fatty change . In the specimen showing
necrosis (lower left) the transmural light area in the posterolateral left ventricle represents and acute myocardial
infarction

Adaptations are reversible changes in the number , size,
phenotype, metabolic activity, or functions of cells in response
to changes in their environment.
PHYSIOLOGIC ADAPTATIONS: Usually represent responses
of cells to normal stimulation by hormones or endogenous
chemical mediators (e.g., hormone – induced enlargement
of the breast and uterus during pregnancy)
PATHOLOGIC ADAPTATIONS: Are responses to stress that
allow cells to modulate their structure and functions and thus
escape injury

 The cells of the body continue to grow, divide and differentiate
throughout life. Normally, growth and differentiation are
controlled in such a way as to maintain the normal structure of a
particular tissue.
 The growth of a tissue reflects the net balance of cell proliferation
on one hand and cell differentiation, leading to cell death on the
other hand.
 Cells can respond to excessive physiologic stresses or pathologic
stimuli by undergoing a number of physiologic and morphologic
Cellular Adaptations , in which a new but altered steady state is
achieved, preserving the viability of the cell and modulating its
function as a response to such stimuli.

Cellular Adaptations can proceed by a number of
mechanisms:
(i) Up or down regulation of specific cellular receptors
(ii) Induction of new protein synthesis by target cells.
(iii) Switch from producing one type of protein to
another.
(iv) Marked overproduction of a specific protein.
(v) By the virtue of the interplay of a variety of growth
factors with their corresponding receptors

Different Cellular adaptive responses are:
(i) Hyperplasia
(ii) Hypertrophy
(iii) Atrophy
(iv) Metaplasia
CELLUAR ADAPTATIONS:

ABNORMALITIES OF CELL GROWTH AND MATURATION
•Abnormal Differentiation •Abnormal Differentiation • Abnormal Differentiation
•Replacement of mature and maturation and maturation
cells of one type with • Partial loss of control • Marked increase in cell
cells of another type and organization number
•Regular organization of • Slight increase in cells • Complete loss of control
of tissues maintained number • Variable loss of organization
• Cytologic abnormalities • Cytologic abnormalities
•Reversible • Partially Reversible • Irreversible
METAPLASIA DYSPLASIA NEOPLASIA
NORMAL CELL
ATROPHY HYPERTROPHY HYPERPLASIA
Decrease in cell size & Number Increase in cell size Increase in cell number

HYPERTROPHY
Hypertrophy constitutes an increase in the size of cells and with such
change an increase in the size of organ . Thus, there are no new cells, just large
cells. Moreover, these cells are not enlarged by simple cellular edema but by the
increased synthesis of more structural proteins and organelles.
Hypertrophy can be Physiologic or Pathologic and is caused by
increased functional demand or due to specific hormonal stimulation.
Pure hypertrophy without accompanying hyperplasia occurs in muscle ,
and the stimulus is almost a mechanical one
a) Cardiac Muscle Hypertrophy: Any demand for increased work load on cardiac
muscle, i.e., in hypertension, valvular lesions or congenital heart diseases, leads
to hypertrophy of the fibers of the chamber affected.

b) Smooth Muscle Hypertrophy: Any obstruction to the outflow of the
contents of a hollow viscus results in hypertrophy of its muscle coat. The
following are examples of smooth muscle hypertrophy:
(i) Bladder: Seen in Prostatic enlargement and Urethral stricture
(ii) Oesophagus: Seen in carcinoma
(iii) Stomach: Seen in pyloric stenosis due to ulcer
or carcinoma
(iv) Intestine: Stricture following Tuberculous enteritis
(v) Colon: Seen in carcinoma and diverticular disease
c) Skeletal Muscle Hypertrophy: The bulging muscle of the athlete
provide a simple illustration of hypertrophy due to a mechanical stimulus

Cardiac Hypertrophy
Cardiac Hypertrophy involving left ventricle. The number of myocardial
fibres does not increase, but their size can increase in response to an
increased work load leading to the marked thickening of the left ventricle
in this patient with Systemic Hypertension

Benign Prostatic Hyperplasia and Hypertrophy
The normal adult male prostate is about 3 to 4 cm in diameter. The
number of Prostatic glands, as well as stroma, has increased in this
enlarged prostate seen in cross section. The pattern of increase in
this case is uniform, but nodular

Physiologic Hypertrophy of the Uterus during Pregnancy
Figure Robbins page 3
A: Gross appearance of a normal uterus (right) and a gravid uterus (left) that was
removed for postpartum bleeding
B: Small spindle – shaped uterine smooth muscle cells from a normal uterus
C: Large , plump hypertrophied smooth muscle cells from a gravid uterus

Hypertrophy And Hyperplasia -Compared
Both are cellular responses to an increased demand for work.
The cells either enlarge or divide depending upon their growth
potentialities. The stimulus for this is usually mechanical in
hypertrophy, and chemical or hormonal in hyperplasia. When the
stimulus is withdrawn, the condition regresses and the tissue reverts
to normal . However, secondary structural alterations in the general
architecture due to an accompanying degeneration may render a
complete return to normal impossible.
Hypertrophy Hyperplasia
Stimulus in
Mechanical
Stimulus is
Chemical and
Hormonal

Hypertrophy And Hyperplasia -Compared

HYPERPLASIA
Hyperplasia constitutes an increase in the number of cells in
an organ or tissue, that also leads to an increase in size of an
organ and tissue
Hypertrophy and Hyperplasia are closely related and often
develop concurrently in tissues, so that both may contribute to an
overall increase in organ size.
It is important to note that those hyperplasia due to a
specific stimulus persist only for so long as that stimulus is
applied. When it is removed, the tissue tends to revert to its
normal size. In this respect hyperplasia differs from neoplasia,
for neoplastic tissue continues to grow even when the stimulus is
withdrawn.

Hyperplasia can be Physiologic or Pathologic:
(I) PHYSIOLOGIC HYPERPLASIA
a) Hormonal Hyperplasia: Exemplified by the proliferation of
glandular epithelium of the female breast at puberty and during
pregnancy
b) Compensatory Hyperplasia: Occurs when a portion of tissue
is removed or diseased. For example, when a portion of liver is
removed, hyperplasia by mitotic activity in the remaining cells
begins as early as 12 hours later, eventually restoring restoring
the liver to its normal weight – at which time cell proliferation
ceases. The stimuli for hyperplasia in this setting are
polypeptide growth factors. After restoration of the liver mass,
cell proliferation is “turned Off” by growth inhibitors

Pathologic Hyperplasia and Hypertrophy occur in the absence of an
appropriate stimulus of increased functional demand
(i) Endometrial Hyperplasia: After a normal menstrual period there is
a burst of essentially physiologic hyperplasia. This proliferation is
normally tightly regulated between stimulation by pituitary
hormones and ovarian Estrogen, and inhibition by Progesterone.
However, if the balance between estrogen and progesterone is
disturbed (e.g., if there is absolute or relative increases in estrogen),
Pathologic Hyperplasia results. Endometrial Hyperplasia is a
common cause of abnormal menstrual bleeding. It is important to
note that the hyperplasic process remains controlled. If Estrogenic
stimulation abates, the hyperplasia disappears. This differentiates
the process from cancer, in which cells continue to grow despite the
absence of hormonal stimulus.
Nevertheless, pathologic hyperplasia constitutes a fertile soil in
which cancerous proliferation may eventually arise. Thus patients
with hyperplasia of the endometrium are at increased risk of
developing endometrial cancer
PATHOLOGIC HYPEPRLASIA

(ii)Compensatory hyperplasia of bone marrow: Following
haemorrhage
(iii) Reactive hyperplasia of lymphoid tissue in response to antigenic
stimulation.
(iv) Thyroid Hyperplasia (Graves’ Disease): Result from the action of
auto antibodies which act on follicular cells of thyroid and then
lead to hyperplasia of follicular cells, which in turn leads to
increased release of T3 and T4
(v) Hyperplasia of the Prostate Gland: It is common in older age and
is due to hyperplasia of both glandular and the stromal element

Benign Prostatic Hyperplasia
Many glands with some intervening stroma. In the lumens of the
glands Corpora Amylacea is visible. The cells making up the glands
are normal in appearance, but they are increased in number.

HYPREPLASIA NEOPLASIA
Excited by a stimulus A stimulus is not always detected
Reversible, i.e., pathological
hyperplasia stops and
disappears if stimulus is
removed
Irreversible. i.e., cell proliferation
is unlimited and progresses
independent of stimuli
Proliferated cells are normal
shaped
Proliferated cells are abnormal in
shape
May be useful , i.e.,
compensatory hyperplasia
Harmful

ATROPHY
Atrophy is the decrease in size of cell or of an
organ by loss of cell substance
Atrophy represents a reduction in the structural components of the cell.
In the changing circumstances the cells adopt themselves to survive with
lesser amounts of cellular substance, hence a new equiblrium is
achieved.
Although atrophic cells may have diminished function, they are not
dead.
If the blood supply is inadequate even to maintain the life of shrunken
cells then atrophy may progress to the point at which cells are injured
and die. The atrophic tissue is then replaced by fatty in growth.

(I) PHYSIOLOGIC ATROPHY:
Physiologic Atrophy occurs at times from very early
embryonic life, as part of the process of morphogenesis. The process
of atrophy contributes to the physiological involution of different
organs
Some examples of Physiologic Atrophy are:
(i) Physiologic involution of Thymus.
(ii) post menopausal atrophy of Uterus
and Endometrium
(iii) Senile atrophy of cerebrum
(iv) Bone marrow atrophy in old age

(II)PATHOLOGIC ATROPHY
Pathologic atrophy depends on the basic cause and can
be local or generalized. The common causes of atrophy are:
(i) Decreased workload (Atrophy of Disuse):
a) Skeletal muscle atrophy , when a broken limb is immobilized
in a plaster cast.
b) Skeletal muscle atrophy when a patient is restricted to
complete bed rest.
(ii) Loss of innervation (Denervation Atrophy): Damage to the nerves
leads to the rapid atrophy of the muscle fibers supplied by those nerves,
for example in poliomyelitis and in paraplegics.
(iii) Diminished Blood Supply (Ischemia): In late adult life, the brain
undergoes progressive atrophy , presumably as atherosclerosis narrows
its blood supply.

(iv) Inadequate Nutrition:
a) Profound protein – calorie malnutrition (marasmus) is
associated with marked muscle wasting.
b) In starvation.
c) Cachexia: An extreme form of systemic atrophy, usually
seen in cancer patients
(v) Loss of Endocrine Stimulation:
Many endocrine glands, the breast, and the reproductive
organs are dependent on endocrine stimulation for normal function. Loss
of estrogen stimulation after the menopause results in physiologic
atrophy of the endometrium, vaginal epithelium and breast.
(vi) Aging (Senile Atrophy): The aging process is associated with cell loss.
Morphologically, it is seen in tissues containing permanent cells,
particularly in the brain and heart.

(vii) Pressure: Tissue compression for any length of time can cause
atrophy. An enlarging benign tumour can cause atrophy in the
surrounding compressed tissues. Atrophy in this setting is probably
the result of ischemic changes caused by a blockade of blood supply
produced by the expanding mass

Testicular Atrophy
Atrophy testis : Right testis undergo atrophy and is much smaller
than the normal testis at the left

Atrophy Brain
Cerebral atrophy in a patient with Alzheimer disease. The gyri are
narrowed and the intervening sulci widened particularly pronounced
towards the frontal lobe

A. Physiologic atrophy of the brain in an 82 years old man
B. Normal brain of a 36 years old male

METAPLASIA
Metaplasia is a reversible change in which one adult
cell type (epithelial or mesenchymal) is replaced by another
cell type.
Metaplasia often represents an adaptive response of a
tissue to some stress, and is presumed to be due to the activation and/or
repression in tissue stem cells of group of genes involved in tissue
differentiation. The transdifferentiated cells replace the original cells.
Metaplasia is of two types
1. Epithelial Metaplasia
- Columnar to Squamous
- Squamous to Columnar
2. Connective Tissue Metaplasia

Stress Stimuli
Elaboration of Growth Factors, Cytokines, etc
Pluripotent Mesenchymal Stem Cell
Reprogramming of Stem Cell
Metaplasia
Can lead to Dysplasia, if stress or stimulus persists
Dysplasia can then lead to Carcinoma

EPITHELIAL METAPLASIA
(i)Squamous metaplasia:
The most common epithelial metaplasia is Columnar to
Squamous . In different conditions under conditions of stress, the
fragile columnar epithelium is replaced by more rugged stratified
epithelium, which can withstand the adverse environment. Common
examples of squamous metaplasia are :
a) In respiratory tract of cigarette smokers the normal columnar
ciliated epithelial cells of trachea and bronchi are often replaced by
stratified squamous epithelial cells.
b) Stones in the excretory ducts of the salivary glands, pancreas or
bile ducts may cause replacement of the normal secretary columnar
epithelium by non functioning stratified squamous epithelium
c)Transitional bladder epithelium in the presence of stones, and in
the presence of ova of the trematode Schistosoma Haematobium get
transformed into squamous epithelium.

Schematic Diagram of Columnar to Squamous Metaplasia

Metaplasia of Respiratory Epithelium
Metaplasia of laryngeal respiratory epithelium has occurred here in a
smoker . The chronic irritation has led to an exchange of one type of
epithelium (the normal respiratory epithelium at the right ) for another
( more resilient squamous epithelium at the left). Metaplasia is not a
normal physiologic process and may be a first step toward neoplasia

(ii)Columnar Metaplasia:
Metaplasia from squamous to columnar type may also occur:
a)Barrett Esophagitis: In this condiiton the
squamous esophageal epithelium is replaced
by intestinal-like columnar cells. The resulting
cancers that may arise are glandular (adeno)
carcinomas.
b) Cervical Erosion: Squamous epithelium of cervix
is replaced by columnar epithelium.
Metaplastic transformation
Of esophageal stratified
squamous epithelium
to mature columnar
epithelium (so-called
Barrett metaplasia)

Metaplasia of the normal esophageal squamous mucosa has occurred,
with the appearance of gastric type columnar epithelium

In all these instances the more rugged stratified squamous
epithelium is able to survive under the circumstances in which the
more fragile specialized epithelium most likely would have
succumbed, so the metaplastic tissue is better able to withstand the
adverse environmental changes.
Epithelial Metaplasia is a two –edged sword and, in most
circumstances, represents an undesirable change. Moreover, the
influences that predispose to such metaplasia, if persistent, may
induce cancer transformation in metplastic epithelium.

CONNECTIVE TISSUE METAPLASIA
Connective tissue metaplasia is the formation of cartilage,
bone or adipose tissue (mesenchymal tissues) in tissues that
normally do not contain these elements. For example, bone
formation in muscle, designated Myositis Ossificans ,
occasionally occur after bone fracture.
This type of metaplasia is less clearly seen as an adaptive
response.

Hyperplasia Versus Metaplasia
Hyperplasia Metaplasia
Definition
It is an increase in the number of cells in an organ or
tissue usually resulting in an increase in volume of
the organ or tissue
It is a reversible change in which one type of cell is
differentiated into another type of differentiated
epithelium
Cause
Physiological or Pathological Pathological
Mechanism
Increased production of growth factors, growth
factor receptors, activation of signaling pathways,
production of transcription factors leading to
cellular proliferation
Result of reprogramming of stem cells; Precursor
cells differentiate along a new pathway; Tissue
specific and differentiation genes are involved in
process
Examples
Physiological: Uterus, breast growth during
pregnancy; Compensatory hyperplasia in unilateral
nephrectomy and partial hepatectomy
Pathological: Parathyroid hyperplasia occurring in
chronic renal failure; thyroid hyperplasia in graves
disease; Benign prostatic hyperplasia ;endometrial
hyperplasia
Squa mous metaplasia : gall bladder, renal pelvis
and bladder, uterus/cervix, bronchial, prostatic
Columnar Metaplasia: Barret’s esophagus, cervical
erosion, chronic bronchitis, bronchiactasis,
fibrocystic disease with apocrine metaplasia
Osseous metaplasia: Aging process in costal and
thyroid cartilage, in scars, areas of dystrophic
calcification , myositis ossificans

DYSPLASIA
Dysplasia is a premalignant condition characterized by the
loss of the uniformity of the individual cells as well as a loss in their
architectural orientation.
•Dysplasia can be caused by longstanding irritation of a
tissue, with chronic inflammation, or by exposure to carcinogenic
substances.
•Dysplasia may occur in tissues which has coincident
metaplasia, e.g. dysplasia developing in metaplastic squamous epithelium
from the bronchus of smokers
•Dysplasia may also develop without co-existing
metaplasia , for example in squamous epithelium of the uterine cervix,
glandular epithelium of the stomach or the liver
•Dysplasia may be present for many years before a
malignant neoplasm develops, and this observation can be used to screen
populations at high risk of developing tumours

Dysplatic cells exhibit following characteristic findings:
I) Cellular Pleomorphism: Cells show variations in size & shape
ii)Hyperchromatic Nuclei: Deeply stained nuclei, which are
abnormally large for the size of cell.
iii)Increased Mitotic Activity: Mitotic figures are more
abundant than usual, although almost invariably they conform
to normal patterns. In dysplasia the mitoses are not confined
to the basal layers and may appear at all levels and even in
surface cells.
(iv) Architectural Anarchy : There is considerable architectural
anarchy. For example, the usual progressive maturation of tall
cells in the basal layer to flattened squames on the surface
may be lost and replaced by a disordered scrambling of dark
basal- appearing cells. This is also labeled as ‘loss of
epithelial polarity’
(v)Carcinoma in situ: When dysplastic changes are marked and
involve the entire thickeness of the epithelium, but the
basement membrane is intact the lesion is considered as
preinvasive neoplasm and is referred as carcinoma in situ.

DysplasiaNormal
Carcinoma in situ
Invasion
Metastasis

DYSPLASIA CERVIX
The normal cervical squamous epithelial at left transform to dysplastic
change at right. There is also underlying chronic inflammation because
abnormal epithelial surfaces do not provide the same protective barrier
as normal epithelial surfaces do

PAP SMEAR CERVIX
PAP SMEAR: Cytologic features of normal squamous epithelial cells can be
seen at the center top bottom, with orange to pale blue plate- like squamous
cells that have small pyknotic nuclei . The dysplastic cells in the center
extending to upper right are smaller with darker, more irregular nuclei

Overview of
Cell Injury
&
Cell Death

Cell injury results when cells are stressed so severely that
They are no longer able to adept or when cells are exposed
to inherently damaging agents or suffer from intrinsic
Abnormalities
Reversible Cell Injury
In early stages or mild forms of injury the functional and
morphological changes are reversible if the damaging
stimulus is removed.
At this stage ,although there may be significant structural
and functional abnormalities, the injury has typically not
progressed to severe membrane damage and nuclear
dissolution
Cell Death
With continuing damage the injury becomes irreversible,
at which time the cell cannot recover.
There are two types of cell death:
(i) Necrosis
(ii) Apoptosis

Causes of Cell Injury
Causes of cell injury range from the gross
physical trauma of a motor vehicle accident to
the single gene defect that results in a defective
enzyme underlying a specific metabolic disease

CAUSES OF CELL INJURY
1. Oxygen Deprivation (Hypoxia)
(i) Ischemia: Loss of blood supply to a tissue
(ii) Anaemia: Decreased haemoglobin, which in turns leads to
decreased oxygenation
2. Physical Agents
(I )Mechanical trauma.
(ii) Extremes of temperature (burns and deep cold)
(iii) Radiation and Electric shock
3. Chemical Agents and Drugs
(i) Poisons such as Arsenic and Cyanide
(ii) Glucose or salts in hypertonic concentrations
(iii) Environmental or Air Pollutants
(iv) Alcohol and Narcotic Drugs
(v) Insecticides and herbicides

4. Infectious Agents
Like Viruses, Bacteria, Fungi, Parasites
5. Immunologic Reactions: Immune system serves as defense against
biologic agents; Immune reactions may in fact, cause cell injury ,
for example:
(i) Autoimmune Diseases
(ii) Anaphylactic Reactions
6. Genetic Derangements: Genetic defects may result in pathologic
changes as conspicuous and obvious as the congenital
malformations associated with down syndrome or a subtle as the
single amino acid substitution in haemoglobin S of Sickle Cell
Anaemia
7. Nutritional Imbalances
(i) Protein Calorie Deficiencies
(ii) Vitamin Deficiency
(iii) Lipids excess predispose to Atherosclerosis
8. Aging
Cellular senescence leads to alterations in replication
and repair abilities of individual cells and tissues.
All of these changes result in a diminished ability to respond to
damage and, eventually , the death of cells and of the organism

Morphology
of
Cell
and
Tissue Injury

All stresses and noxious influences exert their effects first
at the molecular or biochemical levels.
Cellular functions may be lost long before cell death occurs,
and the morphologic changes of cell injury (or death) lag
behind both .
The cellular derangements of reversible injury can be
repaired and, if the injurious stimulus abates , the cell
will return to normalcy.
Persistent or excessive injury , however , causes cell to pass
into the stage of irreversible cell injury and cell death.

Schematic diagram demonstrating the relationship between cellular function,
cell death, and the morphologic changes of cell injury. Note that cells may
become rapidly nonfunctional after the onset of injury , although they are
still viable with potentially reversible changes; a longer duration of injury
may eventually lead to irreversible injury and cell death

Point of No Return
Two phenomena consistently characterize irreversibility :
(1)The inability to reverse mitochondrial dysfunction
(lack of oxidative phosphorylation and ATP generation)
even after resolution of original injury
(2) Profound disturbances in membrane function

Reversible Cell Injury: Morphologic Changes
The two main morphologic correlates of reversible
cell injury are:
(i) Cellular Swelling: It is the result of failure of energy
dependent ion pumps in the plasma membrane, leading
to an inability to maintain ionic and fluid homeostasis.
(ii) Fatty Change: It occurs in hypoxic injury and various
forms of toxic or metabolic injury. It is manifested by the
appearance of small or large lipid vacuoles in the cytoplasm.
It occurs mainly in cells involved in and dependent on
fat metabolism, such as hepatocytes and myocardial cells

Reversible Cell Injury: Morphologic Changes….. contd
(i) Cellular Swelling
It is the first manifestation of almost all forms of injury to cells.
It is difficult to appreciate with light microscope; it may be more
apparent at the level of whole organ.
Gross Examination: When it effects many cells in an organ,
it causes some pallor, increased turgor, and increase
in weight of the organ.
Microscopic Examination: May reveal small, clear vacuoles ,
within the cytoplasm ; these represent distended and pinched
off segments of the endoplasmic reticulum .
This pattern of non- lethal injury is sometimes called hydropic
change or vacuolar degeneration.

(ii) Fatty Change
It is manifested by the appearance of lipid vacuoles in the
cytoplasm . Injured cells may also show increased
eosinophilic staining . This eosinophilic staining becomes
more pronounced with progression to necrosis

Ultra structural changes of Reversible Cell Injury
(1)Blebbing of plasma membrane
(2)Blunting or distortion of microvilli
(3)Loosening of intercellular attachments
(4)Swelling and appearance of phospholipid – rich
amorphous densities in mitochondria
(5) Dilation of endoplasmic reticulum
(6) Detachment of ribosomes
(7) Nuclear alterations with clumping of chromatin

Morphologic changes in reversible and irreversible
cell injury (necrosis)
Normal kidney tubules with viable epithelial cells

Early (reversible) ischemic injury showing surface blebs,
Increased eosinophilia of cytoplasm ,and swelling of
occasional cells.

Necrotic (irreversible) cell injury of epithelial cells with loss of nuclei
and fragmentation of cells and leakage of contents

A normal cell and changes in
reversible and irreversible
cell injury (Necrosis)

NECROSIS
“Sum of the morphologic changes that follow
cell death in a living tissue or organism’’.
Two mechanisms are involved in necrosis:
1. Enzymatic digestion of cells by catalytic
enzymes
(i) Autolysis: Catalytic enzymes derived from
the lysosomes of dead cells.
(ii) Heterolysis: Catalytic enzyme derived from
lysosomes of immigrant leucocytes.
2. Denaturation of Proteins

TYPES OF NECROSIS
Several distinct types of necrosis are
recognized:
1. Coagulative Necrosis
2. Liquefactive Necrosis
3. Caseous Necrosis
4. Gangrenous Necrosis
5. Fibrinoid Necrosis
6. Fat Necrosis

Morphologic Changes in Necrosis
A. Changes in Cytoplasm
•Increased Eosinophilia: It is due to:
a) Loss of normal basophilia imparted by RNA in the
cytoplasm
b) Increased binding of Eosin to denatured
intracytoplasmic proteins
•Cell will assume a glassy homogenous appearance . It is
due to loss of glycogen particles
•Due to digestion of cytoplasmic organelles by enzymes, the
cytoplasm will appear vacuolated and appear moth- eaten
•Calcification of dead cell may occur
B. Changes in Nucleus
•Pyknosis: Shrinkage of nucleus
•Karyolysis: Dissolution of nucleus
•Karyorrhexis: Fragmentation of nucleus

I.CAOGULATIVE NECROSIS
Coagulative Necrosis is the most common type of necrosis.
The process of coagulative necrosis, with preservation of the
general tissue architecture is characteristic of hypoxic death of
cells ( due to lack of blood supply) in all tissues except brain
The pathogenesis of coagulative necrosis is denaturation of
proteins.
Myocardial Infarction is an important example of
coagulative necrosis. It is also seen in infarcts of heart, kidney
and spleen.
Part of kidney deprived of its blood
supply by an arterial embolus. This
is an example of caogulative necrosis
Cellular and nuclear detail has been
Lost. The ghost outline of a glomerulus
can be seen in the centre, with
remnants of tubule elsewhere

Fig A Fig B
Fig A: Normal Myocardium
Fig B: Myocardium with coagulation necrosis (upper two thirds of figure),
showing strongly eosinophilic anucleate myocardial fibers.
Leucocytes in the interstetium are an early reaction to necrotic
muscle .
Compare with A and with normal fibers in the lower part of figure

COAGULATIVE NECROSIS – MYOCARDIAL INFARCTION
When there is marked cell injury, there is cell death. This microscopic
appearance of myocardium is a mess because so many cells have
died that the tissue is not recognizable. Many nuclei have become
Pyknotic (shrunken and dark) and have then undergone Karorrhexis
(fragmentation) and Karyoloysis (dissolution) . The cytoplasm and
cell borders are not recognizable

II. LIQUEFACTIVE NECROSIS
Liquefactive Necrosis is characteristically seen in:
(i) Hypoxic death of cells within the central nervous
system
(ii) Bacterial or occasionally fungal infections.
Liquefaction completely digests the dead cells. The
end result is transformation of the tissue into a liquid
viscous mass. If the process had been initiated by acute
inflammation, the material is frequently creamy yellow
because of the presence of dead white cells and is called
pus.
A focus of liquefactive necrosis in the
kidney caused by fungal seeding. The
focus is filled with white cells and
cellular debris, crating a renal abscess
that obliterates the normal architecture

LIQUEFACTIVE NECROSIS BRAIN
Grossly , the cerebral infarction at the upper left here demonstrates
liquefactive necrosis. Eventually, the removal of dead tissue leaves
behind a cavity.

Normal Cell
Lethal
Injury
Cytoplasm organelles lost,
Cytoplasm appears
Eosinophilic and uniform
Nuclear
Pyknosis
End Result: Cell retaining
membrane and coagulated
cytoplasm with absent nucleus
Karyorrhexis
Cells retain outline
necrotic area is
solid composed of
ghost cells
Cells have undergone
lysis, so that necrotic
area is converted to
fluid- filled cyst
LIQUEFACTIVE
NECROSIS
COAGULATIVE
NECROSIS

III. CASEOUS NECROSIS
A distinctive form of coagulative
necrosis . It is encountered most often in foci of
Tuberculosis Infection.The term caseous is derived
from gross appearance of tissue (white and cheesy)
Microscopic Appearance: The necrotic focus
appears as amorphous granular debris composed of
fragmented, coagulated cells and amorphous
granular debris enclosed within a distinctive
inflammatory border known a
“ Granulomatous Reaction”

Gross Appearance of Caseous necrosis: Foci of caseous necrosis in
Tuberculosis of Lung
Microscopic Appearance of Caseation Necrosis: Characteristic Tubercle
showing central necrosis, along with epithelioid cells, multinucleated
Giant cells and lymphocytes

EXTENSIVE CASEOUS NECROSIS LUNG IN TUBERCULOSIS
Extensive caseous necrosis lung in Tuberculosis, with confluent cheesy
granulomas in the upper portion.

IV. GANGRENOUS NECROSIS
• Gangrene is massive necrosis (Caused by acute ischemia or severe
bacterial infection) followed by putrefaction
•Gangrene is a special type of necrosis, in which bacterial infection
is superimposed on coagulative necrosis and coagulative necrosis is
modified by the liquefactive action of the bacteria
•The bacteria proliferate in and digest the dead tissue often with the
production of foul smelling gases. The tissue becomes green or black
because of the production of iron sulphide from degraded
haemoglobin (PUTREFACTION)
There are two main types of gangrene: (i) primary ; (ii)
Secondary
(I) Primary (Gas Gangrene): It is due to infection
of deep contaminated wounds in which there is
considerable muscle damage, by bacteria of the
CLOSTRIDIA group- anaerobic spore forming gram
positive bacilli which produce saccharolytic and
proteolytic enzymes resulting in digestion of muscle
tissue with gas formation. The infection rapidly
spreads and there is associated severe toxaemia
(spread of poisons in the blood)

(ii) Secondary Gangrene: This is due to invasion of necrotic tissue
usually by a mixed bacterial flora including putrefactive organisms
and occurs in two forms:
a) Wet gangrene: It occurs due to Arterial and venous occlusion. The
tissues are moist at the start of the process either due to oedema or
venous congestion. Examples are in strangulation of viscera and
occlusion of leg arteries in obese diabetic patients
b) Dry Gangrene: It occurs due to
Arterial occlusion. Occurs especially in the toes
and feet of elderly suffering from gradual
arterial occlusions; the putrefactive process
is very slow and only small numbers of
putrefactive organisms are present.
In Dry gangrene distal to arterial occlusion, tissue fluid formation will
stop, but since veins are patent, the already present tissue fluid will be
drained into the veins as normal

DRY GANGRENE WET GANGRENE
Due to Arterial occlusion Due to Arterial and Venous occlusion
Occurs n limbs in cases of
- Senile gangrene
- Berger's gangrene
- Raynaud’s disease
- Sometimes in diabetic gangrene
Occurs in limbs in
- Crush injuries
- Tight tourniquets
- Bed sores
- Diabetic gangrene
Does not occurs in internal organs Occurs in internal organs (intestine)
Very slow Putrefaction Rapid Putrefaction decomposition of dead
tissue by bacteria leading to formation of
iron sulphide, which in turns impart
greenish – black colour to tissue)
Mild Toxemia Severe Toxemia
Gangrenous part is dry and mummified Gangrenous part is swollen
Prominent line of demarcation(Dead
gangrenous part separates from the
living part very distinctively)
Poor line of demarcation

DRY GANGRENE TOES
This is Gangrene, or necrosis of toes. The toes were involved in
a frost bite injury. This is an example of ‘dry gangrene’ in which
there is mainly coagulative necrosis due to anoxic injury

WET GANGRENE LEG
This is Gangrene of the lower extremity . In this case the term ‘wet
gangrene’ is more applicable because of the liquefactive component
from superimposed infection in addition to the coagulative
necrosis from loss of blood supply. This patient had Diabetes
Mellitus.

V: FAT NECROSIS
Fat Necrosis may be due to:
(i) Direct Trauma to adipose tissue and extracellular
liberation of fat. The result may be a palpable mass,
particularly at a superficial site such as the breast
(ii) Enzymatic lysis of fat due to release of
Lipases. In Acute Pancreatitis there is release of
pancreatic lipase. As a result, fat cells have their stored fat
split into fatty acids, which then combine with calcium to
precipitate out as white soaps.

FAT NECROSIS PANCREAS
Cellular injury to the pancreatic acini leads to release of powerful
enzymes which damage fat by the production of soaps (combination
of calcium salts with fat’ ;fat saponification)), and these appear
grossly as the soft Chalky white areas seen in this cut
surface

Fat Necrosis in acute pancreatitis: The areas of chalky white deposits
represents foci of fat necrosis with calcium soap formation
(Saponification) at sites of lipid breakdown in the mesentery

VI. FIBRINOID NECROSIS
Fibrinoid Necrosis is a type of Connective Tissue Necrosis It
is seen particularly in conditions where there is Deposition of
Antigen – Antibody Complexes . The important examples
are Autoimmune Disorders like Systemic Lupus Erythematosus ,
Rheumatic Fever and Polyartirtis Nodosa. In these conditions the
media and smooth muscle of blood vessels are especially involved
Fibrinoid Necrosis is characterized by loss of normal
structure and replacement by a
homogenous, bright pink-staining
necrotic material that resembles
fibrin microscopically.
Note, however, that “fibrinoid” is not
The same as occurs in inflammation
and blood coagulation. Areas of
fibrinoid necrosis contains various
amounts of Immunoglobulins,
complement, albumin, break down
products of collagen and fibrin

Fibrinioid Necrosis in an artery in a patient with polyarteritis nodosa.
The wall of the artery shows a circumferential bright pink area of necrosis
with protein deposition and inflammation ( dark nuclei of neutrophils)

Differences Between Different Types of Necrosis
CAGULATIVE
NECROSIS
LIQUEFACT-
IVE
NECROSIS
CASEOUS
NECROSIS
FAT
NECROSIS
FIBRINOID
NECROSIS
Occurs due to
ischemia
Occurs due to
ischemia
Occurs due to
granuloma-tous
disease
Occurs due to
trauma or
enzymatic fat
injury
Due to vascular
inflammation
In various
tissues
In Brain In any tissue In Pancreas
and Breast
Around Blood
Vessels
Tissue
architecture
preserved
Architecture
destroyed
Cheesy
material;
Architecture
disturbed
Architecture
distorted
Architecture
not much
affected
Involves
denaturation of
protein &
lysosomal
enzymes
Denaturation
of Proteins &
Autolysis
Caseation Rupture of Fat
cells
Accumulation
of Fibrinoid
material

Biochemical Markers of Necrosis
Enzymes Tissue
Creatinine Kinase(MB isoenzyme) Heart
Certainties Kinase(BB isoenzyme) Brain
Creatinine Kinase(MM isoenzyme) Skeletal Muscle
Lactic Dehydrogenase(Isoenzyme 1) Heart, Erythrocytes, Skeletal Muscle
Lactic Dehydrogenase (Isoenzyme 5) Liver, Skeletal Muscle
Aspartate Aminotransferase(AST)
(Glutamic Oxaloacetate
Transferase ; SGOT)
Heart, Liver, Skeletal Muscle
Alanine Aminotransferase (ALT)
(Glutamic Oxaloacetic Transferase ;
SGPT)
Liver, Skeletal Muscle
Amylase Pancreas, Salivary Gland

SEQUALAE OF CELL DEATH
Eventually, in the living patient, most necrotic cells and
their debris disappear by a combined process of extracellular enzyme
digestion and leucocyte phagocytosis. If necrotic cells and cellular debris
are not promptly eliminated, they tend to attract calcium salts and other
minerals and become calcified
Cell Death
Necrosis
Further Autolysis Putrefaction Dystrophic
and Inflammation Calcification
Demolition Gangrene
Absorption
Repair Regeneration

Necrosis: Summary
• Necrosis is death of tissues: causes include ischemia, metabolic,
trauma.
• Coagulative necrosis is seen in the most tissues; firm pale area,
with ghost outlines on microscopy.
• Liquefactive necrosis is seen in the brain; the dead area is
liquefied.
• Caseous necrosis is seen in tuberculosis; there is pale yellow semi-
solid material
• Gangrene is necrosis with putrefaction: it follows vascular
occlusion or certain infections and is black .
• Fibrinoid necrosis is a microscopic feature in arterioles in where
there is antigen- antibody complexes accumulation.
• Fat necrosis may follow trauma (e.g., in breast) and cause a mass,
or may follow pancreatitis visible as multiple white spots

APOPTOSIS
“Programmed Cell Death”
• It is a form of cell death designed to eliminate unwanted host cells
through activation of coordinated, internally programmed series of
events effected by a dedicated set of gene products.
• Apoptosis occurs when a cell dies through activation of an
internally controlled suicide program.
• It is a subtly orchestrated disassembly of cellular components
designed to eliminate unwanted cells, during embryogenesis and in
various physiologic processes.
• Doomed cells are removed with minimum disruption to the
surrounding tissue.
• It also occurs, however, under pathologic conditions , in which it
is sometimes accompanied by necrosis

Control of tissue growth by induction or inhibition of
Apoptosis: Quiescent (mitotically inactive) cells in G0 are recruited into a high
turnover (mitotically active) state by growth factors. Their subsequent fate depends
on the presence or absence of apoptosis inducers or inhibitors.
Apoptosis inducers are mediated by bax protein
Apoptosis inhibitors are mediated by bcl – 2 protein

Apoptosis refers to a mechanism of cell death affecting
usually single cells or a group of cells scattered in a population
of healthy cells. It differs from necrosis and represents most of
the times a physiological or at times a pathological response by
which effete cells and abnormal cells die and are eliminated.
The process is rapid and ( completed in few hours), and is
considered in 2 stages:
Stage 1 (Dying Process):
a) Active metabolic changes in the cell cause cytoplasmic and
nuclear condensation and nuclear membrane is intact.
b) Cell disintegrates into multiple Apoptotic Bodies , each
surrounded by a part of plasma membrane.
Stage 2 (Elimination Process): Phagocytosis of Apoptotic
Bodies by surrounding cells ,e.g., liver cells, tumour cells.
This is followed by rapid digestion. The surrounding cells move
together to fill the vacant space leaving virtually no evidence of
the process.

PATHOGENESIS OF APOPTOSIS
Apoptosis results from the action of intacellular
cysteine protease called CASPASES which are activated
following cleavage and lead to endonuclease digestion of DNA and
disintegration of the cell skeleton.
There are two major pathways by which caspases are
activated:
(i) Activation through Death Factor (Fas Ligand): The is by signaling
through membrane proteins such as Fas or TNF receptor intracellular
death domain. An example of this mechanism is shown by activated
cytotoxic T cells expressing Fas ligand.
(ii) Release of Cytochrome – C from the Mitochondria: The second
pathway is via the release of Cytochrome – C from mitochondria .
Cytochrome – C binds to Apaf – 1 which then activates caspases.
DNA damage induced by irradiation or chemotherapy may act
through this pathway.

Representation of apoptosis. Apoptosis is initiated via two main stimuli (i) Signaling
through cell membrane receptors such as FAS tumor necrosis factor (TNF) receptor
or (ii) release of cytochrome c from mitochondria. Membrane receptors signal apoptosis
through an intracellular death domain leading to activation of caspases
which digest DNA. Cytochrome C binds to the cytoplasmic protein Apaf -1 leading to
activation of caspases.The intracellular ratio of pro(e.g. BAX) or anti-apoptotic
(e.g. BCL) factors may influence mitochondrial Cytochrome- C release. Growth factors raise
the level of BCL -2 inhibiting Cytochrome - C release whereas DNA damage, by activating
p53 , raises the level of BAX which enhances cytochrome c release

Balance Between Pro- Apoptotic and Anti –
Apoptotic Proteins Expression and their effects on
Cytochrome C
1. Proapoptotic Protein : BAX Protein : The protein p53 has an
important role in the sensing DNA damage. It activates apoptosis by
raising the cell level of BAX which then increases Cytochrome – C
release. It also shuts down the cell cycle to stop the damaged cell
from dividing . Following death, apoptotic cells display molecules
that lead to their ingestion by macrophages.
DNA damage, by activating p53, raises the level of
BAX which enhances Cytochrome – C release
2. Anti- Apoptotic Protein: BCL – 2; As well as molecules that
mediate apoptosis there are several intracellular proteins that
protect cells from apoptosis. The best characterized example is BCL
– 2. Growth factors raise the level of BCL -2 thereby inhibiting
Cytochrome – C release.

Postulated sequence of events in Apoptosis
Extrinsic Triggers Intrinsic Triggers
*Withdrawal of growth Intrinsic Protease activation
factors or hormones
*Receptor – ligand interactions
FAS / FAS ligand
TNF / TNF receptor
*Injury (radiation; toxins; free radicals)
* Cytotoxic T cells
Intrinsic Protease ( Caspases) activation
Endonuclease mediated Breakdown of Cytoskeleto
fragmentation of nuclear chromatin
Formation of Apoptotic bodies containing various intracellular organelles
Expression of “Phosphatidylserine” & “Thrombospondin” on Apoptotic bodies
Recognition by macrophages and phagocytosis without proinflammatory
cellular components

Mechanisms of Apoptosis
1. Mitochondrial (Intrinsic) pathway of Apoptosis
:Mitochondria contain several proteins that are capable
of inducing apoptosis; these proteins include
Cytochrome-c and other proteins that neutralize
endogenous inhibitors of apoptosis
2. Death receptor (Extrinsic) pathway of Apoptosis: Many
cells express surface molecules called death receptors ,
that trigger apoptosis.
3. Activation of Caspases : Mitochondrial and death
receptor pathways lead to the activation of Initiator
Caspases .Active forms of these enzymes are produced,
and these cleave and thereby activate another series of
caspases that are called Executioner Caspases
4. Clearance of Apoptotic Cells: Apoptotic cells entice
phagocytes by producing “eat me” signals .In normal
cells phosphotidylserine is present on the inner
leaflet of the plasma membranes, but in apoptotic cells
this phospholipid “flips” to the outerleaflet ,where it is
srecognized bt macrophages

Mechanisms of Apoptosis: the two pathways of apoptosis differ in their
induction and regulation, and both culminate in the activation of caspases.
In the mitochondrial pathway, proteins of Bcl-2 family, which regulate
mitochondrial permeability become imbalanced and leakage of various
substances from mitochondria leads to caspase activation.
In the death receptor pathway , signals form plasma membrane
receptors lead to assembly of adaptor protiens into a “death – inducing
signaling complex” ,which activates caspases and the end result is
the same

Examples of Apoptosis
1. Growth Factor Deprivation :Hormone sensitive cells
deprived of the relevant hormon,lymphocytes that are
not stimualted by antigens and cytokines and
neurpons deprived of nerve growth factor die by
apoptosis
2. DNA Damage: Exposure of cells to radiation or
chemotherapeutic agents induces DNA damage ,which
if severe may trigger apoptotic death.
3. Accumulation of Misoflded Proteins: ER Stress: During
normal protein synthesis, chaprones in the ER control
proper folding of newly synthesized proteins and
misfolded polypeptidies are ubiquitinated and targeted
for proteolysis. Various external stresses or mutations
induce a state called Endoplasmic Reticulum Stress ,
in which the cell is unable to cope wit hthe load of
misfolded proteins. Accumulation of these proteins in
the ER triggers the unfolded response, which tires to
restore protien homeostasis; if this respons eis
inadequate, the cell dies by apoptosis

The unfolded protein response and ER stress:
A: In healthy cells, newly synthesized proteins are folded with the help of
chaperones and are incorporated into cell or secreted
B. Various external stresses or mutations induce a state called
Endoplasmic Reticulum Stress , in which the cell is unable to cope wit
hthe load of misfolded proteins. Accumulation of these proteins in the ER
triggers the unfolded response, which tires to restore protein
homeostasis; if this respons eis inadequate, the cell dies by apoptosis

APOPTOSIS SPECIFIC GENE
Gene that stimulates Apoptosis
e.g., bax – gene
APOPTOSIS INHIBITING GENE
Gene that blocks apoptosis
e.g., bcl - gene

PHYSIOLOGIC CONDIITONS
HAVING EVIDENT APOPTOSIS
1.The programmed destruction of cells during embryogenesis.
2. Hormone dependent involution in the adults, such as endometrial
breakdown during menstrual cycle and regression of lactating breast
after weaning
3. Cell depletion in proliferating cell population, such as intestinal crypt
epithelia, in order to maintain a constant number
4. Elimination of cells that have served their useful purpose, such as
neutrophils in an acute inflammatory response and lymphocytes at the
end of an immune situations
5. Elimination of potentially harmful self-reactive lymphocytes either before
or after they have completed their maturation , in order to prevent
reactions against the body’s owns tissues
6. Cell death induced by cytotoxic T lymphocytes , a defense mechanism
against viruses and tumours that serves to kill virus-infected and
neoplastic cells

PATHOLOGIC CONDIITONS
HAVING EVIDENT APOPTOSIS
1.DNA damage: Radiation, cytotoxic anticancer drugs, extremes of
temperatures and even hypoxia can damage DNA, either directly or
through production of free radicals.
2. Accumulation of misfolded proteins :Importantly folded proteins may
arise because of mutations in the genes encoding these proteins or
because of extrinsic factors , such as damage caused by free radicals.
Excessive accumulation of these proteins in the ER leads to a
condition called Endoplasmic Reticulum Stress (ER Stress) ,which
culminates in a apoptotic death of cells
3. Cell injury in certain infections, particularly viral infections, in which
loss of infected cells is largely due to apoptotic death may be induced
by the virus ( as in adenovirus and HIV infections)
4 .Pathologic atrophy in parenchymal organs after duct obstruction, such as
occurs in the pancreas , parotid gland and kidney

MORPHOLOGIC CHANGES IN APOPTOSIS
•Cell Shrinkage: Cell is smaller in size; Cytoplasm is dense;
organelles are tightly packed.
•Chromatin Condensation: Chromatin aggregates peripherally,
under the nuclear membrane; nucleus may break in fragments
•Formation of cytoplasmic blebs and apoptotic bodies.
•Phagocytosis of apoptotic bodies by adjacent healthy cells
•ON HISTOLOGIC SECTIONS: Apoptosis involves single cell or
small clusters of cells. The apoptotic cell appears
as a round or oval mass of intensely
essinophilic cytoplasm with dense nuclear
chromatin

The sequential ultra structural changes seen in coagulation necrosis (left)
& Apoptosis (right). In apoptosis, the initial changes consist of nuclear
chromatin condensation and fragmentation, followed by cytoplasmic
budding and phagocytosis of the extruded apoptotic bodies. Signs of
coagulation necrosis include chromatin clumping, organellar swelling,
and eventual membrane damage.

A. Apoptosis in the skin in an immune-mediated
reaction. The apoptotic cells are visible in the epidermis
with intensely eosinophilic cytoplasm and small dense
nuclei.
B. High power view of apoptotic cell in the lever in
immune-mediated hepatic cell injury.

Apoptosis: Apoptotic cells (some indicted by
arrows) in a normal crypt in the colonic
epithelium.
Note the fragmented nuclei with condensed
chromatin and the shrunken cell bodies ,
some with pieces falling off

Apoptosis: More orderly process of cell death; there is individual cell
necrosis , not necrosis of large number of cells. In this example the
Liver cells are dying individually (arrows) from injury by Viral
Hepatitis . The cells are pink and without nuclei

Apoptosis of a liver cell in viral hepatitis. The cell is reduced in size and contains
brightly eosinophilic cytoplasm and a condensed nucleus

DYSREGULATED APOPTOSIS
(“too little or too much’)
•Disorders associated with reduced apoptosis: An
inappropriately low rate of apoptosis may prolong survival of
abnormal cells. These accumulated cells then give rise to
a) Cancers, especially those carcinomas with p53 mutations
b) Autoimmune disorders, which could arise, if autoreacitve
lymphocytes are not removed after immune response.
•Disorders associated with increased apoptosis. These
disorders are characterized by a marked loss of normal or protective
cells and include :
a) Neurodegenerative diseases
b) Virus – induced lymphocyte depletion
c) Aplastic Anaemia

Apoptosis: Summary
• Individual cell deletion in physiological growth control and in
disease.
• Activated or prevented by a variety of stimuli.
•Reduced apoptosis contributes to cell accumulation, e.g. neoplasia
• Increased apoptosis results in excessive cell loss, e.g. atrophy
•

COMPARISON OF CELL DEATH BY APOPTOSIS & NECROSIS
FEATURE APOPTOSIS
Cell Suicide
NECROSIS
Cell Homicide
Induction May be induced by
physiological or pathological
stimuli
Invariably due to pathological
injury
Extent Single cells Cell groups
Biochemical events (I) Energy- dependent
fragmentation of DNA by
endogenous endonucleases
(ii) Lysosomes intact
(i) Impairment or cessation of
ion homeostasis
(ii) Lysosomes leak lytic
enzymes
Cell membrane
integrity
Maintained Lost
Morphology Cell fragmentation to form
apoptotic bodies
Cell swelling and lysis
Inflammatory
response
None Usual
Fate of dead cells Ingested by neighbouring
cells
Ingested by neutrophils and
macrophages

Principles underlying most forms of cell injury
1. The cellular response to injurious stimuli depends
on the type of injury, its duration, and its severity
2. The consequences of an injurious stimulus depend on
the type, status, adaptability and genetic makeup of the
injured cell.
3. Cell injury results from functional and biochemical
abnormalities in one or more of several essential cellular
components

Most important targets of injurious stimuli
(1)Mitochondria, the site of ATP generation
(2)Cell Membrane, on which the ionic and osmotic
homeostasis of the cell and its organelles depends
(4) Protein synthesis
(5) Cytoskeleton
(6) Genetic apparatus of the cell

Principal cellular and biochemical sites of damage in cell injury
Principal targets and biochemical mechanisms of cell injury are:
(1)Mitochondria and their ability to generate ATP and reactive oxygen
species under pathologic conditions
(2)Disturbance in Calcium homoestasis
(3)Damage to cellular (plasma and lysosomal )membranes
(4)Damage to DNA and misfolding of proteins
(1) (2) (3) (4)

Depletion of ATP
High energy phosphate in the form of ATP is required
for many synthetic and degredative processes within
the cells. These include :
(i) Membrane transport
(ii) Protein Synthesis
(iii) Lipogenesis
(iv) Deacylation – reacylation reactions necessary for
phospholipids turnover

Consequences of Decreased ATP
Depletion of ATP to less than 5% to 10% of normal levels
has widespread effects on many critical cellular systems:
The activity of plasma membrane energy dependent sodium
pump is reduced, resulting in intracellular accumulation of
sodium and efflux of potassium. The net gain of solute is accompanied
by iso – osmotic gain of water, causing cell swelling and dilation of
endoplasmic reticulum
Compensatory increase in anaerobic glycolysis in an attempt to maintain
the cell’s energy sources.
Failure of calcium pump leads to influx of Ca++
, with damaging effects
on numerous cellular components.
Structural disruption of the protein synthetic apparatus manifested as
detachment of ribosomes from the rough endoplasmic reticulum and
dissociation of polysomes into monosomes, with a consequent reduction
in protein synthesis.
Ultimately, there is irreversible damage to mitochondrial
and lysosomal membrane s. and the cell undergo necrosis

The initial functional and morphologic consequences of decreased
intracellular adenosine triphosphate (ATP) during cell injury

ROLE OF MITOCHONDRIA IN CELL INJURY
● Directly or indirectly , mitochondria are
important targets for virtually all types of
injurious stimuli, including hypoxia and
toxins.
● Mitochondria can be damaged by:
(i) Increase in cytosolic Ca++
(ii) Oxidative stress
(iii) Breakdown of phospholipids through the
phospholipase A2

Consequences of Mitochondrial damage
wo major consequences of mitochondrial damage:
) Mitochondrial damage results in the formation of a high
onductance channel in the mitochondrial membrane, called
he mitochondrial permeability transition pore. The opening
f this channel leads to the loss of mitochondrial membrane
otential and pH changes, resulting in failure of oxidative
phosphorylation and progressive depletion
of ATP, culminating in necrosis of cell
) Increased permeability of mitochondrial membrane leads to
elease of enzymes having an active role in Apoptosis
cytochrome –C) . It may lead to death by Apoptosis

Consequences of
mitochondrial dysfunction,
culminating in cell death by
necrosis or apoptosis

Defects in Membrane Permeability
Early loss of selective membrane permeability leading
ultimately to overt membrane damage is a consistent feature
of most forms of cell injury (except apoptosis).
The plasma membrane can be damaged by:
Ischemia
Microbial toxins
Lytic complement components
Physical and chemical agents
Different biochemical mechanisms may contribute to
membrane damage:
Decreased phospholipids synthesis
Increased phospholipids breakdown
Reactive Oxygen species
Cytoskeletal abnormalities
Lipid breakdown products

Mechanisms of Membrane Damage in cell Injury
Decreased O2 and increased cytosolic Ca 2+
are typically seen in ischemia
but may accompany other forms of cell injury.
Reactive oxygen species (not shown in figure), which are often produced
on reperfusion of ischemic tissues, also cause membrane damage

Important sites of membrane damage
during cell injury
1. Mitochondrial Membrane Damage: It leads to decreased
production of ATP, culminating in necrosis and release of
proteins that trigger apoptotic death
2. Plasma Membrane Damage: Plasma membrane damage
leads to loss of osmotic balance and influx of fluids and
ions, as well as loss of cellular contents
3. Injury to Lysosomal Mmebranes: it results in leakage of
their enzymes into the cytoplasm which leads to enzymatic
digestion of cell components .

ROLE OF CALCIUM INFLUX
•Toxins or ischemia allow a net influx of extra
cellular calcium across the plasma membrane,
followed by release of calcium from the
intracellular stores
•Increased cytosolic calcium activates different
enzymes:
(i) Phospholipases: Promote membrane damage
(ii) Proteases: Catabolize structural and
membrane proteins
(iii) ATPases: Accelerate ATP depletion
(iv) Endonucleases: Fragment genetic material

Sources and Consequences of increased CytosolicSources and Consequences of increased Cytosolic
Calcium in cell injuryCalcium in cell injury

Increased Ca ++
levels also result in the induction of
apoptosis, by direct activation of caspases and by
increasing mitochondrial permeability

FREE RADICAL MEDIATION OF CELL INJURY
• Free radicals are chemical species with a single
unpaired electron in their outer orbit and therefore highly
reactive
•Such chemical states are extremely unstable and readily
react with inorganic or organic chemicals
•The excess energy attributable to the unstable
configuration is released through chemical reactions with
adjacent molecules.
•One of the best known reactions is that between oxygen
based free radicals and cell membrane lipids (lipid
peroxidation) which leads to membrane damage.
• Free radicals , when generated in cells they attack and
degrade nucleic acids, as well as a variety of membrane
molecules ;
•Molecules that react with free radicals, are in turn
converted into free radicals, further propagating the chain
of damage.

IMPORTANT FREE RADICALS
1. Hydroxyl (OH -
) and Hydrogen (H -
) free radicals generated from
hydrolysis of water through ionizing radiation.
2. Super oxide radical generated from oxygen
3. Fe+++
generated during Fenton reaction
MECHANISM OF INJURY BY FREE RADICALS
1. Lipid peroxidation of membranes
2. Lesions in deoxyribonucleic acid (DNA)
3. Cross linking of proteins
CELLULAR ANTIOXIDANT MECHANISM
1. Glutathione peorxidase
2. Catalse
3. Superoxidase Dismutase
4. Vitamin E
5. Vitamin C

Generation of free radicals
A, Top: Generation of free radicals
B, bottom left : the cell injury resulting from the action of unopposed free radicals
C, bottom right : Free radicals neutralization by cellular antioxidants

Three important Free Radicals Generated
effects
1. Membrane lipid peroxidation
2. DNA fragmentation
3. Protein cross linking and fragmentation

The role of reactive oxygen species in cell injury
O2 is converted to superoxide by oxidative
enzymes in the endoplasmic reticulum,
Mitochondria, plasma membrane,
perioxisomes and cytosol. Superoxide
is converted to H2O2 by dismutation
and thence to OH -
by the Cu2+
/Fe2+
catalyzed Fenton reaction. H2O2 is also
directly derived from oxidases
in perioxisomes not shown in figure.
Also not shown a potentially toxic
free radical singlet oxygen. Resultsant
free-radical damage to lipid
(by peroixdation), proteins and DNA
leads to various forms of cell injury.

FREE RADICAL & CELL INJURY
Various Agents that produce Free Radicals
Ionizing Radiation
Chemical Oxidants
Oxygen Therapy
Acute Inflammation (Granulocytes)
Chemical Poisons (Carbon tetrachloride)
Free Radical Produced
Super oxide; Hydroxyl Radical; Free Hydrogen Radical ; Hydrogen Peroxide
Effects of Free Radicals
Lipid Per oxidation of Cell Membrane
Lipid Peorxidation of Mitochondrial Membranes
Breakdown of DNA
Cross linking of Proteins

Examples of Free Radical Induced Injury
1. Ischemia- reperfusion
2. Chemical injury
3. Radiation injury
4. Toxicity of Oxygen and other gases
5. Cellular aging
6. Microbial killing by phagocytic cells
7. Tissue injury caused by inflammatory cells

Removal of Free Radicals
Free radicals are inherently unstable and
decay spontaneously
There are non-enzymatic and enzymatic
systems which contribute to inactivation
of free radicals

INTRACULLAR ACCUMULATIONS
One of the manifestations of metabolic derangements in
cells is the intracellular accumulation of abnormal amounts of
various substances
The stockpiled substance fall into three categories:
(I) A normal cellular consistent accumulates in excess
a. Fatty change liver
b. Haemosidrosis
c. Bilirubin accumulation
(II) A normal or abnormal substance, accumulates because of the
genetic or acquired defects to metabolize it:
a. Glycogen Storage diseases
(III) An abnormal exogenous substance accumulates because body
can not metabolize it (PIGMENTATION)
a. Accumulation of carbon particles in lungs
b. Tattooing
(IV) Specialized Accumulations
a. Calcification
b. Amyloidosis

(i) A normal endogenous substance is produced at a
normal or increased rate, but the rate of
metabolism is inadequate to remove it
Example: Fatty Change of Liver

Fatty Change of Liver
The term Steatosis and Fatty Change describe abnormal
accumulation of triglycerides within parenchymal cells.
Fatty change is often seen in the liver because it is the
major organ involved in the fat metabolism, but it also
occurs in heart, muscle, and kidney
The causes of fatty change include:
(i) Toxins.
(ii) Protein malnutrition.
(iii) Diabetes mellitus.
(iv) Obesity.
(v) Anorexia
(vi) Alcohol abuse ( In industrialized world it is
the most common cause)

Possible mechanisms leading to
Accumulation of triglycerides in
Fatty liver: Defects in any six
Numbered steps of uptake,
Catabolism, or secretion can
Result in Lipid Accumulation

Mechanisms involved in triglycerides accumulation in liver:
•Free fatty acids from adipose tissues or ingested foods are normally
transported into hepatocytes. In liver they are :
- Estrified to triglycerides
- converted to cholestrol or phospholipids
- Oxidized to ketonebodies
• Some fatty acids are synthesized from acetate as well.
• Release of triglycerdies from hepatocytes requires association with
Apoproteins to form lipoproteins.
• Lipoproteins then enter into circulation.
Excess accumulation of triglycerdies can result within the liver
may result from defects in any of the events in the sequence from
fatty acid entery to lipoprotein exit
Alcohol: A hepatotoxin that alters mitochondrial and microsomal functions
Protein malnutrition: Act by decreased synthesis of lipoproteins
Starvation: Increased fatty acids mobilization from peripheral tissues

High power detail of Fatty changeIn liver:
In most cells well preserved. Nucleus is squeezed into the
displaced rim of cytoplasm about the fat vacuole

Fatty Change Liver
Intracellular accumulation of a variety of materials can occur in response
to cellular injury. Here is fatty metamorphosis (Fatty change) of the liver
in which deranged lipoprotein transport from injury (most often
Alcoholism) leads to accumulation of lipid in the cytoplasm of
hepatocytes.

Slide No 4
Section in the liver shows:
Empty fat vacuoles in the
cytoplasm of the liver cells
The vacuoles had dissolved in
xylol during preparation.
•The nuclei of the liver cells
are pushed against the cell
membrane and become
flattened giving the cell
signet ring appearance.
•Diagnosis:
Fatty Liver

Cholesterol and Cholesterol Esters accumulation
Most cells use cholesterol for cell membrane synthesis, without
intracellular accumulation of cholesterol esters.
In several pathologic conditions intracellular accumulation of
cholesterol can be manifested
Atherosclerosis: In atherosclerotic plaques smooth muscle cells and
macrophages are filled with fat vacuoles most of which are made of
cholesterol and cholesterol esters ( Foam Cells)
Xanthomas: In hereditary and acquired hyperlipedimic states clusters of
foam cells are found in the sub epithelial connective tissue of the skin
and tendons producing tumourous masses known as Xanthomas
Inflammation and Repair: Foamy macrophages are frequently found at
sites of cell injury and inflammation , owing to phagocytosis of
cholesterol from membranes of injured cells
Cholesterolosis: This refers to focal accumulation of cholesterol – laden
macrophages in the lamina propria of gall bladder,

Cholesterol and Cholesterol Esters accumulation
Atheroma
Xanthomas

Proteins accumulation
•Protein appears as eosinophilic droplets in the cytoplasms
• In certain disorders excessive accumulation of protein
takes place:
Reabsorption droplets in proximal renal tubules: Seen in
renal diseases associated with protein loss in the urine
(Proteinuria)
Excessive synthesis of proteins: occurs in plasma cell
dyscrasisias like Multple Myeloma where there is excessive
immunoglobulin synthesis
Amylodosis:

Multiple myeloma-Plasma Cells With
Inclusions

Glycogen accumulation
•Excessive intracellular accumulation of glycogen are seen
in patients with an abnormality in either glucose or glycogen
metabolism .
Diabetes mellitus: It is the prime example of a disorder of
glucose metabolism
Glycogen storage diseases: A group of genetic disorders , In
these enzymatic defects in glycogen synthesis or breakdown
leads to excessive accumulation of glycogen in cells

Special stains to demonstrate intracellular
accumulations
Special stains to demonstrate fat:
-Sudan IV
- Oil Red O
Special stains to demonstrate Glycogen:
- PAS stain
- Sudan Black B

2. A normal or abnormal substance accumulates because
of genetic or acquired defects in the metabolism,
packaging, transport, or secretion
of these subsrtances
Examples:
Storage Diseases: Genetic defects of specific enzymes involved in
the metabolism of lipids and carbohydrates leads to intracellular
deposition of these substances.

Bone marrow aspirate showing a Niemann pick cell. Monocytes
with foamy appearance of cytoplasm due to lipid vacuoles
Niemann Pick Disease

.
Bone marrow aspirate showing Gaucher cells. Monocytes with pale
blue cytoplasm and round to oval nuclei. Cytoplasm appear fibriller
Gaucher Disease

These disorders are also called familial sphingolipidoses, since
inherited deficiency of certain enzymes ( glucoceribrosidase in
Gaucher’s disease and sphingomylinase in Niemenn Pick disease )
required for the catabolism of lipid compounds lead to the
accumulation of these lipids and polysaccharides.
The stock-pilled substance is mainly accumulated in the
macrophages. Accumulation of these lipid- laden
macrophages in the blood, bone marrow, spleen, liver and other
organs leads to manifestations like anaemia, leucopenia,
thrombocytopenia and hepato-splenomegaly.
.

3. An abnormal exogenous substance is deposited because the cell
has neither the enzymatic machinery to degrade the substance nor
the ability to transport to other sites
Example: Accumulation of Carbon particles in lungs

CALCIFICATION
•Calcification is the abnormal deposition of Calcium
salts, at sites other than osteoid and enamel along
with smaller amounts of iron, magnesium and other
mineral salts
•Calcification is of two types:
1. Dystrophic Calcification: Deposition in dead or
dying tissue
2. Metastatic Calcification: Deposition in living
tissue

DYSTROPHIC
CALCIFICATION
METASTATIC
CALCIFICATION
Deposition of calcium
in dead or dying tissue
Deposition of calcium
in living tissue
Not associated with
abnormalities in
calcium metabolism
Associated with
abnormalities in
calcium metabolism
Hypercalcemia absent Hypercalcemia present

Dystrophic calcification: Examples
1. In areas of necrosis. The necrosed tissue can get converted
in a calcified mass
2. The atheromas of advanced atherosclerosis.
3. Aging or damaged heart valves
4. Aged pineal gland.
5. Dead parasites
6. Dead retained fetus.
7. Dystrophic Calcification can be seen in carcinomas. For
example “Psammoma bodies” seen in capillary carcinoma
of thyroid.

Aortic valve in a heart with calcific aortic stenosis. The
semilunar cusps are thickened and fibrotic . Behind each
cusp are seen irregular masses of pilled- up dystrophic
calcification

Dystrophic calcification
Aortic valve calcification

Dystrophic Calcification
This is dystrophic calcification in the wall of the stomach. At the far
left is an artery with Calcification in its wall. There are also irregular
bluish – purple deposits of calcium in the sub mucosa . Calcium
is more likely to be deposited in the tissues that are damaged.

Psamomma Bodies- Dystrophic
Calcification Seen in
Malignant Tumours
Psamomma Bodes: Are lamellated bodies of
dystrophic calcification.
Seen in:
-Papillary carcinoma thyroid
-Meningioma
Serous ovarian malignant tumours

Pathogenesis of Dystrophic Calcification
Initiation
Calcium from mitochondria
Calcium combines with Phospholipids in
cell membrane
Membrane associated phosphatases generate phosphate
groups that bind to bound calcium
Propagation
Cycle of Calcium and Phosphate binding is repeated again
and again
Micro crystals develops after a rearrangement
in the phosphate and calcium ions
Dystrophic Calcification

Model of membrane facilitated calcification: calcium ions bind the
phospholipids present in a membrane. Membrane associated
phopshateses generate phosphate groups that bind to that bind to the
bound calcium.The cycle of phosphate and calcium binding is repeated,
increasing the size of deposit. A micro crystal develops after a
rearrangement in the phosphate and calcium ions

Metastatic Calcification: Examples
There are four principal causes in groups of patients with
Hypercalcemia who can have Metastatic Calcification:
1. Increased secretion of Parathyroid Hormone with subsequent
bone resorption seen in
a. Hyperparathyroidism due to parathyroid tumours
b. Ectopic secretion of Parathyroid hormone by
malignant tumours
2. Destruction of bone tissue seen with
a. primary tumours of bone marrow like:
- Multiple Myeloma
- Leukaemias
b. Diffuse skeletal metastasis (e.g., breast cancer)
c. Accelerated bone turn over like in Paget disease or in
immobilization.
3. Renal Failure , which causes retention of Phosphate, leading
to secondary hyperparathyroidism.
4. Vitamin – D related disorders including Vitamin- D
intoxication and Sarcoidosis.

Calcification: Morphology
Regardless of the site , calcium salts are seen on gross examination as
fine white granules or clumps.
Often felt as gritty deposits
Dystrophic calcification is common in areas of caseous necrosis
On histologic exmination calcification appears as intracellular and/or
extracellular basophilic daposits .
Overtime , hetrotropic bone may be formed in the focus of calicification
Metastic calcification can occur widely throughout the body but
principally affects the interstitial tissues of the vasculature ,kidneys,
lungs and gastric mucosa.
Calcium deposits, in metastatic calcification, morphologically resemble
those as in dystrophic calcification .

Metastatic Calcification
Metastatic calcification in the lung of a patient with a
very high serum Calcium level (Hyperplasia)

Metastatic calcification, lung

PIGMENTS
Pigments are colured substances which
accumulate in cells.
Based on the source pigments can be of two types
1. Exogenous pigments
2. Endogenous pigments

PIGMENTS
(I) Endogenous Pigments
1.Lipofuscin
2. Melanin
3. Bilirubin
4. Haemosidrin
(II) Exogenous Pigments
1. Anthracosis
2. Pneumoconiosis
3. Tattoing

(i) ENDOGENOUS PIGMENTS
These are the pigments which are synthesized inside the body
a. Lipofuscin or Wear and tear pigment: It is composed of
polymers of lipid and phospholipids complexed with proteins ,
suggesting that it is derived through lipid peroxidation of
polyunsaturated lipids of sub cellular membranes. It is the tell tale
sign of free radical injury.
Microscopic appearance: Yellow brown intracytoplasmic granules.
b. Melanin: Brown black pigment derived from melanocytes of
skin. Examples of melanin accumulation;
- Suntan
- Melasma
- In pregnancy

c. Haemosidrin: Golden yellow to brown granular pigment . It is
the form in which iron is accumulated in cells.
The main storage form of iron is ferritin. But when there is
local or systemic excess of iron, ferritin aggregates in the form of
haemosidrin.
Haemosidrosis ( increased sysmteimic accumulation of iron)
is seen in:
(i) Increased absorption of dietary iron.
(ii) Impaired use of iron.
(iii) Haemolytic anaemias , for example beta thalassaemia
major
(iv) Repeated blood transfusions.
d. Bilirubin: Jaundice is the common clinical disorder caused by
excesses of Bilirubin within cells and tissues.

Lipofuscin Accumulation
The yellow brown granular pigment seen in the hepatocytes here is
Lipochrome (LIpofuscin) which accumulates over time in cells (particularly
liver and heart) as a result of “wear and tear” with aging . It is of no major
consequence , but illustrates the end result of the process of autophago-
cytosis in which intracellular debris is sequestered and turned into these
residual bodies of lipochrome within the cell cytoplasm

Endogenous pigment
Liver haemosiderosis

Haemosidrosis: Brown coarsy granular material in macrophages in
alveoli is hemosidrin that has accumulated as a result of breakdown
of red blood cells

Haemosidrin: Prussian Blue Reaction (Iron stain) of liver showing
large amount of hemosidrin in Hepatocytes and Kuppfer cells

Haemosidrin deposition in Kidney
Renal tubules contain large amount of haemosidrin, as demonstrated by
Prussian Blue Iron Stain. This patient had intravascular haemolysis

Jaundice
The Sclera of the eye is yellow because the patient has jaundice,
or Icterus. The normally white sclera of the eyes is a good place on
physical examination to look for jaundice.

Bilirubin: Yellow – green globular material seen in
small bile ductules in liver

Haemosidrin granules in liver cells
A: H& E showing golden brown , finely granular pigment
B: Prussian Blue , specific for iron

(ii) EXOGENOUS PIGMENTS
These are the pigments which come from outside the body.
Anthracosis (Carbon or coal dust accumulation): It is the main
pollutant of the urban life. When inhaled, it is picked up by
macrophages within the alveoli and is then transported through
lymphatic channels to regional lymph nodes. Accumulation of this
pigment blackens the tissues of lung ( Anthracosis).
b. Coal worker’s pneumoconiosis: In coal miners and those living in
heavily polluted environments , the aggregates of carbon dust may
induce a fibroblastic reaction or even emphysema and thus cause a
serious lung disease known as coal worker’s pneumoconiosis.
c. Tattooing: A form of localized exogenous pigmentation. The pigments
inoculated are ingested by dermal macrophages, where they reside
permanently .

Anthrocosis pigment in macrophages in hilar lymph node:
Anthrocosis is accumulation of carbon pigment from breathing
bad sir. Smokers have the most pronounced Anthrocosis.

Exogenous pigment
Anthracosis of lung

Endogenous substances accumulating in tissues as a result of
deranged metabolism
Accumulated
Substance
Effects in
Parenchymal cells
Effects in
interstitial cells
Water Cloudy swelling
Hydropic changes
Edema
Triglycerides Fatty change
Cholesterol Atherosclerosis
Xanthomas
Complex lipids Lipid storage diseases
Protein -Ubiquitin/ Protein
complexes
Amylodosis
Glycogen Glycogen storage
diseases
Mucopolysaccharides Mucopolysaccharidoses Myxoid degeneration

Endogenous substances accumulating in tissues as a result of
deranged metabolism
Accumulated
Substance
Effects in
Parenchymal cells
Effects in
interstitial cells
Iron Hemochromatosis Localized
Haemosidrosis
Calcium Contributes to necrosis Calcification
Copper Wilson’s disease Wilson’s disease
Bilirubin Kernicterus Jaundice
Lipofuscin Brown Atrophy in old
age
Urate Gout
Homogensitic Acid Alkaptonuria

Cell Ageing
•A number of cellular functions decline progressively with age
•With advancing age there is progressive accumulation of
sublethal injury that comprises cellular accumulation of
sublethal injury that comprises cellular function and may lead
to cell death, or at least to diminished capacity of cells to
respond to injury.

A number of cellular functions decline with age:
Mitochondrial oxidative phospohorylation is reduced
Synthesis of structural, enzymatic and receptor proteins
is reduced.
Capacity for nutrients uptake is diminished.
Capacity to repair chromosomal damage is jeopardized.

All these leads to morphologic alterations
in senescent cells like:
Irregular nuclei
Pleomorphic cytoplasmic vacuolations
Distorted Golgi apparatus
Steady accumulation of Lipofuscin
pigemnts( indicating past oxidative damage and
membrane injury)
“Lipofuscin Pigment” OR “Lipochrome Pigment” OR
“Wear and Tear Pigment” OR “Ageing Pigment” OR
“Free Radical Induced Pigment”

Lipofuscin granules in cardiac myocyte

Hypotheses about cell ageing
1. Inbuilt genetic mechanisms
( Clonal Senescence Theory)
2. Wear and Tear mechanisms
( Replication Senescence)
3. Telomere Shortening

Mechanisms of cell aging .Among the several pathways contributing
to aging of cells and organisms many have been defined in
simple model organisms ,and their relevance to aging in
humans remains area of active investigation.

Suggested cellular mechanisms of ageing and death: There is direct or
circumstantial evidence supporting each of the mechanisms illustrated.
Some mechanisms interact with others; for example , free radicals may be
responsible for DNA mutations .

Inbuilt Genetic Mechanisms
(Clonal Senescence Theory)
Common experience supports the idea that there is an
inbuilt ‘allotted life- span’ for humans and animals .
It is clear that cellular senescence is multifactorial . It
involves the cumulative effects of both an intrinsic
molecular clock of cellular aging and the extrinsic
stressors of the cellular environment .

Wear and Tear Mechanisms
Replication Senescence
•Due to vicissitudes of daily life and due to the accumulation of sublethal
damage in cells there is system failure of sufficient magnitude that the
whole organism succumbs
•The common pathway resulting in cellular deterioration is currently
thought to be the generation of highly reactive molecular species – ‘free
radicals’
•With advancing age there is decreased formation of ‘antioxidants’ , so
defense against free radical induced injury becomes weak with advancing
age
•Accumulation of Lipofuscin or aging pigment in old age is a tell tale sign
of free radical induced injury.
Defective DNA Repair: There are mechanism in the cell that deals with
damage, particularly DNA damage. With advancing this repair mechanims
become weak.

Telomere Shortening
At the tip of each chromosome there is a non – coding
tandemly repetitive DNA sequence , this is the telomere.
These telomric sequences are not fully copied during
DNA synthesis prior to mitosis. As a result , a single –
stranded tail of DNA is left at the tip of each
chromosome ; this is excised and , with each cell
devision , the telomeres are shortened . Eventually the
telomeres are so short that DNA polymerase is unable to
engage in the subtelomeric start positions for
transcription and the cell is incapable of further
replication.
Telomeric shortening could explain the replication limit
of cells. This is supported by the finding that telomric
length decreases with age of individual.

Telomeres, telomerase and
replicative capacity: Telomeres are
Essential for chromosomal copying
during the S- phase of cell cycle.
However , most Somatic cells lack
telomerase (the enzymes that
regenerates telomeres)
so the telomeres shorten with each
Cell division until chromosomal
copying become impossible.
Germ cells and some neoplastic
cells express telomerase and thereby
have extended replicative capacity.

Mechanisms of Cellular Injury
Mechanisms that cause and counteracts cellular aging. DNA damage,
replicative senescence and decreased and misfolded proteins are
among the best described mecahnisms of cellular aging .
Some envirnmental stresses, such as calorie restriction, counteract aging
by activating various signaling pathways and transcription factors

The Role of Telomeres and telomerase in
Replicative Senescence of cells
In normal somatic cells there is no
telomerase activity, and telomeres
progressively shorten with
increasing cell divisions until
growth arrests, or senescence,
occurs.
 Germ cells, and stem cells both
contain active telomerase, but
only the germ cells have
sufficient levels of the enzyme
to stabilize telomere length
completely.
In cancer cells, telomerase is
often reactivated.
Telomere length is plotted against
the number of cell divisions

Cell injury, cell death & adaptations by Dr Nadeem (RMC)

Cell injury, cell death & adaptations by Dr Nadeem (RMC)

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