Anatomy and physiology of heart, lung ,

ANATOMY AND PHYSIOLOGY OF
HEART, LUNG ,THORACIC CAVITY,
BLOODVESSELS

LOCATION OF THE HEART
It is about 12 cm long, 9 cm wide at its broadest
point, and 6 cm thick, with an average mass of 250
g (8 oz) in adult females and 300 g (10 oz) in adult
males. The heart rests on the diaphragm, near the
midline of the thoracic cavity. It lies in the
mediastinum. About two-thirds of the mass of the
heart lies to the left of the body’s midline . The
pointed apex is directed anteriorly, inferiorly, and to
the left. The broad base is directed posteriorly,
superiorly, and to the right.

PERICARDIUM
 The membrane that surrounds and protects the
heart is the pericardium . It confines the heart to its
position in the mediastinum, while allowing
sufficient freedom of movement for vigorous and
rapid contraction. The pericardium consists of two
main parts: the fibrous pericardium and the serous
pericardium.

LAYERS OF THE HEART WALL
 The wall of the heart consists of three layers: the
epicardium , the myocardium, and the endocardium .
The epicardium, the thin, transparent outer layer of the
heart wall, is also called the visceral layer of the serous
pericardium. It Is composed of mesothelium and delicate
connective tissue .The middle myocardium , which is
cardiac muscle tissue, makes up the bulk of the heart
and is responsible for its pumping action.
 The innermost endocardium is a thin layer of
endothelium overlying a thin layer of connective tissue.
It provides a smooth lining for the chambers of the heart
and covers the valves of the heart. The endocardium is
continuous with the endothelial lining of the large blood
vessels attached to the heart

CHAMBERS OF THE HEART
 The heart has four chambers. The two superior chambers are
the atria , and the two inferior chambers are the ventricles .
On the anterior surface of each atrium is a wrinkled pouchlike
structure called an auricle. Also on the surface of the heart
are a series of grooves, called sulci, that contain coronary
blood vessels and a variable amount of fat. Each sulcus
marks the external boundary between two chambers of the
heart. The deep coronary sulcus encircles most of the heart
and marks the boundary between the superior atria and

inferior ventricles. The anterior interventricular sulcus is a
shallow groove on the anterior surface of the heart that marks
boundary between the right and left ventricles. This sulcus
continues around to the posterior surface of the heart as the
posterior interventricular sulcus, which marks the boundary
between the ventricles on the posterior aspect of the heart

RIGHT ATRIUM
 The right atrium receives blood from three veins: the superior
vena cava, inferior vena cava, and coronary sinus. The
anterior and posterior walls of the right atrium are very
different. The posterior wall is smooth; the anterior wall is
rough due to the presence of muscular ridges called
pectinate muscles which also extend into the auricle .
Between the right atrium and left atrium is a thin partition
called the interatrial septum . A prominent feature of this
septum is an oval depression called the fossa ovalis, the
remnant of the foramen ovale, an opening in the in- tera-trial
septum of the fetal heart that normally closes soon after birth .
Blood passes from the right atrium into the right ventricle
through a valve that is called the tricuspid valve because it
consists of three leaflets or cusps . It is also called the right
atrioventricular valve. The valves of the heart are composed of
dense connective tissue covered by endocardium.

RIGHT VENTRICLE
 The right ventricle forms most of the anterior surface of
the heart. The inside of the right ventricle contains a
series of ridges formed by raised bundles of cardiac
muscle fibers called trabeculae carneae . The cusps of
the tricuspid valve are connected to tendonlike cords,
the chordae tendineae, which in turn are connected to
cone- shaped trabeculae carneae called papillary
muscles. The right ventricle is separated from the left
ventricle by a partition called the interventricular
septum. Blood passes from the right ventricle through
the pulmonary valve into a large_artery called the
pulmonary trunk, which divides into right and left
pulmonaryarteries.

LEFT ATRIUM
 Left atrium forms the most of the base of the heart.
It receives blood from the lungs through four
pulmonary veins. Like tghe right atrium, the inside
of the left atrium has smooth posterior wall.anterior
wall also smooth. Blood passes from the left atrium
to the left ventricle through the bicuspid valve.it is
also called as the left atrioventricular valve.

LEFT VENTRICLE
 The left ventricle forms the apex of the heart.like the
right ventricle, the left ventricle contain trabeculae
carnae and has cordae tendinae that anchor the cusps
of the bicuspid valve to the papillary muscles.

 Blood passes from the left ventricle through the aortic
valve into the ascending aorta.
 Some of the blood in the aorta flows into the coronary
arteries, which branch from the ascending aorta and
carry blood to the heart wall. The remainder of the blood
passes into the arch of the aorta and descending aorta
(thoracic aorta and abdominal aorta). Branches of the
arch of the aorta and descending aorta carry blood
throughout the body.

HEART VALVES
 As each chamber of the heart contracts, it pushes a
volume of blood into a ventricle or out of the heart
into an artery. Valves open and close in response to
pressure changes as the heart contracts and
relaxes. Each of the four valves helps ensure the
oneway flow of blood by opening to let blood
through and then closing to prevent its backflow.

SYSTEMIC AND PULMONARY CIRCULATIONS
 The left side of the heart is the pump for the
systemic circulation.it receives oxygenated
blood from the lungs.the left ventricle ejects
blood into the aorta. From the aorta, the blood
devides into separate small streams, entering
progressively smaller systemic arteries that
carry it to all organs throughout the body-except
for the air sacs of the lung , which is
supplied by the pulmonary circulation

 In systemic tissues , arteries give rise to
smaller- diameter arterioles, which finally lead
in to the extensive beds of systemic capillaries.
Exchange of nutrients and gases occurs across
the thin capillary walls. Blood unloads o2 and
picks up co2 . In most cases blood flows
through only one capillary and then enters
systemic venule. Venules carry deoxygenated
blood away from tissues and merge to form
larger systemic veins. Ultimately the blood
flows back to the right atrium

 The right side of the heart is the pump for the
pulmonary circulation; it receives all the dark red,
deoxygenated blood returning from the systemic
circulation. Blood ejected from the right ventricle
flows into the pulmonary trunk, which branches into
pulmonary arteries that carry blood to the right and
left lungs. In pulmonary capillaries, blood unloads
CO,, which is exhaled, and picks up inhaled 02. The
freshly oxygenated blood then flows into pulmonary
veins and returns to the left atrium

CORONARY CIRCULATION
 Nutrients are not able to diffuse quickly enough
front blood in the chambers of the heart to supply
all the layers of cells that make up the heart wall.
For this reason, the myocardium has its own
network of blood vessels, the coronary or cardiac
circulation. The coronary arteries branch from
the ascending aorta and encircle the heart like a
crown encircles the head . While the heart is
contracting, little blood flows in the coronary
arteries because they are squeezed shut. When the
heart relaxes, however, the high pressure of blood
in the aorta propels blood through the coronary
arteries, into capillaries, and then into coronary
veins .

CORONARY CIRCULATION
 Heart is supplied by TWO CORONARY arteries:
1- Right coronary artery---(RCA)
2- Left coronary artery---(LCA)
 These coronary arteries arise at the root of the
aorta.
19

Coronary artery & their branches
 LCA---- -Lt Anterior Descending (LAD)
-Marginal Artery
-Circumflex Artery
 RCA ---- -Marginal Artery
-Posterior descending
branch
20

Left coronary artery (LCA) –Divides in
Anterior Descending (LAD)
Circumflex artery
 LAD--- Supplies anterior and apical parts of heart
,and Anterior 2/3rd of interventricular septum.
 Circumflex branch-- supplies the lateral and
posterior surface of heart.
21

Right coronary artery(RCA) supplies:
 Right ventricle
 Part of interventricular septum (posterior 1/3rd)
 Inferior part of left ventricle
 AV Node
22

 After blood passes through the arteries of the
coronary circulation, it flows into capillaries, where it
delivers oxygen and nutrients to the heart muscle
and collects carbon dioxide and waste, and then
moves into coronary veins. Most of the
deoxygenated blood from the myocardium drains
into a large vascular sinus in the coronary sulcus on
the posterior surface of the heart, called the
coronary sinus . The deoxygenated blood in the
coronary sinus empties into the right atrium.

Blood flow to Heart during Systole & Diastole
 During systole when heart muscle contracts it
compresses the coronary arteries therefore blood
flow is less to the left ventricle during systole and
more during diastole.
 To the subendocardial portion of Left ventricle it
occurs only during diastole
25

 Blood flow to subendocardial surface of left
ventricle during systole is not there, therefore, this
region is prone to ischemic damage and most
common site of Myocardial infarction.
26

 Venous return of Heart
Most of the venous blood return to heart occurs
through the coronary sinus and anterior cardiac
veins, which drain into the right atrium
27

CORONARY VEINS
 After blood passes through the arteries of the
coronary circulation, it flows into capillaries, where it
delivers oxygen and nutrients to the heart muscle
and collects carbon dioxide and waste, and then
moves into coronary veins. Most of the
deoxygenated blood from the myocardium drains
into a large vascular sinus in the coronary sulcus on
the posterior surface of the heart, called the
coronary sinus . The deoxygenated blood in the
coronary sinus empties into the right atrium. The
principal tributaries carrying blood into the coronary
sinus are the following:

 Great cardiac vein in the anterior interventricular
sulcus, which drains the areas of the heart supplied by
the left coronary artery (left and right ventricles and left
atrium)
 Middle cardiac vein in the posterior interventricular
sulcus, which drains the areas supplied by the posterior
interventricular branch of the right coronary artery (left
and right ventricles)
 Small cardiac vein in the coronary sulcus, which drains
the right atrium and right ventricle
 Anterior cardiac veins, which drain the right ventricle
and open directly into the right atrium
 When blockage of a coronary artery deprives the heart
muscle of oxygen, reperfusion, the reestablishment of
blood flow, may d

CORONARY BLOOD FLOW
 Coronary blood flow in Humans at rest is about
225-250 ml/minute, about 5% of cardiac output.
 At rest, the heart extracts 60-70% of oxygen from
each unit of blood delivered to heart [other tissue
extract only 25% of O2.
30

CORONARY BLOOD FLOW
Why heart is extracting 60-70% of O2?
 Because heart muscle has more mitochondria, up
to 40% of cell is occupied by mitochondria, which
generate energy for contraction by aerobic
metabolism, therefore, heart needs O2.
 When more oxygen is needed e.g. exercise, O2 can
be increased to heart only by increasing blood flow.
31

 Factors Affecting Blood Flow to CORONARY
ARTERIES
-Pressure in aorta
-Chemical factors
-Neural factors
Coronary blood flow shows considerable
Autoregulation.
32

Chemical factors affecting Coronary blood flow
 Chemical factors causing Coronary vasodilatation
(Increased coronary blood flow)
 -Lack of oxygen
 -Increased local concentration of Co2
 -Increased local concentration of H+ ion
 -Increased local concentration of k + ion
 -Increased local concentration of Lactate, Prostaglandin,
Adenosine, Adenine nucleotides.
 NOTE – Adenosine, which is formed from ATP during
cardiac metabolic activity, causes coronary vasodilatation.
33

CORONARY ARTERY HEART DISEASE
 ISCHEMIC HEART DISEASE (IHD) (ANGINA PECTORIS)
 MYOCARDIAL INFARCTION
ANGINA PECTORIS:
 THERE IS REDUCED CORONARY ARTERY BLOOD FLOW DUE
TO ATHEROSCLEROSIS (CHOLESTROL DEPOSITION
SUBENDOCARDIALLY -- Plaque)
34

Applied Aspect
THE C A D.
35

THE CONDUCTION SYSTEM
 An inherent and rhythmical electrical activity is the
reason for the heart’s lifelong beat. The source of
this electrical activity is a network of specialized
cardiac muscle fibers called autorhythmic fibers
because they are self-excitable. Autorhythmic fibers
repeatedly generate action potentials that trigger
heart contractions.

 They act as a pacemaker, setting the rhythm of
electrical excitation that causes contraction of the
heart.
 They form the conduction system, a network of
specialized cardiac muscle fibers that provide a
path for each cycle of cardiac excitation to progress
through the heart. The conduction system ensures
that cardiac chambers become stimulated to con-tract
in a coordinated manner, which makes the
heart an effective pump.

 Cardiac action potentials propagate through the
conduction system in the following sequence .
 Cardiac excitation normally begins in the sinoatrial (SA)
node, natural pacemaker located in the right atrial wall
just inferior to the opening of the superior vena cava. SA
node cells do not have a stable resting potential. Rather,
they repeatedly depolarize to threshold spontaneously.
The spontaneous depolarization is a pacemaker
potential. When the pacemaker potential reaches
threshold, it triggers an action potential. Each action
potential from the SA node propagates throughout both
atria via gap junctions in the intercalated discs of atrial
muscle fibers. Following the action potential, the atria
contract.

 By conducting along atrial muscle fibres, the action
potential reaches the atrioventricular (AV) node,
located in the septum between the two atria, just
anterior to the opening of the coronary sinus .
 From the AV node, the action potential enters the
atrioventricular (AV) bundle (also known as the
bundle of His). This bundle is the only site where
action potentials can conduct from the atria to the
ventricles. (Elsewhere, the fibrous skeleton of the
heart electrically insulates the atria from the
ventricles.)

 After propagating along the AV bundle, the action
potential enters both the right and left bundle
branches. The bundle branches extend through the
interventricular septum toward the apex of the
heart.
 Finally, the large-diameter Purkinje fibers rapidly
conduct the action potential from the apex of the
heart upward to the remainder of the ventricular
myocardium. Then the ventricles contract, pushing
the blood upward toward the semilunar valves

CARDIAC CYCLE
 term referring to all or any of the events related to
the flow or blood pressure that occurs from the
beginning of one heartbeat to the beginning of the
next. The frequency of the cardiac cycle is
described by the heart rate

THE CARDIAC CYCLE
 In each cariac cycle, the atria and ventricles
alternately contract and relax, forcing blood from
areas of lower pressure. As a chamber of the heart
contracts , blood pressure within it increases.
Pressure of the right is lower than that of the left.
Each ventricle , hoeever , expels the same volume
of blood per beat, and the same pattern exist for
both the chambers. When hart rate is 75beats /min
, a cardiac cycle lasts 0.8 sec. To examine and
correlate the events taking place during a cardiac
cycle.

 The first stage, "early diastole," is when the
semilunar valves close, the atrioventricular (AV)
valves are open, and the whole heart is relaxed.
The second stage, "atrial systole," is when the
atrium contracts, and blood flows from atrium to the
ventricle. The third stage, "isovolumic contraction"
is when the ventricles begin to contract, the AV and
semilunar valves close, and there is no change in
volume. The fourth stage, "ventricular ejection," is
when the ventricles are contracting and emptying,
and the semilunar valves are open.

 . During the fifth stage, "isovolumic relaxation time",
pressure decreases, no blood enters the ventricles, the
ventricles stop contracting and begin to relax, and the
semilunar valves close due to the pressure of blood in
the aorta.
 Throughout the cardiac cycle, blood pressure increases
and decreases. The cardiac cycle is coordinated by a
series of electrical impulses that are produced by
specialized heart cells found within the sinoatrial node
and the atrioventricular node. The cardiac muscle is
composed of myocytes which initiate their own
contraction without the help of external nerves (with the
exception of modifying the heart rate due to metabolic
demand). Under normal circumstances, each cycle
takes 0.8 seconds

 . Each beat of the heart involves five major stages.
The first two stages, often considered together as
the "ventricular filling" stage, involve the movement
of blood from the atria into the ventricles. The next
three stages involve the movement of blood from
the ventricles to the pulmonary artery (in the case
of the right ventricle) and the aorta (in the case of
the left ventricle).

 Atrial systole
 Systole , which lasts about 0.1 sec, the atria are
contracting. At the same time, the ventricles are relaxed.
 Depolarisation of the SA node causes atrial
depolarisation, marked by the P wave in the ECG.
 Atrial depolarisation causes atrial systole . as the atria
contracts , they exrt pressure on the blood within , which
forces blood through the open AV valves into the
ventricles.
 Atrial systole contributes a final 25 mL of blood to the
volume already in each ventricle the end of atrial systole
is also end of ventricular diastole. Thus each ventricle
contain about 130mLat the end of its relaxation
period(diastole) .This blood volume is called the end-diastolic
volume.(EDV)

 Ventricular systole
 During ventricular systole which last about 0.3sec the
ventricles are contracting. At the same , the atria
are relaxed, in atrial diastole.
 5. Ventricular depolarisation causes ventricular systole.
As ventricular systole begins , pressure rise inside the
ventricles and pushes blood up against the AV valves ,
forcing them shut for about 0.05 seconds , both the SL
and AV valves are closed this is the period of isometric
contraction . During this interval cardiac musclefibres
are contracting and exerting force but are not
shortening. Thus the muscle contraction is uiso metric .
moreover , because all four valves are closed, the
ventricular volume remains the same( isovolumic)

 . Continued contraction of the ventricles cause
pressure inside the chambers to rise sharply. when
left ventricular pressure surpasses the aortic
pressure at about 80 mmHg and the right
ventricular pressure rises above the pressure in the
pulmonary trunk(about 20 mmHg), both SLs are
open is ventricular ejection and lasts for about 0.24
sec. The pressure in the left ventricle continues to
rise to about 120mmHg, where as pressure in the
the right ventricle climbs to about 25-30mmHg.


 The left ventricle ejects about 70mLof blood into the
aorta and right ventricle and ejects the same
volume of blood into the pulmonary trunk. The
voume remaining in each ventricle at the end of the
systole, about 60mL, is the end systolic
volume(ESV). Stroke volume , the volume
ejectedper beat fro each ventricle, equals end-diastolic
volume minus end systolic
volume.SV=EDV-ESV. At rest, the stroke volume is
about 130mL-60mL=70 mL
 The T wave in the ECG marks the onset of
ventricular repolarisation

CARDIAC OUTPUT
 Cardiac output (CO) is the volume of blood ejected
from the left ventricle (or the right ventricle) into the
aorta (or pulmonary trunk) each minute. Cardiac
output equals the stroke volume (SV), the volume
of blood ejected by the ventricle during each
contraction, multiplied by the heart rate (HR), the
number of heartbeats per minute:
 CO = SV X HR

REGULATION OF STROKE VOLUME
 A healthy heart will pump out the blood that entered its
chambers during the previous diastole. In other words, if
more blood returns to the heart during diastole, then
more blood is ejected during the next systole. At rest,
the stroke volume is 50-60% of the end-diastolic volume
because 40-50% of the blood remains in the ventricles
after each contraction (end-systolic volume). Three
factors regulate stroke volume and ensure that the left
and right ventricles pump equal volumes of blood: (1)
preload, the degree of stretch on the heart before it
contracts; (2) contractility, the forcefulness of contraction
of individual ventricular muscle fibers; and (3) afterload,
the pressure that must be exceeded before ejection of
blood from the ventricles can occur.

 Preload: Effect of Stretching
 A greater preload (stretch) on cardiac muscle fibers
prior to contraction increases their force of
contraction. Preload can be compared to the
stretching of a rubber band. The more the rubber
band is stretched, the more forcefully it will snap
back. Within limits, the more the heart fills with
blood during diastole, the greater the force of
contraction during systole. This relationship is
known as the Frank-Starling law of the heart. The
preload is proportional to the end-diastolic volume

 Contractility
 The second factor that influences stroke volume is myocardial
contractility, the strength of contraction at any given preload.
Substances that increase contractility are positive inotropic
agents; those that decrease contractility are negative inotropic
agents.Thus, for a constant preload, the stroke volume
increases when a positive inotropic substance is present.
Positive inotropic agents often promote Ca2+ inflow during
cardiac action potentials, which strengthens the force of the next
contraction. Stimulation of the sympathetic division of the
autonomic nervous system (ANS), hormones such as
epinephrine and norepinephrine, increased Ca2+ level in the
interstitial fluid, and the drug digitalis all have positive inotropic
effects. In contrast, inhibition of the sympathetic division of the
ANS, anoxia, acidosis, some anesthetics, and increased K+ level
in the interstitial fluid have negative inotropic effects. Calcium
channel blockers are drugs that can have a negative inotropic
effect by reducing Ca2+ inflow, thereby decreasing the strength of
the heartbeat.

AFTER LOAD
 Ejection of blood from the heart begins when pressure in
the right ventricle exceeds the pressure in the
pulmonary trunk (about 20 mmHg), and when the
pressure in the left ventricle exceeds the pressure in the
aorta (about 80 mmHg). At that point, the higher
pressure in the ventricles causes blood to push the
semilunar valves open. The pressure that must be
overcome before a semilunar valve can open is termed
the afterload. An increase in afteiload causes stroke
volume to decrease, so ^ more blood remains in the
ventricles at the end of systol^ Conditions that can
increase afterload include hypertension (eie vated blood
pressure) and narrowing of arteries by atherosclerosis

REGULATION OF HEART RATE
 Cardiac output depends on both heart rate and stroke
volume. Adjustments in heart rate are important in the short-term
control of cardiac output and blood pressure. The
sinoatrial (SA) node initiates contraction and, if left to itself,
would set a constant heart rate of about 100 beats/min.
However, tissues require different volumes of blood flow under
different conditions. During exercise, for example, cardiac
output rises to supply working tissues with increased amounts
of oxygen and nutrients. Stroke volume may fall if the
ventricular myocardium is damaged or if blood volume is
reduced by bleeding. In these cases, homeostatic
mechanisms maintain adequate cardiac output by increasing
the heart rate and contractility. Among the several factors that
contribute to regulation of heart rate, the most important are
the autonomic nervous system and hormones released by the
adrenal medullae (epinephrine and norepinephrine).

AUTONOMIC REGULATION OF HEART RATE
 Nervous system regulation of the heart originates in
the cardiovascular centre in the medulla oblongata.
This region of the brain stem receives input from a
variety of sensory receptors and from higher brain
centres, such as the limbic system and cerebral
cortex. The cardiovascular centre then directs
appropriate output by increasing or decreasing the
frequency of nerve impulses in both the
sympathetic and parasympathetic branches of the
ANS .

DETERMINANTS OF BP AND REGULATION
 These are the fundamental factors which determine
the value of BP. They are 1. Cardiac
output2.peripheral vascular resistance these are
also called as factors controlling BP.
 BP= cardiac outputperipheral resistance
 Regulation of BP means physiological mechanism
by which BP homeostasis is maintained. Two types
of regulatory mechanisms are there.

 1) Short term: Short term regulations are achieved by
neural regulations where as long term regulations are
achieved by controlling blood volume and Na retension
via renal mechanisms.
 Nervous SystemControl :BP by changing blood
distribution in the body and by changing blood vessel
diameter. Sympathetic & Parasympathetic activity will
affects veins, arteries & heart to control HR and force of
contraction .The vasomotor center cluster of
sympathetic neurons found in the medulla.It sends
efferent motor fibers that innervate smooth muscle of
blood vessels.
 .


SHORT-TERM REGULATION OF RISING
BLOOD
 Pressure :Rising blood pressure Stretching of
arterial walls .Stimulation of baroreceptors in
carotid sinus, aortic arch, and other large arteries of
the neck and thorax Increased impulses to the brain
 Baroreceptors :The best known of nervous
mechanisms for arterial pressure control
(baroreceptor reflex)Baroreceptors are stretch
receptors found in the carotid body, aortic body and
the wall of all large arteries of the neck and thorax.
Respond progressively at 60-180 mm Hg.Respond
more to a rapidly changing pressure than stationary
pressure.
 .

 Effect of Baroreceptors :Baroreceptors entered
the medulla (tractussolitarius)Secondary signals
inhibit the vasoconstrictor center of medulla and
excite the vagal parasympathetic center effect
vasodilatation of the veins and arterioles
decreased heart rate and strength of heart
contractiontherefore, excitation of baroreceptors
by high pressure in the arteries reflexly causes
arterial pressure to decrease (as decrease in PR
and CO) Conversely, low pressure has opposite
effects,reflexly causing the pressure rise back to
normal

 Increased Parasympathetic Activity: Effect of
increased parasympathetic and decreased sympathetic
activity on heart and blood pressure: Increased activity
of vagus (parasympathetic) nerve .Decreased activity of
sympathetic cardiac Nerves Reduction of heart rate
.Lower cardiac output .Lower blood pressure
 Decreased Sympathetic Activity Effect of decreased
sympathetic activity on arteries and blood pressure:
Decreased activity of vasomotor fibers (sympathetic
nerve fibers)Relaxation of vascular smooth
muscle.Increased arterial diameterLower blood pressure
 2)

 Long term:long term control is achieved by
adjusting the blood volume and lowering Ca
concentration in the VSM.
 Hormones :1)ADH reduces water excreation and
causes water conservation.2) Renin ultimately
cause production of angiotensin II causes
aldosterone production which leads to the water
and sodium retension.
 ANP:released when atria are stretched . it causes
dieresis and reduce blood volume and BP.
 Role of Ca ions in the VSM : Its accumulation
causes rise in the vascular tone and increases the
vascular tone

STRUCTURE OF THE RESPIRATORY SYSTEM
 The respiratory system consists of the nose,
pharynx, larynx, trachea, bronchi, and lungs.
Structurally, the respiratory system consists of two
portions [1] the term upper respiratory system
refers to the nose, pharynx, and associated
structures. [2] The lower respiratory system refers
to the larynx, trachea, bronchi, and lungs.

 . Functionally, the respiratory system also consists
of two portions. [1] The conducting portion consists
of a series of interconnecting cavities and tubes-nose,
pharynx, larynx, trachea, bronchi,
bronchioles, and terminal bronchioles-that conduct
air in to the lungs.[2] the respiratory portion consists
of those portions of the respiratory system where
the exchange of gases occurs-respiratory
bronchioles, alveolar ducts, alveolar sacs and
alveoli

 upper respiratory system -nose, pharynx &
associated structures.
 lower respiratory system –
larynx,trachea,bronchi & lungs.

TRACHEA/WIND PIPE
 12 cm long, 2.5 cm in diameter. Located anterior to
esophagus and extends from the larynx to the
superior border of the 5th thoracic vertebra, where it
divides into right & left primary bronchi.
 layers of trachea [ deep to superficial]- mucosa,
submucosa, hyaline cartilage and
adventitia[composed of areolar connective tissue].
 supported by 16-20, C-shaped rings of hyaline
cartliage.

 The open part of ‘C’ faces posteriorly, where it is
spanned by a smooth muscle- trachealis.
 The gap in the ‘C’ allows room for the esophagus
to expand as swallowed food passes by.
 At the point where the trachea divides into right &
left primary bronchi, there is an internal ridge called
carina, it is the most sensitive part for triggering a
cough reflex.

BRONCHI
 At superior border of thoracic vertebra, trachea
divides into right & left primary bronchi.
 Right bronchus is more vertical, shorter and wider
than the left. As a result aspirated object is more
likely to enter & lodge in the right primary bronchus
than left.
 On entering the lungs, primary bronchi divide to
form secondary [lobar ] bronchi, one for each lobe
of the lung. [right has 3 & left has 2 lobes].

BRONCHIAL TREE
secondary bronchi
tertiary[ segmental] bronchi
bronchioles
terminal bronchioles
respiratory bronchioles

CONTD..
alveolar ducts
alveolar sacs[ grape like clusters of alveoli]

LUNGS
 essential organs of respiration, two in number,
placed on either side within the thorax, separated
by mediastinum
 conical organ, with broad concave base resting on
the diaphragm& a blunt peak called the apex,
projecting slightly superior to the clavicle.

PARTS OF THE LUNG
 Each lung has an apex,base,3 borders and 2
surfaces.
 has mediastinal & costal surface[ two surfaces].
 costal surface- broad and pressed against the rib
cage.
 mediastinal surface- smaller, concave and faces
medially.
 Apex[apex pulmonis]-rounded & extends to the
root of the neck[2.5-4cm above the level of sternal
end of first rib]

 The base[basis pulmonis]- is broad, concave & rest
on the convex surface of diaphragm.
 borders- inferior border, posterior border & anterior
border.
 inferior border- separates the base from the costal
surface .
 posterior border- is broad & rounded& is received
into the deep concavity on either side of the
vertebral column.
 anterior border- thin& sharp, and overlaps the front
of pericardium.

STRUCTURE OF THE LUNG
 composed of an external serous coat, a subserous
areolar tissue & the pulmonary substance[parenchyma].
 serous coat- is the pulmonary pleura ; it is thin,
transparent.
 subserous pleura- contains a large proportion of elastic
fibers.
 the parenchyma- is composed of secondary lobules,
which are connected by interlobular areolar tissue.
 each secondary lobule – is composed of several
primary lobules[ the anatomical unit of the lung].
 primary lobule- consists of an alveolar duct, the air
spaces connected with it & their blood
vessels,lymphatics and nerves.

VESSELS AND NERVES OF THE LUNGS
 Bronchial arteries- supply blood for the nutrition the
lungs; they derived from the thoracic aorta or from
the the upper aortic intercostal arteries.
 pulmonary artery- conveys the venous blood to the
lungs; it divides & redivides to form a dense
capillary network in the walls of the alveoli. In the
septa between the alveoli the capillary network
forms a single layer.
 pulmonary vein- commence in the pulmonary
capillaries& enter into larger ranches.

 Bronchial vein- is formed at the root of the lung and
ends on the right side in the azygous vein , & on the
left side in the highest intercostal or in the
accessory hemiazygous vein.

LUNGS
 right lung- three lobes;- superior, middle, inferior.
Two fissures.[oblique and horizontal]
 left lung- little smaller than right, cardiac
impression, two lobes-superior& inferior, one
fissure[oblique fissure].
 Hilum- a roughly triangular shaped slit in the
mediastinal surface through which bronchus, blood
vessels, lymphatics& nerves pass. It constitutes
the root of the lung

ALVEOLI
 alveolus- is a pouch about 0.2-0.5 mm in diameter.
 Its wall consists predominantly of squamous [type 1]
alveolar cells-thin cells that allow for rapid gas diffusion
between the alveolus & bloodstream; about 5% of the
alveolar cells are round to cuboidal great [type 2]
alveolar cells
 type 2 alveolar cells- secrete a detergent-like lipoprotein
called pulmonary surfactant, which form a thin film on
the insides of the alveoli & bronchioles.
 Alveolar macrophages[dust cells]- wander the lumen of
the alveoli & the connective tissue between them.

 Each alveolus is surrounded by a basket of blood
capillaries supplied by the pulmonary artery. The
barrier between the alveolar air and blood , called
the respiratory membrane; consists only of the
squamous type1 alveolar cell, the squamous
endothelial cell of the capillary, and their fused
basement membranes. These have a total
thickness of only o.5 μm.

THE PLEURAE
 visceral pleurae- serous membrane covering the
surface of the lung.
 parietal pleura- outer surface.
 pleural cavity- space b/w visceral & parietal
pleurae.
 functions- reduction of friction, creation of pressure
gradient, compartmentalization.

PHYSIOLOGY OF RESPIRATION
 inspiration- breathing in..
 principle inspiratory muscles- the diaphragm &
external intercostals.
 stimulation of diaphragm by the phrenic nerve
diaphragm becomes tenses & flattens
this enlarges the thoracic cavity& reduces its
internal pressure

this force air in to the lungs
 other muscles also help-the scalenes fix the first
pair of ribs while the external intercostal muscle lift
the remaining ribs like bucket handles, making
them swing up and out- this also forces air into the
lungs.
 deep inspiration – is aided by the pectoralis minor,
sternocleidomastoid, and erector spinae muscles.

 expiration- passive process . It is achieved by the
elasticity of the lungs and the thoracic cage- i.e.,
the tendency to return to their original dimensions
when released from tension.
 pause- when inspiration ceases, the phrenic
nerves continue to stimulate the diaphragm for a
little longer; it makes the transition from inspiration
to expiration smoother.

LUNG VOLUMES AND CAPACITIES
 Lung volumes and lung capacities refer to
the volume of air associated with different phases
of the respiratory cycle. Lung volumes are directly
measured; Lung capacities are inferred from lung
volumes.
 The healthy adult averages 12 respirations a
minute and moves about 6 liters of air into and out
of the lungs while at rest.

CNTD..
 tidal volume- the total amount of air moves into and
out of the airways with each inspiration and
expiration during normal quiet breathing.
[vT][500ml]
 About 150 mL of it (typically 1 mL per pound of
body weight) fills the conducting division of the
airway. Since this air cannot exchange gases with
the blood, it is called dead air, and the conducting
division is called the anatomic dead space.

 Physiologic (total) dead space- is the sum of
anatomic dead space and any pathological alveolar
dead space that may exist. In healthy people, few
alveoli are nonfunctional, and the anatomic and
physiologic dead spaces are identical.
 The total volume of air taken in during 1 minute is
called the minute volume of respiration [MVR] or
minute ventilation. It is calculated by multiplying
the tidal volume by the normal breathing rate per
minute.[500×12= 6000ml/mt].

 The alveolar ventilation rate [AVR] is the volume
of air per minute that reaches the alveoli.


 Inspiratory reserve volume (IRV)[3,000 mL]:-
Amount of air in excess of tidal inspiration that can
be inhaled with maximum effort.
 Expiratory reserve volume (ERV)[1,200 mL]:-
Amount of air in excess of tidal expiration that can
be exhaled with maximum effort.
 Residual volume (RV)[1,300 mL]:-Amount of air
remaining in the lungs after maximum expiration;
keeps alveoli inflated between breaths and mixes
with fresh air on next inspiration.

 Vital capacity (VC)[4,700 mL]:-Amount of air that
can be exhaled with maximum effort after maximum
inspiration (TV + IRV + ERV); used to assess
strength of thoracic muscles as well as pulmonary
function.
 Inspiratory capacity (IC)[3,500 mL]:-Maximum
amount of air that can be inhaled after a normal
tidal expiration (TV + IRV).
 Functional residual capacity (FRC)[2,500 mL]:-
Amount of air remaining in the lungs after a normal
tidal expiration (RV + ERV)

 Total lung capacity (TLC)[6,000 mL]:-Maximum
amount of air the lungs can contain (RV + VC).

PATTERNS OF BREATHING
 Apnea -Temporary cessation of breathing (one or
more skipped breaths).
 Dyspnea-Labored, gasping breathing; shortness of
breath.
 Eupnoea-Normal, relaxed, quiet breathing; typically
500 mL/breath, 12 to 15 breaths/min.
 Hyperpnea -Increased rate and depth of breathing
in response to exercise, pain, or other conditions.

 Hyperventilation-Increased pulmonary ventilation in
excess of metabolic demand, frequently associated
with anxiety; expels C02 faster than it is produced,
thus lowering the blood C02 concentration and
raising the pH.
 Hypoventilation-Reduced pulmonary ventilation;
leads to an increase in blood C02 concentration if
ventilation is insufficient to expel C02 as fast as it is
produced.
 Kussmaul-Deep, rapid breathing often induced by
acidosis, as in diabetes mellitus.

 Orthopnea -Dyspnea that occurs when a person is
lying down.
 Respiratory arrest-Permanent cessation of
breathing (unless there is medical intervention).
 Tachypnea -Accelerated respiration .

GAS EXCHANGE & TRANSPORT
 External[pulmonary] respiration-It is the exchange
of O2 and CO2 between air in the alveoli of the lungs
and blood in pulmonary capillaries. It results in the
conversion of deoxygenated blood coming from
heart to oxygenated blood.
 factors that affect the efficiency of alveolar gas
exchange:-
 concentration gradient of gases[ie, po2 & pco2]
 Solubility of the gases
 Membrane area
 Ventilation-perfusion coupling.

 Internal respiration-The exchange of oxygen and
carbon dioxide between tissue blood capillaries and
tissue cells called internal[tissue]respiration.it
results in the conversion of oxygenated blood into
deoxygenated blood.
 Oxygenated blood entering tissue capillaries has a
pO2 of 100 mm Hg, where as tissue cells have an
average Po2 of 40 mm of Hg. Because of this
difference , oxygen diffuses from the oxygenated
blood through interstitial fluid and into tissue cells
until the pO2 in the blood decreases to 40 mm of
Hg

 While oxygen diffuses from the tissue blood
capillaries to tissue cells, carbon dioxide diffuses in
the opposite direction.

GAS TRANSPORT
 1. oxygen-
 The concentration of oxygen in arterial blood, by volume, is
about 20 mL/dL. About 98.5% of this is bound to hemo-globin
and 1.5% is dissolved in the blood plasma.
 2. Carbon dioxide-
 a] About 90% of the CO2 is hydrated (reacts with water) to
form carbonic acid, which then dissociates into bicarbonate
and hydrogen ions.
 B] About 5% binds to the amino groups of plasma proteins
and hemoglobin to form carbamino compounds—chiefly,
carbaminohemoglobin (HbCO2).
 c] The remaining 5% of the CO2 is carried in the blood as
dissolved gas.

CONTROL OF RESPIRATION
 There are four main centers in the brain to regulate
the respiration:
 1. Inspiratory center
 2. Expiratory center
 3. Pneumotaxic center
 4. Apneustic center. The first two centers are
present on the medulla oblongata whereas the last
two centers on the Pons region of brain.

THORACIC CAVITY
 The thoracic cavity (or chest cavity) is the
chamber of the human body (and other animal
bodies) that is protected by the thoracic wall
(thoracic cage and associated skin, muscle, and
fascia).
 The heart and lungs are situated in the thorax, the
walls of which afford them protection. The heart lies
between the two lungs, and is enclosed within a
fibrous bag, the pericardium, while each lung is
invested by a serous membrane, the pleura.

COMPONENTS
 Structures within the thoracic cavity include:
 structures of the cardiovascular system, including
the heart and great vessels, which include the
thoracic aorta, the pulmonary artery and all its
branches, the superior and inferior vena cava, the
pulmonary veins, and the azygos vein
 structures of the respiratory system, including the
trachea, bronchi and lungs

 structures of the digestive system, including the
esophagus,
 endocrine glands, including the thymus gland,
 structures of the nervous system including the
paired vagus nerves, and the paired sympathetic
chains,
 lymphatics including the thoracic duct.
 It contains three potential spaces lined with
mesothelium: the paired pleural cavities and the
pericardial cavity. The mediastinum comprises
those organs which lie in the centre of the chest
between the lungs

THE CAVITY OF THE THORAX
(1) the space enclosed by the lower ribs is occupied
by some of the abdominal viscera; and (2) the
cavity extends above the anterior parts of the first
ribs into the neck. The size of the thoracic cavity is
constantly varying during life with the movements of
the ribs and diaphragm, and with the degree of
distention of the abdominal viscera. From the
collapsed state of the lungs as seen when the
thorax is opened in the dead body, it would appear
as if the viscera only partly filled the cavity, but
during life there is no vacant space, that which is
seen after death being filled up by the expanded
lungs

THE UPPER OPENING OF THE THORAX
 The parts which pass through the upper opening of the
thorax are, from before backward, in or near the middle
line, the Sternohyoideus and Sternothyreoideus
muscles, the remains of the thymus, the inferior thyroid
veins, the trachea, esophagus, thoracic duct, and the
Longus colli muscles; at the sides, the innominate artery,
the left common carotid, left subclavian and internal
mammary arteries and the costocervical trunks, the
innominate veins, the vagus, cardiac, phrenic, and
sympathetic nerves, the greater parts of the anterior
divisions of the first thoracic nerves, and the recurrent
nerve of the left side. The apex of each lung, covered by
the pleura, also projects through this aperture, a little
above the level of the sternal end of the first rib.

THE LOWER OPENING OF THE THORAX.—
 The lower opening of the thorax is wider transversely
than from before backward. It slopes obliquely
downward and backward, so that the thoracic cavity is
much deeper behind than in front. The diaphragm
closes the opening and forms the floor of the thorax.
The floor is flatter at the center than at the sides, and
higher on the right side than on the left; in the dead body
the right side reaches the level of the upper border of
the fifth costal cartilage, while the left extends only to the
corresponding part of the sixth costal cartilage. From the
highest point on each side the floor slopes suddenly
downward to the costal and vertebral attachments of the
diaphragm; this slope is more marked behind than in
front, so that only a narrow space is left between the
diaphragm and the posterior wall of the thorax.

BLOOD VESSELS
 The blood vessels are the part of the circulatory
system that transports blood throughout the body.
There are three major types of blood vessels: the
arteries, which carry the blood away from the heart;
the capillaries, which enable the actual exchange of
water and chemicals between the blood and the
tissues; and the veins, which carry blood from the
capillaries back toward the heart

ANATOMY
 The arteries and veins have three layers, but the middle
layer is thicker in the arteries than it is in the veins:
 Tunica intima (the thinnest layer): a single layer of
simple squamous endothelial cells glued by a
polysaccharide intercellular matrix, surrounded by a thin
layer of subendothelial connective tissue interlaced with
a number of circularly arranged elastic bands called the
internal elastic lamina.
 Tunica media (the thickest layer in arteries): circularly
arranged elastic fiber, connective tissue, polysaccharide
substances, the second and third layer are separated by
another thick elastic band called external elastic lamina.
The tunica media may (especially in arteries) be rich in
vascular smooth muscle, which controls the caliber of
the vessel.

 Tunica adventitia: (the thickest layer in veins)
entirely made of connective tissue. It also contains
nerves that supply the vessel as well as nutrient
capillaries (vasa vasorum) in the larger blood
vessels.
 Capillaries consist of little more than a layer of
endothelium and occasional connective tissue.
 When blood vessels connect to form a region of
diffuse vascular supply it is called an anastomosis
(pl. anastomoses). Anastomoses provide critical
alternative routes for blood to flow in case of
blockages.

TYPES
 Blood vessel with an erythrocyte (red blood cell, E)
within its lumen, endothelial cells forming its tunica
intima (inner layer), and pericytes forming its tunica
adventitia (outer layer)
 There are various kinds of blood vessels:
 Arteries
 Aorta (the largest artery, carries blood out of the
heart)
 Branches of the aorta, such as the carotid artery,
the subclavian artery, the celiac trunk, the
mesenteric arteries, the renal artery and the iliac
artery.
 Arterioles

 Capillaries (the smallest blood vessels)
 Venules
 Veins
 Large collecting vessels, such as the subclavian vein, the
jugular vein, the renal vein and the iliac vein.
 Venae cavae (the two largest veins, carry blood into the
heart).
 They are roughly grouped as arterial and venous, determined
by whether the blood in it is flowing away from (arterial) or
toward (venous) the heart. The term "arterial blood" is
nevertheless used to indicate blood high in oxygen, although
the pulmonary artery carries "venous blood" and blood flowing
in the pulmonary vein is rich in oxygen. This is because they
are carrying the blood to and from the lungs, respectively, to
be oxygenated.

PHYSIOLOGY
 Blood vessels do not actively engage in the transport of
blood (they have no appreciable peristalsis), but
arteries—and veins to a degree—can regulate their
inner diameter by contraction of the muscular layer. This
changes the blood flow to downstream organs, and is
determined by the autonomic nervous system.
Vasodilation and vasoconstriction are also used
antagonistically as methods of thermoregulation.
 Oxygen (bound to hemoglobin in red blood cells) is the
most critical nutrient carried by the blood. In all arteries
apart from the pulmonary artery, hemoglobin is highly
saturated (95-100%) with oxygen. In all veins apart from
the pulmonary vein, the hemoglobin is desaturated at
about 75%. (The values are reversed in the pulmonary
circulation.)

 The blood pressure in blood vessels is traditionally
expressed in millimetres of mercury (1 mmHg = 133 Pa).
In the arterial system, this is usually around 120 mmHg
systolic (high pressure wave due to contraction of the
heart) and 80 mmHg diastolic (low pressure wave). In
contrast, pressures in the venous system are constant
and rarely exceed 10 mmHg.
 Vasoconstriction is the constriction of blood vessels
(narrowing, becoming smaller in cross-sectional area)
by contracting the vascular smooth muscle in the vessel
walls. It is regulated by vasoconstrictors (agents that
cause vasoconstriction). These include paracrine factors
(e.g. prostaglandins), a number of hormones (e.g.
vasopressin and angiotensin) and neurotransmitters
(e.g. epinephrine) from the nervous system.

 Vasodilation is a similar process mediated by
antagonistically acting mediators. The most
prominent vasodilator is nitric oxide (termed
endothelium-derived relaxing factor for this reason).
 Permeability of the endothelium is pivotal in the
release of nutrients to the tissue. It is also
increased in inflammation in response to histamine,
prostaglandins and interleukins, which leads to
most of the symptoms of inflammation (swelling,
redness, warmth and pain).

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