General histology & classification of glands

2. Objectives
• Introduction
• General Features
• Development
• Classifications
• Examples
• Applied

3. Gland - Introduction
• Some epithelial cells converted in to specialized
cells to perform a secretory function - form glands
• Definition:
An organ of secretion made up of specialized
secretory cells; derived from surface epithelium
on which it opens

4. General Features of Glands
• Can be present as “Discrete Organ” or “ in the
layers of viscera”
• Epithelial in origin (Derived from surface
epithelium)
• Functional unit of gland is formed by specialized
secretory cells known as – Secretory End Piece
• Fluid secreted by glands contain enzymes, mucus,
hormones, protein, fat etc…

5. General Features of Glands
• Rate of secretion is modulated by Nervous &
Hormonal influence
• Secretory end piece of some exocrine glands is
surrounded by star shaped contractile cells that lies
between cells & basement membrane
–Called Myo-epithelial cells
–Share features of both
epithelium & muscle cell
–Help in expulsion of
secretions

6. Glandular Epithelium

7. Development of Glands
Developed as cords of
epithelial cells from the
surface of membrane
Invaginates in to underlying
Connective tissue &
Form 2 parts
Proximal
Part
Distal Part

8. Development of Glands
Form duct
Connect secretory end piece
with surface of epithelium
Proximal Part
Distal Part
Exocrine Glands
Differentiated in to
the secretory cells
Secretory End Piece
Pours the secretion through ducts / directly on
surface of the glands or epithelium

9. Development of Glands
DisappearProximal Part
Distal Part
Endocrine Glands
Form islands of the secretory
cells permeated / surrounded
by the blood capillaries
Pours their secretion in to directly in to blood
through the blood capillaries
Ductless Gland *

10. • Develop as invagination of the epithelium into
the underlying vascular connective tissue.
• Distal part forms glandular or Secretory end
Piece – functionally an active portion.
• Proximal part - Excretory Duct-opens on the
surface of the epithelium = Exocrine Gland
• Some cells get detached from the epithelial
surface- Ductless or endocrine glands
Development of Glands

11. Based on Site of Secretion
Exocrine
With Ducts
Endocrine
Ductless
Exocrine +
Endocrine
Paracrine
Classification of Glands
Unicellular /
Multicellular
Cord & Clump type/
Follicular Type
Pancreas &
Liver
APUD &
DNES
APUD – Amine Precursor Uptake & Decarboxylation
DNES - Diffuse NeuroEndocrine System

12. Classifications of Exocrine Glands
Based on numbers of cell
Unicellular Multicellular
Goblet Cell

13. Multicellular Exocrine Glands
1. Based on branching pattern of ducts
Simple
No Branching
Compound
Branched

14. Multicellular Exocrine Glands
2. Based on Shape of Secretory End Piece
Tubular Alveolar /
Acinar
Tubulo-
alveolar

15. Multicellular Exocrine Glands
3. Based on Nature of Secretion
Mucous Serous Mixed /
Sero-mucous

16. Multicellular Exocrine Glands
4. Based on Manner of Secretion
Merocrine Apocrine Holocrine Cytocrine

17. Multicellular Exocrine Glands
5. Based on Development of gland
Ectodermal Endodermal Mesodermal

18. Glands -Based on Site of Secretion
• Endocrine :- Ductless
• Exocrine :- With Ducts
• Exocrine + Endocrine
• Paracrine

19. • Ductless / Internally secretory gland
• Secrete hormones & useful chemical
substances in blood capillaries
• Cells & blood vessels are supported
by connective tissue & surrounded by
capsule
• 2 types:
– Cord & Clump type
– Follicular Type
Endocrine Glands

20. Cord & Clump Type Follicular Type
Endocrine Glands
Cells arranged in irregular
Cords / clumps permeated
by capillaries
Cells arranged in follicles
surrounded by capillaries
Secretions directly delivered
outward in capillaries
Secretions delivered
inward inside the follicles

21. Cord & Clump Type Follicular Type
Endocrine Glands
Secretions stored inside
the cells
“Intra-cellular method”
Secretions stored outside
the cells inside follicles
“Extra-cellular method”
E.g. Most endocrine glands
Pituitary, Adrenal,
Parathyroid, Pineal
E.g.
Thyroid Gland

23. • Act locally / Secretions do not
travel through blood
• Secrete its products(hormones) in
to local extracellular environment
• Exert effects only on neighboring
cells in vicinity of secreting cells
• E.G.
– Enteroendocrine cells of GIT
– Diffuse neuroendocrine system
(DNES)
Paracrine Glands

24. Entero-endocrine cells of GIT

25. • With Ducts / Externally secretory
gland
• Secrete its products on to the
surface through it’s duct
• Consist of 3 components
– Secretory end piece
– Duct System
– Supporting Connective
tissues
• E.G. All Salivary Glands
Exocrine Glands
Parenchyma
Stroma
Parenchyma

26. Exocrine Glands
Lobes
Lobules
Blood Vessels & Nerves
Parenchyma Stroma
Inter-lobar
Septa
Capsule
Ducts
Inter-lobular Septa

27. General Architecture of a Exocrine Gland
Parenchyma-
• Secretory end pieces- Acini / tubules / tubulo-acinar
• Ducts- Intralobular, interlobular, main excretory duct
Stroma-
• Capsule
• Septa (interlobular, interlobar)
• Loose inter-lobular connective tissue supporting the
parenchyma
• Divide the gland into lobes and lobules.

28. Based on Number of cells:
• Unicellular
• Multicellular
Exocrine Glands - Classification

29. • Has only single cell
• Interspersed among other non-secretory epithelial cells
• E.G.
– Goblet cells in respiratory & intestinal tract
• Secrete mucous by partial destruction of cell memb.
• In H&E staining – looks empty
• Mucous stained by PAS (Periodic acid schiff) & Alcian
Blue staining
Unicellular Gland

30. Unicellular Gland
PAS (Periodic acid schiff) Alcian Blue

31. Exocrine glands
Based on number of ducts
• Simple(single duct)
• Compound(minor & major ducts)
Based on shape of secretory piece:
• Simple tubular/ alveolar
• Simple branched tubular/ alveolar
• Simple coiled tubular
• Compound tubular/ acinar
• Compound tubulo-alveolar / acinar

32. • Simple:
– Secretion poured to surface by
un-branched duct
• Compound:
– Duct divides in to branches to form
elaborated / complex duct system;
– Each smaller terminal duct receive
secretion from it’s own secretory end
piece
– These ducts unite to form larger
ducts which finally drain on to surface
Based on Number of Ducts:

33. • Tubular: (Simple / Compound)
– Secretory end piece is like tubule
– Straight, branched or coiled
Based on Shape of Secretory End Piece:
Simple
Straight
Intestinal Crypts
Simple
Coiled
Sweat Gland
Simple Branched
Uterine gland
Fundic & pyloric
glands of stomach
Compound
Cardiac glands
of stomach &
Brunner’s gland
of duodenum

34. Simple Straight Tubular Gland
Intestinal Crypts

35. • Alveolar: (Simple / Compound)
– Secretory end piece Flask shaped
with large lumen
– Un-branched or branched
Simple
Un-branched
Urethral Glands
Simple Branched
Sebaceous &
Tarsal Glands
Compound
Mammary gland betn
puberty & 1st Pregnancy
Based on Shape of Secretory End Piece:

36. • Acinar: (Mostly Compound)
– Secretory end piece Round shaped
with small lumen
– Mostly branched
Compound Acinar
Pancreas
Parotid
Based on Shape of Secretory End Piece:

37. • Tubulo – Alveolar / Acinar:
– Combination of both Tubular &
alveolar / Acinar
– Mostly branched
Compound
Tubulo – Alveolar / Acinar
Sublingual gland
Submandibular gland
Lactating mammary gland
Based on Shape of Secretory End Piece:

38. Simple Glands

39. Compound Glands

40. According to Mode of secretion:
• Merocrine
• Apocrine
• Holocrine
• Cytocrine
Exocrine glands

41. • Merocrine:
– A.K.A.: Eccrine / Epicrine
– Secretion discharged through intact
cell membrane
– By Exocytosis
– No loss of cytoplasm
Based on Mode of Secretion:
E.G.
Protein content of mammary gland
Parotid
Pancreas
Typical sweat gland

42. Merocrine
Exocytosis
Exocrine glands

43. • Apocrine:
– Apical portion (luminal) of cell
disintegrate to discharge its secretion
– Nucleus & basal portion remain intact
from which cell can regenerate
– Partial loss of cytoplasm
Based on Mode of Secretion:
E.G.
Lipid content of mammary gland
Atypical sweat gland (Axilla & Groin)
Ceruminous gland of Ear
Moll’s Gland in Eyelid
Modified Sweat
gland

44. Exocrine glands
Apocrine

45. • Holocrine:
– Entire cell disintegrate to discharge
its secretion
– Result in death of cell
– Complete loss of cytoplasm
Based on Mode of Secretion:
E.G.
Sebaceous gland
Tarsal Glands in Eyelid

46. Exocrine glands
Holocrine

47. • Cytocrine:
– Cell are released
as secretion
Based on Mode of Secretion:
E.G.
Spermatozoa from Testis
Ovum from Ovary
Bone Marrow

48. Exocrine glands
Cytocrine

49. Exocrine glands
Cytocrine

50. According to Nature of secretion:
• Serous
• Mucous
• Mixed
Exocrine glands
Mucous Serous Mixed

51. Serous Acinus / Gland
• Secretion: Thin, watery,
– Rich in enzymes, protein in nature
• Cells: Pyramidal & Small with
Indistinct boundaries
• Cytoplasm: Granular (Zymogen)
– Rich in rER
– Stain darkly with H/E stain
• Nuclei: rounded & basal / central
• Size of lumen: Small
• Function: Enzymatic
• E.G.: Parotid & Lacrimal glands

52. • Secretion: Thick Viscous
– Which collects in the apical part
• Cells: Low Columnar & Large with
distinct boundaries
• Cytoplasm: Mucinogen droplets
– Stain very lightly with H/E stain &
– Looks empty
• Nuclei: Flattened & basal
(mucoid pushes nuclei towards base)
• Size of lumen: Large
• Function: Protection & Lubrication
• E.G.: Sublingual glands
Mucous Acinus / Gland

53. • Contain both serous & mucous
secretory units
• Sometimes serous cells form
crescentic caps on mucous acini
called as Serous Demilunes
Mixed Acinus / Gland

54. Serous
Thin, watery
Proteinaceous
Zymogen granules
Central rounded
Small Lumen
Indistinct
Darkly stained
Enzymatic action
Parotid Gland
Mucous
Thick, viscous
Mucopolysaccharides
Mucinogen droplets
Flat & peripheral
Large Lumen
Distinct
Lighly stained
Protection & lubrication
Sublingual gland
Consistency
Content
Cytoplasm
Nucleus
Lumen
Cell boundaries
H&E Staining
Function
Examples

55. Serous Acini Mucous Acini

56. Serous Acini Mucous Acini

57. According to Development:
• Ectodermal
– Glands of skin, Mammary gland, Lacrimal gland,
– Salivary glands, Pituitary gland & Chromaffin organs
• Mesodermal
– Suprarenal cortex, Gonads, Kidney & Spleen
• Endodermal
– Thyroid, Parathyroid, Thymus
– Liver, Pancreas, Prostate
– Urethra, Bulbo-urethral gland, Greater vestibular gland
– Glands in lining epithelium of respiratory tract
Exocrine glands

58. Clinical
• ADENOMA: Benign tumors arising in the
gland
• ADENOCARCINOMA: Malignant growth in the
gland