The document summarizes the structure and function of several endocrine glands, including the pituitary gland, thyroid gland, parathyroid gland, and adrenal glands. The pituitary gland has an anterior and posterior lobe. The anterior lobe contains chromophils that secrete hormones like growth hormone and prolactin, and chromophobes that act as reserve cells. The thyroid gland contains follicles lined with follicular cells that secrete thyroid hormones and parafollicular cells that secrete calcitonin. The parathyroid glands contain chief cells that secrete parathyroid hormone. The adrenal glands have an outer cortex that produces steroid hormones and an inner medulla that secretes catecholamines.

1. ENDOCRINE SYSTEM
BY GROUP (6)

2. BY GROUP (6)
Endocrine glands= ductless glands
Definition: the sites of synthesis & secretion of
hormones which spread throughout the body
by the bloodstream where they act on target
organs.

3. BY GROUP (6)

4. PITUITARY GLAND (HYPOPHYSIS CEREBRI):
Anatomically:
It is situated inside the hypophyseal fossa (sella
turcica) of the sphenoid bone, connected to the brain
by a stalk called the infundibulum& covered by the
diaphragma sellae.
Histologically:
It is divided into:
a) Anterior lobe (adenohypophysis):
dark& cellular.
b)Posterior lobe (neurohypophysis):
Pale&fibrous.
Development of Pituitary gland:
BY GROUP (6)

5. I- Anterior lobe (Adenohypophysis):
It lies anterior to the hypophyseal cleft.
It iss
ubdivided into 3 parts:
1 Pars distalis.
2 Pars tuberalis.
3 Pars intermedia.
1- Pars distalis:
It iscompos
ed of:
A- Irregular cords of polygonal cells,
B- Surrounded by fenestrated sinusoidal capillaries,
C- Supported by a network of reticular fibers.
It cons
is
tsof 2 typesof cells
:
1- Chromophobes (52%):
 Have weak affinity to stains.
They are cells smaller than the chromophils
 Have a non-granular pale cytoplasm (few organelles).
Function:They do not secrete hormones. They are
reserve cells or degranulated chromophils.
BY GROUP (6)

6. 2- Chromophils (48%):
Have great affinity to stains.
They have granular darkly stained cytoplasm
They are classified according to their granules into
two types:
Acidophils: which have great affinity to acidic stains.
Basophils: which have great affinity to basic stains.
BY GROUP (6)
Chromophils Chromophobes
1- Percentage 48% 52%
2- size Larger Smaller
3- Cytoplasm Granular, dark Non granular, pale
4- Function Secretion of hormones A- Act as a reserve.
B- Degranulated
chromophils.

7. BY GROUP (6)
a- Acidophils (37%):
They secrete hormones of protein in nature. They are
periodic acid Schiff (PAS) negative.
They are smaller than the basophils but contain larger secretory
granules.
EM: protein secreting cells.
Acidophilsareof two types:
1 Somatotrophs: secret growth hormone.
2 Mammotrophs: secret prolactin.
Mammotrophs:
•The secretory granules in these cells are small, but in pregnant and
lactating females they become large and numerous& are called
pregnancy cells or Erdheim cells.
•When suckling is terminated, lysosomes eliminate the excess
secretory granules, a process known as
crinophagy.

8. BY GROUP (6)
b- Basophils (11%):
They secrete hormones of glycoprotein in nature.
They are PAS +ve (except the corticotrophs which secrete a polypeptide hormone (so, it is
PAS –ve).
They are larger than the acidophils but contain smaller secretory granules.
EM: protein secreting cells.
Bas
ophils are three types:
1 Thyrotrophs: secrete thyroid stimulating hormone (TSH).
2 Gonadotrophs: They secrete two hormones:
 Follicle stimulating hormone (FSH).
 Luteinizing hormone (LH)
3- Corticotrophs: secrete adrenocorticotrophic hormone (ACTH).

9. BY GROUP (6)
Acidophils Basophils
1- Percentage 37% 11%
2- Nature of
hormones
Protein Glycoprotein
3- PAS Negative Positive
4- size Smaller Larger
5- Granules Larger Smaller
6- Secretion Somatotrophs
(growth h.)
Mammotrophs
(prolactin)
Thyrotrophs (TSH)
Gonadotrophs
(FSH& LH)
Corticotrophs (ACTH)

10. BY GROUP (6)
2- Pars Tuberalis:
It is a superior extension that surrounds the
infundibular stalk. It is highly vascular.
It isformed of:cords of cells (show
immunoreactivity to ACTH,FSH&LH).
Function:nonspecific.
3- Pars Intermedia:
It lies between the pars distalis and pars nervosa.
It ismade up of: cords of faint
basophilic cells with few secretory
granules.
Function:nonspecific.

11. BY GROUP (6)
II- Posterior lobe (Neurohypophysis):
• It lies posterior to the hypophyseal cleft.
• It consists of 3 parts:
1The Median Eminence: a funnel shaped downward
extension of the hypothalamus.
2 The Infundibular s
talk.
3The Pars Nervosa: which is connected to the base
of the brain by the infundibular stalk and the median
eminence.
It cons
is
tsof:
1- Unmyelinated axons of neurosecretory cells:
Their cell bodies present in the supraoptic& paraventricular
nuclei of the hypothalamus.
 Their axons form the hypothalamo-hypophyseal tract
carrying the neurosecretion from the hypothalamic nuclei to
the pars nervosa.
2- Herring bodies:
 Acidophilic homogenous bodies.
Represent accumulation of neurosecretory granules at
the dilated terminal ends of axons.
3 Pituicytes: modified glial cells to support nutrition&
isolation.
4 Rich fenestrated blood capillaries.
ParsNervosa :

12. BY GROUP (6)
Neurosecretion:
Acts on smooth muscles of the uterus&mammary glands
2- Vasopressin (ADH)
↑ water reabsorption from collecting ducts → concentrated
urine.
1-Oxytocin
Blood supply of pituitary gland:

13. BY GROUP (6)
Anatomically:
It lies in the anterior aspect of the lower part of the neck.
It consists of two lobes connected by an isthmus.
STRUCTURE OF THYROID GLAND :
1- Stroma:
 A double capsule:
a. The outer: is the pretracheal fascia.
b. The inner: is the true CT capsule of the gland.
 CT septa: dividing the gland into incomplete lobes
& lobules.
Reticular fibers: form a
network supporting the
thyroid parenchyma.
2- Parenchyma:
 It is composed of follicles.
The follicles are surrounded by network of fenestrated
blood capillaries.
 They contain a gelatinous acidophilic material in their
lumina called colloid.
They are lined by cuboidal
cells of two types:
follicular cells & parafollicular
cells.

14. 1- Follicular cells:
•Function:Synthesis & secretion of thyroid
hormones (T3&T4).
• LM:
1 Shape: simple cuboidal cells.
2Nucleus: central& rounded.
3- Cytoplasm: basophilic.
N.B: The cells change their shape according to the degree of activity:
 Columnar when they are active.
 Squamous when they are inactive.
•EM
A-Basally:
Numerous profiles of rER.
B- Apically:
1 Supranuclear Golgi.
2 Secretory vesicles containing thyroglobulin.
3- Microvilli.
4- Endocytotic vesicles & lysosomes.

15. BY GROUP (6)
2-Parafollicular (Clear cells or C cells):
• Function: synthesis & secretion of calcitonin.
•They are found as part of the follicular
epithelium, in between the follicular cells or as
isolated clusters between the follicles.
• Number: 0.1% of the follicular epithelium.
• LM:
 S
ize: larger than the follicular cells.
 Cytoplasm: pale (clear cells).
Their basal surfaces rest on the follicular
basement membrane but their apical surfaces never reach the lumen of the follicles.
• EM: Polypeptides secreting cells:
 Moderate amount of organelles.
 Infra nuclear Golgi (Why).
 The secretory granules are small & basal (Why).

16. BY GROUP (6)
Steps of synthesis of thyroid hormones:
1.Synthesis of thyroglobulin
(glycoprotein):
A- The protein part of the thyroglobulin are
synthesized from the amino acids tyrosine by the
rough endoplasmic reticulum.
B- The Golgi apparatus adds carbohydrate to the
protein to form the thyroglobulin& packed into
secretory vesicles.
C- The secretory vesicles are discharged into the
lumen of the follicle by exocytosis where
thyroglobulin contributes in the formation of the
colloid.
2 Uptake of iodide:
The follicular cells trap the iodide from the capillaries
released into the follicular lumen. oxidion into iodine

17. BY GROUP (6)
3 Iodination of thyroglobulin: takes place in the colloid to form
monoiodotyrosine& diiodotyrosine.
4 Formation of T3 & T4: by coupling reaction in the colloid, where they are
stored in the lumen of the follicle.
5 Release of T3 & T4:
 In response to TSH endocytosis of the colloid in endocytotic vesicles by the follicular cells
fusion of the vesicles with lysosomes hydrolysis release of T3&T4 blood stream.
n.

18. BY GROUP (6)
Follicular cells Parafollicular cells
1- Size Smaller Larger
2- Number Numerous Few
3- Extension Reach the lumen Never reach the lumen
4- Cytoplasm Basophilic Pale basophilic
5- rER Rich, basally Moderate
5- Golgi Supranuclear Infranuclear
5- Lysosomes Numerous Less
6- Secretion Stored extracellular Stored intracellular, inside secretory granules.
7-Function Secrete T3&T4 Secrete calcitonin

19. BY GROUP (6)
Anatomically: 4 glands situated behind thyroid gland.
I-Stroma:
 CT capsule: of that of the thyroid gland.
 CT septa.
Network of reticular fibers: support the
parenchymal cells.
II-Parenchyma:
•It consists of cords of polygonal cells
surrounded by a rich network of
fenestrated blood capillaries.
•The cells are of 2 types: Chief & oxyphil
cells.
STRUCTURE OF PARATHYROID :

20. BY GROUP (6)
A- The chief cells:
•Function:Secretion of parathyroid
hormone.
• Number:numerous.
• LM:
 Shape: small polygonal cells
 Nucleus: large vesicular nuclei
 Cytoplasm: pale (WHY).
• EM: Polypeptide secreting cells
The cytoplasm contains moderate amount of
organelles (rER, Golgi complex, mitochondria&
secretory granules.
Glycogen granules& lipid droplets: cause the
pale cytoplasm seen with the LM.
Parathyroid gland

21. BY GROUP (6)
B- Oxyphil cells •Function:Unknown.
•Number:few.
• LM:
 Shape: large polygonal.
 Nucleus: small& dense.
 Cytoplasm: deep eosinophilic (Why).
EM: The cytoplasm contains many
mitochondria.
• With increas
ing age:
 The chief cells are replaced by fat cells
which may constitute more than 50% of the
gland.
 The number of oxyphil cells increases.
Chief cell Oxyphil cell
1- Size Smaller Larger
2- Number Numerous Few
3- Cytoplasm Pale Deep acidophilic
4- Nucleus Large& vesicular Small & dense
5- rER More Less
6- Mitochondria Less Numerous
7- Function Secretion of
parathyroid
hormone
Unknown

22. BY GROUP (6)
•Anatomically:
Two glands, each one situated at the
upper pole of the kidney.
•Histologically:
Each gland consists of a cortex& medulla.
STRUC TURE OF SUPRARENAL GLANDS :
I.Cortex:
 Yellow in color (Why).
 It originates from the mesoderm.
 It constitutes 80- 90% of the gland.
II. Medulla:
 Reddish brown in color (Why).
 It originates from the neural crest (the same origin as the sympathetic nervous
system).
 It is considered as a modified sympathetic ganglion, where the neurons have
acquired an endocrine activity and secrete catecholamines.
STRUC TURE OF SUPRARENAL GLANDS :
A- Stroma:
 A connective tissue capsule.
 A CT septa.
 A network of reticular fibers.

23. BY GROUP (6)
B- Parenchyma: it is divided the cortex & the medulla.
I- Suprarenal Cortex:
• It is the steroid secreting portion of the gland.
• It is divided into 3 zones:
1Zona glomerulosa (15% of the cortex): Secretes
mineralocorticoids mainly aldosterone control
blood volume& blood pressure.
2Zona fasiculata (65-80%): Secretes
glucocorticoids control CHO, fat & protein
metabolism.
3 Zona reticularis (7%): Secretes androgen
development of axillary& pubic hair in females.
Structure of cells in adrenal cortex:
•Steroid secreting cells:
•LM:
 Cytoplasm: acidophilic& vacuolated.
•EM:
 Abundant sER.
 Mitochondria with tubular cristae.
Lipid droplets: they are numerous in zona
fasiculata & less in
 zona glomerulosa and reticularis.

24. BY GROUP (6)
A- Zona Glomerulosa:
• LM:
 It lies immediately under the capsule.
 Arrangement of the cells: in closely packed
arched clusters surrounded by fenestrated blood
capillaries.
 Shape of the cells: columnar.
 Nucleus: dense.
 Cytoplasm: acidophilic & slightly vacuolated.
•EM: The cells show the ultrastructural
features of steroid secreting cells with few lipid
droplets.
B- Zona Fsciculata:
•LM:
 It is the middle layer of the cortex
 Arrangement of the cells: in long straight
cords, perpendicular to the capsule.
The cords are one or two cells thick& separated
by sinusoidal blood capillaries.
 Shape of the cell: large polyhedral.
 Nucleus: large& pale.
Cytoplasm: pale acidophilic& highly vacuolated
so called spongiocytes.
EM: The cells show the ultrastructural features
of steroid secreting cells with
numerous lipid droplets.

25. BY GROUP (6)
C- Zona Reticularis:
•LM:
 It is the inner layer of the cortex.
 Arrangement of the cells: in irregular
cords enclosing fenestrated capillaries in
between.
 Shape of the cell: small polyhedral.
 Cytoplasm: acidophilic& slightly vacuolated.
 Dark cells: are seen near the medulla. They have
dark cytoplasm with pyknotic nuclei, suggesting that
they are degenerating cells.
 Lipofuscin pigments: are present in this layer.
EM: The cells show the ultrastructural features of
steroid secreting cells with few lipid droplets.
NB: Steroid secreting cells Never store their Hormones.

26. BY GROUP (6)
Zona glomerulosa Zona fasiculata Zona reticularis
1- Percentage 15% 65-80% 7%
2-Arrangement Closely packed arches Long straight
cords
Irregular cords
3- Shape of
the cells
Columnar Large polyhedral Small polyhedral
4- Nucleus Dense Large& pale
5- Cytoplasm Acidophilic& slightly
vacuolated
Acidophilic& highly
vacuolated
Acidophilic&
slightly
vacuolated
6-Lipid
droplets
Few Numerous Few
7- Function Secrets
mineralocorticoids
Secretes
glucocorticoids
Secretes
androgen
II- Suprarenal Medulla:
It contains two types of cells:
1 Chromaffin cells: secrete catecholamines
(epinephrine&norepinephrine).
2 Sympathetic ganglion cells.

27. BY GROUP (6)
1- Chromaffin cells = Pheochromocytes:
•They are called chromaffin cells due to
the affinity of their granules to react
with chromium salts and give brown color
(chromaffin reaction).
•LM:
 Arrangement of the cells: in irregular
cords enclosing the blood capillaries.
 Shape of the cell: large ovoid.
 Nucleus: large spherical.
 Cytoplasm: pale basophilic.
• EM: polypeptide secreting cells
Moderate amount of rER, prominent
Golgi and secretory granules.

28. BY GROUP (6)
-Adrenal medulla is considered as modified sympathetic ganglia
-Chromaffin cells are modified postganglionic neurons
2- Sympathetic ganglion cells:
Functions:
A-Modulate the secretory activity of the
cortex.
B- Innervate the blood vessels of the cortex.

29. BY GROUP (6)
B LOOD S UPPLY OF THE ADRENAL GLAND:
• The medulla hasa dual blood supply:
1 Arterial: from the medullary arterioles.
2 Venous: from the cortical sinusoids draining the
cortex (glucocorticoids reaching the medulla are
essential for production of epinephrine by
chromaffin cells).

30. BY GROUP (6)
Anatomically:
Pancreas is one of the largest glands of
the digestive tube. It lies in C- shaped
cavity of the duodenum. It is divided into
head, body & tail.
Histologically:
It is a mixed gland: composed of both
exocrine (described in GIT module) &
endocrine parts.
THE ENDOCRINE PANCREAS (THE ISLETS OF LANGERHANS)
• The islets of Langerhans are more numerous in
the tail than in the head & the body of the
pancreas.
• They appear in histological sections as lightly
stained areas (Why).

31. BY GROUP (6)
HISTOLOGIC AL STRUC TURE OF ISLETS OF LANGERHANS
A- Stroma:
 They are not encapsulated.
 Supported by network of reticular fibers.
B- Parenchyma:
• LM:
Arrangement of the cells: in short cords and separated
by network of fenestrated blood capillaries.
Shape of the cells: polygonal.
Cytoplasm: pale basophilic
•EM: Polypeptide secreting cells
Moderate amount of rER, Golgi complex & secretory
granules.
3 main typesof cellscan be identified:A cells, B
Cells& D cells.
1-A cells (alpha):
increases blood
•Function:secretion of glucagon
sugar level.
• S
ize: large.
• Number: 20%.
• S
ite: at the periphery of the islet.
•EM:the secretory granules are numerous and have a
homogeneous dense core.

32. BY GROUP (6)
2-B cells (Beta):
• Functions:
1- Secretion of insulin lower blood sugar level.
2- Secretion of C-peptide: as a consequence of insulin
production. It prevents neuropathy and other symptoms
of diabetic vascular deterioration. Measuring its level
can give an idea about the viable beta cell mass.
3- Secretion of GABA (γ amino butyric acid): suppress
glucagon secretion.
• S
ize of the cells:small.
• Number: 70% of the islet cells.
• Site: centrally located within the islet.
•EM:their secretory granules have a rectangular crystalline dense core surrounded
by an electron lucent halo.
3-D cells (Delta):
•Function: secretion of somatostatin
secretion of GH, insulin & glucagon.
• Number: 5 - 10% of the islet cells.
• S
ite: at the periphery of the islet.
inhibits

33. BY GROUP (6)
Alpha Beta Delta
Number 20% 70% 5-10%
Site Periphery Central Periphery
Size Large Small Small
Granules:
EM
Granuleswith
homogenous
dense core
Granules with rectangular
crystalline dense core
surrounded by an electro
lucent halo.
Function Glucagon Insulin, C peptide & GABA Somatostatin

34. BY GROUP (6)
•Definition: single or small groups of endocrine
cells with diffuse distribution in different tissues
and organs of the body.
• These cells secrete hormones, usually peptides.
•They synthesize monoamines by the uptake of
amine precursors and their decarboxylation(
APUD cells=Amine Precursor Uptake &
Decarboxylation).

35. BY GROUP (6)
Modes of action of their hormones:
1 Paracrine: act on the neighboring cells.
2 Autocrine: act on the cell that secrete the
hormone itself.
3 Endocrine: act on target cells in remote
tissue.
1 H&E: These cells are not well seen.
2 Special stain:
 chromium salts (chromaffin cells).
 silver salts (argentaffin cells).
3 Immunohistochemical stain: using antibodies against their peptide hormone.
Chromaffin cells Argentaffin cells
How to identify the DNES in histological sections?

36. BY GROUP (6)
Structure of DNES:
•EM:
1 Shape: pyramidal with narrow apex and a wide base.
2Cytoplasm: polypeptide secreting cells with moderate amount of organelles due
to slow rate & small amount of secretion:
 rER.
 Mitochondria.
 Golgi apparatus.
 Secretory granules.
Types of DNES:
1 Open type: the cell has long microvilli
extending into the lumen of the organ.
2Clos
ed type: where the cell apex is
covered by other epithelial cells of the
organs.

37. BY GROUP (6)
Distribution of DNES:
 Gastrointestinal tract (enteroendocrine cells).
 Respiratory system.
 Supraoptic and paraventricular hypothalamic nuclei.
 Parafollicular cells of thyroid gland.
 Chief cells of parathyroid gland.
 Chromaffin cells of the suprarenal medulla.
 Cells of islets of Langerhans.
 Pinealocytes.

38. BY GROUP (6)
Site: on the posterior part of third ventricle at the mid
line between two cerebral hemispheres.
Structure: It is covered by pia matter which sends CT
septa carrying the blood vessels.
It consists of 2 types of cells:
A- Pinealocytes (secretory cells).
B- Glial cells (resemble astrocytes): for support.
Pinelocytes
• Shape: branching with long tortuous processes end as
flat dilatations near blood capillaries (WHY).
• Nucleus: large, lobulated with prominent nucleoli.
• Cytoplasm: pale basophilic (WHY) with secretory
vesicles.
• Function: secretion of
melatonin.

39. BY GROUP (6)
• Definition: Formation of calcified
bodies which increase in number & size
by age.
• Importance: it can be used as a clinical landmark for the midline location of the
pineal gland during radiological examination of the brain.
Corpora arenacea (brain sand)
Functions of melatonin
1 Controls circadian rhythm.
2Induces feeling of sleepiness.
3- Decreases gonadotropin.
4- Protects CNS from oxidative stress.

40. BY GROUP (6)