ENRP Module

Histology of the reproductive and

endocrine system
Dr. Solomon Tibebu (BSc, MD, MSc)
Anatomy department, AAU, CHS-SOM
The endocrine system
• regulates metabolic activities in certain organs and
tissues of the body, thereby helping to bring about
homeostasis.
• a series of ductless glands that secrete messenger
molecules called hormones into the circulation.
• The circulating hormones travel to distant body cells
and signal characteristic physiological responses in
those cells.
• The endocrine glands include the pineal body, the
pituitary gland, the thyroid gland, the parathyroid
glands, and the suprarenal glands
• Hormones?
1) Proteins and polypeptides-mostly water-soluble
(e.g., insulin, glucagon, FSH, LH, GH
2) Amino-acid derivatives-mostly water-soluble (e.g.,
thyroxine and epinephrine
3) Steroid and fatty acid derivatives-mostly lipid-
soluble (e.g., progesterone, estradiol and
testosterone, Aldosterone).
PINEAL GLAND
• an endocrine gland whose secretions are influenced by the light and dark periods of the day
• It is a cone-shaped, midline projection from the roof of the diencephalon, within a recess of the third ventricle
• It is 5 to 8 mm long and 3 to 5 mm wide; it weighs approximately 120 mg.
• The gland is covered by pia mater, forming a capsule from which septa extend, dividing the pineal gland into incomplete
lobules.
• Blood vessels enter the gland via the connective tissue septa.
• The parenchymal cells of the gland are composed primarily of pinealocytes and interstitial cells.
• Melatonin, synthesized from tryptophan by pinealocytes and released at night, inhibits the release of growth hormone
and gonadotropin by the hypophysis and hypothalamus, respectively.
• It has been suggested that melatonin induces the feeling of sleepiness
PITUITARY GLAND (HYPOPHYSIS)
• Produces several hormones that are responsible for regulating growth, reproduction, and
metabolism.
• It has two subdivisions, which develop from different embryologic sources:
• (1) the adenohypophysis develops from an evagination of the oral ectoderm (Rathke's pouch) that lines
the primitive oral cavity (stomodeum), and
• (2) the neurohypophysis develops from neural ectoderm as a downgrowth of the diencephalon.
Parts of adenohypophysis and neurohypophysis
ADENOHYPOPHYSIS (true gland)
A) The pars distalis
• Accounts for 75% of the adenohypophysis and is
covered by a thin fibrous capsule.
• The main components are cords of epithelial
cells interspersed with fenestrated capillaries
• The main glandular tissue
B) Pars intermedia
The pars intermedia lies between the pars distalis and
the pars nervosa and contains cysts that are remnants
of Rathke's pouch.
C) Pars tuberalis
The pars tuberalis surrounds the hypophyseal stalk and
is composed of cuboidal to low-columnar basophilic
cells.
Pars distalis
The parenchymal cells of the pars distalis consist of
the chromophils and chromophobes.
Based on the affinity of the secretory granules within
the cells to the dyes, not to the parenchymal cell
cytoplasm.
1) Chromophils (have an affinity for dyes)
 Acidophils (those that stain orange-red with acid dyes)
 Basophils (those that stain blue with basic dyes)

2) Chromophobes (have no affinity for dyes)

Acidophil – growth hormone or prolactin
Basophil – TSH , ACTH , FSH or LH
Chromophobe - either nonspecific stem cells or partly
degranulated chromophils
 ACIDOPHILS
(Cells - Somatotrophs and mammotrophs)

• The most abundant cells in the pars distalis.

• whose granules are large enough to be seen by the light microscope and
• stain orange-to-red with eosin

1) Somatotrophs (hormone => somatotropin or GH)

 A centrally placed nucleus,
 A moderate Golgi complex,
 Small rod-shaped mitochondria,
 Abundant rough endoplasmic reticulum (RER), and
 Numerous secretory granules that are 300 to 400 nm in diameter
 Stimulated by SRH and inhibited by somatostatin
• Somatotropin has a generalized effect of increasing cellular metabolic rates.
• This hormone also induces liver cells to produce somatomedins (insulin-like growth factors I and II),
which stimulate mitotic rates of epiphyseal plate chondrocytes and thus promote
elongation of long bones and, hence, growth.
2) Mammotrophs (produce - Prolactin)
Arranged as individual cells rather than as clumps.
distinguished by their large secretory granules, formed by the fusion of smaller
granules that are released by the trans Golgi network.
These fused granules, which may be 600 nm in diameter, contain the hormone
prolactin,
Prolactin - promotes mammary gland development during pregnancy as well as
lactation after birth.
During pregnancy, circulating estrogen and progesterone inhibit secretion of prolactin.
Following birth, estrogen and progesterone levels drop; thus their inhibitory effect is
lost.
Secretion of prolactin is under tonic inhibitory control by dopamine, which acts via D2-
type receptors located on lactotrophs.
• Hyperprolactinemia (> 250 ng/mL), less likely
if it is < 100 ng/mL)
• Prolactinoma(micro, macro),
• Hypothyroidism
• Pituitary stack compression,
• Dopamine-receptor antagonists)

• Oligomenorrhea, amenorrhea, or infertility (due to

hypogonadotrophic hypogonadism)
• Galactorrhea, or
• For male patients presenting with sexual dysfunction
 BASOPHILS
(Thyrotrophs, Corticotrophs, Gonadotrophs)
• Basophils stain blue with basic dyes (especially with periodic acid-Schiff reagent) and are usually
located at the periphery of the pars distalis - the B is in the P
1) Corticotrophs, which are scattered throughout the pars distalis, are round to ovoid cells.
• Their secretory granules are 250 to 400 nm in diameter.
• secrete adrenocorticotropic hormone (ACTH) and lipotropic hormone (LPH).
• Secretion is stimulated by CRH. The hormone ACTH stimulates cells of the suprarenal cortex to
release their secretory products.
2) Thyrotrophs
distinguished by their small secretory granules (150 nm in diameter), which contain TSH, also known
as thyrotropin.
Secretion of TSH stimulated by TRH and inhibited by the presence of thyroxine (T4) and
triiodothyronine (T3) (thyroid hormones) in the blood
• Gonadotrophs - round cells that have a well-developed Golgi complex and
abundant RER and mitochondria.
• Their secretory granules vary in diameter from 200 to 400 nm.
• secrete FSH and LH.
• Secretion is stimulated by GnRh.
Chromophobes (52%)
• Chromophobes have very little cytoplasm; therefore, they do not take up stain
readily.
• Groups of small, weakly staining cells in the pars distalis are called chromophobes.
• They may represent either nonspecific stem cells or partly degranulated
chromophils, although some retain secretory granules.
 Neurohypophysis
• The neurohypophysis is divided
into the median eminence, the
infundibulum (continuation of the
hypothalamus), and the pars
nervosa.
• The pars nervosa, unlike the adenohypophysis, does
not contain secretory cells.
• It is composed of neural tissue, containing some
100,000 unmyelinated axons of secretory neurons
situated in the supraoptic and paraventricular
nuclei of the hypothalamus.
• [Pars nervosa is mainly made up of neural tissue]
• [ Pars nervosa is derived from surface ectoderm ]

• Also present are highly branched glial cells called

pituicytes that resemble astrocytes and are the most
abundant cell type in the posterior pituitary
ADH and OXYTOCIN

• ADH - Principally produced by neurons that have their cell bodies within the
supraoptic nuclei of the hypothalamus. There is also production, albeit in smaller
quantities, in neurons with cell bodies located in the paraventricular nuclei, the site
primarily responsible for oxytocin
 Stored and released by pars nervosa of the posterior pituitary gland
 Action - ADH principally exerts its effects by binding to the kidneys
principal cells within the late distal tubule and collecting ducts.
 ADH binds to the V receptor on these cells and leads to the activation of adenylate cyclase,
which causes a subsequent increase in the second messenger cyclic AMP (cAMP). cAMP
activates protein kinase A (PKA), a phosphorylating enzyme that initiates an intracellular
phosphorylation cascade. Ultimately, intracellular aquaporin-2 (AQP2) storage vesicles are
phosphorylated, which promotes their movement and insertion into the apical membrane.
1) EXCESS = SIADH, DEFI.= Diabetic insipidus
• OXYTOSIN – Supraoptic nuclei of the hypothalamus
 Blood Supply & the Hypothalamo-Hypophyseal Portal System

• The blood supply derives from two groups of vessels

coming off the internal carotid artery.
1) The superior hypophyseal arteries supply the
median eminence and the infundibular stalk;
2) the inferior hypophyseal arteries provide blood
mainly for the neurohypophysis, with a small
supply to the stalk.
• The superior hypophyseal arteries form a primary
capillary network irrigating the stalk and median
eminence. The capillaries then rejoin to form venules
that branch again as a larger secondary capillary
network in the adenohypophysis.
• It carries neuropeptides from the median eminence to
the adenohypophysis where they either stimulate or
inhibit hormone release by the endocrine cells there.
•
Thyroid gland
• located in the anterior portion of the neck, Has two
lobes, isthmus, some times pyramidal lobe
• secretes the hormones thyroxine, triiodothyronine,
and calcitonin.
Thyroid follicle
• Cyst like structures ranging from 0.2 to 0.9 mm in
diameter
• structural and functional unit of the thyroid gland.
• the thyroid gland stores its secretory substances in
the lumina of follicles(makes it unique from other
endocrine glands).
• are composed of a simple cuboidal epithelium
surrounding a central colloid-filled lumen.
• Each follicle can store several weeks' supply of
hormone within the colloid.
• Follicular cells, parafollicular cells, basal lamina
• Iodide transport
• Oxidation of I– to I°
• Thyroglobulin synthesis in the follicular cells=> exocytosis=> iodination
• Coupling ( two DIT=> Tetraiodothyronine(T4), one DIT + one MIT=> Triiodothyronine(T3) => Storage
• Secretion – endocytosis of thyroglobulin with T3, T4=> Proteolysis of thyroglobulin=> secretion
Parathyroid gland
• The parathyroid glands, usually four in
number, are located on the posterior surface
of the thyroid gland; each gland is enveloped
in its own thin, collagenous connective tissue
capsule.
• Each parathyroid gland is a small, ovoid
structure about 5 mm in length, 4 mm wide,
and 2 mm in thickness and weighs about 25 to
50 mg
• The glands function in producing PTH, which
acts on bone, kidneys, and the intestines in
maintaining the optimal concentrations of
calcium within blood and interstitial tissue
fluid.
• [ doesn’t act on liver ]
Chief Cells
• Chief cells synthesize parathyroid hormone.
• The major functional parenchymal cells of the parathyroid glands are the
slightly eosinophilic-staining chief cells (5 to 8μm in diameter).

• Smaller, dense granules, 200 to 400 nm in diameter, represent the secretory

granules and contain parathyroid hormone (PTH).

Oxyphil Cells
• Oxyphil cells are believed to be the inactive phase of chief cells.
• Oxyphil cells are less numerous, larger (6 to 10μm in diameter), and stain
more deeply with eosin than chief cells do.
• Oxyphils appear in groups and as isolated cells. They have more abundant
 Physiological Effect of Parathyroid
Hormone
• PTH, produced by chief cells of the parathyroid glands, helps to maintain the extracellular fluid as
well as the plasma concentration of calcium ions (8.5 to 10.5 mg/dL).
• This hormone acts on cells of the bones, the kidneys, and, indirectly, the intestines, leading to an
increased calcium ion concentration in body fluids.
• When calcium ion concentration in body fluids falls below normal, the chief cells increase their
production and release of PTH, quickly increasing their normal secretion rate 10-fold.
 Adrenal/suprarenal glands
• Located at the superior poles of the kidneys and are
embedded in adipose tissue.
• Both glands are about 1 cm in thickness, 2 cm in width at
the apex, and up to 5 cm at the base; each weighs 7 to
10 g.
• The parenchyma of the gland is divided into two
histologically and functionally different regions:
1) Suprarenal cortex- An outer yellowish portion,
accounting for about 80% to 90% of the organ.
2) Suprarenal medulla -A small, dark, inner portion
Both have a different embryological origin and performs a
different role.
 The suprarenal cortex -mesoderm, produces a group of
hormones called corticosteroids.
 The suprarenal medulla, arising from neural crest, is
functionally related to and regulated by the sympathetic
nervous system.
Adrenal cortex
1) Zona glomerulosa-
- contains cells arranged in spherical clusters.
 acidophilic cytoplasm contains an abundant and extensive
SER, short mitochondria with shelf-like cristae, a well-
developed Golgi complex, abundant RER, and free
ribosomes.
 The parenchymal cells of the zona glomerulosa synthesize
and secrete the mineralocorticoid hormones, principally
aldosterone and some deoxycorticosterone. Synthesis of
these hormones is stimulated by angiotensin II and ACTH,
both required for normal existence of glomerulosa cells.
 The mineralocorticoid hormones function in controlling
fluid and electrolyte balance in the body by affecting the
function of the renal tubules, specifically the distal
convoluted tubules
2) Zona fasciculata-
• cells are arranged in parallel cords ( fascicle bundle of parallel sticks) and contain an
abundance of lipid droplets
• the largest layer of the cortex, which accounts for up to 80% of the total volume of the
gland.
• This zone contains sinusoidal capillaries that are arranged longitudinally between the
columns of parenchymal cells.
• The polyhedral cells in this layer are larger than the cells of the zona glomerulosa and
one to two layers thick, and stain lightly acidophilic. Because they have many lipid
droplets in their cytoplasm, which are extracted during histological processing, these
cells appear vacuolated and are called spongiocytes.
• Spongiocytes have spherical mitochondria with tubular and vesicular cristae, extensive
networks of SER, some RER, lysosomes, and granules of lipofuscin pigment.
• synthesize and secrete the glucocorticoid hormones- cortisol and corticosterone. The
synthesis of these hormones is stimulated by ACTH.
• Glucocorticoids function in the control of carbohydrate, fat, and protein metabolism.
3) Zona Reticularis
• whose cells are arranged in a branching network (reticulum network) and
stain intensely with the pink dye eosin
• constituting about 7% of gland volume.
• The darkly staining acidophilic cells in this layer are arranged in
anastomosing cords.
• synthesize and secrete androgens, principally dehydroepiandrosterone and
some androstenedione.
• Additionally, these cells may synthesize and secrete small amounts of
glucocorticoids.
• The secretion of these hormones is stimulated by ACTH.
• Both dehydroepiandrosterone and androstenedione are weak, masculinizing
hormones with negligible effects under normal conditions.
The suprarenal medula
• The central portion of the suprarenal gland.
• comprises two populations of parenchymal cells:
1) chromaffin cells- which produce the catecholamines (epinephrine and
norepinephrine),
• Chromaffin cells of the suprarenal medulla are large epithelioid cells, arranged in clusters or
short cords; they contain granules that stain intensely with chromaffin salts.
• The reaction of the granules, which turn deep brown when exposed to chromaffin salts,
indicates that the cells contain catecholamines, transmitters produced by postganglionic cells
of the sympathetic nervous system.
• Thus, the suprarenal medulla functions as a modified sympathetic ganglion, housing
postganglionic sympathetic cells that lack dendrites and axons.
• These transmitters are secreted by the chromaffin cells in response to stimulation by
preganglionic sympathetic (cholinergic) splanchnic nerves

2) sympathetic ganglion cells, which are scattered throughout the connective tissue.
Pancreas
(Pancreatic Islets)
• The pancreatic islets (islets of Langerhans) are compact spherical or egg-shaped masses of
endocrine tissue embedded within the acinar exocrine tissue of the pancreas.
• Most islets are 100–200 m in diameter and contain several hundred cells, but some are much
smaller with only a few cells.
• There are more than 1 million islets in the human pancreas, with the gland's narrow tail region
most enriched for islets, but they only constitute 1–2% of the organ's volume.
• A very thin capsule of reticular fibers surrounds each islet, separating it from the adjacent
acinar tissue.
• Pancreatic islets are clumped masses of pale-
staining endocrine cells embedded in the
exocrine acinar tissue of the pancreas. (a): A
low-magnification micrograph through the tail
of the pancreas reveals many islets stained
lighter than the surrounding tissue.