PITUITARY GLAND THYROID GLAND HYPOPHYSIS CEREBRI PITUITARY GLAND

PITUITARY GLAND THYROID GLAND

HYPOPHYSIS CEREBRI ( PITUITARY GLAND )

PITUITARY GLAND

COMPONENTS (A) ADENOHYPOPHYSIS CEREBRI: 1 - Pars Distalis (pars anterior) 2 - Pars Tuberalis 3 - Pars Intermedia (B) NEUROHYPOPHYSIS CEREBRI: 1 - Median eminence 2 - Infundibulum: Neural (Infundibular) Stalk 3 - Pars Nervosa

DEVELOPMENT

DEVELOPMENT (A) ADENOHYPOPHYSIS: Arises as outpocketing (evagination) of ectoderm from the roof of the primitive mouth of embryo → Rathke’s Pouch → Separates from oral cavity. (B) NEUROHYPOPHYSIS: Arise as a down growth from the floor of diencephalon, without detaching from the brain.

PITUITARY GLAND

NEUROHYPOPHYSIS xxxxxx XXXXX

PARS NERVOSA

NEUROHYPOPHYSIS (A) PARS NERVOSA CONTENTS: 1 - Unmyelinated axons of secretory neurons situated in supraoptic & paraventricular nuclei (i. e. Axons of hypothalamhypophyseal tract). 2 - Herring’s Bodies: contain neurosecretory granules. 3 - Fenestrated blood capillaries. 4 - Pituicytes: branched glial-like cells. N. B. No secretory cells in pars nervosa.

HERRING BODIES - Are blue-black stained distentions of the axons in p. nervosa. - Representing accumulation of neurosecretory granules at axon termini and along the length of the axons in p. nervosa.

PITUICYTES Are glial-like cells in p. nervosa. Structure: Have numerous cytoplasmic processes with gap junctions. Functions: 1 - Support the axons of the p. nervosa. 2 - May have a trophic function.

Function of p. nervosa: Storage & release of: 1 - Vasopressin (ADH) 2 - Oxytocin

P. DISTALIS, P. INTERMEDIA & P. NERVOSA

PARS DISTALIS Blue arrow: acidophils Red arrow: basophils Yellow arrow: chromophobes

Blue arrow: acidophils Red arrow: basophils Yellow arrow: chromophobes

PARS DISTALIS

GH CELLS

PROLACTIN CELLS

ACTH CELLS

PARS DISTALIS Stroma: 1 - Fibrous capsule. 2 - Scant C. T. located mainly around aa &vv. (hypophyseal arteries & portal veins). 3 - Reticular fibers: around the cords of cells & “ the sinusoidal capillaries.

PARS DISTALIS Parenchyma: 1 - Cords of parenchymal cells. 2 - Sinusoidal capillaries: With fenestrated endothelium.

PARS DISTALIS Types of parenchymal cells (1) Chromophils: a- Acidophils: 1 - Somatotrophs (Somatotropic cells). 2 - Mammotrophs (Mammotropic cells). b- Basophils: 1 - Thyrotrophs (Thyrotropic cells)(TSH) 2 - Gonadotrophs (Gonadotropic cells) (FSH, LH) 3 - Corticotrophs (ACTH, Lipotropic H) 4 - Melanotropes ? ? ? ?

Types of parenchymal cells (2) Chromophobes: may represent: 1 - stem cells. 2 - degranulated chromophils. 3 - degenerated cells. (3) Folliculostellate cells: Structure: have long processes with gap j. Function: Not clear ( are non-secretory) ? ? ? (may be: 1 -supporting, 2 -phagocytic).

PARS TUBERALIS Structure: Cuboidal basophilic cells. Function: Possibly contain FSH & LH.

PARS INTERMEDIA (ZONA INTERMEDIA) L/M: 1 -Numerous colloid-containing cysts (Rathke’s cysts): Are lined with cuboidal cells. Are remnants of Rathke’s pouch. 2 -Cords of weakly basophilic cells. 3 - Network of blood capillaries. Function: Secrete proopiomelanocortin→ Gives: α-MSH, Corticotropin, ß-lipotropin & ß-endorphin. N. B. α-MSH in human stimulates prolactin release.

BLOOD SUPPLY

BLOOD SUPPLY (1)Sup. Hypoph. Arteries (Rt & Lt): To median eminence & Neural stalk → 1 ry capillary plexus of fenestrated capillaries → Hypophyseal portal Veins (or venules) → 2 ry capillary plexus of capillaries in adenohyp [ Hypophyseal Portal System ] [“ “ Circulation ] It carries neurohormones from median eminence to adenohypophysis. (2) Inf. Hypoph. Arteries (Rt & Lt): Mainly to pars nervosa, They are Not participating in hypophyseal portal circulation. !!!!!!!!!!!!!!!!!!!

THYROID GLAND

THYROID GLAND

THYROID GLAND (E/M)

PARAFOLLICULAR CELL

STROMA OF THYROID GLAND 1 - Capsule: dense irregular collagenous C. T. 2 - Septa (Interlobular septa): “ “. 3 - Reticular fibers: Thin C. T. , composed mostly of reticular fibers with rich capillary plexus surrounds each thyroid follicle.

PARENCHYMA OF THYROID GLAND THYROID FOLLICLES: Are the structural and functional units of the thyroid gland.

THYROID FOLLICLES L/M: 1 - Simple cuboidal epithelium: a- Follicular cells. b- Parafollicular cells. 2 - Colloid: central colloid-filled lumen. N. B. Each follicle is surrounded by thin basal lamina.

FOLLICULAR (PRINCIPAL) CELLS L/M: Simple cuboidal cells May be squamous or low columnar. Round nucleus with prominent nucleoli. Basophilic cytoplasm.

FOLLICULAR (PRINCIPAL) CELLS E/M: - Mitochondria. - RER - Supranuclear Golgi Complex. - Numerous apically-located lysosomes. - Numerous dispersed small vesicles: contain newly formed thyroglobulin. - Numerous apical short microvilli.

FOLLICULAR (PRINCIPAL) CELLS Function: Synthesis of thyroid hormones (T 4 & T 3). 1 - Synthesis of thyroglobulin (glycoprotein). 2 - Trapping of circulating iodide. 3 - Oxidation of iodide into activated iodide (by lysosomal peroxidase). 4 - Iodination of tyrosine of thyroglobulin in the colloid at the colloid-follicular cell interface. 5 - Endocytosis of hormone-bound thyroglobulin→ Cleavage of T 4 & T 3 by lysosomal proteases.

PARAFOLLICULAR CELLS (CLEAR CELLS) (C CELLS) L/M: - Pale stained cells. - Are found singly or in clusters in between the follicular cells. - Do not reach the lumen of the follicle. - Are larger than follicular cells (2 -3 times). - Only 0. 1% of the epithelial cells. - Have round nucleus

PARAFOLLICULAR CELLS (CLEAR CELLS) (C CELLS) E/M: - Mitochondria. - RER (moderate). - Well-developed Golgi. - Small dense secretory granules located mainly in the basal cytoplasm. Function: Secrete calcitonin.