The

Pituitary Gland The Hypophysis (Pituitary gland)  Is the master gland, produces several hormones which influence the activity of other endocrine glands.  Suspended from by means of a short stalk.  Tissue derived from two different sources.  Adenohypophysis from oral ectoderm,  Neurohypophysis arises as a ventral evagination from the floor of diencephalon (forebrain).  Oral component originates as an out pocketing of ectoderm, known as Rathke's pouch, which grows cranially from the primitive mouth (stomodeum) of embryo.

Next slide The Pituitary Gland Pituitary Gland

 Anterior wall of Rathke's pouch becomes greatly thickened, so that the lumen of pouch is reduced to a narrow fissure.  Ant. lobe is divided by residual lumen of Rathke's pouch into two unequal parts:  Pars distalis and  Thicker pars distalis lies anterior to the fissure. An extension of the pars distalis, called , surrounds the infundibulum.  Posterior to the fissure lies pars intermedia. which forms a thin cellular partition between the pars distalis and Neurohypophysis.

PITUITARY GLAND

 Anterior lobe (Adenohypophysis) comprises pars distalis, pars tuberalis & pars Intermedia.

 Posterior lobe (Neurohypophysis) includes pars nervosa, Infundibular stem and . PITUITARY GLAND  Neurohypophysis comprises three parts:

 1.Pars nervosa

 2. Infundibular stem

 3. Median eminence (of the hypothalamus).

 Pars nervosa lies immediately posterior to pars intermedia, continuous above with infundibular stem and median eminence, which together constitute the infundibulum.

 Hypophyseal stalk comprises infundibulum and pars tuberalis. THE ADENOHYPOPHYSIS

 Adenohypophysis comprises Pars distalis, Pars intermedia and Pars tuberalis.

 Pars distalis constitutes about 75 % of hypophysis, surrounded by a dense fibrous capsule.

 Parenchyma of pars distalis consists of cords and clusters of cells, supported by a scanty stroma composed of fibroblasts and reticular fibers.

 Between cellular masses are present sinusoidal capillaries.

THE ADENOHYPOPHYSIS

 Depending on their affinity for ordinary stains, cells of pars distalis are classified into two main types:

 (1) Chromophobes, and (2) Chromophils.

 1) Chromophobes, have little or no affinity for stains (chroma = color, phobein = to be afraid of), about 50% of the cells in pars distalis. THE ADENOHYPOPHYSIS

 Under L.M, Chromophobes are rounded or polygonal cells, boundaries of which are not clearly distinguishable.

 Cytoplasm does not exhibit any secretory granules. Formerly it was believed that the chromophobes represent undifferentiated or reserve cells which give rise to chromophils:

 But now it has been established that chromophobes are actually degranulated chromophils, i.e., they represent those cells which have secreted their cytoplasmic granules into the blood. THE ADENOHYPOPHYSIS

 2) Chromophils, 50% of the pars distalis cells, rounded or polygonal in shape, but they have distinct boundaries.

 Chroma = color, philein = to love

 Chromophils exhibit affinity for stains, due to presence of cytoplasmic granules which are either acidophilic or basophilic.

 Chromophils are divided into two types: Basophils and Acidophils, which are more abundant, constituting about 70% of the total chromophils.

THE ADENOHYPOPHYSIS

 ACIDOPHILS, are larger than chromophobes, but smaller than basophils.

 Cytoplasm has small secretory granules which stain with acid dyes like eosin, acid fuchsin, orange G and azocarmine.

 On the basis of staining reaction of the cytoplasmic granules, acidophils are subclassified into two varieties:

 (i) alpha acidophils

 (ii) epsilon acidophils

THE ADENOHYPOPHYSIS

 i) Alpha Acidophils. are commoner of the 'two varieties. Their cytoplasmic granules stain well with orange G; hence these cells are also known as orangeophils.

 E-M. secretory granules 300 to 400 nm in diameter.

 Secrete growth hormone (somatotropin)  hence known as somatotropes. THE ADENOHYPOPHYSIS

 ii) Epsilon Acidophils. Cytoplasmic granules of these cells stain intensely with azocarmine; hence, these cells are also called carminophils.

 EM. cytoplasmic granules are larger (average diameter 600 nm) than those of alpha acidophils.

 Epsilon acidophils secrete prolactin (lactogenic hormone) and are also known as mammotropes or lactotropes. Their size and number increase during pregnancy and lactation. The Adenohypophysis

 BASOPHILS are larger in size than acidophils

 Cytoplasmic granules are smaller and fewer than those of acidophils.

 Cytoplasmic granules of a basophil do not stain well with hematoxylin but stain intensely with methylene blue.

 Strongly positive reaction when stained by PAS technique.

 Secretory granules are stained by aldehyde fuchsin, and are classified. into three subtypes:

 (i) beta basophils, (ii) delta basophils, and (iii) corticotropes.

The Adenohypophysis

 i) Beta basophils relatively large cells which stain intensely with aldehyde fuchsin.

 E-M. secretory granules 100 to 150 nm in diameter.

 Beta basophils secrete  TSH and are also known as Thyrotropes.

 ii) Delta Basophils. do not stain with aldehyde fuchsin. secrete gonadotropic hormones and, hence, are also termed Gonadotropes. The Adenohypophysis

 Gonadotropes are distinguished into two varieties

 First variety, secretory granules, 100 nm in diameter.  secrete follicle stimulating hormone (FSH).

 Second variety, granules, about 150 nm in diameter which are concentrated to one side of the cell. secrete (LH) which in the male is also known as interstitial cell stimulating hormone (ICSH). The Adenohypophysis

 iii) Corticotropes. do not stain with aldehyde fuchsin.

 E-M.  secretory granules, about 200 nm in diameter, well-developed Golgi apparatus.

 Nucleus occupies an eccentric position in the cell.

 Corticotropes constitute the most numerous variety of basophils, secrete Adrenocorticotropic hormone (ACTH) which is also called corticotropin. The Adenohypophysis

PARS INTERMEDIA

 In humans, pars intermedia is rudimentary, composed mainly of cords of basophilic, polygonal cells.

 Some follicles are also seen which are lined by cuboidal cells and contain colloid material.

 In some lower animals, pars intermedia is well developed.

 In humans the amount of melanin pigment in the skin is believed, to be controlled by ACTH and function of pars intermedia is not well understood.

The Adenohypophysis

PARS TUBERALIS

 Pars tuberalis surrounds infundibular stem in the form of a collar.

 Composed of groups or cords of faintly basophilic cuboidal cells associated with blood vessels of the hypophyseal portal system.

 Function of the pars tuberalis is unknown. The Neurohypophysis

 Neurohypophysis consists of unmyelinated nerve fibers (axons), b.vs and neuroglia- like cells called .

 Axons, about 100,000 in number, originate mainly from neurons located in the supra- optic & paraventricular nuclei of the hypothalamus. The Neurohypophysis

 These axons converge at the median eminence to form a bundle of nerve fibers called Hypothalamo-hypophyseal tract.

 This tract passes through the infundibular stem to pars nervosa, where the axons terminate in dilated nerve endings close to a rich plexus of fenesterated capillaries.

 Dilated axonal terminations contain neurosecretory granules having a diameter of 100-200 nm. The Neurohypophysis

 Neurosecretory material from neurons moves into pars nervosa

 Is stored at the dilated axonal terminations and released into circulation as needed.

 Two hormones are stored and released from Neurohypophysis:

 (I) Oxytocin, and (2) Vasopressin, also called antidiuretic hormone (ADH).

Hormone communication The Neurohypophysis

 H&E, neurohypophysis is rather undistinguishable, because the individual axons and nerve terminations can not be identified.

 Large accumulations of the neurosecretory material are seen as basophilic masses called .

 Most easily seen in substance of neurohypophysis, are round pale staining nuclei of the pituicytes and numerous capillaries.

The Neurohypophysis

has a small cell body with a number of cytoplasmic processes.

 These processes often end in close relation to blood vessels.

 In routine preparations, cytoplasm processes can not be seen.

 Pituicytes are considered to be a special type of neuroglial cells. Pituicytes & Herring bodies Pituicytes & Herring bodies The Hypophysis BLOOD SUPPLY

 Hypophyseal arteries arise from internal carotid arteries and circle of Willis.

 These arteries divide into superior and inferior sets of branches.

 Superior hypophyseal arteries pass to the region of median eminence and give rise to capillaries.

 Capillaries reunite to form veins which run downwards around the hypophyseal stalk to reach pars distalis

 Here these veins open into the sinusoidal capillaries of anterior lobe. The Hypophysis

 This connection between capillaries of median eminence and sinusoidal capillaries of anterior lobe constitutes the hypothalamohypophyseal portal system.

 Through this pathway hormone-releasing (or release- inhibiting) factors from hypothalamus pass to pars distalis.

 Inferior hypophyseal arteries pass directly to posterior lobe of pituitary gland to supply it.

 Veins from the anterior and posterior lobes of the hypophysis drain into the cavernous sinus. Pituitary gland