The Pituitary Gland. Pituitary Gland

Transcription

1 The Pituitary Gland Pituitary Gland

2 The Hypophysis (Pituitary gland) Is the master gland, produces several hormones which influence the activity of other endocrine glands. Suspended from hypothalamus 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

3 The Pituitary Gland

4 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 Pars intermedia Thicker pars distalis lies anterior to the fissure. An extension of the pars distalis, called pars tuberalis, surrounds the infundibulum. Posterior to the fissure lies pars intermedia. which forms a thin cellular partition between the pars distalis and Neurohypophysis.

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8 PITUITARY GLAND Anterior lobe (Adenohypophysis) comprises pars distalis, pars tuberalis & pars Intermedia. Posterior lobe (Neurohypophysis) includes pars nervosa, Infundibular stem and Median eminence.

9 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. PITUITARY GLAND

10 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.

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13 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.

14 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.

15 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.

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17 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

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19 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.

20 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.

21 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.

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

24 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 luteinizing hormone (LH) which in the male is also known as interstitial cell stimulating hormone (ICSH).

25 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.

26 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.

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28 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.

29 The Neurohypophysis Neurohypophysis consists of unmyelinated nerve fibers (axons), b.vs and neuroglialike cells called Pituicytes. Axons, about 100,000 in number, originate mainly from neurons located in the supraoptic & paraventricular nuclei of the hypothalamus.

30 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 nm.

31 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

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

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38 The Neurohypophysis Pituicyte 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.

39 Pituicytes & Herring bodies

40 Pituicytes & Herring bodies

41 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

42 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 releaseinhibiting) 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.

43 Pituitary gland