histological diagram of pituitary gland
The pituitary gland is comprised of the following.
i. capsule and stroma: The gland is covered with a thin capsule of C.T. from which septae penetrate the gland to form a central reticular framework (stroma). The stroma is richly supplied with fenestrated sinusoidal capillaries.
II. PARENCHYMA: Developmentally, the hypophysis is composed of
(a) Adenohypophysls and (b) Neurohypophysis
A. ADENOHYPOPHYSIS consists of three parts
(a) anterior thick pars dlstalls, (b) posterior pars Intermedia and (c) pars tuberalls.
1. PARS DISTALIS (75°/.): It is formed of cords of aggregations of ceils with intervening fenestrated capillaries, fibroblasts and reticular fibres. Based on staining of the cytoplasmic granules, these ceils are classified into following major types: I. CHROMOPHILS (chroma = color, philein = to love) (50%): These are the cells, whose cytoplasmic granules take up the stain. There are of two types; acidophils (35%) and basophils (15%)
a)BASOPHILS (p or BETA CELLS) stain pale blue with hematoxylin (basic dyes).
The basophils are further divisible into three types depending upon the type of cytoplasmic granules, staining properties and the hormone secreted by them.
THYROTROPHS: These are angular cells with rounded nuclei and secrete thyrold-stlmulatlng hormone (TSH). The cytoplasm is rich in small basophilic granules.
CORTICCOTROPHS: These are large sized, spherical or oval or irregular cells rich in coarse basophilic cytoplasmic granules and secrete adrenocorticotropic hormone (ACTH) as well as melanocyte stimulating
hormone. The cells may have short dendritic processes.
GONADOTROPHS: These are fusiform or rounded cells with eccentric oval nuclei. These are further classified into two types.
• Follicle stimulating hormone (FSH) secreting cells. Their cytoplasm contains well-developed Golgi apparatus and granular endoplasmic reticulum.
• Leutinlzlng hormone (LH) secreting cells. These contain dense granules of uniform size, poorly developed Colgi apparatus and smooth endoplasmic reticulum.
b. ACIDOPHILS (ALPHA CELLS) are stained pink with eosin (acidic dyes). They have secretory granules, which are larger than basophils. These are further classified as follows.
I. SOMATOTROPHS (ORANGOPHILS): these are spherical or ovoid cells with central rounded nuclei, rough endoplasmic reticulum, large secretory granules, tubular mitochondria and large sized Golgi body. These secrete somatotropin or growth hormone.
II. MAMMOTROPHS/LACTOTROPHS/CARMINOPHILS: These are spindle shaped cells with oval nuclei, small granules, rough endoplasmic reticulum, and lysosomes. The cytoplasmic granules contain prolactin or lactogenic hormone.
Chromophobes (chroma = color; phobes = fear) (50%): The cytoplasmic granules of these cells don't take up the stain intensely. These are small cells, with large nuclei. There are two types of chromophobes.
a. Chromophobes possessing few secretory granules.
b. Chromophobes possessing no secretory granules.
2. PARS TUBERALIS: This region is remarkable for its large number of blood vessels. It contains cords or follicles filled with colloidal substance. The cells are cuboidal with slightly basophilic cytoplasmic granules. These secrete gonadotropins (FSH & LH).
3. PARS INTERMEDIA: It is not well developed in humans. In animals it is better developed and consists of polygonal cells arranged as cords or follicles containing faintly-stained colloid material. Their cytoplasm is basophilic containing small
secretory granules. The cells perhaps secrete melanocyte-stlmulatlng hormone
(MSH & ACTH)
B. NEUROHYPOPHYSIS comprises of three parts:
(a) pars nervosa; (b) infundibular stem and; (c) median eminence.
1. INFUNDIBULUM: it contains unmyelinated nerve fibres (axons) of supraoptic and paraventricular nuclei of hypothalamus descending into pars nervosa.
2. PARS NERVOSA: It contains the following structures.
• Major portion is formed by nerve fibres/axons, which are rich in Nissl bodies and granular inclusions. The terminals of axons are dilated and their cytoplasm contains refractile granules and yellow brown pigment, which increase with age. These also contain pale-staining Herring bodies (neurosecretory corpuscles), which are the secretions of supraoptic and paraventricular nuclei of hypothalamus, having descended as irregular basophilic masses via the axon terminals. These secrete arglnlne, vasopressin (ADH) and oxytocin.
• Fenestrated blood sinusoid.
• Pitulcytes: These are the modified highly branched neuroglia cells which form 25% volume of pars nervosa
3. MEDIAN EMINANCE: It is usually discussed as a part of floor of diencephalon.
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