Histo - Pituitary Gland

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Histology - Endocrine Glands

Pituitary Gland

Muhammad Ressam Nazir


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PITUITARY GLAND (The Hypophysis Cerebri)


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Pituitary gland

It lies in the base of the skull in a portion of sphenoid bone called Sella Turcica

Weight= 500-900 mg

Size is like that of pea.

It may double in size during pregnancy.


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Gross Anatomy

Because of its dual origin, the pituitary actually consists of two glands

the anterior adenohypophysis (anterior pituitary)

the posterior neurohypophysis (posterior pituitary)

Both are united anatomically but with different functions.

The adenohypophysis, derived from the oral ectoderm, has threeparts: a large pars distalis (or the anterior lobe); the pars tuberalis,

which wraps around the infundibulum; and the thin pars intermedia.

The neurohypophysis retains features of CNS tissue from which it

developed (floor of diencephalon (forebrain)) and consists of a large part, the

pars nervosa, and the smaller infundibulum with its stalk attached tothe hypothalamus at the median eminence.


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The Hypothalamic-Hypophyseal Portal System


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Histology of the Pituitary Gland


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Histology of the Pituitary Gland


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ADENOHYPOPHYSIS(Anterior Pituitary)

Pars Distalis

75 % of the hypophysis.

Main components are cords of

epithelial cells interspersed withfenestrated capillaries.

Gland is surrounded by a C.T.

capsule.

Cells of parenchyma =

chromophobes, chromophils. Stroma = composed of reticular

fibers and fibroblasts.


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Pars Distalis


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Cell Types

Chromphobes: No affinity for stains

50 % cells in the pars disatalis.

Rounded or polygonal cells

No secretory granules

Actually these are degranulated chromophils.


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Chromphils:

Remaining 50 % of the cells.

Rounded or polygonal cells

Have affinity for stains due to presence of cytoplasmic granules.

2 types: acidophils (70%) and basophils.


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Acidophils:

Larger than chromophobes but smaller than basophils

Cytoplasm has granules which stain with aciidc dyes (e.g. eosin, orange G,

azocarmine etc) Alpha acidophils (somatotropes): commoner of the two types, stain well with

orange G. Secrete GH.

Epsilon acidophils (lactotropes or mammotropes): Granules stain with

azocarmine. Secrete prolactin.


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Basophils:

Larger in size than acidophils

Dont stain with hematoxylin but stain intensely with methylene blue.

Beta basophils(thyrotropes): stain intensely with aldehyde fuchsin. secrete

TSH.

Delta cells (gonadotropes): secrete FSH and LH.

Corticotropes:these cells also dont stain with aldehyde fuchsin. They secrete

ACTH.


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Pars Tuberalis

The pars tuberalis is a funnel-shaped region surrounding the infundibulum of

the neurohypophysis.

Most of the cells of the pars tuberalis are basophilic gonadotropic cells that

secrete follice-stimulating hormone (FSH) and luteinizing hormone (LH).

Pars Intermedia

The pars intermedia is a thin zone of basophilic cells between the pars distalis

and the pars nervosa of the neurohypophysis.

MSH increases melanocyte activity and cells of the pars intermedia are often

referred to as melanotropic cells, but the overall physiological significance of

this region remains uncertain, especially in adults.


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The diagram summarizes the major hormones of the anterior pituitary and indicates their most important targets.


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NEUROHYPOPHYSIS

(Posterior Pituitary)


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NEUROHYPOPHYSIS

The neurohypophysis consists of thepars nervosa and the infundibularstalk.

The pars nervosa, unlike theadenohypophysis, does not containsecretory cells.

It is composed of neural tissue,containing some 100,000unmyelinated axons of secretoryneurons situated in the supraopticandparaventricular nuclei of thehypothalamus.

Also present are highly branched glialcells called pituicytes that resemble

astrocytes and are the most abundantcell type in the posterior pituitary. Their main role is to assist in the

storage and release of neurohypophysialhormones.


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Histo - Pituitary Gland

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