Pituitary Gland

Stroma
1- Capsule 2- Septa 3- Reticular C.T. stroma
They are thin, incomplete and irregular septa arising from the Arises from the inner surface of the capsule and both surfaces
The gland is surrounded by a thin capsule formed of dense
inner surface of the capsule, dividing the gland into of the of the septa to fill the background of the gland and takes
irregular C.T. "represents continuation of dura matter"
intercommunication indistinct lobules. the arrangement of parenchyma.
Parenchyma
- It's formed of: 1- endocrinal secretory cells AND 2- fenestrated blood capillaries whose fenestra are closed with diaphragms.
- The type and arrangement of the cells and blood capillaries is variable from one region of the gland to another.
Parenchyma of Adenohypophysis ( Anterior Pituitary )
A) Pars Distalis A) Pars tuberalis
- The Parenchyma is formed of branching and anstomosing cords of cells with wide fenestrated blood capillaries inbetween in which - It forms a thin sleeve that surrounds the ant. and lateral
the fenestra are closed by diaphragms aspects of the infundibular stalk.
- The cells of the pars distalis are classified according to the presence or absence of stainable granules in their cytoplasm into:
Chromophils - It's only 25-60 um in thickness, and separated from the
infundibular stalk by a thin layer of C.T.
- The contain stainable granules in their cytoplasm ( represent about 50% of the pars distalis cells ) .
- Chromophils are subdivided according to the staining affinity of their granules into : - It's formed of cords of cells separated by fenestrated
Acidophils Basophils blood capillaries .
medium-sized. Large cells
Rounded or polygonal in shape. Rounded or polygonal - The cells :
They are more located in periphery of pars distalis specially in its They are more located in the central part of the gland. • maybe grouped to form follicle-like structures.
postrolateral regions
Represent 35% of the cells of pars distalis Represent 15% of the cells of pars distalis
• They are cuboidal or polygonal in shape,
Nucleus: Nucleus: • Nucleus: single central rounded nucleus.
Single, central, rounded & vesicular nucleus with prominent Single, central ( eccentric ), rounded & vesicular nucleus with prominent • Cytoplasm: contains the ordinary cell organoids and
nucleolus. nucleolus. inclusions, and good content of glycogen.
Cytoplasm: Cytoplasm:
- Mild basophilic - Mild basophilic • Function: Unknown.
- By L.M, it appears to be crowded with acidophilic - By LM, it appears to contain basophilic granules which can be stained :
granules which can be stained by orange G. 1- deeply by the basic dye; methylin blue A) Pars Intermedia:
2- positively by PAS
- By E.M, ( like any protein secretory cell ). It - By E.M,
- It's the layer that lies between the hypophyseal cleft
contains well-developed rER, Golgi complex, small - ( like any protein secretory cell ). It contains well developed rER, Golgi anteriorly and the pars nervosa posteriory and surrounds
rod-shaped mitochondria and membrane-bound complex, small rod-shaped mitochondria and membrane-bound secretory it's ant. and lateral aspects.
secretory granules. granules.
- In Human Fetus moderately thick forming 3% of the
There are 2 kinds of acidophils which can be There are 3 kinds of basophils ehich can be distinguished by cells of adenohypophysis.
distinguished by immunocytochemical techniques immunocytochemical techniques & by E.M:
- In Adults no longer identified as a distinct layer.
& by E.M:
1- Somatotophs 1- Thyrotrophs 2- Corticotrophs 3- Gonadotrophs - The Cells:
- Their membrane-bound granules are 300-350 nm in diameter. - They have granules, - They have granules of
- They have smallest • It's formed of cells which are forming irregular cords
- The cisternae and their rER are well-developed and lie parallel whose diameter is variable sizes ranging
to the cell surface.
granules, whose
150-200 nm. from 200-400 nm in
or small groups with fenestrated blood capillaries
diameter is 100-150 inbetween.
- They secrete GH. diameter.
nm. - They secrete ACTH.
2- Mammotrophs (lactotrophs) • In rats where the pars intermedia is well-developed,
- They secrete:
- They secrete TSH. the cells are large, polygonal.
- Their membrane-bound granules 500 – 900 nm in diameter - Some secrete MSH. - FSH
- These granules can bestained specifically by erythrocin for - LH • Nucles: single, central, rounded & vesicular nucleus.
light microscope. - These granules can be
stained specifically by • Cytoplasm: is pale basophilic containing well-
- They secrete the prolactin
aldehyde fuchsine developed rER, Golgi comples, mitochondria and
In males & cycling females:
for light microscope numerous membrane0bound secretory granules 200-
They small cells with few elongated cisternae of rER, medium-
sized Glogi complex, few small membrane-bound granules. 250nm in diameter.
• Function: They secrete MSH .
In femaile during pregnancy & lactation:
The cells increase in size (hypertrophy) & in number (hyperplasia)
and their rER and Golgi complex become more developed.

At the termination of lactation, these changed regress.

Chromophobes
General appearance: Nucleus: Each cell contains a single, central, rounded and vesicular nucleus.
- They are small polygonal cells, with ill-defined cell boundaries. Cytoplasm:
- They present mainly in the central regions of the cell cords - Pale basophilic, or relative little amount around the nucleus.
- Represent 50% of the cells of pars distalis. - By L.M., appears to have no granules
- By E.M., it has poorly developed rER, Golgi complex, mitochondria, few
small membrane-bound granules.
Function:
Most chromophobes are partially degranulated chromophils, and small percentage of them maybe reserve or non-secretory cells.

Parenchyma of Neurohypophysis ( Posterior Pituitary )

- The neurohypophysis consists of median eminence of the hypothalamic tuber cinereum, the infundibular stem and the infundibular process (Pars nervosa).
- The pars nervosa is the only site of storage and release of hormones synthesized in the nerve cells of the hypothalamic supraoptic and paraventricular nuclei.
- The axons of these nerve cells :
• Collect to form a thick bundle of unmyelinated nerve fibers called the hypothalamo-hypophyseal tract. These axons pass in the neurohypophysis to terminate in its
pars nervosa.
• Have numerous dilatations along their length & their terminations in the pars nervosa. In these dilatations, the hormones synthesized by the nerve cells are
accumulated to form spherical basophilic masses of secretory material called Herring bodies.
• In the pars nervosa, the nerve, the nerve fibers & their Herring bodies are separated and supported by fenestrated blood capillaries & pituicytes.
Structure of pars nervosa
Accordingly, the pars nervosa is composed of:

1- About 100,000 unmyelinated nerve fibers which are the axons of the paraventricular & supraoptic nuclei that
form the hypothalamo-hypophyseal tract.
2- Herring bodies, which are spherical basophilic masses of secretory material which accumulate along the course
of the nerve axons and their terminations.
3- Fenestrated blood capillaries .
4- Pituicytes, which are stellate-shaped cells with slender processes that are joined to the process of other
pituicytes to form three-dimensional network among the nerve fibers.( these cells seem to have no role in
secretory process, but are believed to have a supportive and trophic function - neuroglia cell - ).
5- Some cells migrating from the pars intermedia.
Fuction of pars nervosa

- The pars nerovosa is the site of storage and release of two peptide hormones synthesized in the hypothalamic
paraventricular and supraoptic nuclei.

- These hormones are:

1- Oxytocin, produced by the paraventricular nucleus.
2- Vasopressin, produced by the supraoptic nucleus.