الفهرس 
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Abstract
The histological and histochemical structure of the pituitary (pars distalis) and the mammary glands of 80 buffalo females were studied at different ages and during various reproductive states.
The pars distalis is surrounded by a fibrous capsule which is increased in thickness with the advance of age. The interstitial stroma is represented by a delicate net of reticular fibers.
The gland’s parenchyma is composed of 3 populations of cells and 5 types of actively-secreting cells; acidophils (somatotrophs and lactotrophs), basophils (thyrotrophs, gonadotrophs and corticotrophs ) and chromophobe cells. Each cell type possesses a special structure and a particular action on the mammary gland.
The somatotrophs are large oval cells containing large eccentric and vesicular nuclei and coarse acidophilic granules which are stained yellow with orange G.
The lactotrophs differ from somatotrophs by being elongated cells with dark eccentric nuclei and diffuse orange-coloured cytoplasm. The reaction was found to be due to the presence of fine confluent secretory granules.
The thyrotrophs are rectangular cells with few cytoplasmic processes. The cytoplasm contains fine, discrete, basophilic granules and eccentric, vesicular and spherical nuclei. The gonadotrophs are medium-sized and oval-shaped cells. The nuclei are spherical, eccentric and vesicular and the cytoplasm contains coarse granules stainable with basic dyes.
The corticotrophs are characterized by their large size, irregular outline and by their cytoplasmic granules which are stained lightly with basic dyes and exclusively with lead haematoxylin. The eccentric nuclei are spherical and vesicular.
The pars distalis cells were found to show significant changes which could be correlated with the age and the physiological state of the females. Parameters of evaluation include the number and the size of the cells, number and staining affinity of secretory granules and the frequency of active secretory cells (sparsely-granulated cells).
It has been found that the somatotrophs, the lactotrophs, the thyrotrophs and the gonadotrophs show a typical growth curve. The cells are gradually increased in number and after reaching a peak percentage during lactation, they are markedly reduced in the glands of senile animals.
Associated with the above mentioned changes is the enlargement of cells due to their ability to accumulate increasing numbers of secretory granules. When fully-granulated cells release their content of hormones, sparsely-granulated cells appear. The number of degranulated cells is directly proportional with the activity of the cells. The cells are active during puberty, more active during pregnancy and lactation and at least actively in senile females. Unlike the other chromophil cells, the corticotrophs, don’t regress during the age of senility but remain numerous and active.
The mammary glands in calves are formed principally of adipose CT. The gland’s parenchyma is represented by few branching ducts lined with simple columnar epithelium occurring adjacent to the teats.
The mammary gland was found to be age and hormone dependant organ. It is stimulated to grow at 2 definite periods; at puberty and during pregnancy and lactation when the pituitary cells release their content of hormones.
At puberty, newly-formed non-functioning alveoli and tubules are developed on the expense of the adipose tissue.
During pregnancy, the duct system is developed first. When the premordia of the adenomeres are stimulated, they are increased progressively in number and in size. In late pregnancy, growth of the mammary gland reaches the peak and the lobules are closely-packed with enlarged adenomeres.
After labour, the maximally-grown adenomeres become active and secrete milk. The secretion is squeezed out of the alveoli by myoepithelial cells. The structure of the adenomeres during the synthesizing, secretory and storage phases are described. When the lactating animals are allowed to become pregnant, the mammary glands are dried by cessation of milk removal. Stagnation of milk causes pressure atrophy of the adenomeres, and the regressed alveoli are replaced by CT.
As the animals get elder, the activity of the pituitary hormone secreting-cells is reduced and the mammary tissue is reverted to the non-functioning state. It is characterized by disappearance of all alveoli and most of the duct system. Only few wide ductules lined with simple cuboidal epithelium persist. Some of the ducts may contain corpora amyleacea.
Changes in the pars distalis cells and in the structure of the mammary glands were correlated and discussed with the available literature.