The anterior lobe of pituitary gland (adenohypophysis) is the glandular portion of the hypophysis and the main gland of the endocrine system. It consists mainly of hormone-producing cells, which are arranged in sac-like dilations called 'acini' (sing. acinus) delineated by a basement membrane, a reticulum network, and capillaries. These endocrine cells are controlled by regulatory hormones released by parvocellular neurosecretory cells in the capillaries of hypothalamus that lead to the infundibular blood vessels, which in turn lead to a second capillary bed in the anterior pituitary. This vascular relationship form the hypothalamo-hypophyseal portal system.
The anterior lobe of pituitary gland in the adult consists of adenose epithelium which contains three kinds of cells: 1) the eosinophils, which is disposed especially in the lateral wings; 2) the basophils, which is localized mainly in the mucoid wedge region; 3) and the chromophobes, scattered throughout the anterior pituitary. The chromophobe cells are the reserve material from which the basophil and eosinophil cells develop. The proportions of eosinophils and basophils in the anterior lobe vary with the sex, age, and physiological state of the organism. For example, after removal of the thyroid gland (thyroidectomy), the number of eosinophil cells decreases sharply, to the point of complete disappearance, while basophil cells degenerate and are transformed into so-called thyroidectomy cells. After removal, basophil cells hypertrophy and are transformed into so-called castration cells. The changes that take place in the composition of the cells of the anterior pituitary after thyroidectomy or castration can be prevented or corrected by the administration of thyroxine or sex hormones. The intermediate lobe of the pituitary consists of epithelial tissue. The anterior lobe is formed by neuroglia, which contains large pyramidal or spindle cells (so-called pituicytes).
Function and hormones
The physiological functions, or role, of the anterior pituitary are most complex and varied. Growth, reproduction, and basal, carbohydrate, mineral, fat, and protein metabolism depend upon its normal functioning. Seven hormones have been isolated from anterior pituitary extract: growth (somatotropic) hormone, thyrotropic hormone, follicle-stimulating hormone, luteinizing hormone, luteotropic hormone, prolactin (lactogenic hormone), and adrenocorticotropic hormone (ACTH). All these hormones are protein in nature and can be obtained in pure form. Some of them, such as growth hormone and lactogenic hormone, have been isolated in crystalline form, and others, such as ACTH, have been synthesized. Thyrotropic and gonadotropic hormones are produced by the basophil cells, which are divided accordingly into thyrotrophs and gonadotrophs. The eosinophil cells manufacture growth hormone and prolactin. The cells that produce ACTH have not been determined, although it is probable that the basophilic cells are involved.
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| Above, the anterior pituitary and the hypophysial portal system. |
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