Page 809 - Textbook of Pathology, 6th Edition

1. The anterior lobe or adenohypophysis is an ectodermal of the hypothalamus but are stored in the cells of posterior 793
derivative formed from Rathke’s pouch which is an upward pituitary.
diverticulum from the primitive buccal cavity. The 1. ADH causes reabsorption of water from the renal tubules
adenohypophysis has no direct neural connection but has and is essential for maintenance of osmolality of the plasma.
indirect connection through capillary portal circulation by Its deficiency results in diabetes insipidus characterised by
which the anterior pituitary receives the blood which has uncontrolled diuresis and polydipsia.
already passed through the hypothalamus.
2. The posterior lobe or neurohypophysis is a downgrowth 2. Oxytocin causes contraction of mammary myoepithelial
from the primitive neural tissue. The neurohypophysis, cells resulting in ejection of milk from the lactating breast
therefore, has direct neural connection superiorly with the and causes contraction of myometrium of the uterus at term.
hypothalamus. It is obvious from the description above that pituitary,
though a tiny organ, is concerned with a variety of diverse
HISTOLOGY AND FUNCTIONS. The histology and functions in the body. The pituitary gland and hypothalamus
functions of the anterior and posterior lobes of the pituitary are so closely interlinked that diseases of the pituitary gland
gland are quite distinct. involve the hypothalamus, and dysfunctions of the
hypothalamus cause secondary changes in the pituitary. The
A. ANTERIOR LOBE (ADENOHYPOPHYSIS). It is com- pituitary gland is involved in several diseases which include:
posed of round to polygonal epithelial cells arranged in cords non-neoplastic (e.g. inflammations, haemorrhage, trauma,
and islands having fibrovascular stroma. These epithelial
cells, depending upon their staining characteristics and infarction and many other endocrine diseases) and neoplastic
diseases. However, functionally and morphologically,
functions, are divided into 3 types, each of which performs diseases of the pituitary can be classified as below, each of
separate functions:
which includes diseases of the anterior and posterior
1. Chromophil cells with acidophilic granules: These cells pituitary and the hypothalamus, separately:
comprise about 40% of the anterior lobe and are chiefly i) Hyperpituitarism
located in the lateral wings. The acidophils are further of 2 ii) Hypopituitarism
types: iii) Pituitary tumours CHAPTER 27
i) Somatotrophs (GH cells) which produce growth hormone
(GH).
ii) Lactotrophs (PRL cells) which produce prolactin (PRL). HYPERPITUITARISM
Cells containing both GH and PRL called mammo- Hyperpituitarism is characterised by oversecretion of one or
somatotrophs are also present. more of the pituitary hormones. Such hypersecretion may

2. Chromophil cells with basophilic granules: These cells be due to diseases of the anterior pituitary, posterior pituitary
constitute about 10% of the anterior lobe and are mainly or hypothalamus. For all practical purposes, however,
found in the region of median wedge. The chromatophils hyperfunction of the anterior pituitary is due to the
include 3 types of cells: development of a hormone-secreting pituitary adenoma
i) Gonadotrophs (FSH-LH cells) which are the source of the (discussed later), and rarely, a carcinoma. For each of the The Endocrine System
FSH and LH or interstitial cell stimulating hormone (ICSH). hormonal hyperfunction of the anterior pituitary, posterior
ii) Thyrotrophs (TSH cells) are the cells producing TSH. pituitary and hypothalamus, a clinical syndrome is described.
iii) Corticotrophs (ACTH-MSH cells) produce ACTH, A few important syndromes are as follows:
melanocyte stimulating hormone (MSH), β-lipoprotein and
β-endorphin. A. Hyperfunction of Anterior Pituitary
Three common syndromes of adenohypophyseal hyper-
3. Chromophobe cells without visible granules: These cells
comprise the remainder 50% of the adenohypophysis. These function are: gigantism and acromegaly, hyperprolacti-
cells by light microscopy contain no visible granules, but on naemia and Cushing’s syndrome.
electron microscopy reveal sparsely granulated cortico- GIGANTISM AND ACROMEGALY. Both these clinical
trophs, thyrotrophs and gonadotrophs. syndromes result from sustained excess of growth hormone
All these functions of the adenohypophysis are under the (GH), most commonly by somatotroph (GH-secreting)
indirect control of the hypothalamus through stimulatory and adenoma.
inhibitory factors synthesised by the hypothalamus which Gigantism. When GH excess occurs prior to epiphyseal
reach the anterior lobe through capillary portal blood. closure, gigantism is produced. Gigantism, therefore, occurs
B. POSTERIOR LOBE (NEUROHYPOPHYSIS). The in prepubertal boys and girls and is much less frequent than
neurohypophysis is composed mainly of interlacing nerve acromegaly. The main clinical feature in gigantism is the
fibres in which are scattered specialised glial cells called excessive and proportionate growth of the child. There is
pituicytes. These nerve fibres on electron microscopy contain enlargement as well as thickening of the bones resulting in
granules of neurosecretory material made up of 2 considerable increase in height and enlarged thoracic cage.
octapeptides—vasopressin or antidiuretic hormone (ADH), and Acromegaly. Acromegaly results when there is overproduc-
oxytocin, both of which are produced by neurosecretory cells tion of GH in adults following cessation of bone growth and