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Human Body
of transforming into positive sex-expression, either of male or female.
Islets of Langerhans
Endocrine tissue making up the islets of Langerhans accounts for about 1 to 2 % of the total weight of the pancreas. They are supplied with blood more abundantly than other parts of the pancreas. Three kinds of cells are distinguished in the islets: (i) beta-cells-located near the centre of the islets and comprising 60 to 70 % of all its cells; (ii) delta-cells which are predecessors of other cells (2 to 8 %); (iii) alpha-cells-located near the periphery.
Glucagon is formed in the alpha-cells, insulin in the beta-cells, and somatostatin in the delta-cells. We have already discussed about the glucagon and insulin in the 8th chapter.1 Somatostatin is one of the regulators of the secretion of insulin and glucagon.
(vi) The Adrenal Dlands
Adrenals are a pair of three cornered hat-shaped glands capping the upper end of the kidneys. They are about as big as the ends of one's fingers. The weight of both adrenals ranges from 6 to 12 gms. Their langth is 40-60 mm, breadth 20-35 mm, and thickness 6-10 mm. Each adrenal is a double gland, composed of a cortex-an outer layer, and a medulla-an inner layer. The cortex makes up the bulk of the gland, which is bright yellow outside and reddish brown inside. The medulla is much thinner and grey in colour. Cortex itself is divided into three zones;
(a) a narrow outer,
(b) a wide heavier middle, and (c) an irregular inner.
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In childhood and youth, the glands are relatively larger and more prominent than in the adult life. At all ages, the amount of blood passing through the adrenals is very great compared to their size. They are supplied with blood by the superior, middle, and inferior adrenal arteries. The tremendous importance of these glands is better understood when it is known that death occurs very quickly after removal. They are innervated by sympathetic and 1. See pp. 94-95.
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