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Endocrine Pituitary Gland Notes

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Pituitary Gland -MASTER GLAND!!!!
Organisation of the pituitary gland
-pituitary gland sits below the hypothalamus of the brain in a midline fossa, pituitary fossa of the sphenoid bone
-it is connected to the median eminence of hypothalamus by a pituitary stalkifundibulum
-it is surrounded by skull so the if the gland enlargens there is no extra space so there are severe headaches.
-functionally, the gland is divided into two lobes- anterior lobe is 2/3 volume of the gland and posterior lobe is one third- both have different embryological orgins and control mechanisms Development of the pituitary gland
- the anterior lobe (adenohypophysis) develops from an upward invagination, Rathke's pouch, of the oropharyngeal ectoderm (roof of the mouth)- the rathke's pouch constricts and is pinched off from the ectoderm.
-the posterior lobe (neurohypophysis) develops from the ifundibulum which is a downward extension of the neural ectoderm in the forebrain region.
-the portion of the rathke's pouch in contact with the posterior pituitary forms the intermediate lobe. In humans the intermediate lobe becomes interspersed with those of the anterior pituitary. anterior lobe (adenohypophysis)-collection of endocrine cells- types of endocrine cells can be identified through electron microscopy and by immunocytochemistry which classes cells depending on the specific protein they secrete 50% of secretory cells in the anterior lobe are somatotrophs- synthesise somatotrophin/GH
-Electron microscopy: the somatotrophs are packed with granules of moderate size 25% are lactotrophs- prolactin 10% are corticotrophs- ACTH
-sparse secretory granules located at the extreme periphery of a cell 15% are gonadotrophs- LH and FSH
-large cells with granules of various size 5% are thyrotrophs-TSH
-smaller granules

-surrounding the endocrine cells are gilial like cells- folliculostellate cells- support the cells and they secrete proteins which control the release of hormones-paracrine activity
-the anterior pituitary is regulated by chemical control...
-neurohormones- released from the nerve terminals of the hypothalamus into the capillary plexus of the internal carotid artery which enters the anterior pituitary through the hypothalamo-hypophyseal portal veins (travels down the pituitary stalk). The neurohormones diffuse from the veins and act on the local endocrine cells -Overall hypothalamic control is stimulatory for all anterior pituitary hormones except prolactin where it is inhibitory. The pulsatile release of hypothalamic releasing factors stimulate pulses of anterior pituitary hormones into the jugular vein. The evidence that showed the hypothalamic control of the pituary was shown rabbits where injected with Indian ink and the result showed there was abundance in the pituary stalk showing there was a vascular connection between the hypothalamus and the pituitary gland. If the pituitary stalk was surgically removed all the target endocrine glands that the anterior pituitary gland control undergo atrophy but they regrow to orginal size when the stalk is reconnected. Cells have a rich capillary network- endothelial lining of capillaries are fenestrated Systemic hormones: hormones released by the target tissues of the anterior pituitary lobe exert a mostly negative feedback control Paracrine interactions: in the anterior pituitary Hormones released by the anterior pituitary 1) Thryotroph cells (Hypothalmic-pituitary-thyroid axis)
-Thyroid stimulating hormone/ thyrotrophin secreted by thryotroph cells Chemical nature TSH-glycoprotein hormone made up of alpha and beta subunits. Receptors: G protein coupled to cAMP on thyroid gland follicular cells Actions: TSH acts in the thyroid and stimulates thyroid hormone production. It also increases iodine uptake by thyroid which is required for thyroid hormone production and stimulates thyroid growth Control: TSH release is stimulated by thryotrophin releasing hormone from the hypothalamus whose secretion is also stimulated by cold and by stress via the CNS. TSH is secreted in pulses with a diurnal rhythm.
-there is also a systemic control and TSH release is inhibited by T3 and T4 by negative feedback. Dysfunction: TSH disorders are very rare

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