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Human Biology Essay

4825 words - 19 pages

The pituitary gland and the hypothalamus are found within the brain and act together as a unit to regulate the activity of most of the other endocrine glands. The hypothalamus is sometimes referred to as the control centre as it controls pituitary function and plays a vital role co-ordinating between tissue and organ activity via the secretion of hormones. The pituitary gland, or master gland, is attached to the hypothalamus by a stalk and is positioned below it in the hypophyseal fossa of the sphenoid bone. A pituitary gland is a pea size object consisting of three distinct parts, the adenohypophysis or anterior lobe, the nerohypophysis or posterior lobe and an intermediate lobe, (Ross and Wilson.1999). Functions of the intermediate lobe are poorly understood and hormones can only be detected in this section during fetal life and in pregnancy. Some of the six hormones secreted by the adenohypophysis, (anterior pituitary lobe), stimulate or inhibit secretion by other target endocrine glands while others have a direct effect on specific tissues. When the hypothalamus detects a change of hormone level in the blood it produces a hormone, which in turn stimulates the anterior pituitary lobe to release more of its own chemical messenger. The whole system is regulated and controlled by this negative feedback mechanism. The hormones synthesised by the adenohypophysis include growth hormone, (GH), thyroid stimulating hormone, (TSH), adrenocorticotrophic hormone, (ACTH), prolactin, (PRL), and gonadotrophic hormones, (FSH and LH). Growth hormone or GH promotes the growth of connective tissues, muscles, the skeleton, and organs such as the pancreas, liver, and kidneys. The production of GH by the adenohypophysis is dependent on the hypothalamus and whether it synthesises growth hormone releasing hormone, (GHRH) or growth hormone release inhibiting hormone, (GHRIH). GHRIH inhibits the secretion of GH, TSH, ACTH, gastric juice and emptying of the stomach. When the hypothalamus generates TRH the adenohypophysis produces TSH or thyroid stimulating hormone. TSH would be transported through the blood stream to the thyroid gland, which in turn may produce T4, (Thyroxine), a substance known to affect basal metabolic rate. Corticotrophin releasing hormone or CRH from the hypothalamus promotes the synthesis and release of ACTH by the adenohypophysis. The hormone ACTH targets the adrenal cortex, which has the responsibility of manufacturing three groups of hormones collectively termed adrenocorticocoids. Hormones produced by the adrenal glands influence the formation and storage of glycogen, and increase or suppress the body's ability to respond to stress, (Tortora and Grabowski.2001). The anterior pituitary lobe may release the chemical prolactin or PRL which stimulates the mammary glands, (breasts), to form milk. Suckling of the breasts stimulates prolactin secretion and the resulting high level present in the blood significantly reduces the incidence of conception...

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