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Figure

An example of a negative feedback system: (1) Gland A secretes a hormone that stimulates gland B to increase secretion of another hormone. (2) The hormone from gland B alters its target cells and inhibits activity of gland A (see fig. 13.14).

Pituitary Gland

The pituitary (p!-tu'!-tar"e) gland (hypophysis) is about 1 centimeter in diameter and is located at the base of the brain. It is attached to the hypothalamus by the pituitary stalk, or infundibulum, and lies in the sella turcica of the sphenoid bone, as figure 13.7 shows.

The pituitary gland consists of two distinct portions: an anterior lobe (adenohypophysis) and a posterior lobe (neurohypophysis). The anterior lobe secretes a number of hormones, including growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL). Although the cells of the posterior lobe (pituicytes) do not synthesize any hormones, two important hormones, antidiuretic hormone (ADH) and oxytocin (OT), are secreted by special neurons called neurosecretory cells whose nerve endings secrete into the bloodstream within the posterior lobe. The cell bodies of these neurosecretory cells are in the hypothalamus.

Average concentration of hormone

Actual concentration of hormone

Time

Average concentration of hormone

Actual concentration of hormone

Time

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