Pituitary gland
This is a small gland lying ventral to the hypothalamus in the Ibrcbrain (Fig. 6. 1). It is also known as the hypophysis and is divided into two lobes, each of which acts as a separate gland.
Anterior pituitary gland
Also known as the adenohypophysis, this produces:
Thyrotrophie/thyroid stimulating hormone ('I*SH) — stimulates the thyroid gland.
Growth hormone or somatotrophin - controls the rale of growth in young animals by:
- Controlling the rate of growth at Iheepiphyses of the bones
- Ileing involved in protein production from amino acids
- Regulating the use of energy during periods of poor food supply. CIucosc is conserved for use by the nervous system and fat is broken down to be ust*d as a source of energy by the rest of the body.
Adreniworlicotrophie hormone (ACTH I - stimulates the adrenal cortex. Oversecretion may cause the symptoms of Cushing’s disease.
Prolactin - stimulates the development of the mammary glands and the secretion of milk during the latter half of pregnancy. The milk cannot be released unless oxytocin is produced at the end of the gestation period.
Eollicle Stinnilatinfi hormone (FSII) — at the start of the OCStrous cycle, or at puberty, external factors, e.g. day length (photoperiod). Iemperatureor pheromones secreted by the male or other females, affect the hypothalamus. This secretes gonadotrophin releasing hormone which stimulates the anterior pituitary gland to secrete PSI I. FSH stimulates germ cells in the ovary to develop into follicles, each containing an ovum.
IJitciiiisinjj hormone IlJO- secretion is stimulated by the presence of oestrogen in the blood. LH stimulates the ripe follicles in the ovary to rupture and release their ova (ovulation I. The remaining tissue becomes 1Iuteinised* to form the corpus luteum.
Interstiti∣ιl cell stimulating hormone (ICSl 11 - stimulates the interstitial cells or cells of Ieydig in the testis to secrete testosterone. This is the male equivalent of FSH.
Posterior pituitary gland
The posterior pituitary gland is also known as the neurohypophysis. The hormones associated with this part of the pituitary gland are secreted by the hypothalamus and only stored here. They are:
AiKidiiiivtic hormone ι AI)H I - also called vasopressin. This hormone alters the permeability of the collecting ducts of the kidney to water. It is secreted in response to the changing volume of extracellular Iluid IECTl and helps maintain homeostasis.
Oxytoein - this has two effects:
- It acts on the mammary glands during late pregnancy and causes the milk to be released or 4Iet down’ in response to suckling by the neonate
- At the end of gestation, oxytocin causes the contraction of the smooth muscle of the uterus, resulting in parturition and delivery of the fetuses.