Hormones of the Pituitary
These are the hormones which are secreted from both lobes of the pituitary and how their secretion affects the body. When the pituitary is functioning normally, the secretion of each of these hormones is closely regulated.
Also known as ACTH, or corticotrophin. This hormone stimulates the production of androgens and stimulates the release of Cortisol from the adrenal glands of the kidney. The adrenal hormones are essential for helping the body cope with stress.
Gonadotrophins - LH and FSH
These are known as the sex hormones; Luteinising hormone (LH) and follicle stimulating hormone (FSH).
- IN WOMEN - These hormones are targeted to the ovaries where they control ovulation therefore they are essential for a normally functioning menstrual cycle and fertility. FSH and LH promote the growth and development of ovarian follicles which in turn produce oestrogen and progestins.
- IN MEN - These hormones are targeted to the testes, where LH stimulates the leydig cells to produce the male hormone Testosterone. FSH activates Sertoli cells to initiate Spermatogenesis.
In children, LH and FSH control sexual development during puberty.
Growth hormone (GH)
This hormone is essential for general growth and development of cells within the body. It targets somatic tissue and is particularly important for childhood growth in height.
This hormone promotes the development of mammary glands; the intiation and maintainance of breast milk production.
This hormone stimulates the breasts to make milk. It is present all the time in both men and women, but is produced in large amounts during pregnancy and breastfeeding.
Thyroid stimulating hormone (TSH) / Thyrotrophin
This acts on the thyroid gland - stimulating it to produce it's own hormones: Triiodothyronine and Thyroxine.
Anti-diuretic Hormone (ADH) / vasopressin (AVP)
This hormone targets the kidneys. It influences the volume of urine produced by altering the permeabilty to water of the collecting ducts within the kidney. By increasing their permeabilty to water, more is reaborbed back into the blood, resulting in increased blood volume. When vasopressin is in high concentrations it causes constriction of blood vessels throughout the body resulting in elevated blood pressure.
Release of this hormone in WOMEN results in unterine contractions. It also premotes contraction of myoepithelial cells in the breasts, resulting in milk being released when the baby suckles.
Regulation of Hormone secretion
The secrection of these hormones is regulated via negative feedback mechanisms. Correct levels of hormones are maintained due to the following sequence of events:
- The pituitary gland has a natural tendancy to oversecrete the hormone
- Due to the oversecretion, the hormone exerts a more and more significant control effect on it's target
- The target performs its function
- When the function has occured or it is occuring at too high a rate, the target elicits a signal which feeds back to the gland telling it that too much hormone is being produced - negative feedback
- the gland secretes less hormone
- Fuction in the target organ decreases, a signal is elicted telling the pituitary that more hormone needs to be secreted - postive feedback.
- the cycle re-starts