All of these are released into the blood in the capillaries and travel immediately – in portal veins – to a second capillary bed in the anterior lobe of the pituitary, where they exert their effects.
All of them are released in periodic spurts. In fact, replacement hormone therapy with these hormones does not work unless the replacements are also given in spurts.
Two other hypothalamic hormones:
|Link to diagram of the endocrine glands (92K)|
GnRH is a peptide of 10 amino acids. Its secretion at the onset of puberty triggers sexual development, and from then on it is essential for normal sexual physiology in both males and females. In both sexes, its secretion occurs in periodic pulses usually occurring every 1–2 hours.
|Primary Effects||Secondary Effects|
|FSH and LH Up||estrogen and progesterone Up (in females)|
|testosterone Up (in males)|
|The signal that stimulates GnRH secretion - Link.|
After puberty, a hyposecretion of GnRH may result from
As its name indicates, GHRH stimulates cells in the anterior lobe of the pituitary to secrete growth hormone (GH).
As its name indicates, its acts on cells in the anterior lobe of the pituitary to release adrenocorticotropic hormone (ACTH)CRH is also synthesized by the placenta and seems to determine the duration of pregnancy.
|Description of the mechanism.|
Somatostatin is a mixture of two peptides, one of 14 amino acids, the other of 28.Somatostatin acts on the anterior lobe of the pituitary to
Somatostatin is also secreted by cells in the pancreas and in the intestine where it inhibits the secretion of a variety of other hormones.
Dopamine-secreting cells are also found in other parts of the body where most of its actions are paracrine; that is, acting on nearby cells.
These peptides are released from the posterior lobe of the pituitary and are described in the page devoted to the pituitary. [Vasopressin] [Oxytocin]