Regulation of Hormone secretion
Regulation of Hormone secretion is placed by three mechanism By metabolite concentration, Feed back control (or) Servo mechanism and Synergism and antagonism.
- By metabolite concentration Mechanism
- Feed back control (or) Servo mechanism
- Synergism and antagonism mechanism
Metabolite concentration Mechanism Regulation of Hormone secretion–
Metabolite concentration Mechanism of hormone regulation is one of the simplest controls of hormone secretion e.g. a rising level of blood glucose signals release of blood sugar lowering hormone, insulin.
Insulin facilitates glucose movement through the cell membrane, which is either metabolised or stored in the form of glycogen in the liver for later use. When the blood glucose level drops below normal, the blood glucose raising hormone, glucagon is released from the alpha cells of the pancreatic islets.
It stimulates glycogenolysis of the glycogen stores of the liver, thereby raising the glucose level back to normal.
Feed back control mechanism of hormone secretion regulation-
Feed back control mechanism of hormone secretion regulation is an automatic means of correcting the hormone output of a gland to a desired level by level-sensing cells in the hypothalamus. The feedback system operates through three pathways-
- Ultra short loop: Between hypothalamic releasing and inhibitory factors; e.g. reciprocal stimulation / inhibition between GHRH and somatostatin
- Short loop: Between hypothalamic factors and pituitary hormones; e.g. TRH, TSH
- Long loop: Between hypothalamic factors and peripheral endocrine glands; e.g. GnRH and gonadal hormones
The feedback control system operates in two mechanisms-
Positive Feedback System
Increase in the level of target organ hormone increases secretion of tropic hormone.
The hypothalamus controls secretion of tropic hormones from anterior pituitary through the secretion of peptide releasing hormones.Increase in the concentration of target organ hormone stimulates hypothalamus.In the hypothalamus, the releasing hormone output increases to effect increased production of tropic hormones by anterior pituitary and subsequently the secretions of the hormones by the target organ.
E.g.,preovulatory release of LH, during the late stages of ovarian follicular development causes increased estrogen production which acts on hypothalamus and stimulates LHRH release and increases pulsatile rate of LH secretion from adenohypophysis to effect ovulation.
NegativeFeedback System It is the most common feedback system.
An increased target organ hormone concentration above certain physiological limit, causes a shut-down of releasing hormone production in the hypothalamus and also tropic hormone secretion from the anterior pituitary, thus decreases the production of hormone by the target organ.
E.g.,ACTH secretion stimulates cortisol secretion, while increased blood cortisol concentration inhibits ACTH secretion from adenohypophysis and CRH release from the hypothalamus to bring cortisol level to normal.
Negative feedback mechanism
Synergism and antagonism mechanism of hormone secretion regulation-
The activity of one hormone may be influenced by its interaction with one or more hormones involved in the regulation of the same function.
The actions of different hormones are concerted or additive if they produce the same response and the combined effect of the hormones is the sum of separate actions of the individual hormones. In this case, the two hormones act by different mechanisms.
In some cases, two hormones can produce the same effect but the effects due to the different hormones are non-additive, i.e. the two hormones act by the same common mechanism.
Some hormones may act together to produce greater total effect than their individual effects known as synergistic effect. E.g., the toxicity of catecholamines is increased by thyroxine.
Some hormones exhibit opposite effects of other hormones known as the antagonism; e.g., Insulin and glucagon actions on blood glucose level.
When one hormone is required for another hormone to exert its effect it is called permissive effect; e.g., small amount of glucocorticoids is needed for catecholamines to produce their calorigenic and lipolytic effects.