Up-regulation
increase in the number of receptors on/within a cell, allows more hormone molecules to bind receptors on target tissues. Usually occurs when hormone levels are low
Downregulation
decrease in number of receptors on/within a cell. Usually occurs when hormone levels are high.
Negative Feedback Mechanims
some glands respond to hormonal stimuli. thus, a negative feedback mechanism serves to turn up or turn down secretion.
Homeostasis is maintained by the negative feedback mechanism.
- Endocrine tissue (A) increases secretion of a hormone in response to stimulus
- Hormone circulates in the blood to produce effects on target tissue; hormone also binds to receptors on A which decrease secretion of hormone
Cascade effect of hormone release from the hypothalamus to the pituitary gland to other endocrine gland to tissues.
- hypothalamus secretes hormone A into pituitary portal vessel
- hormone A stimulates cells in pituitary gland to secrete hormone B into circulation
- hormone B stimulates target tissue to secrete hormone C into the blood
- Hormone C stimulates target tissues and has inhibitory effects on hypothalamus and pituitary gland, decreasing A and B
Hormonal Stimuli - Thyroid Hormone
- hypothalamus secretes thyroid releasing hormone (TRH)
- TRH stimulates pituitary glad to secrete thyroid stimulating hormone (TSH)
- TSH stimulates thyroid gland to secrete thyroid hormones
- Thyroid hormones affect many tissues in the body and inhibit the release of TRH and TSH
Growth hormone: over-or under-production
hyposecretion: dwarfism, reduced muscle mass. (treated with GH replacement therapy)
hypersecretion: gigantism. Acromegaly (enlargement of facial bones). treated with GH receptor antagonists.
Antidiuretic Hormone (ADH) over-or under-production:
Hyposecretion: Diabetes insipidus. large volumes of dilute urine.
hypersecretion: SIADH
Thyroid hormone over-or under-production
- hypersecretion: graves disease
- Hyposecretion: myxedema
Corticosteroids over-or under-production
- hyper: cushings syndrome
- hypo: addisons (aldosterone)
Estrogen over-or under-production
- hypo: menstrual and metabolic dysfunction
Progesterone over-or under-production
hypo: dysfunctional uterine bleeding
Testosterone over-or under-production
- Hyposecretion: hypogonadism
Parathyroid hormone over-or under-production
hyposecretion: hypoparathyroidism. Hypersecretion: hyperparathyroidism.
Side effects of high doses of vasopressin.
- vasopressin is identical to ADH
- replacement therapy for patients with diabetes insipidus
- side effects: hypertension
- monitor I&O, VS, labs tests, signs of FVE, urine osmolality
