Ch. 18 -- Endocrine System -- Secondary Endocrine Organs
Erythropoietin (EPO)
A peptide hormone released by kidneys in response to LOW oxygen levels in kidney tissues Function: - stimulates red bone marrow to produce RBCs - increase in RBCs = elevated blood volume
Calcitriol
A steroid hormone secreted by kidneys in response to parathyroid hormone (PTH) Cholecalciferol (vitamin d3) is synthesized in the skin or diet & is converted to Calcitriol Function: - stimulates Ca2+ & phosphate ion absorption along digestive tract - stimulates formation & differentiation of osteogenic cells & osteoclasts - stimulates bone reabsorption by osteoclasts - stimulating Ca2+ absorption by the kidneys - suppressing PTH production
Heart
If blood volume becomes too high, cardiac muscle cells secrete NATRIURETIC PEPTIDES (has opposing effects of angiotensin II) 2 types: 1) ANP atrial natriuretic peptides 2) BNP brain natriuretic peptides Effects of natriuretic peptides: - promote loss of Na+ & water by the kidneys - inhibit renin release & secretion of ADH + aldosterone - suppress thirst - prevent angiotensin II & NE from elevating blood pressure Net result is a reduction in both blood volume + pressure
Gonads
In males, Interstitial Cells produce ANDROGENS (testosterone most imp.) Nurse cells in testes support physical maturation of sperm; under FSH stimulation, they also secrete Inhibin which inhibits GnRH release In females, ESTROGENS (estradiol most imp.) are produced in the ovaries under FSH & LH stimulation; FSH stimulates secretion of Inhibin by ovarian cells which suppresses FSH in a feedback loop At ovulation, the corpus luteum releases a mix of estrogens & PROGESTERONE
Thymus
Produces THYMOSIN, which promotes development & maturation of lymphocytes
Adipose Tissue
Produces a peptide hormone called LEPTIN Function: - feedback control of appetite - results in a sense of fullness & suppression of appetite
Kidneys
Release Calcitriol, Erythropoietin & Renin
Renin
The juxtaglomerular cells of the kidneys release Renin in response to: - sympathetic stimulation - decline in renal blood flow Starts the enzymatic cascade known as Renin-angiotensin-aldosterone system (RAAS) - RAAS involved with blood pressure regulation & electrolyte metabolism - 1st, renin converts angiotensiongen to angiotensin I - ACE in the lungs converts angiotensin I to angiotensin II - angiotensin II stimulates secretion of aldosterone & ADH; also stimulates thirst & elevates blood pressure - combo of ADH & aldosterone = salt & water rentention by the kidneys
