Intro  The body adjusts for high or low water loss by increasing or decreasing urine input  These changes are causes by the nervous system and 2 hormones 1) antidiuretic hormone (ADH) and 2) aldosterone

ADH and Water Balance  ADH conserves water by reducing urine output How it Works 1) Sensory receptors in the hypothalamus called osmoreceptors detect changes in osmotic pressure in body fluid as they shrink from lack of water in the hypothalamus (the water moves into the blood when there is water loss ie. Sweating)

2) The osmoreceptors stimulate the posterior pituitary gland to release ADH – ADH is carried by the blood to the kidneys 3) ADH causes the kidneys to reabsorb water which results in more concentrated urine

To fix it… 1) The osmoreceptors also stimulate the sensation of thirst 2) When water is taken in, it lowers the osmotic pressure in the blood 3) Blood become more dilute, the water goes into the hypothalamus and the osmoreceptors swell and stop stimulation 4) Homeostasis is restored

ADH and the nephron  About 85% of water in the nephron is reabsorbed in the proximal tubule  ADH causes the upper part of the distal tubule and collecting duct to be permeable to water  NaCl is in the intercellular space and draws water back from the distal tubule and collecting duct  Kidneys only control 15% of water in the nephron

Extra : Diabetes Insipidus  Can be caused by failure of 1) Posterior pituitary to make ADH 2) Failure of kidney to respond to ADH  These people make too much urine (as much as 16 L a day)  Can survive if they can drink enough

Aldosterone: Blood pressure and blood volume  When blood volume is reduced but osmotic pressure of the blood remains the same (ex. In a hemorrhage or severe diarrhea) the renin-angiotensin-aldosterone (RAAS) system responds

RAAS 1) Blood pressure receptors in the juxtaglomerular apparatus (JGA) detects change in blood pressure (the juxtaglomerular apparatus is near the glomerulus in the kidney) 2) When blood pressure is low cells within the JGA release renin

3) Renin causes angiotensinogen (a protein made in the liver) into angiotensin 4) Angiotensin does 2 things a) Constricts blood vessels to increase blood pressure b) Stimulates the release of aldosterone from the adrenal cortex

5) Aldosterone moves through the blood to the kidneys and causes the distal tubule and collecting duct to increase sodium ion retention 6) This causes blood volume and pressure to increase

Look at figure 2 on page 492

 To Do: questions #1-7 on page 493 (not to be handed in) These sets of questions are due Thursday, beginning of the period  #1-11 on page  #1-9 on page