1. Blood Water Homeostasis (Osmoregulation)

2. 1. ADH Control
The water potential of the blood must be regulated to prevent loss or gain of water from cells.
Blood water homeostasis is controlled by the hypothalamus.

3. 1. ADH Control
It contains osmoreceptor cells, which can detect changes in the water potential of the blood passing through the brain. In response, the hypothalamus controls the sensation of thirst, sends nerve signals to the pituitary which causes secretion of the hormone ADH (antidiuretic hormone).

4. 1. ADH Control

5. ADH is stored in the pituitary gland, and its target cells are the endothelial cells of the collecting ducts of the kidney nephrons. These cells are unusual in that water molecules can only cross their membranes via water channels called aquaporins, rather than through the lipid bilayer. ADH causes these water channels to open.

6. 2. ANH Control
Also, In the left atrium of the heart, stretch receptors secrete a hormone ANH(atrial natriuretic factor):

7. that affects the hypothalamus, inhibiting the release of ADH (antidiuretic hormone, or vasopressin) from the posterior pituitary gland, allowing more water to be excreted in the urine.

8. acts on the kidney to promote sodium excretion so that it is excreted in the urine which causes water excretion to follow. This causes a decrease in blood pressure.

9. Summary: ANH Hypothalamus Kidney
-inhibits ADH release -promotes sodium excretion causing water excretion to follow.

10. Effects of Aldosterone on Blood water control

11. angiotensin stimulates adrenal cortex to secrete aldosterone
adrenal cortex is found in the adrenal glands just above the kidneys
aldosterone promotes Na+ reabsorption
Na+ reabsorption promotes water reabsorption
water reabsorption  urine volume
BP drops less rapidly
**Any excess cations such as sodium, potassium, calcium, and magnesium and excess anions, such as chloride, bicarbonate, and phosphate, are excreted in the urine.

12. 4. Control of pH Review pH balance p. 355

13. Excess hydrogen ions (H+) from tissue fluids are secreted into the proximal and distal convlouted tubules.
Here some of them combine with ammonia and are excreted as ammonium ions (NH+) in the urine.
Other hydrogen ions combine with phosphate ions to form hydrogen phosphate ions (HP02, H2P04 )

14. Read Section 7.7 Kidney Disease
Review pH balance p. 355
Homework: p. 356 #1-10
Read Section 7.7 Kidney Disease
Focus especially on Kidney Stones and Dialysis Technology
Chapter 7 Review:
Self Quiz: p. 367 #1-8
Review: p. 368 #1-10