Blood Water Homeostasis

(Osmoregulation)

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.

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).

1. ADH Control

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.

2. ANH Control

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

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.

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.

Summary:

ANH

Hypothalamus Kidney -inhibits ADH release -promotes sodium

excretion causing water excretion to follow.

Effects of Aldosterone on Blood water control

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.

4. Control of pHReview pH balance p. 355

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 )

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