Page 1817 - Saunders Comprehensive Review For NCLEX-RN

secreted.
2. Water and solutes that are not reabsorbed become
urine.
3. The process of selective reabsorption determines the
amount of water and solutes to be secreted.

D. Homeostasis of water

1. Antidiuretic hormone (ADH) is primarily responsible
for the reabsorption of water by the kidneys.
2. ADH is produced by the hypothalamus and secreted
from the posterior lobe of the pituitary gland.
3. Secretion of ADH is stimulated by dehydration or
high sodium intake and by a decrease in blood
volume.
4. ADH makes the distal convoluted tubules and
collecting duct permeable to water.
5. Water is drawn out of the tubules by osmosis and
returns to the blood; concentrated urine remains in
the tubule to be excreted.
6. When ADH is lacking, the client develops diabetes
insipidus (DI).
7. Clients with DI produce large amounts of dilute urine;
treatment is necessary because the client cannot drink
sufficient water to survive.

E. Homeostasis of sodium

1. When the amount of sodium increases, extra water is
retained to preserve osmotic pressure.
2. An increase in sodium and water produces an increase
in blood volume and BP.
3. When the BP increases, glomerular filtration increases,
and extra water and sodium are lost; blood volume is
reduced, returning the BP to normal.
4. Reabsorption of sodium in the distal convoluted
tubules is controlled by the renin-angiotensin system.
5. Renin, an enzyme, is released from the nephron when
the BP or fluid concentration in the distal convoluted
tubule is low.
6. Renin catalyzes the splitting of angiotensin I from
angiotensinogen; angiotensin I converts to
angiotensin II as blood flows through the lung.
7. Angiotensin II, a potent vasoconstrictor, stimulates the
secretion of aldosterone.
8. Aldosterone stimulates the distal convoluted tubules
to reabsorb sodium and secrete potassium.
9. The additional sodium increases water reabsorption
and increases blood volume and BP, returning the BP

1817