Ch.14 -Fluid & Electrolyte Balance

What is the normal osmolarity of body fluids?

300 mOsm

What happens to a cell when the ECF becomes hypo-osmotic?

Water shifts into the cell, causing it to swell.

How much water is reabsorbed in the proximal tubule?

About 70% of filtered water is reabsorbed by osmosis.

What creates the vertical osmotic gradient in the renal medulla?

The loop of Henle, especially in juxtamedullary nephrons.

Which limb of the loop of Henle is impermeable to water?

The ascending limb.

What percentage of the medullary osmolarity is contributed by urea?

About 40%.

What is the strongest stimulus for ADH release?

Increased plasma osmolarity (dehydration).

What does ADH do at the collecting duct?

Inserts aquaporin-2 channels to increase water reabsorption.

What electrolyte primarily regulates ECF osmolarity and blood volume?

Sodium (Na⁺).

What triggers aldosterone release?

• High K⁺ levels (hyperkalemia)

• Angiotensin II

What happens when Na⁺ levels or blood pressure drop in the DCT?

The macula densa stimulates granular cells to release renin.

What are two effects of ANP on blood pressure?

• Increases GFR

• Decreases aldosterone and renin
  → leading to lower BP

What percentage of calcium is reabsorbed in the proximal tubule?

70%

Which hormone is released during hypercalcemia?

Calcitonin

What are the three main defense mechanisms against acid–base disturbances?

• Buffering (first line)

• Respiratory compensation (second line)

• Renal compensation (third line; slowest)