Lab 3: Renal Physiology, Water and Sodium Balance

Water load

Excess water intake; kidneys increase urine production to excrete excess water.

Isosmotic salt load

A load of salts where the osmolarity remains constant; kidneys maintain water balance by reabsorbing water.

ADH (Vasopressin)

Hormone that increases water reabsorption in the kidneys to conserve water.

RAAS (Renin-Angiotensin-Aldosterone System)

Hormonal pathway that helps regulate sodium and water balance, especially under low blood pressure conditions.

Specific Gravity

A measure of urine concentration relative to water; higher values indicate more concentrated urine.

Diuretics

Medications that promote sodium and water excretion.

Aquaretics

Medications that promote water excretion without significantly affecting sodium levels.

How do the kidneys respond to a water load?

By increasing urine output and reabsorbing less water.

What is the effect of ADH on urine concentration?

ADH increases the permeability of collecting ducts, leading to more water reabsorption and concentrated urine.

What occurs during an isosmotic salt load?

The kidneys maintain water reabsorption to keep osmolarity balanced while excreting excess salt.

What triggers the release of renin in the RAAS pathway?

Low blood pressure, low sodium levels, or sympathetic nervous system stimulation.

How does drinking water affect ADH secretion?

It reduces ADH secretion, leading to less water reabsorption and increased urine output.

What is the normal range for urine specific gravity?

1.005 to 1.030.

What effect do loop diuretics have?

They inhibit sodium reabsorption in the loop of Henle, increasing sodium and water loss.

What is the function of aldosterone in the kidneys?

Promotes sodium reabsorption in the distal convoluted tubule and collecting ducts.

What is the main action of aquaretics?

To increase water excretion without significantly affecting sodium levels.

What happens to urine concentration with excess water intake?

Urine becomes dilute with a low concentration of solutes.

How does angiotensin II contribute to fluid balance?

Stimulates aldosterone release and vasoconstriction to raise blood pressure.

What promotes the insertion of aquaporins into kidney membranes?

ADH increases the permeability of collecting ducts to water.

What indicates concentrated urine in terms of specific gravity?

A higher specific gravity means more concentrated urine (low water content).

What is the outcome of taking diuretics on blood pressure?

Diuretics lead to sodium and water excretion, reducing blood volume and blood pressure.

Why does the body retain water during an isosmotic salt load?

To balance the sodium concentration and prevent dehydration.

What does a low specific gravity of urine indicate?

It indicates dilute urine, reflecting low solute concentration.

How does isotonic saline intake influence hormone levels?

May activate RAAS for sodium and water retention without significantly affecting ADH release.

What is the role of the kidneys in handling excess water?

They increase urine output and decrease water reabsorption.

What happens to plasma osmolality after drinking water?

Plasma osmolality decreases, triggering reduced ADH secretion.

Which part of the nephron is primarily involved in water reabsorption?

The proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct.

What is the primary effect of aldosterone on kidney function?

Increases sodium reabsorption, leading to water retention.

What physiological condition leads to increased release of ADH?

Increased blood osmolarity or low blood volume.