Renal Quiz 5: Urine Concentration and Dilution

These flashcards cover key concepts from the lecture on urine concentration and dilution, focusing on kidney function, hormone regulation, and fluid balance.

What is the primary function of the kidney in relation to water in the body?

The kidney controls the total amount of water in the body through urine concentration and dilution.

Where does the process of urine concentration begin in the kidney?

The process begins in the loop of Henle.

What is the effect of antidiuretic hormone (ADH) on the collecting duct?

When ADH is present, the collecting duct wall becomes permeable to water, allowing for reabsorption and resulting in low volume, concentrated urine.

What happens to osmolality as fluid flows down the descending limb of the loop of Henle?

Osmolality increases as fluid flows down the descending limb.

Where is the majority of the body water found in a lean 70 kg individual?

About 60% of body weight, which equals around 42 liters, with two-thirds of that water inside cells and one-third outside of cells.

What is the consequence of water intake exceeding water output?

The total body water increases, leading to a decrease in osmolality in body fluids.

Define antidiuresis.

Antidiuresis refers to a low volume of concentrated urine with high osmolality, indicating the body is retaining water.

What does a diuresis indicate?

A diuresis indicates the body is getting rid of water, resulting in high volume, dilute urine.

What is the role of the kidneys in water output?

The kidneys regulate greater than 90% of the water output from the body.

How does the presence of ADH affect urine osmolality?

In the presence of ADH, urine osmolality can be very high due to increased water reabsorption.

What is free water clearance?

Free water clearance is the urine flow minus the osmolar clearance, measuring water excretion relative to solute.

What occurs when ADH is absent in the collecting duct?

When ADH is absent, the collecting duct is impermeable to water, leading to dilution of urine.

How does blood flow affect the medullary interstitial concentration gradient?

Slow blood flow in the vasa recta maintains the medullary interstitial concentration gradient while supplying nutrients and removing waste.

Describe the relationship between plasma osmolality and ADH release.

An increase in plasma osmolality stimulates ADH release to conserve water.

What are the cells responsible for ADH production?

ADH is produced in the paraventricular and supraoptic nuclei of the hypothalamus.

What happens in diabetes insipidus?

In diabetes insipidus, either no ADH is produced (central) or the kidneys do not respond to ADH (nephrogenic), leading to high volumes of dilute urine.

What is the effect of antidiuretic hormone on urea reabsorption?

ADH also increases the permeability of the collecting duct to urea, facilitating its passive reabsorption.

What can excessive ADH lead to?

Excessive ADH can cause water retention leading to hyponatremia, as seen in conditions such as the syndrome of inappropriate ADH secretion (SIADH).