ADH and the control of osmolality

Flashcards about ADH and osmolality

What is osmolality?

Osmoles per kilogram of water

What is osmolarity?

Osmoles per litre of water

What does isoosmotic mean?

The same osmolality as another solution

What does hypoosmotic mean?

Lower osmolality than another solution

What does hyperosmotic mean?

Higher osmolality than another solution

What is the function of the ascending limb of the Loop of Henle?

Actively reabsorbs solute into the medullary interstitium and is impermeable to water.

What is the function of the descending limb of the Loop of Henle?

Is freely permeable to water.

Why must the body be able to produce urine that is hypoosmotic to hyperosmotic?

To control osmolality of extracellular fluid and produce a range of urine concentrations.

Why is a minimum daily urine production ('obligatory water loss') of ~450 mL required?

Cannot save water by simply avoiding urine production.

What is the countercurrent multiplier?

The creation of a hyperosmotic medullary interstitium by the Loop of Henle.

How does urea trapping contribute to the hyperosmotic medullary interstitium?

Urea is 'trapped' in the medullary interstitium and contributes to the hyperosmotic medullary interstitium

How does ADH cause insertion of aquaporins into the collecting duct membranes?

ADH binds to V2 receptors on medullary collecting duct cell membranes which leads to insertion of aquaporins into the cell membranes, causing absorption of water into the hyperosmotic interstitium.

What is another name for ADH?

Arginine vasopressin

Where is ADH synthesized?

The supraoptic and paraventricular nuclei of the hypothalamus

What causes diabetes insipidus?

An inability to produce or respond to ADH