lec 16-ADH and the Control of Osmolality

Flashcards covering the terminology, renal mechanisms, and hormonal regulation of body osmolality based on the lecture by Dr. Rachel Hunt.

Osmolality

The measure of concentration defined as osmoles per kilogram of water ($mOsmol/kg$).

Osmolarity

The measure of concentration defined as osmoles per litre of water ($mOsmol/L$).

Isoosmotic (Isotonic)

A solution with the same osmolality as another solution; for example, a $290\,mOsmol/kg$ solution is isoosmotic to plasma.

Hypoosmotic (Hypotonic)

A solution with a lower osmolality than another solution, such as a $100\,mOsmol/kg$ solution relative to plasma.

Hyperosmotic (Hypertonic)

A solution with a higher osmolality than another solution, such as a $400\,mOsmol/kg$ solution relative to plasma.

Proximal Convoluted Tubule (PCT)

The segment of the nephron where the bulk of reabsorption takes place, absorbing salt and water in equal proportions using specialized microvilli.

Distal Convoluted Tubule (DCT)

The site in the nephron specialized for the fine-tuning and regulation of absorption.

Obligatory water loss

The minimum daily urine production required to excrete waste, which is approximately $450\,mL$.

Ascending limb of the Loop of Henle

The segment of the loop of Henle that is impermeable to water and actively reabsorbs solutes ($Na^+$, $Cl^-$) into the medullary interstitium.

Descending limb of the Loop of Henle

The segment of the loop of Henle that is freely permeable to water via aquaporins but does not reabsorb solute.

Countercurrent multiplier

The mechanism by which the loop of Henle creates a progressively hyperosmotic medullary interstitium.

Urea trapping

The process where urea is reabsorbed from the medullary collecting duct and secreted into the loop of Henle, contributing to the hyperosmotic medullary interstitium.

Vasa recta

The medullary capillary system consisting of 'straight loops' that maintains the osmotic gradient by equilibrating plasma osmolality with the interstitium.

Antidiuretic hormone (ADH)

A peptide hormone, also known as vasopressin or arginine vasopressin, that causes the insertion of aquaporins into the collecting duct membranes.

V2 receptors

G protein-coupled receptors on the medullary collecting duct cell membranes that ADH binds to in order to trigger water reabsorption.

Aquaporin

A water channel that, when inserted into the collecting duct membranes, allows water to be reabsorbed into the hyperosmotic interstitium.

Supraoptic and Paraventricular nuclei

Neurons in these hypothalamic regions synthesize ADH and receive input from central osmoreceptors.

Posterior pituitary

The structure where ADH is released into the general circulation from the capillaries of the hypothalamus.

Osmoreceptors

Sensory receptors that detect changes in plasma osmolality to control the rate of ADH secretion.

Diabetes insipidus

A condition caused by an inability to produce or respond to ADH, leading to the production of large volumes of dilute urine.