APK2105C Chapter 19: Fluid and Electrolyte Balance

Flashcards covering the key vocabulary and physiological mechanisms of water and sodium balance from Chapter 19.

Normovolemia

A state characterized by normal plasma volume.

Hypervolemia

A state characterized by increased plasma volume.

Hypovolemia

A state characterized by decreased plasma volume.

Hypernatremia

A condition defined by having high plasma levels of $Na^+$.

Hyponatremia

A condition defined by having low plasma levels of $Na^+$.

Water Inputs

Daily intake consisting of ingestion ($2.2\,L/day$) and cellular metabolism ($0.3\,L/day$), totaling $2.5\,L/day$.

Water Outputs

Daily losses consisting of urine ($1.5\,L/day$), insensible loss and sweating ($0.9\,L/day$), and feces ($0.1\,L/day$), totaling $2.5\,L/day$.

Sodium Reabsorption in the Proximal Tubule

The process where $70\%$ of all $Na^+$ is reabsorbed in the proximal convoluted tubule, causing water to follow by osmosis.

Medullary Osmotic Gradient

An osmotic gradient established by the Loops of Henle and maintained by urea, ranging from $300\,mOsm$ in the outer regions to $1200-1400\,mOsm$ in the inner regions.

Countercurrent multiplier

The mechanism in the Loops of Henle that establishes the medullary osmotic gradient.

Urea

A solute that maintains the medullary osmotic gradient through facilitated diffusion out of the collecting duct.

Descending limb of the Loop of Henle

A segment of the renal tubule that is permeable to water but has no transport for $Na^+$, $K^+$, or $Cl^-$.

Thick ascending limb of the Loop of Henle

A segment of the renal tubule that is impermeable to water and contains a $Na^+/K^+/Cl^-$ cotransporter.

Aquaporins

Protein channels necessary for water to permeate the epithelial walls of the late distal convoluted tubule (DCT) and the collecting duct.

ADH (Antidiuretic Hormone)

A hormone secreted by the posterior pituitary that increases water reabsorption by signaling the kidneys to increase aquaporin-2 activity.

Aquaporin-2

Water channels located on the apical membrane of principal cells, regulated by ADH.

Aquaporin-3

Water channels located on the basolateral membrane of principal cells.

Principal cell

A type of cell lining the late distal tubule or collecting duct that responds to ADH and aldosterone.

Aldosterone

A steroid hormone released from the adrenal cortex in response to Angiotensin II that increases $Na^+$ reabsorption in the late distal tubules and collecting ducts.

Renin

An enzyme released from juxtaglomerular cells in response to low MAP, increased sympathetic activity, or decreased $[Na^+]$ and $[Cl^-]$ in distal tubules.

Angiotensin II (ANG II)

A peptide that stimulates vasoconstriction, aldosterone secretion, thirst, and ADH secretion to increase plasma volume and MAP.

ANP (Atrial Natriuretic Peptide)

A peptide secreted by the atrial walls in response to stretch that increases $Na^+$ excretion.

Natriuresis

The physiological process of increased $Na^+$ excretion in the urine.

Juxtaglomerular cells

Specific cells in the afferent arteriole of the kidney that release renin into the bloodstream.

Macula densa

Distal tubule cells that detect low sodium and chloride concentrations and trigger paracrine secretion to stimulate renin release.