Urinary System: Fluid Volume, Pressure, and Osmolarity Flashcards

A set of 80 vocabulary flashcards covering the urinary system, fluid balance, countercurrent exchange, and the RAAS signaling pathway based on the lecture transcript.

Isosmotic

A condition where two solutions have the same osmotic pressure or solute concentration.

Hyposmotic

A solution with a lower solute concentration compared to another solution.

Hyperosmotic

A solution with a higher solute concentration compared to another solution.

Concurrent flow

Flow pattern where fluids move in the same direction and eventually reach equilibrium.

Countercurrent flow

Flow pattern where fluids move in opposite directions, allowing the maintenance of concentration gradients.

Renin-Angiotensin-Aldosterone System (RAAS / RAA)

A hormone system that regulates blood pressure and fluid balance by tying together many body systems.

Renin

An enzyme secreted by juxtaglomerular cells in response to decreased blood pressure or volume.

Angiotensinogen

A precursor protein produced by the liver that is converted into Angiotensin I by renin.

Angiotensin I

A peptide hormone formed by the action of renin on angiotensinogen.

Angiotensin II

A potent vasoconstrictor that increases blood pressure, stimulates aldosterone, and triggers ADH release.

Angiotensin 1,7

A peptide produced from Angiotensin II by ACE2 that keeps Angiotensin II in check and helps lower blood pressure.

Angiotensin Converting Enzyme (ACE)

The enzyme responsible for converting Angiotensin I into Angiotensin II.

Angiotensin Converting Enzyme 2 (ACE2)

The enzyme that converts Angiotensin II into Angiotensin 1,7.

Atrial natriuretic peptide (ANP)

A hormone secreted when the atria are stretched that inhibits the RAAS system to lower blood pressure.

Edema

The accumulation of excess fluid in body tissues.

Mass balance of water

The principle that total water gain must equal total water loss to maintain homeostasis.

Metabolism (Water Gain)

A source of water gain providing approximately $0.3\,L/day$.

Food and drink (Water Gain)

The primary source of water gain providing approximately $2.2\,L/day$.

Insensible water loss

Water loss through the skin and lungs, totaling approximately $0.9\,L/day$.

Urine (Water Loss)

A primary source of water loss, typically around $1.5\,L/day$.

Feces (Water Loss)

A minor source of water loss, typically around $0.1\,L/day$.

Total daily water gain/loss

The physiological balance normally maintained at $2.5\,L/day$.

Glomerular filtration rate (GFR)

The rate at which fluid is filtered into the kidneys, which can be adjusted to regulate body fluid volume.

Proximal tubule osmolarity

The site where isosmotic fluid ($300\,mOsM$) leaves for the next segment of the nephron.

Descending limb characteristics

Segment of the nephron loop where only water is reabsorbed, generating hyperosmotic fluid.

Ascending limb characteristics

Segment of the nephron loop where only ions are selectively reabsorbed, generating hyposmotic fluid.

Urine osmolarity range

The variable output of the urinary system ranging from $50\,mOsM$ to $1200\,mOsM$ based on body state.

Cortical Nephron

A nephron with a short loop of Henle located primarily in the renal cortex.

Juxtamedullary Nephron

A nephron with a long loop of Henle extending deep into the renal medulla, better at making concentrated urine.

Glomerulus

A network of capillaries where filtration of the blood occurs.

Vasa recta

Capillaries that surround the nephron loop of juxtamedullary nephrons and maintain medullary hyperosmoticity.

Afferent arteriole

The blood vessel that carries blood into the glomerulus.

Efferent arteriole

The blood vessel that carries blood away from the glomerulus after filtration.

NKCC

A transporter in the ascending limb that moves ions into the interstitial fluid to maintain hyperosmolarity.

Vasopressin (ADH)

Anti-diuretic hormone that controls water reabsorption in the collecting duct cells.

Plasma osmolarity threshold

The value (typically starting around $280\,mOsM$) at which plasma vasopressin begins to increase linearly.

Hypothalamus (Urinary Regulation)

Brain region containing sensory receptors for plasma osmolarity that signals the pituitary to release ADH.

Atrial stretch receptors

Sensory receptors that detect changes in blood volume to regulate ADH release.

Baroreceptors

Sensory receptors that detect changes in blood pressure to influence urinary system regulation.

G-protein coupled receptor

The type of receptor ADH binds to on the membrane of collecting duct tubule cells.

cAMP

The second messenger activated by ADH to signal the insertion of aquaporins.

Aquaporins

Water channels inserted into the apical membrane of collecting duct cells by ADH action.

Zona glomerulosa

The specific region of the adrenal cortex where aldosterone is produced.

Aldosterone function

A mineralocorticoid that alters gene expression to increase Na+ reabsorption and K+ secretion.

Salt balance (NaCl)

Maintained via a kidney response to salt ingestion which increases plasma osmolarity and ECF volume.

Thirst

A behavioral response stimulated by the hypothalamus following increased plasma osmolarity or Angiotensin II.

Juxtaglomerular cells

Cells in the kidney that secrete renin when blood pressure or GFR decreases.

Adrenal cortex (RAAS)

Organ stimulated by Angiotensin II and increased K+ in the ECF to secrete aldosterone.

Vasoconstriction of arterioles

A rapid response by Angiotensin II to increase blood pressure by narrowing blood vessels.

H+ secretion

The movement of hydrogen ions into urine, stimulated by the RAAS system in the kidneys.

Homeostatic pH regulation

One of the six major things the urinary system does, involving $CO_2$, $H_2O$, $HCO_3^-$, and $H^+$.

Ion balance

Maintenance by the kidney of various electrolyte concentrations including Na+ and K+.

Waste excretion

The process by which the urinary system removes metabolic byproducts from the body.

Hormone production (Kidney)

One of the six major functions of the urinary system, besides simple excretion and regulation.

Renal cortex osmolarity

The relatively stable environment of the outer kidney, maintained at approximately $300\,mOsM$.

Renal medulla osmolarity

The inner kidney environment characterized by a high osmotic gradient from $300\,mOsM$ to $1200\,mOsM$.

Apical membrane

The surface of the collecting duct cell facing the lumen where aquaporins are inserted.

Medullary interstitial fluid

The fluid surrounding the nephron in the medulla, which must be hyperosmotic to drive water reabsorption.

Angiotensin II and Thrombin

Angiotensin II increases thrombin levels, which leads to increased blood clotting.

Inflammation (Angiotensin II)

A pathological result of unchecked Angiotensin II leading to blood vessel damage.

Pulmonary edema

A severe condition resulting from unchecked high blood pressure and fluid imbalance.

Mineralocorticoids

A class of lipid-soluble hormones regulated by the zona glomerulosa, with aldosterone as a primary example.

$$50\,mOsM$$

The minimum osmolarity of urine typically excreted when no vasopressin is present.

$$1200\,mOsM$$

The maximum osmolarity of urine excreted, matching the medullary interstitial fluid gradient.

$$300\,mOsM$$

The standard osmolarity of isosmotic fluid entering the descending limb.

$$100\,mOsM$$

The osmolarity of hyposmotic fluid after ions are reabsorbed in the ascending limb.

Lipid soluble (Aldosterone)

A property of aldosterone that allows it to enter distal tubule and collecting duct cells directly.

Gene expression (Aldosterone)

The process through which aldosterone creates new ion channels and pumps from the cell nucleus.

CV response to NaCl

Circulatory system response that works alongside the kidneys to manage changes in blood pressure post-salt intake.

ECF volume

Extracellular fluid volume, which increases as a result of water reabsorption and increased water intake.

Increased K+ in ECF

A direct trigger for the adrenal cortex to secrete aldosterone independently of Angiotensin II.

Pituitary gland (ADH)

The gland that releases ADH into the blood after receiving signals from the hypothalamus.

Collecting duct lumen

The area from which water is reabsorbed into the collecting duct cells via osmosis.

Sensory receptors (Hypothalamus)

Cells that detect changes in plasma osmolarity to initiate the ADH response.

Filtrate reabsorption

The process of reclaiming water and solutes from the nephron back into the blood.

Blood volume increase

The end goal of the RAAS pathway through coordinated water and sodium retention.

Blood pressure increase

The final outcome of the RAAS system, achieved via vasoconstriction and volume expansion.

Dehydration / Hemorrhage

Specific physiological stressors that trigger the initial secretion of renin.

ACE inhibitors

A common target for medication based on the enzyme that converts Angiotensin I to Angiotensin II.

Countercurrent exchange purpose

To prevent the washout of the osmotic gradient in the renal medulla while providing blood to the tissue.