Urinary System and Acid-Base Balance

Comprehensive vocabulary flashcards covering the anatomy, physiology, and clinical aspects of the urinary system and acid-base balance.

Functions of the Urinary System

Includes regulation of body water volume, blood osmolarity, blood pressure, acid-base balance, excretion of wastes/toxins, production of erythropoietin, vitamin D activation, and gluconeogenesis.

Blood Osmolarity

The concentration of dissolved solutes in the blood, regulated by the kidneys through the filtration and conservation of water and ions.

Renin

A hormone synthesized and secreted by the kidneys that initiates a chain of reactions to produce angiotensin II, leading to vasoconstriction and aldosterone secretion.

Erythropoietin (EPO)

A hormone produced by the kidney that stimulates the production of red blood cells ($RBCs$).

Calcitriol

The active form of vitamin D, converted from cholecalciferol (inactive form) in the kidney by the enzyme $1-\text{alpha-hydroxylase}$.

Gluconeogenesis

The process by which kidney cells make glucose from non-carbohydrate sources, such as amino acids or lactate, during prolonged fasting.

Kidney

A retroperitoneal organ located from $T12$ to $L3$ that filters blood and forms urine.

Ureter

Paired tubes that transport urine from the renal pelvis of the kidney to the urinary bladder.

Urinary Bladder

A smooth, collapsible muscular sac that serves as a temporary storage reservoir for urine.

Urethra

A thin-walled muscular tube that carries urine from the urinary bladder to the exterior of the body.

Renal Hilum

An opening on the concave medial surface of the kidney that opens into the renal sinus and provides access for ureters, blood vessels, and nerves.

Renal Pelvis

The deepest region of the kidney; a medial expansion of the ureter that collects urine from the major calices.

Renal Medulla

The middle region of the kidney organized into cone-shaped renal pyramids separated by renal columns.

Renal Cortex

The superficial, lighter-colored region of the kidney.

Nephron

The structural and functional unit of the kidney, consisting of a renal corpuscle and renal tubules.

Renal Corpuscle

The site of blood filtration, composed of the glomerulus (fenestrated capillaries) and the glomerular (Bowman's) capsule.

Podocytes

Cells with interdigitating foot processes that cover the glomerulus and form filtration slits.

Proximal Convoluted Tubule (PCT)

The first region of the renal tubule, adapted with microvilli to reabsorb approximately $65\%$ of filtered water and solutes like $NaCl$, glucose, and $HCO_3^-$.

Nephron Loop (Loop of Henle)

A U-shaped tube consisting of a descending limb (permeable only to water) and an ascending limb (permeable only to solutes).

Principal Cells

Cells found in the collecting duct that maintain water and sodium balance and serve as targets for $ADH$ and $ATII$.

Intercalated Cells

Cells in the collecting duct (alpha and beta types) responsible for regulating acid-base balance.

Cortical Nephrons

The class representing $85\%$ of nephrons, which are located primarily within the renal cortex.

Juxtamedullary Nephrons

The class representing $15\%$ of nephrons, characterized by long loops that dip deep into the medulla to generate a concentration gradient.

Peritubular Capillaries

Capillary beds arising from the efferent arteriole that surround renal tubules and reabsorb filtered solutes and water.

Vasa Recta

Specialized capillaries that surround the loop of Henle in juxtamedullary nephrons and preserve the medullary osmotic gradient.

Juxtaglomerular Complex (JGC)

A contact point between the ascending limb and afferent arteriole containing Macula densa cells (chemoreceptors) and Granular cells (mechanoreceptors).

Glomerular Filtration Rate (GFR)

The amount of filtrate formed each minute, with a normal rate generally being $90\,ml/min$ and higher.

Myogenic Response

An intrinsic control where the stretch of the afferent arteriole triggers smooth muscle contraction to reduce blood flow and maintain stable $GFR$.

Fenestrated Endothelium

The first layer of the filtration membrane that allows passage of water and tiny solutes but prevents the passage of blood cells.

Glomerulonephritis

Inflammation of the glomerulus that damages the filtration membrane, leading to proteinuria ($protein$ in urine) and hematuria ($blood$ in urine).

Hydrostatic Pressure in Glomerular Capillaries ($HP_{GC}$)

The outward pressure of $55\,mmHg$ that promotes the formation of filtrate.

Aquaporins

Water channels in the renal tubule; their presence in the collecting duct is regulated by Antidiuretic Hormone ($ADH$).

Atrial Natriuretic Peptide (ANP)

A hormone that inhibits $Na^+$ reabsorption at the collecting duct to decrease blood volume and pressure.

Renal Clearance ($C$)

The volume of plasma completely cleared of a substance in one minute; a value less than $125\,ml/min$ indicates a substance has been reabsorbed.

Urobilin

A pigment molecule and breakdown product of hemoglobin that gives urine its yellow color.

Specific Gravity

The ratio of the density of urine to pure water, normally ranging from $1.001$ to $1.035$.

Detrusor

The thick muscular layer of the urinary bladder that contracts during micturition.

Trigone

The triangular region at the base of the bladder marked by the openings of the ureters and the urethra, often the site of UTIs.

Internal Urethral Sphincter

An involuntary smooth muscle sphincter that keeps the urethra closed when not urinating.

External Urethral Sphincter

A voluntary skeletal muscle sphincter that surrounds the urethra as it passes through the deep perineal space.

Micturition

The act of emptying the urinary bladder, involving detrusor contraction and the opening of both urethral sphincters.

Acidosis

A state where blood $pH$ falls below $7.35$.

Alkalosis

A state where blood $pH$ rises above $7.45$.

Bicarbonate Buffer System

The most important chemical buffer system in the blood and extracellular fluid ($ECF$).

Alkaline Reserve

The available amount of bicarbonate ($HCO_3^-$) in the blood used to buffer excess hydrogen ions.

Ammoniagenesis

The process by which kidneys convert glutamine into bicarbonate to raise blood $pH$, producing ammonium ion ($NH_4^+$) as a byproduct.

Respiratory Acidosis

A condition caused by the lungs retaining too much $CO_2$, characterized by a $PCO_2 > 45\,mmHg$.

Metabolic Acidosis

A condition where the kidneys lose too much $HCO_3^-$, characterized by an $HCO_3^- < 22\,mEq/L$.