Urinary System – Key Vocabulary (Marieb A&P, Ch. 25)

A comprehensive set of vocabulary flashcards covering key structures, cell types, hormones, pressures, processes, pathologies, and mechanisms involved in Chapter 25 – The Urinary System.

Kidneys

Paired retroperitoneal organs that filter blood, form urine, and regulate water, ions, pH, hormones, and vitamin D.

Ureters

Slender muscular tubes that convey urine from each kidney to the urinary bladder via peristalsis.

Urinary Bladder

Distensible, muscular storage sac (detrusor) that temporarily holds urine before micturition.

Urethra

Thin-walled muscular tube that carries urine (and semen in males) from the bladder to the exterior.

Renal Hilum

Medial cleft of kidney where ureter, blood vessels, nerves, and lymphatics enter or exit.

Renal Cortex

Light, superficial region of kidney containing glomeruli and convoluted tubules.

Renal Medulla

Deep, darker region formed by renal pyramids and surrounding columns.

Renal Pyramid

Cone-shaped tissue mass in medulla; its papilla projects urine into a minor calyx.

Renal Column

Inward extension of cortical tissue that separates adjacent pyramids.

Renal Lobe

A pyramid plus its surrounding cortical tissue; about 8 per kidney.

Renal Pelvis

Funnel-shaped tube continuous with ureter; collects urine from major calyces.

Major Calyx

Branch of renal pelvis that collects urine from minor calyces.

Minor Calyx

Cup-like structure that encloses a papilla and drains urine into a major calyx.

Perirenal Fat Capsule

Adipose cushion surrounding each kidney to protect against trauma.

Renal Fascia

Dense connective tissue layer anchoring kidney to surrounding structures.

Fibrous Capsule

Transparent kidney covering that prevents infection spread to renal tissue.

Nephron

Structural and functional unit of kidney that forms urine; about one million per kidney.

Renal Corpuscle

Part of nephron composed of a glomerulus enclosed by a glomerular (Bowman’s) capsule.

Glomerulus

Tuft of fenestrated capillaries specialized for filtration within the renal corpuscle.

Glomerular (Bowman’s) Capsule

Cup-shaped structure surrounding glomerulus, collecting filtrate.

Podocytes

Visceral epithelial cells of capsule whose foot processes create filtration slits.

Filtration Slits

Gaps between podocyte foot processes through which filtrate enters the capsular space.

Proximal Convoluted Tubule (PCT)

First segment of renal tubule; reabsorbs most filtrate with brush-border cells.

Nephron Loop (Loop of Henle)

U-shaped segment with descending water-permeable limb and ascending salt-pumping limb.

Descending Limb

Portion of nephron loop permeable to water but not to solutes.

Ascending Limb

Portion of loop impermeable to water; actively transports Na⁺, K⁺, Cl⁻.

Distal Convoluted Tubule (DCT)

Tubule segment after nephron loop; hormone-regulated reabsorption and secretion.

Collecting Duct

Receives filtrate from many nephrons; adjusts water, acid–base balance, and delivers urine to papilla.

Principal Cells

Collecting-duct cells that regulate Na⁺/water balance; targets of ADH and aldosterone.

Intercalated Cells

Collecting-duct cells (types A & B) that regulate acid–base balance via H⁺/HCO₃⁻ secretion.

Cortical Nephron

Nephron with short loop confined mostly to cortex; 85 % of all nephrons.

Juxtamedullary Nephron

Nephron near cortex-medulla junction with long loop vital for concentrated urine.

Peritubular Capillaries

Low-pressure porous capillaries surrounding cortical tubules; reclaim water/solutes.

Vasa Recta

Long straight vessels paralleling juxtamedullary loops; act as countercurrent exchangers.

Juxtaglomerular Complex (JGC)

Region where DCT/loop contacts afferent arteriole; regulates filtrate formation and BP.

Macula Densa

Tall, NaCl-sensing cells of ascending limb within JGC.

Granular (JG) Cells

Afferent-arteriole smooth-muscle cells acting as mechanoreceptors; secrete renin.

Extraglomerular Mesangial Cells

Cells linking macula densa and granular cells; relay signals via gap junctions.

Glomerular Filtration

First step of urine formation; passive movement of plasma filtrate into capsule.

Filtration Membrane

Three-layer barrier (fenestrated endothelium, basement membrane, podocyte slits) filtering blood.

Net Filtration Pressure (NFP)

Sum of forces driving filtration (~10 mm Hg = outward – inward pressures).

Glomerular Filtration Rate (GFR)

Volume of filtrate produced per minute by both kidneys (~120–125 ml/min).

Hydrostatic Pressure in Glomerular Capillaries (HPgc)

Blood pressure (~55 mm Hg) pushing fluid out of glomerulus.

Colloid Osmotic Pressure (OPgc)

Pull of blood proteins (~30 mm Hg) opposing filtration.

Renal Autoregulation

Intrinsic mechanisms that keep GFR constant despite moderate BP changes.

Myogenic Mechanism

Afferent-arteriole smooth muscle constricts/dilates in response to stretch to stabilize GFR.

Tubuloglomerular Feedback

Macula densa-mediated adjustment of afferent tone based on filtrate NaCl flow.

Renin

Enzyme released by JG cells that initiates angiotensin cascade to raise BP.

Angiotensin II

Potent vasoconstrictor hormone increasing BP and stimulating aldosterone/ADH release.

Aldosterone

Adrenal cortical hormone that increases Na⁺ (and water) reabsorption and K⁺ secretion.

Antidiuretic Hormone (ADH)

Posterior-pituitary hormone that inserts aquaporins in collecting-duct principal cells to conserve water.

Atrial Natriuretic Peptide (ANP)

Heart hormone promoting Na⁺ and water excretion, lowering blood volume and pressure.

Obligatory Water Reabsorption

Water reabsorption that follows solutes in PCT and descending loop via always-present aquaporins.

Facultative Water Reabsorption

Variable water reabsorption in collecting duct depending on ADH levels.

Transport Maximum (Tm)

Maximum reabsorption rate when carrier proteins are saturated (e.g., glucose Tm).

Tubular Secretion

Active movement of substances from blood into filtrate for elimination.

Creatinine

Muscle-metabolism waste; slightly secreted; clearance used to estimate GFR.

Renal Clearance

Volume of plasma from which a substance is removed per minute; UV/P formula.

Inulin

Freely filtered polysaccharide used experimentally to measure exact GFR (C ≈125 ml/min).

Countercurrent Multiplier

Process in nephron loop that establishes medullary osmotic gradient via differential water/solute movement.

Countercurrent Exchanger

Vasa recta mechanism that preserves medullary gradient while supplying nutrients.

Medullary Osmotic Gradient

Progressive increase in osmolality (300 → 1200 mOsm) from cortex to medulla enabling urine concentration.

Diuretic

Chemical that increases urine output; e.g., alcohol (ADH inhibitor) or loop diuretics (Na⁺ symporter blockers).

Anuria

Abnormally low urine output (<50 ml/day), often from extremely low glomerular BP or renal failure.

Pyelonephritis

Inflammation/infection of kidney (renal pelvis & calyces), commonly ascending from UTI.

Glomerulonephritis (GN)

Immune-mediated inflammation of glomeruli causing increased membrane permeability and proteinuria.

Renal Calculi

Kidney stones formed of crystallized Ca²⁺, Mg²⁺, or uric acid salts; may obstruct ureters.

Glycosuria

Glucose in urine when blood levels exceed renal Tm (common in uncontrolled diabetes).

Hemodialysis

Artificial filtration of blood used when kidneys fail (GFR <15 ml/min).

Urinalysis

Laboratory examination of urine’s physical, chemical, microscopic properties to assess health.

Detrusor Muscle

Three-layered smooth muscle of bladder wall that contracts during micturition.

Internal Urethral Sphincter

Involuntary smooth muscle at bladder-urethra junction controlled by ANS.

External Urethral Sphincter

Voluntary skeletal muscle in deep perineal space controlling urine release.

Micturition Reflex

Spinal reflex causing bladder contraction and sphincter relaxation when stretch receptors fire.

Stress Incontinence

Urine leakage due to sudden increased abdominal pressure (laughing, coughing).

Overflow Incontinence

Bladder overfills and dribbles urine, often from obstruction or nerve damage.

Cystitis

Inflammation/infection of urinary bladder producing frequency and dysuria.

Countercurrent Mechanisms

Combined multiplier and exchanger systems that establish, maintain, and use medullary gradient.

Obligatory Minimum Urine Volume

~500 ml/day—the least volume required to excrete metabolic wastes at 1200 mOsm.

Horseshoe Kidney

Congenital fusion forming a single U-shaped kidney; usually asymptomatic.

Polycystic Kidney Disease (PKD)

Genetic disorder with fluid-filled cysts that enlarge kidneys and lead to renal failure.

Peritubular Fluid (Interstitial Fluid, IF)

Extracellular fluid surrounding renal tubules into which reabsorbed substances move.

Mesangial Cells

Glomerular support cells; contract to regulate filtration surface area and phagocytize debris.