Chapter 20: Urinary System

Vocabulary practice flashcards covering renal anatomy, nephron microanatomy, glomerular filtration, tubular exchange mechanisms, micturition, and clinical pathologies from Chapter 20.

Kidneys

A pair of reddish brown, bean-shaped retroperitoneal organs enclosed in a tough fibrous capsule that filter blood, maintain fluid homeostasis, and form urine.

Ureters

Tubular organs approximately $25\,\text{cm}$ in length that convey urine from the renal pelvis of the kidneys to the urinary bladder via peristaltic waves.

Urinary Bladder

A hollow, distensible, muscular storage organ located in the pelvic cavity posterior to the pubic symphysis that holds urine prior to micturition.

Urethra

A tube lined with a mucous membrane that conveys urine from the neck of the urinary bladder to the outside of the body.

Retroperitoneal

Describing the anatomical position of the kidneys behind the parietal peritoneum on the posterior abdominal wall.

Renal Fascia

A tough layer of dense connective tissue that surrounds the kidney and perirenal fat capsules to anchor them to the abdominal wall.

Renal Sinus

A medial hollow chamber within the concave depression of the kidney that houses blood vessels, nerves, lymphatic vessels, and the renal pelvis.

Hilum of the Kidney

The indented medial opening leading into the renal sinus through which the renal artery, renal vein, nerves, and ureter pass.

Renal Pelvis

A funnel-shaped sac formed at the superior expanded end of the ureter inside the renal sinus that collects urine from major calyces.

Major Calyces

Two or three large funnel-like branch tubes formed by the convergence of minor calyces that merge to form the renal pelvis.

Minor Calyces

Small cup-shaped collection tubes that directly cup each renal papilla to collect newly formed urine and convey it to major calyces.

Renal Medulla

The inner region of the kidney parenchyma composed of striated conical structures termed renal pyramids.

Renal Cortex

The light-colored, outer shell region of the kidney tissue that covers the bases of the renal pyramids and dips between them as renal columns.

Renal Columns

Bands of cortical tissue that dip inward between adjacent renal pyramids within the renal medulla.

Nephrons

The functional units of the kidney, numbering roughly $1\,\text{million}$ per kidney, each comprising a renal corpuscle and a renal tubule.

Renal Corpuscle

The blood-filtering component of a nephron, consisting of a capillary cluster termed the glomerulus surrounded by a glomerular (Bowman's) capsule.

Glomerulus

A tangled cluster of specialized, highly permeable capillaries within the renal corpuscle that filters fluid and solutes from blood.

Glomerular Capsule

A double-walled, cup-like sac (also known as Bowman's capsule) that encloses the glomerulus and receives the glomerular filtrate.

Podocytes

Specialized modified epithelial cells composing the visceral layer of the glomerular capsule that extend primary and secondary branching foot processes around capillaries.

Pedicels

Secondary foot-like extensions branching from primary podocyte processes that interdigitate to form narrow filtration slits.

Proximal Convoluted Tubule

The highly coiled section of the renal tubule leading away from the glomerular capsule, characterized by simple cuboidal epithelium with a dense brush border that reabsorbs approximately $70\%$ of filtered water and solutes.

Nephron Loop

The U-shaped loop of Henle consisting of a descending limb and an ascending limb that extends into the renal medulla to establish an osmotic gradient.

Distal Convoluted Tubule

The coiled tubule segment distal to the ascending limb of the nephron loop that terminates by draining into a collecting duct.

Collecting Duct

A tubular passageway into which several distal convoluted tubules drain; it passes down through the medulla to empty urine through a renal papilla.

Cortical Nephrons

Nephrons whose renal corpuscles sit high in the renal cortex and possess short nephron loops that barely enter the medulla; they constitute the majority of nephrons.

Juxtamedullary Nephrons

Nephrons with renal corpuscles located deep in the cortex near the medulla and long loops of Henle extending deep into the medulla, essential for concentrating urine.

Juxtaglomerular Apparatus

A regulatory structure formed where the ascending limb of the nephron loop contacts the afferent and efferent arterioles, consisting of the macula densa and juxtaglomerular cells.

Macula Densa

A cluster of tall, densely packed epithelial cells within the ascending limb of the nephron loop that monitors electrolyte composition of tubular fluid.

Juxtaglomerular Cells

Enlarged, specialized vascular smooth muscle cells in the wall of the afferent arteriole that produce and secrete the enzyme renin.

Afferent Arteriole

The relatively wide arteriole that branches from a cortical radiate artery to transport blood directly into the glomerular capillaries.

Efferent Arteriole

The arteriole that drains blood out of the glomerular capillaries and conveys it to peritubular capillaries or the vasa recta.

Peritubular Capillaries

A network of low-pressure capillaries that branches from the efferent arterioles to surround the renal tubules in the cortex.

Vasa Recta

Long, straight hairpin capillary loops that extend deep into the renal medulla alongside the nephron loops of juxtamedullary nephrons.

Glomerular Filtration

The initial stage of urine formation in which blood hydrostatic pressure drives water and small dissolved solutes across the fenestrated glomerular membrane into the capsular space.

Fenestrae

Microscopic pores within the glomerular endothelial cell walls that significantly increase permeability to water and small molecules while restricting blood cells.

Net Filtration Pressure

The overall force moving fluid across the glomerular wall, equal to glomerular hydrostatic pressure minus the sum of plasma colloid osmotic pressure and capsular hydrostatic pressure ($\approx +10\,\text{mm}\,\text{Hg}$).

Glomerular Filtration Rate

The volume of filtrate produced by both kidneys combined each minute, averaging approximately $125\,\text{mL/min}$ or $180\,\text{L/day}$ in an adult.

Renal Plasma Threshold

The critical plasma concentration of a substance at which the transport capacity of renal tubular carrier proteins is exceeded, causing the excess to appear in urine.

Tubular Reabsorption

The selective transport of water and filtered solutes from the tubular lumen through the tubular epithelium into interstitial fluid and peritubular capillaries.

Tubular Secretion

The movement of substances such as $\text{H}^+$, $\text{K}^+$, and drugs from peritubular capillary plasma into the renal tubular fluid for elimination.

Countercurrent Multiplier

A mechanism dependent on the opposing fluid flows and distinct permeabilities of the nephron loop limbs that builds a progressively hypertonic medullary interstitial gradient.

Antidiuretic Hormone

A peptide hormone produced by the hypothalamus and released from the posterior pituitary that stimulates water reabsorption by increasing water permeability in distal convoluted tubules and collecting ducts.

Urea

A nitrogenous by-product of amino acid catabolism that enters tubules via filtration, with approximately $80\%$ reabsorbed and $20\%$ excreted in urine.

Uric Acid

A nitrogenous waste product resulting from nucleic acid metabolism that is completely reabsorbed by active transport, with about $10\%$ subsequently secreted into urine.

Renal Clearance

The rate at which a specific substance is cleared from blood plasma by the kidneys per unit time, evaluated using substances like inulin or creatinine to assess GFR.

Detrusor Muscle

The interlaced smooth muscle coat comprising the wall of the urinary bladder that contracts under parasympathetic control to expel urine.

Trigone

A triangular landmark region on the internal floor of the urinary bladder delineated by the two ureteral openings and the internal urethral orifice.

Internal Urethral Sphincter

An involuntary smooth muscle sphincter located at the neck of the urinary bladder that prevents bladder emptying until relaxed during micturition.

External Urethral Sphincter

A voluntary skeletal muscle band located within the urogenital diaphragm that encircles the urethra and permits conscious inhibition of urination.

Micturition

The urination reflex by which the urinary bladder discharges urine, regulated by a reflex center in the sacral spinal cord and controlled by brain centers.

Ureterorenal Reflex

A reflex triggered by ureteral obstruction (such as a calculus) that increases ureteral peristalsis while constricting renal arterioles to reduce filtration in the affected kidney.

Nephrotic Syndrome

A renal disease complex characterized by damaged, highly permeable glomerular capillaries, severe proteinuria, hypoalbuminemia, and generalized edema.

Acute Glomerulonephritis

An immune-mediated inflammation of glomerular capillaries occurring $1\text{ to }3\,\text{weeks}$ after an infection with beta-hemolytic Streptococcus, caused by deposited antigen-antibody complexes.

Horseshoe Kidney

A congenital developmental abnormality characterized by the midline fusion of both kidneys at one pole (most commonly the lower pole).

Polycystic Kidney Disease

An inherited developmental disease characterized by the progressive expansion of fluid-filled cysts in renal tubules and collecting ducts.