URINARY SYSTEM

Kidneys

Paired organs that produce urine.

Urinary tract

Stores and eliminates urine.

Ureters

Paired tubes carrying urine from kidneys to bladder.

Urinary bladder

Muscular sac for temporary urine storage.

Urethra

Tube carrying urine from bladder to outside.

Urination (micturition)

Contraction of bladder forcing urine out through urethra.

Excretion

Removal of metabolic wastes from bodily fluids.

Elimination

Discharge of wastes from the body.

Homeostatic regulation

Controls blood volume, pressure, ion concentration, pH, nutrient conservation, detoxification support.

Kidneys retroperitoneal

Located behind peritoneum; left kidney slightly superior.

Adrenal gland

Located on superior surface of each kidney.

Hilum

Indentation where vessels and ureter enter/exit kidney.

Renal cortex

Superficial region of kidney.

Renal medulla

Inner region of kidney.

Renal pyramids

Triangular structures in medulla.

Renal columns

Tissue bands between pyramids.

Minor calyx

Collects urine from renal pyramid.

Major calyx

Formed by merging 4–5 minor calyces.

Renal pelvis

Merging of major calyces.

Kidney blood flow

Receives 20–25% of cardiac output (~1200 mL/min).

Nephron

Microscopic functional unit of kidney where urine production begins.

Renal corpuscle

Filters blood within nephron.

Bowman's capsule

Surrounds glomerulus; contains podocytes.

Podocytes

Specialized cells with pedicels forming filtration slits.

Glomerulus

Ball of ~50 capillaries filtering blood.

Afferent arteriole

Brings blood to glomerulus.

Efferent arteriole

Removes blood from glomerulus.

Filtration membrane

Endothelium, basement membrane, podocyte slits.

Renal tubule

Long tubular passage altering filtrate composition.

Proximal convoluted tubule

First nephron segment for major reabsorption.

Nephron loop (Loop of Henle)

U-shaped loop involved in concentration gradient.

Distal convoluted tubule

Final nephron segment before collecting tubule; part of JGC.

Juxtaglomerular complex

Regulates blood pressure and filtrate formation.

Macula densa

Chemoreceptors/baroreceptors of DCT.

Juxtaglomerular cells

Baroreceptors releasing renin.

Extraglomerular mesangial cells

Communicate between macula densa and JG cells.

Collecting system

Tubes carrying fluid from nephrons to renal pelvis.

Cortical nephrons

85% of nephrons; short loops; peritubular capillaries.

Juxtamedullary nephrons

Long loops; vasa recta maintain gradient.

Filtration

Movement of water/solutes from blood to capsular space.

Reabsorption

Movement of substances from filtrate to blood; glucose reabsorbed 100%.

Secretion

Movement from blood into filtrate.

Excretion rate formula

Filtration + secretion − reabsorption.

Inulin

Marker for GFR; filtered not reabsorbed/secreted.

PAH

Used to measure renal blood flow; filtered and secreted.

Glomerular filtration

Driven by hydrostatic pressure; filters water/small solutes.

GFR

Amount of filtrate per minute (~125 mL/min).

Myogenic autoregulation

Adjusts arteriole diameter to maintain GFR.

Sympathetic GFR regulation

Constrains afferent arteriole; decreases GFR.

RAAS

Hormonal mechanism increasing BP and fluid retention.

Renin

Converts angiotensinogen → angiotensin I.

ACE

Converts angiotensin I → angiotensin II.

Angiotensin II

Raises BP, fluid retention, aldosterone, ADH.

Reabsorption purpose

Returns useful materials back to blood (99% reabsorbed).

Countercurrent multiplication

Nephron loop mechanism concentrating urine.

Descending limb

Permeable to water, not solutes.

Ascending limb

Pumps out Na+, impermeable to water.

Osmolarity range

100–1200 mOsm/L urine.

ADH effect

Inserts aquaporins → concentrated urine.

No ADH

No aquaporins → dilute urine.

Vasa recta

Countercurrent exchange preserving medullary gradient.

Transitional epithelium

Allows stretching without damage.

Ureters

Retroperitoneal tubes preventing backflow to kidneys.

Urinary bladder rugae

Folds that flatten as the bladder fills.

Trigone

Smooth triangular region between ureter openings and urethra.

Female urethra length

3–5 cm.

Male urethra length

18–20 cm in 3 segments.

External urethral sphincter

Skeletal muscle controlling urination.