Chapter 26 Learning Objectives

Structures of the urinary system

Kidneys, ureters, urinary bladder, urethra

Functions of the kidneys

Regulate blood composition, pH, volume, pressure, osmolarity; produce hormones; excrete wastes

Retroperitoneal

Located behind the peritoneum

Kidney capsule

Tough outer layer that maintains kidney shape

Hilum

Entry/exit for ureter, blood vessels, nerves

Renal cortex

Outer region containing glomeruli

Renal medulla

Inner region containing pyramids and tubules

Renal pyramids

Cone-shaped structures that drain urine

Renal columns

Tissue between pyramids

Calyx

Collects urine from pyramids

Renal pelvis

Funnel that drains urine into ureter

Blood flow through kidney

Renal artery → segmental → interlobar → arcuate → interlobular → afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries → veins → renal vein

Afferent arteriole

Brings blood to glomerulus

Efferent arteriole

Carries blood away from glomerulus

Peritubular capillaries

Surround tubules for reabsorption/secretion

Nephron functional unit

Glomerulus + Bowman's capsule (renal corpuscle) + tubules

Nephron tubule order

Bowman's capsule → PCT → descending loop → ascending loop → DCT → collecting duct

Three processes of urine formation

Filtration, reabsorption, secretion

Process in renal corpuscle

Filtration of blood

Process in PCT

Reabsorbs most water, glucose, amino acids, ions; secretes wastes

Process in loop of Henle

Descending: water reabsorption; Ascending: salt reabsorption

Process in DCT

Fine-tunes ion balance; Ca2+ reabsorption (PTH)

Process in collecting duct

Water reabsorption depends on ADH

Glomerular filtrate

Fluid filtered from blood into capsule

Filtered substances

Water, glucose, amino acids, ions, urea

Not filtered

Blood cells, proteins, platelets

Reabsorbed substances

Water, glucose, amino acids, Na+, Cl-, Ca2+, urea

Secreted substances

H+, K+, NH4+, creatinine, drugs

Water reabsorption

Most in PCT; descending loop; regulated in DCT/collecting duct by ADH

Glomerular filtration rate (GFR)

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

RAA system triggered

Low blood pressure/volume

RAA system steps

Renin → angiotensin I → angiotensin II → aldosterone

Effect of angiotensin II

Vasoconstriction, decreases GFR, increases BP

Effect of aldosterone

Increases Na+ and water reabsorption; increases BP

Autoregulation of GFR

Myogenic + tubuloglomerular feedback maintain constant GFR

Sympathetic effect on GFR

Decreases GFR and urine output

Hormonal control of GFR

Angiotensin II ↓ GFR; ANP ↑ GFR

Effect of ADH

Increases water reabsorption in collecting duct

Effect of ANP

Increases GFR and decreases BP

Effect of PTH

Increases Ca2+ reabsorption in DCT

GFR effect on BP and volume

↑GFR → ↑urine → ↓blood volume/BP; ↓GFR → opposite

ADH and urine concentration

With ADH = concentrated urine; without ADH = dilute urine

Countercurrent flow

Opposite flow in loop of Henle creates osmotic gradient

Purpose of countercurrent mechanism

Allows concentration of urine

BUN test

High levels indicate kidney dysfunction

Glycosuria

Glucose in urine indicates diabetes mellitus

Plasma creatinine

High levels indicate poor kidney function

Renal clearance

Measures how well kidneys remove substances

Protein in urine

Indicates kidney damage

Urinalysis

Predicts disease based on urine composition

Bladder anatomy

Transitional epithelium, ureter openings, internal/external sphincters

Internal urethral sphincter

Involuntary control

External urethral sphincter

Voluntary control

Micturition reflex

Stretch receptors → parasympathetic contraction of bladder + sphincter relaxation

Other waste removal systems

Lungs (CO2), skin (sweat), liver (detox), GI tract (feces), blood (transport)