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The Urinary System
Urinary System Contribution to
Homeostasis
 Regulates body water levels
 Excess water taken in is excreted
 Output varies from 2-1/2 liter/day to 1 liter/hour
 Regulates nitrogenous and other solute waste
 Nitrogen from amino acids are made into urea in liver and
transported to kidney as waste
 Other solutes
 Sodium, chloride, potassium, calcium, hydrogen ions,
creatinine
Urinary System
Cortex
Kidney
Renal artery
Renal vein
Nephrons
Aorta
Inferior
vena cava
Cortex
Renal
pelvis
Medulla
Ureter
Bladder
Medulla
Collecting
duct
Ureter
Urethra
a) The components of the urinary system.
b) Internal structure of the kidney.
c) The cortex and medulla of the kidney
are composed of numerous nephrons.
Organs of the Urinary System
 Kidneys
 Principle organ
 Cortex - outer
 Medulla - inner
Urinary System
Cortex
Kidney
Renal artery
Renal vein
Nephrons
Aorta
Inferior
vena cava
Cortex
Renal
pelvis
Medulla
Ureter
Bladder
Medulla
Collecting
duct
Ureter
Urethra
a) The components of the urinary system.
b) Internal structure of the kidney.
c) The cortex and medulla of the kidney
are composed of numerous nephrons.
Organs of the Urinary System
 Ureters
 Transport urine to bladder
 Urinary bladder
 Stores urine (600–1000 ml)
 Urethra
 Carries urine from body
 Two sphincters
 Males about 20 cm, females about 4 cm
Organs of the Urinary System
Urinary
bladder
Rectum
Prostate
gland
Internal
urethral
sphincter
Uterus
Vagina
Penis
External
urethral
sphincter
Rectum
Urethra
Testis
a) The male
b) The female
Tubular and Vascular Nephron Components
Nephrons: Produce Urine
 Tubules
 Function

Filter fluid and reabsorb needed substances
 Structures




Proximal tubule
Loop of Henle
Distal tubule
Collecting duct
Nephrons: Produce Urine
 Blood vessels associated with tubules
 Arterioles


Afferent
Efferent
 Capillaries



Glomerular
Peritubular
Vasa recta
Formation of Urine
Formation of Urine: Glomerular
Filtration
 Glomerular filtration
 Filters fluid from capillaries into glomerular capsule
 Rate of filtration


Resting rate under local chemical control
Stress causes sympathetic nervous system to reduce blood
flow to kidneys
Formation of Urine: Tubular
Reabsorption
 Tubular reabsorption returns water and needed solutes
to blood capillaries




Sodium moved by active transport from tubule cells to
interstitial fluid and diffuses to capillaries
Chloride passively accompanies sodium (balanced
charge)
Water reabsorbed with salts
Movement of sodium creates energy to transport glucose
and amino acids into renal tubule then diffuses to the
interstitial fluid
Tubular Secretion
 Tubular secretion removes other substances from
blood
 Purpose


Regulation of chemical levels in body
Excretion of harmful chemicals
 Substances secreted

Penicillin, cocaine, marijuana, pesticides, preservatives,
hydrogen ions, ammonium, potassium
Concentration or Dilution of Urine: ADH (antidiuretic hormone)
 Formation of Dilute urine (see next slide for diagram)
 Excreting excess water
 Mechanism

Cycling of NaCl and urea create a concentration gradient in
the medulla that allows water to diffuse from the renal tubules
into the interstitial fluid and then into the blood capillaries
Formation of Dilute Urine
Concentration or Dilution of
Urine: ADH
 Formation of concentrated urine (see next slide)
 Conserving water
 Mechanism


Countercurrent exchange
Increased ADH causes increased permeability to the
collecting tubules and increased conservation of water
Formation of Concentrated Urine
Urination
 Micturition reflex
 Internal urethral sphincter

Smooth muscle
 External urethral sphincter

Skeletal muscle
Kidney’s Role in Homeostasis
 Maintains water balance
 Adjusts blood volume and blood pressure
 Aldosterone, renin, ANH help maintain salt balance in
order to control blood volume
 Maintains acid–base balance and blood pH
 Regulates red blood cell production via erythropoietin
 Activates an inactive form of vitamin D
Kidney’s Role in Homeostasis
Kidney’s Role in Homeostasis