Urinary System
URINARY SYSTEM ORGANS:
• Ureters
– Collect urine from kidneys, bring to bladder
• Bladder
– Muscular, elastic organ – holds about 250ml
• Urethra
– Longer in males than in females
– Two sphincters: involuntary & voluntary
KIDNEYS
• Filter blood, produce urine (24 hrs a day)
• Cortex and medulla; At hilus, artery in,
vein and ureter out
Nephron Structure
• Bowman’s capsule & glomerulus
– Filtration occurs here
– Pressure forces filtrate through cell gaps
– Formed elements (blood cells), large proteins stay in
blood
– Water, ions (salts), nutrients, wastes go through
• 180 liters filtrate per day
• Proximal convoluted tubule
– Majority of reabsorption occurs here. 179 liters
reclaimed to peritubular capillary network
– Water, salt, glucose, amino acids back to the
blood (nutrients in general)
• Secretion – removal from blood of wastes
that escaped filtration
– Loop of Henle ( ascending and descending
limbs)
– Distal convoluted tubule
– Collecting duct
Nephron Functions
• Filtration: Bowman’s capsule, glomerulus)
• Reabsorption: Proximal convoluted tubule
• Secretion: Loop of Henle, Distal
convoluted tubule , Collecting duct
Concentration of Urine
• Kidneys regulate water-salt balance of the
blood.
• Kidney cells use ATP to set it up (pump
NaCl & urea leaks into renal medulla)
• Descending loop of Henle: water diffuses
into salty medulla tissue
• Ascending loop of Henle: not water
permeable!!!!! Salt is actively pumped out
• Distal convoluted tubule and collecting duct:
water permeability under hormonal control
• ADH (Antidiuretic hormone-secreted by pituitary
gland)
– Increases urine concentration
– When ADH decreases, kidneys make dilute urine
– Alcohol interferes with ADH secretion  dilute
urine, you lose water – coffee too
Urine Composition
• 95% water by volume; rest is solutes
• Nitrogenous wastes: urea, creatinine, uric
acid
• Ions: sodium, potassium, sulfate,
• Associated with medical problems:
glucose, blood proteins (albumin), red or
white blood cells, bile pigments
Renal Failure
• Symptoms:
– Acidosis – low blood pH - kidneys excrete
hydrogen ions
– Anemia – low RBC count – erythropoietin
– Edema – water and salts retention
– Hypertension – high blood pressure
– Accumulation of nitrogenous wastes (urea)
• Hemodialysis – artificial kidney
• Kidney transplant
Kidney Stones
• Mineral crystals (often calcium) that form
in the kidney and pass down ureter.
• Prevention: drink plenty of water