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