3.12 The Excretory System

Pages 210-214

Kidneys

• The kidney is the size of a fist and a mass of approximately 500 grams.

Metabolic Waste

• Waste is produced from the break-down of proteins.

Deamination

• We eat protein.• We use protein for building and repair.• The liver breaks down extra protein.• The amino group, NH2 , is converted to

ammonia, NH3 ,

Toxic

• The amino group, NH2 , is converted to ammonia, NH3

• Ammonia is toxic! 0.005 mg can kill you!

Solution…

• Combining ammonia with carbon dioxide makes urea, [NH2]2CO

• Urea is less toxic than ammonia• The blood carries urea to the kidneys where it

is excreted in the urine

Kidneys

• Filter blood

Renal arteries

• Bring blood to the kidney.

Renal Veins

• Return “cleaned” blood to the circulatory system.

Ureters

• Carry urine from the kidneys to theBladder.

Bladder control

• A sphincter at the base controls the bladder• 200 mL …signal sent “Go to the bathroom”

• 400 mL …urgent signal sent “ Go to the bathroom right now!”

• 600 mL …too late

Ureter

• The tube that carries urine from the bladder to the exterior of the body.

Urine formation

• Step #1 filtration• Step #2 reabsorption• Step #3 secretion

Nephrons

• One million per kidney

Bowman’s capsule

• The cup-like structure that surrounds the glomerulus.

The glomerulus

• Cluster of capillaries• The area of fluid filtration

Proximal tubule

• a hollow, winding large diameter tube • for the reabsorption of glucose, sodium,

amino acids • these are pumped back into the capillaries• urea stays in the tube

Descending loop of Henle

• Straight part of the loop moving away from the proximal tubule

• Water flows out by osmosis

Ascending Loop of Henle

• Straight part of loop heading to distal tubule• Sodium pumped out of tube

Distal tubule

• A hollow winding large diameter tube.• Reabsorption of water if needed.

Collecting Duct

• System of urine collecting ducts that widen as they near the renal pelvis

• Wastes are transferred from the capillary network to the duct.

• Water moves by osmosis from the duct to the surrounding blood.

#1 Filtration

Moves from glomerulus to Bowman’s capsule:• Water• Salt• Glucose• urea

#1 Filtration

Does not move from glomerulus to Bowman’s capsule:• Plasma proteins• Blood cells• Large platelets

volume

• 600 mL blood through each kidney per minute

Reabsorption

• 119 of every 120 mL of fluid is returned to the blood

Urine

• 95% water• 5% salts, urea etc.