Excretory System

Excretion – removal of metabolic waste

Urinary system

• made-up of the kidneys, ureters, bladder, and urethra

• kidneys filter waste from blood; collected as urine

• flows through ureters to the bladder

• stored then leaves through urethra

Kidney Structure

• 3 regions;

• Renal medulla - inner

• Renal cortex – outer part (contains nephrons)

• Renal pelvis - funnel shaped structure in the center of the kidney.

• 2 blood vessels enter and leave each kidney– renal artery enters – renal vein exists

Functional Unit of the Kidneys• nephrons

– approx 1 million per kid

• 3 functions: – filtration of water and solutes from the blood – reabsorption of water and molecules back into

the blood – secretion of waste products from surrounding

capillaries

Filtration• Blood enters a nephron into the glomerulus

• The glomerulus is encased by the Bowman’s capsule– fluid from the blood is filtered– the filtrate contains water, urea, glucose, salts, amino

acids, and vitamins

• urea - - nitrogenous product made by the liver 

• brought to liver as ammonia , converted to less harmful substance (urea) and enters the blood stream 

Reabsorption• Material removed from blood at Bowman’s

cap makes it way back into the blood

• happens along nephron’s tubular parts

Secretion• waste and toxic material secreted from

blood

• purified blood returned to circulatory sys through renal vein

Nephron

The Kidneys ensure that the composition of our Blood remains Constant

• Concentration of water in blood– Drink too much liquid, and the Kidneys will

decrease the rate of reabsorption, excess water is excreted.

• Level of salt in blood– Eat Salty Foods and the Kidneys will respond

by returning less salt to the Blood by reabsorption.  Excess is excreted

• water reabsorption is controlled by the antidiuretic hormone (ADH)

• ADH is released from the pituitary gland in the brain

Kidney Stones

• excess wastes crystallize