1. Excretion Purpose: - Maintain Homeostasis –Keeping the “status quo” externally and internally Function: Rids body of metabolic wastes –Salts, Carbon Dioxide, Urea Excretory Organs –Skin – water and salts –Lungs – CO 2 –Kidneys and associated organs - Urea

2. The Excretory System ((Liquid/salts) Kidneys (2, lower back) –Filtration system  urine Ureters –Tubes carrying urine from kidneys to bladder Urinary bladder –Saclike organ where urine is stored Urethra –Tubes from which urine is released from the body

3. Kidney (Cross Section) Cortex Medulla Vein Artery Kidney Ureter Urinary bladder Urethra Excretory System

4. Kidney Nephron Cortex Medulla Renal artery Renal vein Ureter To the bladder Bowman’s capsule Glomerulus Capillaries Collecting duct To the ureter Loop of Henle Artery Vein

5. Structure of Kidney Renal Cortex –outer portion Renal Medulla –Inner portion (loop of Henley) Nephrons –Straddle the cortex and medulla –Functional unit of kidneys; filters blood Flow –Blood enters arteriole  capillaries (filtration)  waste products accumulate in collecting duct  Duct joins ureter

6. Function of Kidney Purification of blood Three processes: –Filtration, –Reabsorption –Secretion

7. Filtration Most filtration occurs in the glomerulus. Blood pressure forces water, salt, glucose, amino acids, and urea into Bowman’s capsule. Proteins and blood cells are too large to cross the membrane; they remain in the blood. The fluid that enters the renal tubules is called the filtrate. Reabsorption As the filtrate flows through the renal tubule, most of the water and nutrients are reabsorbed into the blood. The concentrated fluid that remains is called urine. Secretion Substances such as hydrogen ions are transferred from the blood to the filtrate.

8. Nephron Bowman’s capsule –Found in Cortex –Contains glomerulus (capillary bed) and collecting duct –Filters the blood (extracts waste products) Renal tubes –Reabsorb essential nutrients (glucose and aa) –Secrete H+ Loop of Henle –Found in medulla –Water conservation (reabsorb)

9. Result: Purified blood returned to circulatory system Urine is collected in the bladder –Released through the urethra

10. Kidneys Regulate water and waste content of blood –Blood volume, pH, waste products –Really controlled by blood levels What happens when you drink more water? What happens if you eat salty food?

11. Dialysis Artificial cleansing of the blood