1. The Excretory System
Biology 12
Ms. Marcos

2. Why excrete? We need to get rid of waste products: CO2
Bile pigments and heme (from blood)
Nitrogenous wastes from breakdown of amino acids
Ammonia (NH3) is VERY TOXIC
NH3 converted to urea in the liver (less toxic)
Urea is water soluble  excrete in urine

3. Nitrogenous waste excretion

4. Homeostasis… keeping things in balance
What do we need to keep constant?
Temperature
Balance of major ions (salts)
Balance of water (Osmoregulation)
pH balance
Hormone secretion

5. Structures involved in excretion
Lungs
Skin
Liver
Intestine
Kidneys!

6. The Urinary System

7. The Kidney

8. Major parts of the kidney
Renal medulla
Renal cortex
Renal pelvis
Ureter

9. Most systems produce urine by refining a filtrate derived from body fluids

10. Basic steps to any excretory system
Filtration  Use pressure to put things in the blood into a tube (make a filtrate)
Reabsorption  take back the good stuff into the blood again
Secretion  add any extra toxins or other wastes that didn’t make it in the first time
Excretion  the filtrate leaves the system and goes out of the body

11. The Nephron

12. Major parts of the nephron
ORIENTATION OF A NEPHRON WITHIN THE KIDNEY
Renal cortex
Proximal tubule
Bowman’s capsule
Distal tubule
Collecting duct
Loop of Henle
Renal medulla

13. Filtration Blood from an arteriole enters capillaries
 the Glomerulus
High pressure forces parts of the blood into the Bowman’s capsule (the start of the nephron)
Small molecules get through (water, wastes, nutrients, ions)
Large molecules can not get through (proteins, blood cells)

14. Reabsorption Filtrate enters the proximal convoluted tubule
Take back the stuff you need:
Glucose
Sodium (Na+), Chlorine (Cl-)
Water
Amino acids
Leave the stuff you don’t want:
Some water
Nitrogenous wastes
Some salts (extra)

15. Road map… check in 2
DETAILED STRUCTURE OF A NEPHRON

16. On to the Loop of Henle…
99% of water in the original filtrate is reabsorbed
The higher concentration of salts in the middle of the kidney helps bring water out

17. Secretion Filtrate enters the distal convoluted tubule
Any extra things you do not want enter the filtrate:
Chemicals or other toxins (drugs)
Excess ions
Not much flow of water

18. Excretion Filtrate enters the collection duct (it’s now urine)
Collecting duct is permeable to water, but not to salt
More water is brought back into the blood as the duct passes through the medulla
Enters ureter, then bladder, then through the urethra and OUT!

19. Review… where did the urine come from?