1. The Importance of Excreting Wastes

2. Many by-products of metabolism are toxic to the body and need to be excreted
Example:
Carbon Dioxide (produced during cellular respiration) is removed by the lungs
Toxic wastes are removed from the digestive system by the large intestine
Alcohol is transformed by the liver into compounds that can be removed by the kidneys

3. Kidneys The kidneys play a crucial role in: Removing waste
Balancing blood pH
Maintaining water balance

4. Deamination
Deamination- the removal of an amino group from an organic compound
Most people consume more protein than is required to maintain tissues an promote cell growth
Excess protein is often converted into carbohydrates
Proteins, however, contain nitrogen! (and carbohydrates do not)

5. The nitrogen atom in a protein is attached to two hydrogen atoms (amino group)
This amino group molecule must be removed from the body
The by-product of deamination is ammonia (water soluble gas)

6. Ammonia Ammonia is extremely toxic (0.005mg can kill a human)
Fish avoid a build of ammonia by continually excreting it through their gills
Since land animals must find a way to store their waste products, ammonia is not an option

7. Urea and Uric Acid
In the liver, two molecules of ammonia combine with one another and carbon dioxide (another waste product) to form urea
Urea is times less toxic than ammonia
Uric acid is another waste product that is formed by the breakdown of nucleic acids

9. Water Balance Regulated by the kidneys
Humans may survive for weeks without food
Water, however, is more essential and humans will die after a few days with no water
We lose about 2L of water a day (urine, perspiration, exhaled air)

10. Humans must replenish all water lost during the day
Loss of 1% body water = thirst
Loss of 5% body water = extreme pain
Loss of 10% body water = death
(Buy a Brita!...or else)

11. The Urinary System - Anatomy

12. Overview of the Urinary System
Kidneys have a mass of about 0.5kg and can hold as much as 25% of the body’s blood at any given time
Renal Arteries – branch from the aorta and carry blood to the kidneys

14. Overview of the Urinary System
Wastes are filtered from the blood by the kidneys and are carried to the urinary bladder by the ureters
A urinary sphincter muscle is located at the base of the bladder and acts as a valve

16. When 200mL of urine has been collected in the bladder, the bladder stretches and nerves send a signal to the brain
At 400mL the signal becomes stronger (more stretching = more signal)
At 600mL the sphincter releases, urine enters the urethra and the bladder is voided

17. Structure of the Kidney
The kidney has three main structures
The cortex – outer layer of connective tissue
The medulla – the inner layer beneath the cortex
The renal pelvis – a hollow chamber where the kidney and ureter is joined

19. Nephrons - Anatomy
Nephrons are the one million slender tubules that make up the functional units of the kidney
Afferent arterioles – small branches that carry blood to the glomerulus
Glomerulus – high pressure capillary bed that is the site of filtration
Efferent arterioles – small branches that carry blood away from the glomerulus to a capillary net

21. Glomerulus

22. More Anatomy
Peritubular capillaries – network of small blood vessels that surround the nephron Bowman’s capsule – cuplike structure that surrounds the glomerulus Proximal tubule – section of the Bowman’s capsule with the loop of Henle Loop of Henle – carries filtrate from the proximal tubule to the distal tubule

23. Still More
Distal Tubule – conducts urine from the loop of Henle to the collecting duct Collecting Duct – tube that carries urine from nephrons to the pelvis of the kidney