1. Waste Removal & the Human Urinary System
Sections 3.7 – 3.8
Bio 391

2. Waste Removal Organisms in water … Some removal mechanisms
Removing wastes is essential to homeostasis.
Organisms in water …
Don’t worry about drying out
Must worry about excreting excess water
Ex: Paramecium’s contractile vacuole
Some removal mechanisms
Simple Organisms
Excretes all wastes through external surface
Hydra, sponges
More complex organisms (ie. Fish)
CO2 – removed through gills
Salt is removed through gills in salt water fish

3. Metabolic Nitrogenous Wastes
Created from the digestion of proteins
Amino acids Amino groups  ammonia
Ammonia is very TOXIC to cells
Methods of Removal:
Immediate, direct ammonia release
More simple aquatic organisms
water “flushes” it out
Convert ammonia to urea
Less toxic, can be stored for a while
Allows for conservation of water
Humans, mammals, some fish, amphibians
Convert to uric Acid
Released as crystal form, “pastey”
Conserves even more water
Birds & desert reptiles

4. Ammonia >>> urea >>> uric acid
Metabolic N-Wastes
Ammonia >>> urea >>> uric acid
Most toxic Least toxic
Requires most water Requires least water
Evolution of different methods…
Related to water availability and whether or not ammonia can be diluted
Further adaptations aid in conserving water

6. Lungs Skin Human Urinary System Kidneys Nephrons
Excretory tubules in humans
Processes blood, filtering out N-wastes
Regulates water balance – adjusts salt concentration in blood
Lungs
Skin

7. Nitrogenous Waste Digestion: Protein to amino groups
Amino acids turned into ammonia and converted to urea in the liver
Urea enters circulation (blood)
Urea is concentrated by the kidneys
Removed as urine
Unused, unwanted chemicals will eventually get into our blood stream. They are often diluted in our body fluids (plasma). We want the chemicals to leave the body, but we want to keep our water (and some of the nutrients/chemicals) 7

8. Nephron = “functional unit”
The Urinary System
2 Kidneys
2 ureters
1 bladder
1 urethra
Nephron = “functional unit”
A “division” of the excretory system. All vertebrates have paired kidneys. 8

9. Urinary System
Blood into kidney via renal artery Blood filtered in nephron (waste=urine) Urine leaves kidney via ureter Urine stored in urinary bladder Drains out urethra

12. Components of The Nephron
Glomerulus: mechanically filters blood
Bowman's Capsule: mechanically filters blood
Proximal Convoluted Tubule: Reabsorbs 75% of the water, salts, glucose, and amino acids
Loop of Henle: Countercurrent exchange, which maintains the concentration gradient
NaCl moves by active transport and diffusion
Distal Convoluted Tubule: Tubular secretion of H+ ions, potassium, and certain drugs.
Collecting Duct: Collects all wastes

14. Functions of the Nephron
FILTRATION: in the glomerulus and Bowman’s capsule.
Driven by blood pressure
REABSORPTION: begins in proximal tubule
Salts, amino acids, sugars, vitamins
Water follows
Active Transport & Osmosis
Tubular SECRETION into the distal tubule
K+, H+, drugs, NH3
Products are removed via excretion

16. Homeostasis by the Kidney
Maintain volume of extracellular fluid
Maintain ionic balance in extracellular fluid
Maintain pH and osmotic concentration of the extracellular fluid.
Excrete toxic metabolic by-products such as urea, ammonia, and uric acid.

17. CONTROL OF THE KIDNEY Blood pressure is low due to dehydration
ADH: Antidiuretic Hormone:
“Against peeing”
Blood pressure is low due to dehydration
Sensed by hypothalamus in brain
stimulates pituitary gland to release ADH (travels to kidney)
Water is reabsorbed into blood from distal tubule
Blood pressure increases
 water in blood =  blood volume =  pressure = ADH presence is reduced

18. CONTROL OF THE KIDNEY Aldosterone (adrenal hormone)
Controls excretion of Na+ and K+
High [K+] in blood aldosterone released by adrenal gland
Causes more secretion of K+ into nephron, lowering blood K+ and therefore aldosterone
Negative Feedback Regulation – substances inhibit their own formation

19. Production to Urine