Waste Removal & the Human Urinary System
Sections 3.7 – 3.8
Bio 391http://www.youtube.com/watch?v=glu0dzK4dbU
Waste Removal• 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
Metabolic Nitrogenous WastesMetabolic 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
Metabolic N-Wastes
AmmoniaAmmonia >>> >>> ureaurea >>> >>> uric aciduric 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
Human Urinary Human Urinary SystemSystem
• Kidneys– Nephrons
• Excretory tubules in humans
– Processes blood, filtering out N-wastes
– Regulates water balance – adjusts salt concentration in blood
• Lungs
• Skin
Nitrogenous WasteDigestion: 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
The Urinary System
• 2 Kidneys
• 2 ureters
• 1 bladder
• 1 urethra
NephronNephron = “functional
unit”
Urinary SystemBlood into kidney via renal artery
Blood filtered in nephron (waste=urine)
Urine leaves kidney via ureter
Urine stored in urinary bladder
Drains out urethra
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
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
http://www.youtube.com/watch?v=glu0dzK4dbU
http://www.youtube.com/watch?NR=1&v=aQZaNXNroVY&feature=fvwp
http://www.youtube.com/watch?v=3THZeaMfuSw&NR=1&feature=endscreen
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.
CONTROL OF THE KIDNEY
• 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
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
Production to Urine