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