Excretory System

Kidneys Ureters Bladder Urethra

Serves 2 Primary Functions:

1) Osmoregulation – how animals regulate solute conc. and balance gain/loss of water.

2) Excretion – getting rid of N-containing waste of metab.

When macromolecs are broken, N is removed in the form of NH3 – very toxic

Types of waste:

1) Ammonia – most aquatic organsisms (fish); requires a lot of water to rid.

2) Urea – common in terrestrial (mammals, sharks, some fish) liver combines NH3 with CO2; 100,000X less toxic than NH3; requires energy to produce.

3) Uric Acid – reptiles and birds; very little water loss; requires even more energy.

Nephrons and Blood Vessels are functional units.

Renal Artery supplies kidneys.

Kidney has two distinct regions:

1) Renal Cortex

2) Renal Medulla

1100 to 2000 L of blood flow through kidneys/day

Renal Artery – supplies kidney

Afferent Arteriole

Efferent Vessel

Renal Cortex

Glomerulus – ball of capillaries

Bowman’s Capsule – tube surrounding glomerulus.

Proximal Tubule

Loop of Henle

Distal Tubule

Collecting Duct

Ureter

Nephron

     

 

1) Proximal Tubule [located in the cortex]

*Controlled secretion of H+ into the filtrate maintains pH.

*NH3 enters the filtrate from the blood.

*HCO3, NaCl, H2O, Nutrients, and K+ leave the filtrate.

2. Descending Loop of Henle [drops from the cortex into the medulla

*H2O leaves the filtrate (reabsorbed)

3. Ascending Loop of Henle [rises back up towards cortex]

*NaCl leaves the filtrate

4. Distal Tubule [in the cortex]

*NaCl, H2O, and HCO3 leave the filtrate.

*K+ and H+ reenter the filtrate.

5. Collecting Duct

*NaCl, Urea, and H2O leave the collecting duct.

The diffusion of ions and molecules into or out of the filtrate is the result of both Passive and Active Transport.

The permeability of the collecting duct is determined by the presence or absence of Anti-Diuretic Hormone (ADH) which secreted by the pituitary gland.

When ADH levels are high, the collecting ducts becomepermeable to H2O and H2O leaves the collecting duct.

This causes urine to become concentrated.

 

When ADH levels are low, the collecting ducts remainimpermeable to H2O, so it stays in the ducts causing urine to become more dilute.

  

Molecule Amount in blood plasma in mg 100 ml-1

Amount in glomerular

filtrate in mg 100 ml-1

Amount in urine  in mg

100 ml-1

Proteins >700 0 0Glucose >90 >90 0

Urea 30 30 >1800