Excreting wastes 7.3

Introduction Many products from metabolism harmful. Lungs eliminate CO2 Large intestine removes toxic waste digestive system Liver transforms toxins (alcohol & heavy metals) into soluble compounds that kidneys can deal with. Kidneys play crucial role in removing waste, balancing pH, and maintaining water balance.

Protein metabolism Average Canadian consumes more protein than needed. Excess protein  carbohydrates Nitrogen + 2H need to be removed from amino acids Deamination: occurs in the liver. Ammonia is a water-soluble gas: extremely toxic. Build-up of 0.005 mg can kill a human. Two ammonia + CO2 urea: 100 000 x less toxic

Nucleic acid metabolism Uric acid: formed by breakdown of nucleic acids. Kidneys help in excretion

Water balance Maintained by kidneys Humans lose approx. 2L of water a day: urine, perspiration, exhaled air. Drop in fluid intake by 1% = thirst. 5% = pain and collapse. 10% = death.

Excretion: simple Unicellular & simple multicellular (sponge) Every cell in contact with external environment Wastes released directly from cell Fluid regulation? Ameoba & paramecium: hypertonic to freshwater: contractile vacuoles.

Excretion: complex Not every cell in contact with external environment. Wastes need to be collected and temporarily stored. Excretory system: cells work together to remove wastes from body or store waste until signalled to remove them.

earthworm Nephrostome: funnel-like structure: draws fluids from body cavity into tiny tubules. Collecting tubule: collects fluids from nephrostome. Bladder. Nephridiopore: small pores in which wastes are released.

Grasshopper Malpighian tububles: throughout body cavity: absorb wastes by diffusion. Wastes released into gut and eliminated as solid wastes from the anus.

..to more complex...

summary

Seatwork/homework Page 345 # 1-4.