What generates nitrogenous waste?
- Break down of protiens and nucleic acids
- In digestive system
- Amino group (NH2) is removed
Why do we need to get rid of nitrogenous waste?
- Forms toxic ammonia
- Raises pH of body fluids
- Inhibits key enzymes
What are 3 different organisms get rid of nitrogenous waste? and what organisms use which?
1) Ammonia- bony fishes, aquatic amphibians and invertebrates
2) Urea- mammals, most amphibians, cartilaginous fish
3) Uric acid- birds, insects, reptiles, some amphibians
4 facts about ammonia excretion
1) Doesnt require energy
2) Small molecule so rapid diffusion
3) Very toxic
4) Highly soluble in water
Where is urea produced and what from? It is less toxic than ammonia but at what cost?
- Produced in the liver
- From ammonia
- Requires energy to make
What are the costs and benefits of uric acid?
Benefits:
- insoluble
- less toxic
- excreted as semi solid, conserves water
- useful if development takes place in an egg
Costs: requires 3x as much energy to make as urea
What are generalised excretory organs for protozoa, amelids, insects, fish and birds?
Protozoa- contractile vacuole Annelids- pores in skin Insects- malpighian tubules Fish- gills Birds- nasal salt glands
Describe how malpighian tubules work to produce uric acid
- Salts and nitrogenous waste actively transported into gut lumen through tubules
- Water follows by osmosis
- Valuable ions pumped back into hacnolymph and water follows
- Uric acid eliminated with faeces
Describe the structure of malpighian tubules in insects and why they are useful
- Blind ended tubes
- Walls = one cell thick
- Open to hindgut
- Float in haemolymph
Useful because they are highly effective at conserving water
What are the 4 main steps in the human excretory system (kidneys)?
1) Filtration
2) Re-absorption
3) Secretion
4) Excretion of filtrate
What are 2 key features of the human excretory system?
1) Selectively permeable membranes
2) Blood in close contact with excretory structures
What is the job of the renal cortex and renal medulla?
Renal cortex- ultrafiltration
Renal medulla- regulates water and salt in blood
What is the nephron and its job?
- Single long tubule surrounded by a network of capillaries
- Constantly brings in waste products that need excreting
Describe the process of ultrafiltration?
- High blood pressure in glomerulus forces fluid into bowman capsule
- All solutes are pushed into nephron
- Water and salt is reabsorbed in proximal tubule
- In descending limb water leaves filtrate increasing osmolates
- Salt leaves filtrate, water in ascending limb
What is the countercurrent multiplier system?
Concurrent: tubule fluid in descending limb flows in opposite direction from ascending limb
Multiplier: creates steep osmotic gradient by increasing solute potential in surrounding fluid
