How is the excretory system related to
l ---> ammonia
glucose + O2
-> CO2 + H2O + useable
do animal need to be concerned with water loss if water is a by-product
of cellular respiration?
So the excretory system is involved with:
- removal of nitrogenous wastes
- water regulation
Marine and freshwater organisms face the
opposite problem of water movement due to
osmotic differences between their internal
fluids and the external environment.
loss through body surfaces, terrestrial vertebrates have keratin
water-resistant, insoluble protein) in their epidermis, and arthropods
have a waxy cuticle.
Some desert mammals are so efficient at water regulation that drinking
is not required for survival; how
then is water aquired?
Problems associated with water regulation are closely tied to
bodies production of nitrogenous waste
produced by the breakdown and conversion of amino acids and nucleic
What kind of environments might select for
an excretory system that would produce each of the above compounds?
- Ammonia is highly toxic
and if not converted to another form requires large amounts of water to
flush it from the organism.
- Uric acid is insoluable
and can be excreted as a paste requiring little water, though it is
metabolically expensive to produce.
- Urea, like uric acid, in
relatively non-toxic though require some water for excretion and energy
of the excretory system in humans:
-Removal of nitrogenous waste
Three main concepts in the function of
the nepheron (the functional unit of the kidney)
1) Pressure in the circulatory system
crudely filters certain solutes and water from the capillaries
(glomerulus) into the tubules of the nepheron. 20% of the blood
flow is diverted to the kidneys (What
percentage of blood flow is diverted to the lungs during on circulatory
What would this mean in terms of
loss if this filtrate was excreted from the body as is?
Would pressure filtration be very selective in terms of ions?
2) Both active transport and passive transport remove certain solutes
from the filtrate.
3) The loop structure (loop of Henle) travels though concentration
gradient resulting in osmotic re-absorption of water from the filtrate
tubules, concentrating urine. Blood flows in the capillaries
(vasa recta) in
the opposite direction of solute flow in the loop (countercurrent) also
aiding in water retention by preventing loss of NaCl from the medulla.
The Loop of Henle allows filtrate
to be concentrated twice. The descending loop is permeable to
water, thus concentrating filtrate. Sodium chloride is remove in
the ascending loop (at high energy cost); though concentration of the
filtrate decreases, so
has volume, so that even more water can be removed as filtrate
descends in the collecting duct (4-fold concentration compared to
concentration of the blood).