lecture 18 Flashcards
what are the four main functions of the excretory system
- regulate volume of the fluid in the body 2. maintain individual solutes (CA2+, NA+, H+) at appropriate concentrations 3. regulate solute concentration in extracellular fluid (osmolarity) 4. eliminate nitrogenous waste
an excretory systems ability to change ECF composition depends on
its ability to make a dilute or concentrate urine
ALL vertebrates can make a urine
less concentrated than the ECF, therefore concentrate the ECF (U/P<1)
kidneys of mammals and birds ONLY can also make urine
more concentrated urine than the ECF there fore can dilute the ECF via the kidneys (U/P>1)
what does u/p = 1 mean
150 mM, no net ECF concentration change, what you put in is what you take out
what does u/p > 1 mean
300 -> 150 mM ECF conc is decreased, more salt less water so you get rid of salt and keep h20
what does u/p < 1 mean
50 -> 150 mM ECF conc is increased water is more salt is less, you take out water and keep salt
what does the U and P stand for
urine and plasma
what i the functional unit of kidneys
nephrons
what do nephrons consist of
renal tubules and surrounding blood vessels
how is urine produced
by filtering blood plasma
where does ultrafiltration occur
glomerulus
after ultrafiltration, where does the plasma go
water and solutes are pushed into BOWMANS capsule by blood pressure
what do renal tubules do
they selectively secrete and reabsorb solutes and water to form urine
what do the proximal segments of vertebrate tubules do
they reabsorb salt water and nutrients back into blood while leaving toxins in the tubules
terrestrial animals that drink a lot of fresh water must produce
lots of volumes of dilute urine
the late tubules of ALL vertebrates can make urine with what ratio
u/p <1
diuresis
a state in which dilute urine is made to eliminate excess water and conserve salts
where does diuresis and antidiuresis occur
the distal/late tubules
in diuresis what happens in the kidneys
osmosis of water doesnt happen (means that water isnt reabsorbed) but active trasport of NaCI yes!
vertebrates in dry environments must conserve water by
producing very little urine that as very concentrated
the most concentrated urine that fish and amphibians can make is
u/p is equal to one
antidiuresis
the state in which concentrated urine is made to conserve water
how is antidiuresis achieved
by increasing water permeability (osmosis of water) in the distal tubules
distal tubules can add or remove what
water channels of aquaporins to become more or less permeable to water
what hormone regulated these aquaporins
ADH or antidiuretic hormone
why does body do all of this renal stuff
homeostasis
ADH is how we regulate
water and salt levels in our bodies
what kind of feedback is this renal stuff
negative
what happens if water level drops
ADH is released and kidneys absorb more water
what happens if water level rises
ADH is released less and kidneys reabsorb less water
diuresis has
low ADH so few aquaporins, dilute urine u/p<1
antidiuresis has
high ADH so more aquaporins , more conc urin u/p=1
how do mammals and birds get a u/p>1 4 steps
1.they use the loop of henle to create a concentration gradient in the medulla of the kidney 2.the collecting ducts pass through tissue that is increasingly high conc 4. resulting urine is more conc than plasma
what is the toxic byproduct of amino acid and protein metabolism
ammonia
what do fish do with ammonia
they have a bunch of water to dissolve it in so they keep the ammonia
what do mammals do with ammonia
they change it to urea
what do reptiles and birds do with ammonia
they change it to uric acid
what nitrogenous compounds are more energetically costly (most to less)
uric acid, urea, and ammonia
what nitrogenous compounds need more water (most to less)
ammonia, urea, uric acid
urine that exits the proximal tubules is
lower volume and same conc as plasma
urine that exits distal tubules is
influenced by homeostatic mechanisms to be more dilute or conc
