Urinary System/Nitrogen Metabolism Flashcards
What is the purpose of the kidney?
Blood filtration and dialysis. Proteins, ions, nutrients and water are reabsorbed while waste products and limited amounts of water are excreted.
How does nephron anatomy differ between desert mammals, aquatic animals and reptiles?
Desert - long loop of Henle to concentrate urine
Aquatic - short loop of henle
Reptiles - No loop of henle
What are the different types of nephron and which animals have each type?
Juxtamedullary - mammals
Cortical - reptiles
Birds have both
Where is urine concentrated in reptiles?
Same make up as the blood when it leaves the kidney so it must be concentrated distally in the bladder/cloaca/GIT.
What are the different types of nitrogenous secretion and the names for them?
Ammonotelic - ammonia
Ureotelic - urea
Uricotelic - uric acid
What are the advantages/dissadvantages to each type?
ammonia is highly toxic and results in high water loss but requires little energy to excrete.
Uric acid is the least toxic and most water sparing but requires high amounts of energy to excrete.
Urea excretion is inbetween the two.
How does urea and uric acid excretion differ?
Urea relies on glomerular filtration so is passive whereas uric acid relies on tubular secretion therefore requiring more energy.
Which animals can vary their method of N excretion?
Birds and aquatic reptiles.
What is the path of urine in amphibians?
Kidney-cloaca-bladder therefore it is not sterile.
How do aquatic and terrestrial amphibians excrete their nitrogenous waste.
Aquatic - gills, skin/kidney ammonia
Terrestrial - ammonia converted to urea in the liver and stored in the bladder
How do reptiles deal with urinary waste?
Only some lizards and chelonians have a bladder. These species have an osmotically permeable bladder. Other species must reflux urine into the distal colon for water reabsorption.
What are the main methods reptiles conserve water?
a) Terrestrial species can secrete nitrogenous waste as uric acid. This is insoluble so means water loss is minimal. It can lead to gout in dehydrated/renal failure reptiles.
B)Cloaca/colon/bladder can reabsorb water by actively transporting NA+ across their membranes and therefore water follows passively
c) Reptilian ADH constricts afferent arterioles which decreases GFR - desert species can tolerate high salt loads.
d) Can secrete salts through salt glands
e) there is a dual blood supply to the kidney. One goes direct to the tubules so uric acid secretion can occur without water loss.
How does kidney structure vary in birds?
Those from arid environments will have greater medullary tissue and therfore more juxtaglomerular nephrons
How do birds remove their nitrogenous waste?
They are uricotelic.
Are there any more water conserving tactics of birds?
Salt glands, marine species can even drink seawater!
