Nitrogenous excretion and osmoregulation Flashcards
How are excess amino acids dealt with as they cannot be stored
Cannot be stored
Some are transaminated (converted into a different amino acid
The rest are deaminated (removal of the amino group to form ammonia and ketoacids (respired by liver))
Ammonia is very toxic, must be removed
Removal of ammonia depends on organism
How do different organisms remove nitrogenous waste?
Aquatic animals, most bony fish Amine groups removed in ammonia Mammals, amphibians, some bony fish Amine groups removed in urea Birds, many reptiles, insects, seals Amine groups removed by uric acid
Solubility, amount of water needed to remove from body, toxicity and molecules of ATP needed to remove ammonia
V high
V large
High
0
Solubility, amount of water needed to remove from body, toxicity and molecules of ATP needed to remove urea
High
Medium
Medium
4
Solubility, amount of water needed to remove from body, toxicity and molecules of ATP needed to remove uric acid
V low
Very little
Low
8
Route of nitrogenous waste around nephron
Bowmans capsule Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting duct
Bowmans capsule
Closed end at start of nephron, cup shaped, surrounds mass of capillaries, podocytes
Proximal convoluted tubule
Series of loops surrounded by capillaries
Walls made of epithelial cells with microvilli
Loop of Henle
Loop capillary loop that extends from cortex into medulla and back again, surrounded by blood capillaries
Distal convoluted tubule
Series of loops, surrounded by blood vessels
Fewer than proximal CT
Collecting duct
Tube into which a no of distal CT empty
Lined by epithelial cells, become wider as it gets nearer to the pelvis into which it empties
Associated blood vessels in nephron
Afferent arteriole glomerulus Efferent arteiole Blood capillaries Venules
Location of the afferent arteriole
Branches off renal artery, supply nephron with blood
Enters Bowman’s capsule where it forms the glomerulus
Location of the glomerulus
Many branched knot of capillaries from which fluid is forced out of the blood
Glomerular capillaries recombine to form efferent arteriole
Location of the efferent arteriole
Blood vessels that leaves Bowman’s capsule
Smaller diameter than afferent arterioles so helps to keep pressure high in glomerulus
Carries blood away from the Bowman’s capsule and branches to form capillaries
Location of the blood capillaries
Concentrated network of capillaries that surrounds proximal CT, Loop of Henle and distal CT from where mineral salts, glucose and water are reabsorbed into blood
Capillaries merge into venules
Location of venules
Merge together to form renal vein
Ultrafiltration
Blood in afferent under high pressure
Efferent has a smaller diameter than afferent
Build up of hydrostatic pressure in glomerulus so water, glucose, mineral ions are squeezed out of capillary to form glomerular filtrate
Blood cells and proteins cannot pass into renal capsule since they are too big
Inner wall of Bowman’s capsule made of podocytes (prevent large molecules from entering the filtrate)
Epithelial cells on outer edge of capsule closely packed
Capillary endothelium is fenestrated (spaces up to 100nm wide)
How is glucose and water reabsorbed by the proximal convoluted tubule?
Na+ AT out of cells lining the proximal CT
Na+ conc is lowered in the cells, tendency for them to fac diff into epithelial cells
Na+ taken up by cotransport proteins, also carry glucose, amino acids or Cl-
Molecules or ions which have been cotransported then diffuse into blood
All glucose reabsorbed as well as other valuable molecules
Most water is reabsorbed in proximal CT (85%) as glucose and amino acids lowers the water potential so more water moves into the cells
How are the epithelial cells of the proximal CT adapted for reabsorption?
Microvilli, high SA for more cotransport proteins
Infoldings at base
Large nos of mitochondria for active transport of Na+ out of epithelial cell
Loop of Henle and gradients
Loop of Henle allows urine to be produced that has a lower water potential than the blood
LOH sets up gradient of Na+, and hence a gradient of water potential across the medulla, the highest concentration of ions is alongside the apex of the LOH
Descending limb properties
Narrow, thin wall, highly permeable to water
Na+ ==> desc limb
Ascending limb properties
Wider, thick wall, impermeable to water
Na+ <== asc limb
Process of absorption in the Loop of Henle
Na+ AT out of asc limb of LOH with ATP provided by the many mitochondria in cells making up the walls. Some Na+ diffuse into desc limb
Creates higher ion conc and lower water potential in medulla between 2 limbs. Water does not move out of the ascending limb as it has impermeable walls
Permeable walls of desc limb, water passes out by osmosis into interstitial space and into blood capillaries by osmosis and so is carried away, hence gradient of ions is not diluted
Filtrate progressively loses water as it moves down the desc limb, lowering water pot, lowest water pot at apex of loop
Distilled convoluted tubule, role, properties and permeability
Have microvilli and many mitochondria
Main role, make fine adjustments to water and salts that are absorbed (not in medulla so no conc grad)
Permeability affected by ADH by vesicle containing aquaporins to increase water flow into CD
Process of water absorption in the collecting duct
Ion conc increases down medulla
CD walls vary in permeability to water
As conc grad increases, amount of water recollected increases so the urine has a very low water potential
Osmoregulation
If there is a fall in water potential of blood, fall detected by osmoreceptors in hypothalamus
Osmoreceptor cells lose water by osmosis and shrink
Hypothalamus produces ADH
ADH passes to posterior pituitary gland where it is secreted into capillaries
ADH travels in blood to kidneys, increase permeability of cell surface membranes that make up DCT and CD walls
ADH binds to receptors on cell surface membrane of cells
Binding leads to activation of phosphorylase within cell
Causes aquaporin containing vesicles to move and fuse with cell surface membrane, making it more permeable
ADH also increases permeability of collecting duct to urea, moves out of CD, further lowering the water potential in the fluid around the duct
Therefore more water moves out of the CD by osmosis down water pot grad, re enters blood
ADH does not raise water potential of blood
Water from CD came from blood, will only prevent it from falling any lower
What happens when there is a rise in the water potential of the blood
Detected by osmoreceptors in hypothalamus
Nerve impulses to pituitary to reduce release of ADH
Less ADH leads to a decrease in permeability of membrane of cells lining collecting ducts to water and urea
Less water is reabsorbed from CD into blood
More dilute urine produced
Water pot of blood falls
Osmoreceptors detect fall in water pot of blood, cause pituitary to raise ADH back to normal levels
