Nitrogenous excretion and osmoregulation

Question 1

How are excess amino acids dealt with as they cannot be stored

Answer 1

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

Question 2

How do different organisms remove nitrogenous waste?

Answer 2

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

Question 3

Solubility, amount of water needed to remove from body, toxicity and molecules of ATP needed to remove ammonia

Answer 3

V high
V large
High
0

Question 4

Solubility, amount of water needed to remove from body, toxicity and molecules of ATP needed to remove urea

Answer 4

High
Medium
Medium
4

Question 5

Solubility, amount of water needed to remove from body, toxicity and molecules of ATP needed to remove uric acid

Answer 5

V low
Very little
Low
8

Question 6

Route of nitrogenous waste around nephron

Answer 6

Bowmans capsule
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct

Question 7

Bowmans capsule

Answer 7

Closed end at start of nephron, cup shaped, surrounds mass of capillaries, podocytes

Question 8

Proximal convoluted tubule

Answer 8

Series of loops surrounded by capillaries

Walls made of epithelial cells with microvilli

Question 9

Loop of Henle

Answer 9

Loop capillary loop that extends from cortex into medulla and back again, surrounded by blood capillaries

Question 10

Distal convoluted tubule

Answer 10

Series of loops, surrounded by blood vessels

Fewer than proximal CT

Question 11

Collecting duct

Answer 11

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

Question 12

Associated blood vessels in nephron

Answer 12

Afferent arteriole
glomerulus
Efferent arteiole
Blood capillaries
Venules

Question 13

Location of the afferent arteriole

Answer 13

Branches off renal artery, supply nephron with blood

Enters Bowman’s capsule where it forms the glomerulus

Question 14

Location of the glomerulus

Answer 14

Many branched knot of capillaries from which fluid is forced out of the blood
Glomerular capillaries recombine to form efferent arteriole

Question 15

Location of the efferent arteriole

Answer 15

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

Question 16

Location of the blood capillaries

Answer 16

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

Question 17

Location of venules

Answer 17

Merge together to form renal vein

Question 18

Ultrafiltration

Answer 18

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)

Question 19

How is glucose and water reabsorbed by the proximal convoluted tubule?

Answer 19

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

Question 20

How are the epithelial cells of the proximal CT adapted for reabsorption?

Answer 20

Microvilli, high SA for more cotransport proteins
Infoldings at base
Large nos of mitochondria for active transport of Na+ out of epithelial cell

Question 21

Loop of Henle and gradients

Answer 21

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

Question 22

Descending limb properties

Answer 22

Narrow, thin wall, highly permeable to water

Na+ ==> desc limb

Question 23

Ascending limb properties

Answer 23

Wider, thick wall, impermeable to water

Na+ <== asc limb

Question 24

Process of absorption in the Loop of Henle

Answer 24

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

Question 25

Distilled convoluted tubule, role, properties and permeability

Answer 25

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

Question 26

Process of water absorption in the collecting duct

Answer 26

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

Question 27

Osmoregulation

Answer 27

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

Question 28

ADH does not raise water potential of blood

Answer 28

Water from CD came from blood, will only prevent it from falling any lower

Question 29

What happens when there is a rise in the water potential of the blood

Answer 29

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