6.4.3 control of blood water potential

Question 1

what is the function of the nephron?

Answer 1

filters the blood to remove waste + selectively reabsorbs useful substances back into the blood

Question 1

what does urine contain?

Answer 1

water, dissolved salts, urea, other dissolved substances

Question 2

what is the first stage of filtering & reabsorption?

Answer 2

• ultrafiltration occurs due to high hydrostatic pressure.
• water & small molecules are forced out of the glomerulus capillaries into the renal capsule

Question 3

what is the second stage of filtering & reabsorption?

Answer 3

selective reabsorption occurs in the PCT

Question 4

what is the third and fourth stage of filtering & reabsorption?

Answer 4

Loop of Henle maintains a sodium ion gradient so water can be reabsorbed by the blood

Question 5

what is the fifth and six stage of filtering & reabsorption?

Answer 5

• water moves out of the DCT + collecting duct to return black to the blood.
• collecting duct carries remaining liquid to the ureter

Question 6

in ultrafiltration, how does blood enter the nephron?

Answer 6

through the afferent arteriole

Question 7

what does the afferent arteriole split int, and what does this cause?

Answer 7

smaller capillaries - causes a high hydrostatic pressure of the blood

Question 8

what is forced into the glomerulus during ultrafiltration?

Answer 8

water, glucose, amino acids, minerals and other small molecules

Question 9

what remains in the blood during ultrafiltration, and how does this leave the nephron?

Answer 9

• large proteins and blood cells are too big to pass through gaps in the capillary endothelium, so remain in blood
• leaves via the efferent arteriole

Question 10

what is selective reabsorption and where does it occur?

Answer 10

when most of the glomerular filtrate is reabsorbed back into the blood - occurs in the PCT

glucose reabsobred

Question 11

Adaptations of the PCT for selective reabsorption x3

Answer 11

Microvilli / folded membrane provide large surface area;

Many channel/carrier proteins for facilitated diffusion;

Many carrier proteins for active transport / sodium-potassium pumps;

Many co-transport proteins (e.g., for sodium-glucose);

Many mitochondria produce ATP for active transport;

Many ribosomes to produce transport proteins.

Question 12

first stage of selective reabsorption:

Answer 12

as Na+ ions are actively transported out into blood (to allow for cotransport)
concentration of sodium ions in PCT cell decreases,

creating low conc in

Question 13

second stage of selective reabsorption:

Answer 13

• due to the conc gradient, Na+ ions diffuse down the gradient in from the lumen

into PCT
by FD bring glucose with it

Question 14

third stage of selective reabsorption:

Answer 14

• glucose can then diffuse from the PCT epithelial cell into the bloodstream.

Question 15

is all the glucose reabsorbed in selective reabsorption?

Answer 15

YES

Question 16

why is a Na+ gradient maintained in the Loop of Henle?

Answer 16

to enable the reabsorption of water (into blood)

Question 17

ascending limb of the loop of henle:

Answer 17

thicker walls
- walls are impermeable to water

Question 18

descending limb of the loop of henle:

Answer 18

• thinner walls
• walls are permeable to water

Question 19

what is the first stage of maintaining a Na+ gradient in the Loop of Henle?

Answer 19

• mitochondria in the walls of the cell provides energy to actively transport Na+ ions out of the ascending limb

Question 20

what is the second stage of maintaining a Na+ gradient in the Loop of Henle?

Answer 20

• the accumulation of Na+ ions outside the nephron in the medulla lowers the water potential

Question 21

what is the third stage of maintaining a Na+ gradient in the Loop of Henle?

Answer 21

• water diffuses out by osmosis into the interstitial space
• and then into the blood capillaries.

Question 22

what is the fourth stage of maintaining a Na+ gradient in the Loop of Henle?

Answer 22

• at the base of the ascending limb, some Na+ ions are transported out by diffusion
• creating a dilute solution

Question 23

why can water be reabsorbed at the DCT and the collecting duct?

Answer 23

• all Na+ ions have been actively transported out of the PCT
• when the filtrate reaches the PCT it is very dilute
• filtrate moves into the DCT and collecting duct
• therefore more water diffuses out of the DCT and collecting duct

Question 24

Describe how ultrafiltration occurs in a glomerulus. (3)

Answer 24

- high blood/hydrostatic pressure - small substances pass through - water and glucose - through small gaps in the capillary endothelium

Question 25

Describe how urea is removed from the blood. (2)

Answer 25

- hydrostatic pressure - causes ultrafiltration - through basement membrane

Question 26

Explain how urea is concentrated in the filtrate. (3)

Answer 26

- water reabsorbed by osmosis - at the DCT/CD - active transport of ions creates a gradient

Question 27

The urine of a non-diabetic person does not contain glucose. Explain why. (2)

Answer 27

- Leaves the blood at kidney (Start) - reabsorbed into blood from kidney tubule (end)

Question 28

If the glomerular filtrate of a diabetic person contains a high concentration of glucose, he produces a larger volume of urine. Explain why. (3)

Answer 28

Glucose in filtrate lowers water potential - lower wp gradient - less water reabsorbed by osmosis

Question 29

what is negative feedback?

Answer 29

mechanisms to restore any deviations from normal in a system back to its original state

Question 30

what can cause blood to have too LOW water potential?

Answer 30

- too much sweating - not drinking enough water - too salty food

Question 31

what is the corrective mechanism for blood with a LOW water potential?

Answer 31

- more water is reabsorbed by osmosis - urine is more concentrated

Question 32

what can cause blood to have too HIGH water potential?

Answer 32

- drinking too much water - not eating enough salt

Question 33

what is the corrective mechanism for blood with a HIGH water potential?

Answer 33

- less water is reabsorbed by osmosis - urine is more dilute

Question 34

what is the role of the hypothalamus + posteriour pituitary gland in maintaining blood water potential?

Answer 34

- changes in wp in the blood are detected by osmoreceptors found in the hypothalamus

Question 35

what happens to osmoreceptors if the wp of blood is too LOW?

Answer 35

- water leaves the osmoreceptors by osmosis and they shrivel - stimulates the hypothalamus to produce more ADH

Question 36

what happens to osmoreceptors if the wp of blood is too HIGH?

Answer 36

- water enters the osmoreceptors by osmosis - stimulates hypothalamus to produce less ADH

Question 37

what does ADH do?

Answer 37

- causes an increase in the permeability of the walls of the collecting duct and the DCT - more water leaves the nephron and is reabsorbed into the blood

Question 38

what are aquaporins?

Answer 38

channel proteins for water to pass through

Question 39

what does ADH do to aquaporins?

Answer 39

- binds to them - activating a phosphorylase enzyme in cells

Question 40

what does phosphorylase do?

Answer 40

- causes the vesicles containing the aquaporins to fuse with the cell membrane - meaning more aquaporins embed in cell membrane more = more water leaves = reasbsorbed

Question 41

with more aquaporins in the cell membrane...

Answer 41

more water leaves the DCT and collecting duct, and is reabsorbed into the blood.

Question 42

in osmoregulation, if the wp is too high, what happens first?

Answer 42

detected by osmoreceptors in hypothalamus

Question 43

n osmoregulation, if the wp is too high, what happens once osmoreceptors detect increase?

Answer 43

hypothalamus releases less ADH

Question 44

in osmoregulation, if the wp is too high, what happens once the hypothalamus releases less ADH?

Answer 44

DCT and collecting duct walls become less permeable to water (less to pass through)

Question 45

in osmoregulation, if the wp is too high, what is the urine like?

Answer 45

higher volume and more dilute

Question 46

in osmoregulation, if the wp is too low, what happens first?

Answer 46

osmoreceptors in hypothalamus detect decrease

Question 47

in osmoregulation, if the wp is too low, what happens once the osmoreceptors have detected the decrease?

Answer 47

- hypothalamus releases more ADH - which is released into the blood by the posterior pituitary gland

Question 48

in osmoregulation, if the wp is too low, what happens when more ADH has been released?

Answer 48

DCT and collecting duct walls become more permeable to water

Question 49

in osmoregulation, if the wp is too low, at the end

Answer 49

what happens when wall become less permeable? - - more H20 is reabsorbed - urine is more concentrated and is a lower volume

Question 50

Give the location of osmoreceptors in the body of a mammal. (1)

Answer 50

hypothalamus

Question 51

When a person is dehydrated, the cell volume of an osmoreceptor decreases. Explain why. (2)

Answer 51

water potential of blood will decrease - water moves from osmoreceptor into blood by osmosis

Question 52

Stimulation of osmoreceptors can lead to secretion of the hormone ADH. Describe and explain how the secretion of ADH affects urine produced by the kidneys. (4)

Answer 52

- Permeability of membrane to water is increased - more water is absorbed from the collecting duct - smaller volume of urine - urine becomes more concentrated

Question 53

Explain how urea is concentrated in the filtrate. (3)

Answer 53

- water reabsorbed by osmosis - at the DCT/CD - active transport of ions creates a gradient

Question 54

what is osmoregulation

Answer 54

control of the water potential of the blood

Question 55

Explain the role of ADH in osmoregulation.

Answer 55

1- Makes cells lining collecting duct and DCT more permeable to water: * Binds to receptor → activates phosphorylase → vesicles with aquaporins on membrane fuse with cell-surface membrane. 2- Makes cells lining collecting duct and ACT more permeable to urea: * water potential in interstitial fluid decreases. * more water reabsorbed = more concentrated urine.

Question 56

Explain how ADH is specific to its receptor.

Answer 56

ADH has a specific tertiary structure; Which is complementary to its receptor

Question 57

decrease in blood pressure stimulates the release of ADH. Give the location of the receptors that detect a decrease in blood pressure and explain how the release of ADH will affect blood pressure.

Answer 57

Detected by osmoreceptors in aorta/carotid artery/sinus; ADH increases water reabsorption in kidney; Blood volume and pressure increase or return to normal.

Question 58

Where is ADH released from?

Answer 58

Posterior pituitary.

Question 59

Symptoms of ADH deficiency?

Answer 59

Dehydration/thirst; Frequent urination; Dilute urine.

Question 60

 Describe the effect of ADH on the collecting ducts in kidneys. [3 marks]

Answer 60

Stimulates aquaporins to membrane; Increases water permeability; more Water reabsorbed by osmosis.

Question 61

describe how ultrafiltration occurs in glamorous (3)

Answer 61

  High hydrostatic pressure; glucose and amino acids pass out Through small pores capillary endothelium; And through the capillary basement membrane;

Question 62

 Scientists investigated the relationship between the thickness of the kidney medulla of different species of mammals and the concentration of their urine. The graph shows their results. Explain the pattern shown by the results in the graph above

Answer 62

 Thicker medulla means a longer loop of Henle The longer the loop of Henle means increase in sodium ion concentration in medulla OR (The longer the loop of Henle means) sodium ion gradient maintained for longer (in medulla) OR The longer the loop of Henle means more sodium ions are moved out into medulla 3.   (Therefore) water potential gradient maintained (for longer), so more water (re)absorbed (from loop and collecting duct); OR More water is (re)absorbed from the loop (of Henle) / collecting duct by osmosis;

Question 63

thicker medulla means

Answer 63

longer loop of henle

Question 64

more than 99% of bio mole are reabsorbed from filtrate in PCT. Despite this the conc of fluid in this tubule remains constant. explain why

Answer 64

water is also reabsorbed

Question 65

explain the shape of the curve of the loop of hence

Answer 65

Concentration rises in descending limb because sodium ions enter and water lost; 2.      Concentration falls in ascending limb because sodium ions (and chloride) ions actively removed; 3.      But water remains (in ascending limb) because its walls are impermeable (to water). 3

Question 66

what is the evidence in the graph that this person was sectrating ADH. explain

Answer 66

(c)     1.      Concentration rises in collecting duct because it loses water by osmosis; 2.      ADH increases permeability (of walls of collecting duct) to water.

Question 67

Creatinine is a breakdown product of creatine found in muscle tissues. Apart from age and gender, give two factors that could affect the concentration of creatinine in the blood.

Answer 67

Muscle / body mass Ethnicity Exercise Kidney disease