L18

Question 1

what % of the body is water

Answer 1

The body is around 60% water (60% - men; 55% - women)

Question 2

what is the most important function of the kidney

Answer 2

Water homeostasis is therefore one of the most important functions of the kidneys.

Question 3

what is the kidneys role in water homeostasis

Answer 3

Any increases in body water (decreased osmolarity) - need to increase excretion of water by kidneys eg in a high water iet we will urinate a lot more water

Any decreases in body water (increased osmolarity) - need increase reabsorption of water by the kidneys

Question 4

how is body water/osmolarity monitored (what reflex)

and what detects that change

Answer 4

This is monitored by the theist reflex which occurs when the body sensors changes in the body.

This is detected by osmoreceptors and baroreceptors (BP).

Question 5

where are the osmoreceptors located

Answer 5

In the kidney the juxtergolmerior apporatis and the maculardencer cells have osmoreceptor function

Hypothalamus also has osmoreceptors

Question 6

where are the baroreceptors located

Answer 6

Baroreceptors in the the carotid arch and in the aortic sinus

Question 7

in water homeostasis, water intake = water output. what does this mean in terms of net flow

Answer 7

net flow = 0 (normally)

Question 8

what factors can effect water homeostasis

Answer 8

menstruation, vomiting and diarrhea

Question 9

what is the equation of water excretion in the nephron

Answer 9

H2O excreatin = H2O filtered - H2O reabsorbed

Question 10

Which segments of the nephron ARE permeable to H2O?

Answer 10

Proximal Tubule

Thin Descending Limb of Loop of Henle

Late Distal Tubule*

Collecting Duct*

• Under influence of Vasopressin (AVP)/ Antidiuretic Hormone (ADH)

Question 11

Which segments of the nephron are NOT

permeable to H2O?

Answer 11

Ascending Limb of Loop of Henle (Thin and Thick)

Early Distal Tubule (there is still debate about this)

Question 12

Which segments of the nephron ARE permeable to H2O under the influence of a hormone (and what hormone is it)

Answer 12

Late Distal Tubule*

Collecting Duct*

• Under influence of Vasopressin (AVP)/ Antidiuretic Hormone (ADH)

Question 13

Which of the following statements is TRUE?

A. 65% of a male’s body is composed of water.

B. Normally, a person has 4 litres of plasma in their blood.

C. The net water intake and water output of person per day is 0.

D. A person can live without water for 3 months.

Answer 13

A. should be 60%

B. should be 3L

C is correct

Question 14

what is the proximal tubules mechanism for water movement

Answer 14

Moves through peri and transcellular pathway

Question 15

what is the Membrane shuttle hypothesis and freeze fracture technique

(the discovery of how water was reabsorbed)

Answer 15

It was assumed that water ‘leaked’ through the cell membrane.
But the very rapid movement of water through some cells was not explained by this theory (too fast to be osmosis)

Membrane shuttle hypothesis – James Wade (1980). he used Freeze fracture microscopy. This is where you froze membranes and then snapped them apart to see what was in them. He found vesicles moving towards a membrane

Presence of water channels (aquaporins) in cells discovered by US
scientist Peter Agre and his team (1988).

Question 16

what are aquaporins

Answer 16

A family of plasma membrane proteins that form channels permitting a high rate of water flow (Higher rate then just by simple diffusion).

Question 17

where are AQP found

Answer 17

Found in organisms as diverse as bacteria, plants and animals.

Question 18

how do AQP allow for water movement

Answer 18

Specific for H2O, single-file movement through pore.

Question 19

what are AQP impermeable to

how many different types of AQP are there

Answer 19

Impermeable to charged species. Therefore some of the 13 different AQ let other uncharged ions through as well

Question 20

how many liters of water does the proximal tubule receive per day

Answer 20

Receives 180 L H2O per day

same as daily filtered load

Question 21

how many liters of water does the proximal tubule reabsorbe per day

Answer 21

Reabsorbs 2/3 of this amount (120 L/day)

67% of the filtered load of H2O

Question 22

what kind of epithelium is the proximal tubule made up of and what does that allow for

Answer 22

Leaky absorptive epithelium

Paracellular and Transcellular movement of H2O

Question 23

what kind of AQP is located in the proximal tubule

Answer 23

Aquaporin 1 (AQP1)
Transcellular movement of water

Present in both apical and basolateral membranes

Question 24

how many liters of water does the thin descending limbs of henle receive per day

Answer 24

Receives 60 L H2O per day

Question 25

what kind of epithelium is in the thin descending limb

Answer 25

Leaky absorptive epithelial cells

Question 26

how much water does the thin descending limb reabsorb per day

Answer 26

Leaky absorptive epithelial cells of Thin Descending Limbs reabsorb about 30 L of H2O per day (16% of the filtered load of H2O)

Question 27

how does reabsorption of water occur in the thin descending limb

Answer 27

Reabsorption occurs via AQP1 in both apical | and basolateral membranes

Question 28

how much water does the thin and thick ASCending limbs reabsorbe

Answer 28

NONE!! they are impermeable to water

Question 29

what do the thick and thin ascending libs play an important role in

Answer 29

the concentration of urine

Question 30

how many liters of water does the late distal tubule receive per day

Answer 30

Receives 30 L H2O per day

Question 31

what kind of epithelium is located in the late distal tubule

Answer 31

Tight absorptive epithelium

Question 32

how much water does the late distal tubule reabsorbe per day

Answer 32

Tight absorptive epithelium of Late Distal Tubule reabsorbs 10 – 20 L H2O each day (~5-10% of the filtered load of H2O)

Question 33

in the late distal tubule what is water reabsorption regulated by

Answer 33

ADH and aquaporin 2,3,4 Reabsorption regulated by vasopressin (AVP) also called antidiuretic hormone (ADH) The distribution of AQPs is the same as the Collecting Duct (AQP2 in apical membrane and AQP 3 and 4 in basolateral)

Question 34

what AQP are in late distal tubule and collecting duct. where are they located

Answer 34

AQP2 is associated with apical membrane AQP3 and AQP4 are associated with basolateral membrane

Question 35

how many liters of water does the collecting duct receive per day

Answer 35

Receives 10 - 20 L H2O per day

Question 36

what kind of epithelium is located in the collecting duct

Answer 36

Tight absorptive epithelial cells

Question 37

how much water does the collecting duct reabsorbe per day

Answer 37

Tight absorptive epithelial cells of the Collecting Ducts reabsorb about 15 L per day – ‘fine-tuning’ (~8% of the filtered load of H2O)

Question 38

what is water reabsorption regulated by in the collecting duct

Answer 38

Water reabsorption is regulated by vasopressin (AVP) also called antidiuretic hormone (ADH)* also AQP 2,3,4

Question 39

what are the 2 major cell types in the collecting duct

Answer 39

Principal cells (NaCL and K transport Intercalated cells is for H+ and K+ balance

Question 40

If you had diabetes you would absorbed very little water in what area of the nephron

Answer 40

collecting duct

Question 41

order the AQP from smallest to largest

Answer 41

AQP1,2,3,4

Question 42

how many membrane domains do AQP have

Answer 42

6

Question 43

where are the different AQP located in the nephron

Answer 43

1 = PT and TDL 2 and 3 = LDT and CD 4 = LDT and CD (and PT in mise)

Question 44

what membranes are the AQP located in

Answer 44

1= apical and basolateral 2 = apical 3 and 4 = basolateral

Question 45

is AQP 1 regulated by ADH

Answer 45

no

Question 46

which APQ does ADH have short and long term effects on

Answer 46

2 = short and long term 3 = short term (mRNA) and long term 4 = short term (mRNA) but NOT long term

Question 47

Which of the following statements is TRUE? A. Aquaporins are only found in animals. B. AQP2 is located on the apical membrane of Thick Ascending limb cells. C. AQP3 is located in the basolateral membrane of collecting duct cells. D. An osmotic gradient is NOT required for water movement

Answer 47

A. found in lots of things B. ascending limbs are NOT permeable to water C is correct

Question 48

where is ADH produced

Answer 48

Produced in hypothalamus - paraventricular nuclei - supraoptic nuclei

Question 49

what stimulates ADH to be released

Answer 49

Increased body osmolarity (osmoreceptors) Decreased plasma volume (baroreceptor reflex)

Question 50

where is ADH stored and released from

Answer 50

Stored and released from the posterior pituitary

Question 51

what kind of hormone is ADH/AVP

Answer 51

a peptide hormone therefore it is hydrophilic and will need to bind to a membrane receptor

Question 52

where does ADH act on the nephron

Answer 52

• Late Distal Tubule and the Collecting Duct

Question 53

what is the name of and where is the vasopressin receptor located

Answer 53

• vasopressin binds to V2 receptor on basolateral membrane

Question 54

once ADH has bound to the V2 receptor what happens intracellularly

Answer 54

• activates Adenylate Cyclase which increases cAMP levels cAMP activates Protein Kinase A (PKA) phosphorylation leads to sub-apical AQP2 vesicles moving to membrane via exocytosis • increased Apical membrane H2O permeability THEREFORE ONLY AQP2 IS REGULATED BY ADH!!!!!

Question 55

how long does it take to get significantly more AQP into the membrane

Answer 55

Within 45 min then you can get more vesicles in the apical membrane

Question 56

what does ADH regulate

Answer 56

ONLY AQP2

Question 57

make sure you know the membrane shuttle hypothesis

Answer 57

pores are sitting in vesicles under the membrane and when they get phosphorylated they move into it

Question 58

The amount of AQP2 can be correlated with certain physiological conditions What would happen to water reabsorption if there were too few AQP2 channels?

Answer 58

diabetes

Question 59

when could you get too many AQP2 channels would lead to?

Answer 59

Upregulated in congestive heart failure When you are pregnant you have an increase in weight gain and water inside the body

Question 60

what is Diabetes Insipidus (DI)

Answer 60

Disease characterised by excessive urination 20-30L of urine per day

Question 61

there are 2 types of Diabetes Insipidus (DI). what are they

Answer 61

Neurogenic (Central) Diabetes Insipidus Nephrogenic Diabetes Insipidus (Kidney)

Question 62

what is Neurogenic (Central) Diabetes Insipidus

Answer 62

Failure to produce or secrete vasopressin to do with the release from the posterior pituitary. you still make in/is sensed that you need to make it in the hypothalamus but for some reason it is never released

Question 63

what is Nephrogenic Diabetes Insipidus (Kidney)

Answer 63

could be because of a ... Mutation of AQP2 channel Mutation of V2 receptor

Question 64

what is bulk reabsorption of water carried out by

Answer 64

AQP1 in the PT

Question 65

fine tuning of water reabsorption is carried out by...

Answer 65

AQP2,3,4 in the LDT and CD