Sodium and water transport along the nephron

Question 1

How many moles of sodium are filtered in the Bowman’s capsule a day?

Answer 1

2500 mmoles

Question 2

How many moles of sodium are excreted a day?

Answer 2

150 mmol

Question 3

How many litres of blood are filtered a day?

Answer 3

180 L

Question 4

How many litres of urine are produced a day?

Answer 4

1.5 L

Question 5

What happens to the sodium and water that are not excreted?

Answer 5

Reabsorbed in the tubules

Question 6

What are the sites of reabsorption in the tubule?

Answer 6

PCT -> PST -> DTLLH -> TALLH -> DCT -> Collecting duct

Question 7

What reabsorption happens in the PCT?

Answer 7

50% water and 50% sodium is reabsorbed Isotonic

Question 8

What reabsorption happens in the PST?

Answer 8

20% water and 20% sodium Isotonic

Question 9

What reabsorption happens in the DTLLH?

Answer 9

5% water

Question 10

What reabsorption happens in the ATLLH?

Answer 10

20% sodium

Question 11

What reabsorption happens in the DCT?

Answer 11

5% sodium

Question 12

What reabsorption happens in the collecting duct?

Answer 12

4% sodium 19% water

Question 13

In which parts of the tubule is reabsorption isotonic?

Answer 13

PCT and PST

Question 14

Which parts of the tubule are impermeable to water?

Answer 14

TALLH and DCT

Question 15

What separates the lumen and interstitial fluid in a renal epithelial cell?

Answer 15

Tight junction

Question 16

What controls most reabsorption in the renal epithelial cells?

Answer 16

Sodium movement

Question 17

What controls movement of sodium in and out of renal epithelial cells?

Answer 17

Sodium potassium pump

Question 18

What does the lumen refer to?

Answer 18

The tubule

Question 19

What does the interstitial milieu refer to?

Answer 19

The blood

Question 20

What substances are reabsorbed in the PCT along with sodium?

Answer 20

Glucose Amino acids Phosphate Chlorine Protons Water

Question 21

What type of transporters control the movement of these molecules along with sodium?

Answer 21

Most are symporters Protons - sodium - proton antiporter Chlorine - channel Water - aquaporins

Question 22

What feature makes cells permeable to water?

Answer 22

Presence of aquaporins

Question 23

What is the role of the TDLLH in controlling salt and water reabsorption?

Answer 23

Mainly control equilibration of sodium and water via channels and aquaporins

Question 24

Is the process of reabsorption in the TALLH active?

Answer 24

Yes - requires lots of ATP

Question 25

What type of cotransporter is uniquely present on epithelial cells of the TALLH?

Answer 25

2-chloride, potassium, sodium cotransporter

Question 26

What does the potassium transporter on TALLH epithelial cells do?

Answer 26

Recycle potassium

Question 27

Why is a positive transepithelial potential created in TALLH epithelial cells?

Answer 27

Chlorine is transported into the blood - 2 chlorines for every sodium Transporting more chlorine ions than sodium = positive transepithelial potential

Question 28

What does this positive transepithelial potential do?

Answer 28

Transports additional chlorine, sodium, potassium and calcium through a paracellular shunt

Question 29

Which cells of the collecting duct regulate water and sodium reabsorption?

Answer 29

ENaC - epithelial sodium channel ROMK - Renal Outer Medullary Potassium Channel

Question 30

Is water and sodium permeability regulated in collecting duct epithelial cells?

Answer 30

Yes

Question 31

What is the name of the cells in the colllecting duct that regulate sodium and water reabsorption?

Answer 31

Principal cells

Question 32

How do ENaC and ROMK work to control sodium and potassium concentration?

Answer 32

Sodium reabsorption is paralleled by potassium excretion into the urine

Question 33

How does the ability to regulate the expression of ROMK and ENaC affect the function of the collecting ducts?

Answer 33

Allows Potassium excretion to be regulated by the cells Sodium concentration in the urine to be regulated

Question 34

What is Tmax?

Answer 34

Point at which increases in concentration of a molecule does not result in an increase in the movement of a substance across a membrane

Question 35

What is the Tmax of glucose?

Answer 35

10 mmol/L

Question 36

What happens if there is glucose in urine?

Answer 36

Osmotic diuresis Dehydration

Question 37

What is glycosuria?

Answer 37

Glucose in the urine

Question 38

What are two conditions that can lead to glycosuria?

Answer 38

Renal glycosuria - defective uptake in PCT due to mutation in SGLT2 (gene encoding for sodium glucose cotransporter) Diabetes mellitus - plasma glucose is very high, exceeds transport capacity of nephrons

Question 39

What are names of diseases affecting salt handling?

Answer 39

Bartter's syndrome EAST syndrome Pseudohypoaldosteronism Gitelman's syndrome Liddle syndrome

Question 40

What is Barterr's syndrome?

Answer 40

Condition that affects the 2 major ion transporters of TALLH NKCC2 ROMK - recycling potassium pathway ClC-K

Question 41

What is EAST syndrome?

Answer 41

Affects basolateral potassium channels in the DCT

Question 42

What is Gitelman's syndrome?

Answer 42

Affects NaCl cotransporters in the DCT

Question 43

What is Pseudohypoaldosteronism?

Answer 43

Gain of function of ENaC in the collecting duct

Question 44

What is Liddle syndrome?

Answer 44

Loss of function of ENaC in the collecting duct

Question 45

What are diseases affecting water handling?

Answer 45

Nephrogenic Central Nephrogenic syndrome of innapropriate antidiuresis Diabetes insipidus

Question 46

What is the reason for central source affecting water handling?

Answer 46

Low secretion of ADH from pituitary Due to pituitary tumours or due to post surgery effects

Question 47

How does diabetes insipidus affect water handling?

Answer 47

Large amounts of severly diluted urine is produced Due to impaired glucose metabolism

Question 48

How does nephrogenic syndrome of innapropriate antidiuresis affect water handling?

Answer 48

Gain of function of V2 ADH receptors

Question 49

How does nephrogenic syndrome affect water handling?

Answer 49

Collecting ducts do not respond to ADH

Question 50

What does a generalised renal epithelial cell look like?

Answer 50

Question 51

What does a PCT epithelial cell look like?

Answer 51

Question 52

What does a TALLH epithelial cell look like?

Answer 52

Question 53

What does a DCT epithelial cell look like?

Answer 53

Question 54

What does a principal cell look like?

Answer 54