7 Sodium, Chloride and Water along the Nephron

Question 1

In simple terms, how does the kidney maintain the volume of ECF within a very narrow margin?

Answer 1

Regulating excretion of sodium and chloride ions

Question 2

What is the ‘sodium ion balance’?

Answer 2

Matching process- kidneys balancing amount of sodium excretion and amount of sodium ingestion (amount NOT concentration)

(Glomerular tubular balance)

Question 3

What happens within the body if the sodium ion content of the ECF increases? (patient in positive balance)

Answer 3

Increase in ECF volume (water from nephron drawn out), blood volume increase, blood pressure increase, oedema may follow

Question 4

What happens within the body if the sodium ion content of the ECF decreases? (patient in negative balance)

Answer 4

Water remains in nephron, ECF volume decreases, Blood volume decreases, blood pressure decreases

Question 5

What is natriuresis?

Answer 5

excretion of sodium in the urine

Question 6

A decrease in filling of the pulmonary vascualture and cardiac atria increases sympathetic nerve activity and causes ADH secretion and therefore more water uptake. What causes the increase in sympathetic nerve activity?

Answer 6

Low- pressure Baroreceptors in atria and pulmonary vascualture

Send signals to brainstem via vagus nerve- modulates sympathetic nerve outflow

Question 7

What % change in pressure in the blood vessels is required to evoke a response (from baroreceptors)?

Answer 7

5-10% pressure change

Question 8

What is the bainbridge reflex?

(More important than baroreceptor reflex when blood volume raised, less important when blood volume= diminished)

Answer 8

Increases in right atrial pressure increases HR

High pressure baroreceptors- arterial side- (carotid sinus and aortic arch) respond to pressure

Send impulses via afferent fibres of:

• Vagus nerve
• Glossopharyngeal nerve

Decrease in BP increases sympathetic nerve activity and secretion of ADH

Question 9

Ingestion of sodium daily varies between what range (usually)?

Answer 9

0.5 g/d and 20-25 g/d

Question 10

Why is it important that we change the amount of sodium in ECF (eg blood plasma) rather than the amount of water?

Answer 10

Because changing the amount of water would change plasma osmolarity

Question 11

What’s the difference between transcellular and paracellular absorption?

Answer 11

Transcellular: through cell

Paracellular: between (next to) cell

Question 12

Name a transporter which is found on the apical membrane at each of these segments in the tubule within the kidney:

• Proximal convoluted tuble
• Loop of Henle
• Early distal convoluted tubule
• Late distal convoluted tubule and Collecting Duct

Answer 12

Question 13

Where in the nephron will we not find aquaporin channels? Why?

Answer 13

• Ascending limb of loop of henle
• Distal convoluted tubule

Regions do not absorb water

Question 14

What are the early and late segments of the proximal convoluted tubules also called?

Answer 14

Early: S1

Late: S2

Question 15

Why is it that the peritubular capillaries and the efferent arterial have a high potential for reabsorption of filtrate?

Answer 15

High oncotic pressure as 20% filtered out but still proteins and large molecules

Question 16

Name the important transporter that can be found on the basement membrane in S1 in the PCT and state its function.

Answer 16

3Na-2K-ATPase

Removing sodium ions from inside epithelial cell

Establishes concentration gradient

Sodium in lumen moves into cell

Question 17

In S1 of the PCT, 3Na-2K-ATPase is transporting sodium out of the basolateral membrane, creating a concentration gradient and causing sodium ions to drawn in from the lumen of the PCT to the tubular epithelia cell. Give an example of a transporter bringing sodium into the cell.

Answer 17

Question 18

What happens to glucose molecules in S1 of the PCT? What other molecules can be transported in the same way that glucose is here?

Answer 18

• Transported with sodium into tubular epithelial cell
• Diffuses into interstitium
• Diffuses from interstitium into capillary

(some of transport into tubular epithelial cell is active as glucose concentration decreases)

Other molecules:

• Carboxylic acids
• Amino acids
• Phosphate

Question 19

What happens to the water in S1 of the PCT?

Answer 19

• Water follows sodium through aquaporin channel
• Moves into interstitium
• Moves into capillary due to hydrostatic pressure

(ie Bulk reabsorption volume)

Question 20

Identify two substances/ions which are left behind in the lumen of the PCT in S1.

Answer 20

• Urea
• Cl^-

Question 21

Why is it that if a patient is diabetic, glucose might be found in their urine?

Answer 21

Transport maximum reached

Question 22

How do we transport bicarbonate from the lumen of the PCT S1 to the capillary?

Answer 22

Carbonic anhydrase- dissociates bicarbonate ion

CO₂ and water transported across

Anion exchanger exchanges bicarbonate for chloride

Question 23

What is the action of the diuretic amiloride in the PCT (S1) and in the DCT?

Answer 23

PCT: Blocks Na⁺/H⁺ antiporter

DCT: Inhibits epithelial sodium channels (ENaC)

Question 24

What is the main process that occurs in the S1 of the proximal convoluted tubule (whats its main function)?

Answer 24

Isosmotic reabsorption: bulk transport

Question 25

What happens to chloride ions in the lumen of the proximal convoluted tubule in S2-3? What makes this possible? (freebie)

Answer 25

Majority- diffuse paracellularly into interstitium Due to build up of Cl^- ions in lumen in S1 of PCT so concentration gradient AND charge gradient DON'T NEED TO EXPEND ENERGY **Water follows chloride ions**

Question 26

What % of each of the following is reabsorbed in the PCT: * Water * Glucose * Amino acids * Na⁺

Answer 26

* Water: 65% * Glucose: 100% * Amino acids: 100% * Na⁺: 67%

Question 27

How is Na⁺ reabsorption stimulated in the proximal convoluted tubule if someone has a low BP?

Answer 27

Stimulated by angiotensin II (RAAS)

Question 28

What happens within the proximal convulted tubule is BP increase (in renal artery)?

Answer 28

* Reduce Na-H anitporter and Na-K ATPase activity * Reduced sodium reabsorption * Increased sodium and water excretion * Pressure natruresis (sodium excretion) * Pressure diuresis (water excretion)

Question 29

What is the main process (movement of molecules) that occurs in the ascending and descending limbs in the loop of henle?

Answer 29

Descending: water moves out Ascending: reabsorption of sodium (diluting segment) (concentrates sodium and chloride ions in lumen of descending limb ready for active transport in ascending

Question 30

At what point in the loop of henle are active transporters required for the transport of sodium?

Answer 30

Thick ascending limb

Question 31

Name the main transporter of sodium in the thick ascending limb of the loop of henle. Where else can it be found?

Answer 31

NKCC2 Also in: Macula densa

Question 32

What effects do loop diuretics have on the NKCC22 transporter?

Answer 32

Blocks channel Therefore lots of fluid lost (Doesn't affect ROMK) (also blocks NKCC22 in macula densa) --\> not constricting afferent arteriole

Question 33

Why is the ROMK (renal outer medullary potassium channel) so important?

Answer 33

Allows NKCC2 to keep functioning- transports K⁺ back into lumen

Question 34

How do K⁺ sparing diuretics work? (eg spirondactone) (less fluid lost than with loop diuretics)

Answer 34

Block function of ROMK

Question 35

The distal convoluted tubule has an important function. What is this function?

Answer 35

Volume determination- ie need more ECF if volume to low- reabsorb more sodium

Question 36

The reuptake of Na⁺ in the distal convoluted tubule is under the control of which system?

Answer 36

RAAS Renin-angiotensin-aldosterone-system Aldosterone- upregulates reuptake of sodium (take more water back in **collecting duct**)

Question 37

NCCT (sodium chloride chloride transporter) can be found in the DCT and also the cortical collecting duct. Name a diuretic it is sensitive to.

Answer 37

Thiazide

Question 38

Name a diuretic which the ENaC channels are sensitive to:

Answer 38

Amiloride

Question 39

How does the reuptake of calcium occur in the DCT? What regulates this reuptake process?

Answer 39

Binds to calbidin Then antiporter Regulated by: **Parathyroid hormone**

Question 40

What are the 2 distinct cell types which can be found in the collecting duct?

Answer 40

1. Principal cells 2. Intercalated cells

Question 41

Describe principle cells (found in collecting ducts).

Answer 41

Have 2 channels: ENaC and ROMK (and 3Na-2K-ATPase) Depends on ADH - variable uptake of water

Question 42

What are the 2 cell types of intercalated cells?

Answer 42

A-IC or B-IC ## Footnote A-IC- secrets hydrogen ions B-IC- secretes bicarbonate ions

Question 43

(For info)