Regulation of Sodium

Question 1

most prevalent solute in the ECF?

Answer 1

sodium

Question 2

describe the association between sodium and water retention

Answer 2

increased sodium intake increases water retention

Question 3

describe the link between dietary sodium and blood pressure

Answer 3

^ Na+ > ^ osmolarity > ^ water intake + retention > ^ ECF volume > ^ blood volume and BP
(and vice versa)

Question 4

what mechanisms are there for regulating sodium intake?

Answer 4

central

peripheral

Question 5

central mechanism depends on what part of the brain?

Answer 5

lateral parabroachial nucleus

Question 6

In euvolemia, is Na+ intake stimulated or inhibited?

Answer 6

inhibited

Question 7

Na+ intake is inhibited by what molecules?

Answer 7

serotonin

glutamate

Question 8

In the sodium deprived state, appetite for sodium is increased via what?

Answer 8

GABA

opioids

Question 9

Peripheral mechanisms for controlling Na+ intake are based on?

Answer 9

taste

Question 10

where is the majority of Na+ reabsorbed in the nephron?

Answer 10

proximal convoluted tubule

next is loop of Henle from countercurrent mechanism

Question 11

how is Na+ reabsorbed in the nephron?

Answer 11

co transport

counter transport with glucose, amino acids, bicarbonate

Question 12

what % of Na+ in the tubular fluid ends up being excreted?

Answer 12

1%

Question 13

what is GFR?

Answer 13

glomerular filtration rate

Question 14

what % of renal plasma enters the tubular system?

Answer 14

20

Question 15

equation linking GFR and RPF

Answer 15

GFR = RPF x 0.2

Question 16

What happens to Na+ reabsorption if GFR increases?

Answer 16

flow rate in the PCT and the LOH will increase, the amount sodium reabsorbed increases

Question 17

Maximum rate of Na+ reabsorption is dependent on?

Answer 17

transporters present and the flow

Question 18

The distal convoluted tubule is separated from the glomerulus by?

Answer 18

extraglomerular mesangial cells and juxtaglomerular cells

Question 19

As more Na/Cl is delivered to the distal convoluted tubule, the amount of sodium and chloride transported by the cells of the _________ increases.

Answer 19

macula densa

Question 20

Above a threshold value, macula densa cells start to release?

Answer 20

adenosine

ATP

Question 21

Adenosine and ATP release activate receptors to have what two effects?

Answer 21

reduction of renin production

stimulation of contraction of smooth muscle cells of the afferent arteriole

Question 22

Contraction of smooth muscle in afferent arteriole leads to what?

Answer 22

reduction in RPF

reduction in perfusion pressure

Question 23

how to reduce Na+ excretion?

Answer 23

reduce glomerular filtration by constricting the afferent arteriole more than the efferent arteriole or relaxing the efferent arteriole more than the afferent arteriole

Question 24

Sympathetic stimulation reduces sodium loss via contraction of afferent and efferent arterioles and by what other mechanism?

Answer 24

increases uptake of Na+ by PCT cells, increasing the activity of the sodium proton exchanger

Question 25

Mechanisms to increase Na+ uptake in the nephron are opposed by the activity of what?

Answer 25

atrial naturietic peptide

Question 26

Action of atrial naturietic peptide on the nephron

Answer 26

promotes dilation of of afferent arteriole inhibits renin release reduces uptake of Na+ in PCT, DCT, CD

Question 27

Overall, if blood volume falls or sodium levels are low and we need to promote sodium retention we see:

Answer 27

``` increased sympathetic activity increased renin production > increased angiotensin II increased NaCl reabsorption vasocontriction release of aldosterone ```

Question 28

Is aldosterone a steroid or peptide hormone?

Answer 28

steroid

Question 29

where is aldosterone synthesised?

Answer 29

adrenal gland cortex zona glomerulosa

Question 30

aldosterone is release in response to?

Answer 30

angiotensin II | decrease in blood pressure

Question 31

what enzyme is required for the last 2 steps of aldosterone synthesis?

Answer 31

aldosterone synthetase

Question 32

Aldosterone in excess leads to?

Answer 32

hypokalaemic alkalosis

Question 33

Aldosterone stimulates?

Answer 33

increased Na+ reabsorption increased K+ secretion increased H+ secretion

Question 34

aldosterone binds to what type of receptor?

Answer 34

mineralocorticoid

Question 35

on aldosterone binding what occurs?

Answer 35

monomer loses association to HSP90 dimerises translocates to the nucleus > binds to DNA promoter region > stimulates expression of target genes

Question 36

target genes of aldosterone?

Answer 36

ENaC (epithelial sodium channel) | Na+/K+ ATPase and sets of regulatory proteins

Question 37

``` Are the following permeable or impermeable to Na+? descending loop of Henle ascending loop of Henle DCT CD ```

Answer 37

impermeable permeable permeable permeable in the presence of aldosterone

Question 38

symptoms of hypoaldosteronism

Answer 38

dizziness low blood pressure salt craving palpitations

Question 39

symptoms of hyperaldosteronism

Answer 39

high blood pressure muscle weakness polyuria thirst

Question 40

Liddle's syndrome

Answer 40

normal to low levels of aldosterone same phenotype as hyperaldosteronism genetic disease mutations to the aldosterone activated sodium channel