Sodium and Potassium Balance

Question 1

What are the 3 effects of angiotensin II

Answer 1

Stimulate vasoconstriction of the vascular system to raise BP
Act on proximal convoluted tubule to increase Na+ reabsorption to increase BP
Stimulate adrenal cortex make aldosterone

Question 2

What is aldosterone? Where is it made and released?

Answer 2

Steroid hormone

Synthesised and released from adrenal cortex

Question 3

What is aldosterone synthesised in response to?

Answer 3

AG II
Decrease in BP via baro receptors
Decrease in osmolarity of ultrafiltrate

Question 4

What does aldosterone stimulate?

Answer 4

Increased Na reabsorption
Increase K secretion
Increase H+ secretion

Question 5

What does excess aldosterone do?

Answer 5

Lead to hypokalaemic alkalosis

Question 6

What are the 3 main effects of aldosterone inside the cell?

Answer 6

Upregulate production of apical sodium transporters
Upregulate production of basolateral Na+/K+ ATPase
Upregulate regulatory proteins

Question 7

What is hypoaldosteronism?

Answer 7

Less Na+ reabsorption in distal tubule
More Na+ lost in urine.
ECF volume falls
increased renin, angII and ADH

Question 8

What are symptoms of hypoaldosteronism?

Answer 8

Dizziness
Low blood pressure
Salt cravings
Palpitations

Question 9

What is hyperaldosteronism

Answer 9

Sodium reabsorption in distal nephron increased
Less Na lost in urine
ECF vol increase - hypertension
Less renin, ang II and ADH
more ANP and BNP

Question 10

What are symptoms of hyperaldosteronism?

Answer 10

High blood pressure
Muscle weakness
Polyuria
Thirst

Question 11

What is Liddle’s syndrome?

Answer 11

Inherited disease of high blood pressure due to a mutation meaning the aldosterone activated sodium channel always on
Leading to Na retention leading to hypertension

Question 12

How to low pressure side of baroreceptors respond?

Answer 12

Responds to lower and higher pressures involving SNS (afferent brainstem fibres - sympathetic activity) and ADH in low pressures and ANP and BNP in high pressures

Question 13

How do the high pressure side of baroreceptors respond?

Answer 13

Only to low pressures using SNS, ADH and renin release - renin only released from responses to low pressure in high pressure side

Question 14

What is ANP?

Answer 14

Atrial natriuretic peptide ATP

Small peptide made in the atria, which also makes BNP

Question 15

When is ANP released?

Answer 15

In response to atrial stretch

Question 16

What are the actions of ANP?

Answer 16

• Vasodilation of renal blood vessels - and other systemic
• Inhibition of sodium reabsorption in PCT and CD
• Inhibits release of renin (therefore aldosterone)
• > to reduce blood pressure

Question 17

Give examples of diuretic drugs

Answer 17

• Osmotic diuretics (glucose and mannitol)
• Carbonic anhydrase inhibitors
• Loop diuretics (furosemide)
• Thiazides
• K+ sparing diuretics (amiloride and spironalactone that prevent K+ loss in distal)

Question 18

What do amiloride and spironalatone do? (K+ sparing diuretics)

Answer 18

Amiloride - block Na channels

Spironolactone - aldosterone antagonist, inhibit activity of Na+ channel and Na/K ATPase

Question 19

What do thiazides do?

Answer 19

Block Na/Cl co transport

In distal convoluted tubule

Question 20

What do carbonic anhydrase inhibitors do?

Answer 20

Lead to Na+ reabsorption and increased urinary activity

Inhibit production of H+ in the PC tubular cells. Less H+ out, so less Na+ in, more sodium excreted

Question 21

What is the concentration of potassium intracellularly? Extracellularly?

Answer 21

Intracellular: 150 mmol/l
Extracellular: 3-5 mmol/l

Question 22

What does extracellular K+ have an effect on?

Answer 22

Excitable membranes of nerves and muscles
High K+: depolarises membranes - action potentials and heard arrhythmias
Low K+: heart arrhythmias (asystole)

Question 23

What happens to in regards to K+ after a meal?

Answer 23

K+ absorption
Plasma K+ conc increase
Insulin, aldosterone, adrenaline released - regulate tissue uptake

Question 24

What is K+ secretion stimulated by?

Answer 24

Increase in:
Plasma [K+]
Aldosterone
Tubular flow rate
Plasma pH

Question 25

What are causes of hypokalemia?

Answer 25

Diuretics due to increase in tubular flow rate Surreptitious vomiting Diarrhoea Genetics (gitelman's syndrome; mutation in Na/Cl transporter in distal nephron)

Question 26

What is gitelman's syndrome?

Answer 26

mutation in Na/Cl transporter in distal nephron | cause hypokalemia

Question 27

Where is sodium reabsorbed?

Answer 27

65% in proximal convoluted tubule 25% in ascending loop of Henle 8% in distal convoluted tubule 2% in collecting duct

Question 28

How to decrease Na+ reabsorption

Answer 28

``` Atrial naturietic peptide Changes diameter of afferent and efferent tubules Reduces activity of PCT Suppresses renin release in the JXA Reduces sodium reabsorption in CT ```

Question 29

What is the JXA

Answer 29

Juxtaglomerular apparatus | Which has granular cells that produce renin

Question 30

What do loop diuretics do? (furosemide)

Answer 30

Block the triple transporter in ascending limb of loop of henle - Stop Na+ reabsorption in tubular fluid Prevent Na+ entering interstitial space MOST POTENT affect up to 25% of filtered load

Question 31

Where in the nephron is K+ absorbed?

Answer 31

``` 30% in PCT 10% in thin ascending loop of loH 10% in DCT 1-80% in CD amount released as urine really varies ```

Question 32

What affect does aldosterone have on potassium?

Answer 32

Stimulates uptake of K+ in principle cells (apical K+ transporter stimulated) Apical Na+ transporter also stimulated Basolateral sodium/potassium ATPase

Question 33

How does tubular flow stimulate K+ release/excretion

Answer 33

``` Cells in collecting tubules have cilia. Flow increases Cilia stimulate PDK1 Cascade system Increase intracellular Ca2+ Activate apical potassium channels Release more potassium ```

Question 34

How is potassium secreted? (mediated by? coupled with?)

Answer 34

Secretion mediated by Na+/K+ ATPase and is coupled with Na+ absorption in the blood

Question 35

What can cause hyperkalemia?

Answer 35

In response to K+ sparing diuretics, which prevents K+ secretion when it's needed ACE inhibitors Elderly

Question 36

Where are baroreceptors found?

Answer 36

``` Heart - atria low pressure - right ventricle low pressure Vascular system - pulmonary vasc low pressure - carotid sinus high pressure - aortic arch high pressure - JGA high pressure ```

Question 37

How much potassium is filtered and excreted daily?

Answer 37

Filtered 10mEq/Kg/day | 15% excreted by kidneys

Question 38

What mediates K+ uptake into cells after a meal?

Answer 38

Insulin | Sodium/potassium ATPase uptake into cells