Renal Regulation of H+

Question 1

What is the normal ECF PH range?

Answer 1

7.35-7.45

Question 2

Why is it so important for PH to remain in range?

Answer 2

To ensure enzymes can work efficiently

Question 3

Why is intracellular PH more acidic than ECF?

Answer 3

• high intracellular acid production 7.2

- cells have adapted to slightly lower PH through increased buffering capacity

Question 4

What are the three types of buffer?

Answer 4

1) Chemical
2) Protein
3) Bicarbonate

Question 5

What is a chemical buffer and where are they found?

Answer 5

• Substances that bind to H+ removing it from solution if higher concentration
• or release H+ if in low concentration
• Present in all body fluids, restores Ph within fraction of second

Question 6

How does bicarbonate buffer?

Answer 6

Carbonic acid can either form CO2 and H20 (to be removed from body) to decrease acidity or H+ and HCO3- to increase acidity

Question 7

What enzyme catalyses breakdown of carbonic acid to water and carbon dioxide?

Answer 7

carbonic anhydrase

Question 8

What are the two systems used as physiological buffers and how do they differ?

Answer 8

1) Renal
- greater buffering capacity
- takes longer
2) Respiratory
- Can only excrete volatile acids but effects within minutes

Breakdown of one system can be compensated by the other

Question 9

How does H+ in filtrate get into the tubular cells of the nephron?

Answer 9

• small excess of H+ in the filtrate at glomerulus along with HCO3-
• combine to form carbonic acid and then dissociate to form H2O and CO2
• These diffuse into tubular cells

Question 10

What happens to the water and CO2 in the tubular cells?

Answer 10

• Combine to form carbonic acid > HCO3- and H+
• broken down originally to get the products into the tubular cells
• HCO3- can then be reabsorbed into the blood
• Hydrogen can be secreted back into the filtrate
• H+ can rebind with more HCO3- and cycle will start again
• Results in HCO3- reabsorbtion and H+ secretion

Question 11

Where is HCO3- reabsorbed in the nephron?

Answer 11

• PCT 80%
• DCT 10%
• Collecting duct 5%
• Excrete almost no bicarbonate

Question 12

Where is H+ reabsorbed then secreted in the nephron?

Answer 12

• PCT 85%
• DCT 10%
• Collecting duct 5%
• Reabsorbed and secreted in all locations

Question 13

How do kidneys regulation of PH change to correct acidosis?

Answer 13

• May be excess CO2 in filtrate which diffuses into tubular cells at same time as CO2 which is product of carbonic acid
• HCO3- reabsorbed into blood as usual and starts to neutralise blood to return it to normal PH
• No more HCO3- is available to combine with the H+ when it re-enters the filtrate so is excreted in urine
• Get low urinary PH

Question 14

How will regulation in the kidneys change with severe excess in hydrogen ions?

Answer 14

• Need a H+ concentration gradient to ensure movement back into filtrate after HCO3- released into blood
• If too many H+ ions still infiltrate no gradient
• so body secretes NH3 which diffuses into filtrate and combines with H+ to from NH4+
• NH4+ can’t move back into tubular cells as charged so must be excreted in urine

Question 15

Where does ammonia used to regulate PH come from?

Answer 15

Protein metabolism

Question 16

What problems are caused by acidosis?

Answer 16

• increase in free Ca2+ as albumin begins binding to H+, means more sodium channels can be blocked and reduction in AP firing of myocytes and nerves
• cells can longer be stimulated as resting membrane of cells is stabilised

Question 17

What are the consequences of the free calcium?

Answer 17

• CV depression - bradycardia followed by a-systole

- CNS depression - stupor followed by coma

Question 18

What are the causes of acidosis?

Answer 18

1) respiratory acidosis (CO2 causing acidosis)
- ventilatory failure
- severe ventilatory defects

Question 19

What would you expect to see in the blood concentrations of respiratory acidosis?

Answer 19

• High CO2
• possibly low O2
• Low PH
• raised HCO3- due to compensation

Question 20

What are the causes of metabolic acidosis (metabolic means as a result of kidney damage)?

Answer 20

• Renal injury/disease (less H+ & less HCO3- reabsorption)
• Aspirin overdose (induces hyperventilation
• diabetic ketoacidosis
• Alcoholism (damage due to inflammation, oxidative stress and hypertension)
• diarrhoea (Na+ lost in filtrate so less H+ secreted and less HCO3- reabsorbed)
• ## Addisons disease (hypoaldosteronism)

Question 21

Why does Addison disease cause acidosis?

Answer 21

low aldosterone means less expression of the Na/H+ pump and so less H+ secretion and so less HCO3- reabsorption

Question 22

What would you expect to see in blood chemistry for metabolic acidosis?

Answer 22

• Low PH
• Low ECF HCO3- concentration
• Normal O2 and CO2 except if have compensatory deep breathing to remove CO2

Question 23

What PH is defined as alkalosis?

Answer 23

7.45

Question 24

How is alkalosis corrected?

Answer 24

• Want either a decrease in H+ or increase in HCO3- in filtrate so less carbonic acid forms
• and less CO2 and H2O absorbed
• results in less H+ secretion and less HCO3- reabsorption
• HCO3- starts to be excreted as no H+ to combine with it
• HCO3- secretion and increase in H+ (as body continues to make it) will decrease PH

Question 25

What are the consequences of Alkalosis?

Answer 25

• increased binding of calcium to albumin so less free calcium
• allows the sodium blocks to remain open as no longer blocked
• increased firing of AP in nerves and mycoytes
• excitable cells depolarise more
• get confusion, muscle spasms, can be fatal

Question 26

What are the respiratory causes of alkalosis?

Answer 26

• Hyperventilation (blowing off too much CO2) get low CO2 and low HCO3- (renal compensation) in blood

Question 27

Causes of metabolic alkalosis?

Answer 27

• bicarbonate overdose (antacids contain bicarbonate), get high HCO3- and high CO2
• hyperaldosteronism will get more H+ secretion
• vomiting due to loss of gastric acids

Question 28

If alkalosis/acidosis is respiratory will compensation be respiratory or metabolic?

Answer 28

• If cause is respiratory compensation will be metabolic

- If cause is metabolic compensation will be respiratory