the role of ventilation in acid base balance

Question 1

How is pH calculated?

Answer 1

pH= -log10[H+]

Question 2

Why is pH homeostasis important?

Answer 2

Protein function depends on a specific structure, achieved by intrachain and interchain bonds. However the structure of these proteins can be denatured by disrupting these bonds and result in an impaired functioning protein. These factors include those that are controlled via homeostasis:

1. pH 
2. Temperature  3. Pressure

Question 3

How is arterial pH tightly regulated?

Answer 3

The regulation of arterial pH is achieved by the presence of buffering systems (which resist changes in pH), and by regulating the level of molecules associated with acid and base production.

Question 4

Why does arterial pH need to be tightly regulated?

Answer 4

The circulatory system innervates all organs and tissues

Question 5

How is pH homeostasis maintained when acid production increases?

Answer 5

The presence of buffers ( a weak acid and a conjugate base) ‘mops up’ the excess H+. An example of such a buffer is the bicarbonate buffering system, with H2CO3 as the weak acid and HCO3- as the conjugate base.
Any H+ formed by the addition of a strong acid reacts with a conjugate base to form a weaker acid, hence the pH remains relatively stable.

Question 6

What is the purpose of weak acid + conjugate base buffers?

Answer 6

Resists sharp change in pH

It resists the linear relationship between [acid] and low pH

Question 7

Give 3 examples of intracellular buffers

Answer 7

1. Phosphate buffer system
   
   2. Amino acid/proteins
2. Haemoglobin in RBCs

Question 8

Give 2 examples of extracellular buffers

Answer 8

1. Bicarbonate buffer system

2. Plasma proteins (eg- albumin)

Question 9

What is the role of CO2 in acid-base balance?

Answer 9

Negative
Addition= accumulation of CO2 = hypoventilation
Increases concentration of H2CO3
Increases concentration of H+ ions = acidosis

Positive
Removal of CO2 = hyperventilation
Decreases concentration of H2CO3
Decreases concentration of H+ ions = alkalosis

Question 10

Describe the Henderson-Hasselbach equation

Answer 10

Using the equation H2CO3 [H+][HCO3-] you can insert the numbers for these into the equation pH= pKa + log10[A-]/[HA] therefore —> pH= pKa + log10[HCO3-]/H2CO3]

Question 11

How do you calculate the [H2CO3] in the blood?

Answer 11

[H2CO3] in the blood is determined by the partial pressure of CO2 (PaCO2) and CO2 solubility (constant of 0.226mM/kPa)
[H2CO3] = 0.266mM/kPa x PaCO2

Question 12

What is blood pH directly proportional to?

Answer 12

pH ∝ log ([HCO3-]/PaCO2)

this is when all the constants from the previous equations are removed

Question 13

What is the role of the kidney and lung in maintaining blood pH homeostasis?

Answer 13

Kidney: renal regulation of HCO3- 
	• Regulating reabsorption/excretion in glomerular filtrate 
	• Takes hours/days
Lungs: respiratory regulation of PaCO2
	• Regulating ventilation 
Takes minutes

Question 14

Summarise the effects of PaCO2 and [HCO3-] on the pH

Answer 14

CO2 IS HIGH: respiratory acidosis
CO2 IS LOW: respiratory alkalosis

HCO3- IS HIGH: metabolic alkalosis
HCO3- IS LOW: metabolic acidosis

Question 15

What is the arterial pH for acidosis?

Answer 15

<7.35

Question 16

What are some causes of acidosis?

Answer 16

• hypercapnia (hypoventilation)
• increased lactic acid (sepsis)
• increased ketone bodies (diabetes)
• decreased kidney acid excretion (renal failure)
• decreased HCO3- reabsorption (renal acidosis)
• diarrhea (loss of HCO3- from the gut)

Question 17

What are some effects of acidosis?

Answer 17

• tachypnoea (rapid breathing)
• muscular weakness
• headaches
• confusion
• coma
• cardiac arrhythmia
• hyperkalaemia

Question 18

What are the 2 compensatory mechanisms for acidosis?

Answer 18

• hyperventilation (decreased PaCO2) (respiratory compensation)
• decreased HCO3- excretion (renal compensation)

Question 19

What is the arterial pH for alkalosis?

Answer 19

> 7.35

Question 20

What are some causes of alkalosis?

Answer 20

• hypocapnia (hyperventilation)
• vomiting (loss of H+ in HCl)
• increased kidney acid excretion (diuretics)
• increased alkalotic agent consumption (antacids, NaHCO3)

Question 21

What are some effects of alkalosis?

Answer 21

• bradypnoea (slow breathing)
• muscular weakness
• cramps
• tetany (muscular spasms)
• headaches
• nausea
• light-headedness
• confusion
• coma
• cardiac arrhythmia
• hypokalaemia

Question 22

What are the 2 compensatory mechanisms for alkalosis?

Answer 22

• hypoventilation (increased PaCO2) (respiratory compensation)
• increased HCO3- excretion (renal compensation)

Question 23

Describe how acidosis can induce hyperkalaemia

Answer 23

Acidosis increases the concentration of extracellular H+, which decreases the H+ concentration gradient.

This means that there is less H+ excretion via the H+-Na+ exchange. The decreased levels of intracellular Na+ affect Na+-K+ exchange, decreasing the K+ absorption into the cell.

The K+ accumulation in the serum is known as hyperkalaemia, and leads to cardiac arrhythmias and muscle weakness.

Question 24

Describe how alkalosis can induce cerebral vasoconstriction

Answer 24

CO2 (via H+) acts as a vasodilator in blood vessels (the cerebral arteries are particularly sensitive).
However, in alkalosis (with decreased CO2 and H+ levels), there is vasoconstriction in the cerebral arteries.
This decrease in cerebral flow leads to headaches, lightheadedness, confusion and seizures.