Acid - base balance 1

Question 1

What is the range in pH in body fluids

Answer 1

7.35-7.45

Question 2

Give sources of acid/alkali due to metabolism

Answer 2

Generates a large amount of acid - 15mol/day of CO2 in the lungs
40mmol/day net H+

Question 3

Give sources of acid/alkali from diet

Answer 3

High protein diet increases acid load
fruit contains high levels of alkali substances
20mmoles of H+

Question 4

What is the net loss of base in a day

Answer 4

10mmol

Question 5

What is the net excess of H+ produced in a day

Answer 5

70mmol/day of H+

Question 6

What is the first system to react to changes in blood pH

Answer 6

Buffer systems - act in seconds to minimise pH changes but can’t reverse them

Question 7

What is the second system to react to blood pH changes

Answer 7

Respiratory system - also minimises changes

Question 8

What is the third system to react to blood pH changes

Answer 8

Renal system - directly excretes excess acid or base

takes hours or even days to up or downregulate pH systems

Question 9

Where are buffers found and give 3 examples

Answer 9

Blood - plasma and the RBC itself 
Extracellular fluid 
Intracellular fluid 
Urine
Haemoglobin, bicarbonate, inorganic phosphate

Question 10

What ratio are HCO3- and CO2 normally in and how does this affect the hederson equation

Answer 10

20: 1 -

6. 1 (constant) +log 20 = 7.4 - normal plasma pH

Question 11

What is a metabolic acidosis caused by and what is the body response

Answer 11

Caused by addition of acid/removal of alkali

Equation shifts to left to reduce impact - HCO3 reduced, pH goes down, H+ above the norm, CO2 up - lost in respiration

Question 12

What is metabolic alkalosis caused by and whats the response

Answer 12

Increased alkali addition / removal of acid

Equation shifts left Decrease in H+ so increase in pH, HCO3 above the norm

Question 13

What is respiratory acidosis and what is the response

Answer 13

Increased PCO2

shifts equation to the right (H+ and HCO3 go up) pH goes down - acidosis with a high bicarbonate

Question 14

What is respiratory alkalosis and what is the response

Answer 14

Decreased PCO2 shifts equation to the left
(H+ and HCO3 go down) pH goes up
Alkalosis low bicarbonate

Question 15

What is the action of both central and peripheral chemoreceptors

Answer 15

Act via a negative feedback loop

Hypoxia, hypercapnia and acidosis all lead to an increase in O2, a decrease in CO2 and an increase in pH

Question 16

Where are the peripheral chemoreceptors found

Answer 16

In the carotid body and the aortic arch

Question 17

Whats the main stimulus of the peripheral chemoreceptors

Answer 17

Hypoxia - reduced O2

Question 18

What is the electrically active cell in the peripheral chemoreceptors

Answer 18

Glomus cell - in low oxygen causes depolarization and generates action potentials in the cell (has nerve inputs and outputs)

Question 19

What is the mechanism of action of the peripheral chemoreceptors

Answer 19

Hypoxia etc lead to inhibition of BK Kchannels - depolarization occurs - AP firing
Opening of Ca channels and influx
Increase calcium intracellularly causes the release of neurotransmitters (Ach, Noradrenaline, adrenaline, atrial natriuretic peptide)
Afferent nerve fibre stimulation - activation of respiratory centres - increase inhalation/depth of breathing

Question 20

What is the effect on impulses if P02 decreases

Answer 20

As O2 decreases the number of impulses per second increase

Question 21

How does sensitivity to oxygen change with pH

Answer 21

As the pO2 falls, the number of impulses per second increase - Low pCO2 and high pH - low sensitivity to O2
High CO2 and low pH - high sensitivity to CO2

Question 22

How does sensitivity to CO2 change with pH

Answer 22

Independent of any changes in O2
High pH - low sensitivity to CO2
Low pH - High sensitivity to CO2
More impulses at lower pH