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What is the range in pH in body fluids



Give sources of acid/alkali due to metabolism

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


Give sources of acid/alkali from diet

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


What is the net loss of base in a day



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

70mmol/day of H+


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

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


What is the second system to react to blood pH changes

Respiratory system - also minimises changes


What is the third system to react to blood pH changes

Renal system - directly excretes excess acid or base
takes hours or even days to up or downregulate pH systems


Where are buffers found and give 3 examples

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


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

20:1 -
6.1 (constant) +log 20 = 7.4 - normal plasma pH


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

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


What is metabolic alkalosis caused by and whats the response

Increased alkali addition / removal of acid
Equation shifts left Decrease in H+ so increase in pH, HCO3 above the norm


What is respiratory acidosis and what is the response

Increased PCO2
shifts equation to the right (H+ and HCO3 go up) pH goes down - acidosis with a high bicarbonate


What is respiratory alkalosis and what is the response

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


What is the action of both central and peripheral chemoreceptors

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


Where are the peripheral chemoreceptors found

In the carotid body and the aortic arch


Whats the main stimulus of the peripheral chemoreceptors

Hypoxia - reduced O2


What is the electrically active cell in the peripheral chemoreceptors

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


What is the mechanism of action of the peripheral chemoreceptors

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


What is the effect on impulses if P02 decreases

As O2 decreases the number of impulses per second increase


How does sensitivity to oxygen change with pH

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


How does sensitivity to CO2 change with pH

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