Chemical control of breating

Question 1

Define the terms hypoxia, hypercapnia, hypocapnia, hyperventilation, and hypoventilation.

Answer 1

hypercapnia: A rise in alveolar and arterial pCO2

hypoventilation: occurs when ventilation is inadequate (hypo meaning “below”) to perform needed gas exchange

Hyperventilation : Removal of CO2 from alveoli is more rapid than its production

Falls in pO2 are known as ‘hypoxia”

Question 2

Describe the effects on plasma pH of hyper and hypo ventilation.

Answer 2

Removal of CO2 from alveoli is more rapid than its production - Hyperventilation.

Alveolar CO2 falls - plasma pH rises - Respiratory Alkalosis.

Removal of CO2 from lungs is less rapid than its production -Hypoventilation.

Alveolar pCO2 rises, so [Dissolved CO2] rises more than [HCO3-] producing a fall in plasma pH - Respiratory Acidosis.

Question 3

Describe the general effects of acute hypo and hyper ventilation.

Answer 3

Hypervetilation: If the condition persists, the kidneys respond by excreting HCO3-, so the ratio [Dissolved CO2] / [HCO3-], returns near to normal, and therefore pH is restored, but buffer base concentration is reduced - Compensated Respiratory Alkalosis.

Hypoventilation: If this condition persists, the kidneys respond to low pH by reducing excretion of HCO3- (hold on to it) , thus restoring the ratio [Dissolved CO2] /[HCO3-], and the pH, near to normal - Compensated Respiratory Acidosis.

Question 4

Define the terms ‘Respiratory Acidosis’, ‘Respiratory Alkalosis’, ‘Compensated Respiratory Acidosis’ and ‘Compensated Respiratory Alkalosis’.

Answer 4

Alveolar pCO2 rises, so [Dissolved CO2] rises more than [HCO3-] producing a fall in plasma pH - Respiratory Acidosis.

If this condition persists, the kidneys respond to low pH by reducing excretion of HCO3-, thus restoring the ratio [Dissolved CO2] /[HCO3-], and the pH, near to normal - Compensated Respiratory Acidosis.

Alveolar CO2 falls - plasma pH rises - Respiratory Alkalosis.

If the condition persists, the kidneys respond by excreting HCO3-, so the ratio [Dissolved CO2] / [HCO3-], returns near to normal, and therefore pH is restored, but buffer base concentration is reduced - Compensated Respiratory Alkalosis.

Question 5

Define the terms ‘Metabolic Acidosis’, ‘Metabolic Alkalosis’, ‘Compensated Metabolic Acidosis’, ‘Compensated Metabolic Alkalosis’.

Answer 5

Metabolic production of Acid: HCO3- is removed from plasma as the acid is buffered; therefore the pH of blood falls. This is a reduction of buffer base - Metabolic Acidosis.

If HCO3- is held in the plasma, there will be Metabolic Alkalosis. The blood pH may be corrected by elevating pCO2, leaving Alkalosis to be corrected by the kidney.

Question 6

Describe the acute effects upon ventilation of

(i) falling inspired pO2,
(ii) increases in inspired pCO2
(iii) falls in arterial plasma pH.

Question 7

Describe the location and function of the peripheral chemoreceptors and their role in the ventilatory and other responses to Hypoxia.

Answer 7

large falls in pO2 stimulate

– increased breathing

– changes in heart rate

– Changes in blood flow distribution

• i.e. increasing flow to brain & kidneys

Question 8

explain BBB blood brain barrier and the selective ions that r allowed to cross!

Answer 8

Question 9

• Describe the location and function of the central chemoreceptors,
• their role in the ventilatory respiratory to changes in arterial pCO2
• roles of the CSF, blood brain barrier and choroid plexus in that response.

Answer 9

location: on the ventral surface of the medulla, and exposed to the CSF

choroid plexus (cells which line ventricular system) have capacity to change HCO^3- concentration

• If arterial pCO² changes, after a short delay, CSF pCO² will follow.*
• This leads to changes in CSF pH, which are sensed by central chemoreceptors, normally producing changes in breathing which tend to restore CSF pH*
• (i.e. if pCO2 rises, ventilation increases, to lower pCO2 again).*

This negative feedback is the principal means by which ventilation is controlled.

Question 10

what is CSF [HCO3-] is determined by ?

Answer 10

by the activity of choroid plexus cells which pump HCO3- into and out of the CSF, and is largely independent of plasma [HCO3-].

Question 11

If feedback does not occur, say because of an additional stimulus to ventilation from hypoxia what happens?

Answer 11

persisting changes in CSF pH stimulate the choroid plexus cells to pump more or less HCO3- into the CSF, and change [HCO3-] to bring the [HCO3-]/ [Dissolved CO2] ratio back towards normal.

CSF pH is corrected much more quickly than blood pH because of its small volume.

As CSF pH is corrected, changes in ventilation driven by alteration of pCO2 disappear, and the control system is ‘reset’ to operate around a different pCO2.

Question 12

in what cases does falling pO2 produces increased ventilation ?

Answer 12

only when the fall is considerable, but respiratory drive from hypoxia is maintained.

Question 13

Small changes in arterial pCO² produce very rapid changes in breathing, to try to stabilise pCO².

…….but if pCO² remains altered for longer length of time. what happens then?

Answer 13

the activity of the choroid plexus cells serves to ‘reset’ the system to control around a different pCO2.

by bringer in HCO^3-

Question 14

Explain feedback control of breathing by pCO²

Answer 14

Question 15

explain what happens when u have persisting Hypoxia?

Answer 15

quickly detected by peripheral chemorecepters!

and increase ventilation!, but then this will reduce PCO² and thereofre this will decrease ventilation

sooooo

so the CSF composition will change to compensate for that change in PCO^{2>> done by choroid plexus>> by adding H+ or HCO3- into the CSF}

now central chemorecepters will now “accept” the PCo2 as normal!

Question 16

explain what happens when u have persisting Hypercapnia?

Answer 16

ex: type 2 respiratory failure

1. u’ll have hypoxia as well!
2. u get respiratory acidosis> decreased CSF pH
3. BOTH peripheral and chemorecepters stimulate breathing!
4. but the acidic environment aint so good for the neurons!
5. therefore choroid plexus needs to adjust pH of CSF!
6. by adding HCO3- back into CSF
7. so central chemorecpeters “accept” the high PCO² as normal!