Cardiovascular + Respiratory System 2 Flashcards
What is the function of the respiratory system?
Exchange O2 and CO2 between cells and the external environment.
O2 required for metabolism
What do respiratory system regulatory mechanisms ensure?
- ensure that ventilation of the lungs is
matched with perfusion (its blood supply) - the O2 supply and CO2 removal vary
appropriately with activity e.g in exercise - the regulation of respiration - homeostasis
What is an integrated cardio respiratory system?
- a gradient from lung to tissue
How are lungs a variable and efficient air pump?
Due to their huge surface area in mammals
What are the 5 key processes in respiration?
- Ventilation (atmosphere)
- Gas exchange –> Lungs and lung capillaries
- Gas exchange –> capillaries and tissues
- Metabolism
- Bulk transport via circulation
What is partial pressure (P) ?
the pressure that would be exerted by one of the gases in a mixture if it occupied the same volume on its own.
What is the formula for partial pressure?
P total = P a + P b + P c
Where is the site of gas exchange?
The lung alveoli
The is a gradient between the alveoli and the capillary allowing gas exchange to take place.
How is blood specialised for the transport of O2 and CO2?
RBCs:
- are small and flexible so can fit through
narrow vessels
- they have a bi-concave shape to maximise
their surface area for absorption of oxygen
- have thin membrane so gasses can diffuse
through easily
- contain haemoglobin to bind to oxygen
- bicarbonate forms in blood - happens most
readily in red blood cells
Why does this reaction never go to equilibrium?
CO2 (from tissues) –> H2O –> H2CO3 –> H+ + HCO3-
Because the products are removed by two mechanisms:
1) chloride / bicarbonate exchange (chloride
shift)
2) H+ buffering by haemoglobin
What determines blood pH?
= PCO2
CO2 + H2O <—-> H2CO3 <—-> H+ + HCO3-
and pH = -log [H+]
for blood pH = pKA + log [HCO3] / [CO2]
[CO2] = pCO2 x solubility
pKa for blood is 6.1 and solubility is a constant so can be expressed as:
pH α (proportional to) log [HCO3-] / [CO2]
What is hyperventilation?
increased ventilation, Pa CO2 < 40 mmHg
What is hypoventilation?
decreased ventilation, Pa CO2 > 45 mmHg
What is the relationship between ventilation and pCO2 ?
Ventilation is normally closely matched with metabolic requirements
PA CO2 α 1/alveolar ventilation
because of gas exchange, pA CO2 appoximates to Pa CO2
Where are chemoreceptors located?
Central chemoreceptors = in the blood brain barrier
Peripheral chemoreceptors = in the Carotid bodies and Aortic bodies –> respiratory centres —> respiratory muscles
How does the O2 dissociation curve give information about the homeostatic requirements in breathing?
Blood pH and tissue pH are VERY tightly controlled variables.
Under normoxic (normal O2) conditions the drive to breath comes from central chemoreceptors from pCO2 via H+ (so depending on pH)
If PA CO2 is constant, PO2 will not produce a drive until ~ < 60 mmHg.
Is breathing a result of O2 supply or CO2 regulation?
Normal breathing is set to regulate pH via CO2 within very narrow limits. Then there is no issue with O2 supply.
What is the effect of hyperventilation on PaO2?
During hyperventilation which lowered arterial PCO2 and increased pH of the blood, the average PO2 decreased in proportion to the decrease in arterial PCO2
Why are hyper- and hypoventilation described in terms of PaCO2 values rather than PaO2 values?
As it is when there is too much or too little CO2 in the blood.
