Cardiovascular + Respiratory System 2

Question 1

What is the function of the respiratory system?

Answer 1

Exchange O2 and CO2 between cells and the external environment.

O2 required for metabolism

Question 2

What do respiratory system regulatory mechanisms ensure?

Answer 2

• 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

Question 3

What is an integrated cardio respiratory system?

Answer 3

• a gradient from lung to tissue

Question 4

How are lungs a variable and efficient air pump?

Answer 4

Due to their huge surface area in mammals

Question 5

What are the 5 key processes in respiration?

Answer 5

• Ventilation (atmosphere)
• Gas exchange –> Lungs and lung capillaries
• Gas exchange –> capillaries and tissues
• Metabolism
• Bulk transport via circulation

Question 6

What is partial pressure (P) ?

Answer 6

the pressure that would be exerted by one of the gases in a mixture if it occupied the same volume on its own.

Question 7

What is the formula for partial pressure?

Answer 7

P total = P a + P b + P c

Question 8

Where is the site of gas exchange?

Answer 8

The lung alveoli

The is a gradient between the alveoli and the capillary allowing gas exchange to take place.

Question 9

How is blood specialised for the transport of O2 and CO2?

Answer 9

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

Question 10

Why does this reaction never go to equilibrium?
CO2 (from tissues) –> H2O –> H2CO3 –> H+ + HCO3-

Answer 10

Because the products are removed by two mechanisms:

1) chloride / bicarbonate exchange (chloride
shift)

2) H+ buffering by haemoglobin

Question 11

What determines blood pH?

Answer 11

= 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]

Question 12

What is hyperventilation?

Answer 12

increased ventilation, Pa CO2 < 40 mmHg

Question 13

What is hypoventilation?

Answer 13

decreased ventilation, Pa CO2 > 45 mmHg

Question 14

What is the relationship between ventilation and pCO2 ?

Answer 14

Ventilation is normally closely matched with metabolic requirements

PA CO2 α 1/alveolar ventilation

because of gas exchange, pA CO2 appoximates to Pa CO2

Question 15

Where are chemoreceptors located?

Answer 15

Central chemoreceptors = in the blood brain barrier

Peripheral chemoreceptors = in the Carotid bodies and Aortic bodies –> respiratory centres —> respiratory muscles

Question 16

How does the O2 dissociation curve give information about the homeostatic requirements in breathing?

Answer 16

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.

Question 17

Is breathing a result of O2 supply or CO2 regulation?

Answer 17

Normal breathing is set to regulate pH via CO2 within very narrow limits. Then there is no issue with O2 supply.

Question 18

What is the effect of hyperventilation on PaO2?

Answer 18

During hyperventilation which lowered arterial PCO2 and increased pH of the blood, the average PO2 decreased in proportion to the decrease in arterial PCO2

Question 19

Why are hyper- and hypoventilation described in terms of PaCO2 values rather than PaO2 values?

Answer 19

As it is when there is too much or too little CO2 in the blood.