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Flashcards in Gas exchange and transport Deck (16)
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1
Q

what are the main function of the lungs

A

Ventilation – movement of air in and out

Gas exchange – the exchange of oxygen and carbon dioxide between the airspace of the alveoli and the blood

2
Q

how does the partial pressure of oxygen change as it goes from atmosphere to mitochondria

A

Breathe in and out to continually add and remove gas to alveoli so pp of oxygen decreases at each tissue level -
Cascade effect

3
Q

how does gas exchange occur in the lungs

A

Air is inspired into the lungs, uneven distribution throughout the lung (lower zones more compliant)
Pulmonary circulation is a low-pressure system, upright position barely enough pressure to perfuse oxygen the apices with overperfusion of the bases (pressure equal to air distribution)
Aka known as ventilation/perfusion (V/Q) matching

4
Q

what is a steady state condition

A

the amount of CO2 produced by the body and the amount of O2 absorbed depends on metabolic activity of the body – respiratory quotient (RQ) (match up CO2 and O2)

5
Q

how is the respiratory quotient calculated

A

RQ= CO2 produced/O2 absorbed

Varies, about 0.8 at rest (fat metabolism at 0.7 or carbs at 1.0)

6
Q

How does the partial pressure of CO2 change in the body

A

CO2 is produced at a relatively constant state by the body, the pp of CO2 (PCO2) of alveolar air (PACO2) depends on alveolar ventilation
AV up then PAC02 down and vice versa

7
Q

what is the difference between PCO2, PACO2 and PaCO2

A

Partial pressure in the atmosphere
Partial pressure in the alveolar air
Partial Pressure in arterial blood

8
Q

How does the partial pressure of O2 change in the body

A

Partial pressure of O2 also varies with AV
AV up then PAO2 up and vice versa
Big enough AV increase will allow PAO2 to approach PO2

9
Q

what determines the rate of gas entering the blood

A

Fick’s Law (diffusion through tissues)
The rate of transfer of gas through a tissue is proportional to the tissue area and the difference of the gas pp between the two sides and inversely proportional to tissue thickness

10
Q

what effect do local differences have on V/Q

A

In the normal lung, most alveoli receive V/Q in correct proportion
Low V/Q, low ventilation relative to blood flow. PCO2 increase and PO2 decrease (dissociation curve reflects this with arterial content of each gas)
High V/Q shows the opposite

11
Q

what is the alveolar gas equation

A

PAO2=PIO2 - (PaCO2/0.8)

The relationship between PaCO2 and PaO2 is summarised

12
Q

What is the A-a (alveolar-arterial) gradient

A

PaCO2 is equal to PACO2 but Pa02 is not equal to PAO2 (Cascade effect)
Healthy young adults = A-a gradient is small (<2 kPa)
if A-a gradient is greater, the abnormality in blood gas cannot be explained by a change in ventilation (must be intrinsic, lung vasculature, causing V/Q mismatch)

13
Q

how does respiratory failure relate to the alveolar gas equation

A

Pure underventilation =increased PaCO2 + proportionate fall in PaO2 – type 2 respiratory failure
Disturbance in V/Q matching = fall in PaO2 but no change in PaCO2 – type 1 respiratory failure
Both can occur concurrently – the alveolar gas equation allows determination of reduced PaO2 due to underventilation or an intrinsic lung issue

14
Q

what is forced vital capacity

A

total lung capacity - residual volume

15
Q

what ratio determines the 3 physiological zones of the lung

A

the ratio between capillary perfusion and alveolar ventilation

16
Q

what is there a small A-a gradient as opposed to no gradient

A

venous admixture and regional areas of V/Q <1