Physiology - Gas Exchange

Question 1

What is anatomical dead space?
Alveolar?
Physiological?

Answer 1

Anatomical dead space refers to the airway where some inspired air becomes trapped and cannot undergo gas exchange.

Alveolar dead space refers to ventilated alveoli that are not adequately perfused with blood.

Physiological = anatomical + alveolar.

Question 2

Difference between pulmonary and alveolar ventilation?

Answer 2

P -Is the volume of air breathed in and out/min (TV*RR)

A - the volume of air exchanged between the atmosphere and alveoli/min (TV - Dead space volume *RR).

Question 3

is pulmonary or alveolar ventilation lower? Why?

Answer 3

Alveolar, due to anatomical dead space.

Question 4

Define ventilation and perfusion.

Answer 4

V - the rate at which gas is passing through the lungs.

P - the rate at which blood is passing through the lungs.

Question 5

What is meant by ventilation perfusion match in the lungs?

Answer 5

Local controls act on the smooth muscles of airways and arterioles to match airflow to blood flow.

Question 6

When perfusion is > ventilation…

Answer 6

CO2 increases in area, dilation of airways, increasing airflow.

O2 decreases in area, constriction of blood vessels, decreasing blood flow.

Question 7

When ventilation is > perfusion…

Answer 7

CO2 decreases in area, constriction of airway, decreasing airflow.

O2 increases in area, vasodilation to increase blood flow.

Question 8

Effects of O2 on pulmonary veins versus arteries.

Answer 8

A - O2 decrease causes vasoconstriction, O2 increase causes vasodilation.

V - Opposite.

Question 9

4 factors affecting rate of gas exchange at alveolar membranes?

Answer 9

Partial pressure gradient of O2 & CO2.

Diffusion coefficient of O2 & CO2

SA of alveolar membrane

Thickness of alveolar membrane.

Question 10

Dalton’s law?

Answer 10

Total pressure exerted by a gas mixture is equal to the sum of the partial pressures of each gas present.

Question 11

What is the partial pressure of a gas?

Answer 11

The pressure that one gas in a mixture of gases would exert if it were the only gas present in the whole volume occupied by the mixture at a given temperature.

Question 12

What is the air in resp tract saturated with?

Answer 12

Water.

Question 13

What contributes about 47mmHg to the total pressure in the lungs?

Answer 13

Water pressure.

Question 14

How do you calculate the pressure of inspired air?

Answer 14

Atmospheric - 47.

Question 15

What encircles each alveoli?

Answer 15

Pulmonary capillaries.

Question 16

List the non-respiratory functions of Resp System.

Answer 16

Route for water/heat loss.
Defends against foreign inhaled matter.
Help maintain normal acid-base balance.
Enables speech.

Question 17

What effect does increasing partial pressure gradient of O2 and CO2 have on rate of gas transfer?

Answer 17

increases rate.

Question 18

What effect does increasing diffusion coefficient have on rate of gas transfer?

Answer 18

increases rate.

Question 19

What effect does increasing SA of alveolar membrane have on rate of gas transfer?

Answer 19

Increases rate.

Question 20

What effect does increasing thickness of membrane have on rate of gas transfer?

Answer 20

Decreases rate.

Question 21

What is Fick’s law of diffusion?

Answer 21

The amount of gas that moves across a sheet of tissue in unit time is proportional to the area of the sheet but inversely proportional to its thickness.

Question 22

What does the airway do to increase SA for gas exchange?

Answer 22

Divides repeatedly.

Also have alveoli.

Question 23

What is the alveolar gas equation?

Answer 23

PAO2 = piO2 - [PaCO2/0.8]

0.8 is respiratory exchange ratio.

Question 24

O2 and CO2 partial pressure gradients across pulmonary and systemic capillaries.

Answer 24

P - O2 - 60 mmHg
CO2 - 6 mmHg

S - O2 - >60 mmHg
CO2 > 6 mmHg

Question 25

Why is partial pressure gradient for CO2 much smaller than for O2?

Answer 25

CO2 is more soluble in membranes than O2.

Question 26

What does a big gradient between PAO2 and PaO2 indicate?

Answer 26

Problems with gas exchange in lungs or right to left shunt in the heart.