Respiratory Physiology- Gas Exchange

Question 1

Pulmonary ventilation

Answer 1

Pulmonary Ventilation (L/min (resting conditions))= TV (L/breath) x RR (breath/min)

Vol of air breathed in and out every minute

Question 2

How to increase pulmonary ventilation?

Answer 2

Increase depth (TV) (more advantageous due to dead space)
Increase rate of breathing (RR)

Question 3

Alveolar ventilation

Answer 3

Vol of air exchanged between atmosphere and alveoli per minute

(TV-dead space)xRR

Less than pulmonary ventilation due to dead space being deducted

Question 4

Factors affecting transfer of gas between body and atmosphere

Answer 4

Ventilation: rate gas passes through lungs
Perfusion: rate at which blood passes through lungs

Question 5

Alveolar dead space

Answer 5

ventilated alveoli which aren’t sufficiently perfused with blood

Question 6

Anatomical dead space

Answer 6

Volume of air that is inhaled that does not take part in the gas exchange, because it either:

• remains in the conducting airways or
• reaches alveoli that are not perfused or poorly perfused

Question 7

Physiological dead space

Answer 7

alveolar and anatomical dead space

Question 8

What happens when perfusion>ventilation?

Answer 8

• CO2 increases; O2 decreases
• local airways dilate; local blood vessels constrict
• airflow increases; blood flow decreases

Question 9

Effect of increased O2 conc on pulmonary arterioles?

Answer 9

Vasodilation (opposite for systemic arterioles)

Question 10

Factors affecting the rate of gas exchange across alveolar membrane?

Answer 10

1. partial pressure gradient
2. diffusion coefficient for O2 and CO2
3. surface area of alveolar membrane
4. thickness of alveolar membrane

Question 11

Partial pressure

Answer 11

The pressure which one gas in a mixture would exert if it were the only gas present in the volume that the whole mixture occupies at a given temp

Question 12

Dalton’s law of partial pressures

Answer 12

Total pressure exerted by a gaseous mixture= the sum of partial pressure of each individual component in the gas mixture

Question 13

Respiratory Exchange Ratio

Answer 13

CO2 produced/ O2 consumed

0.8 for a person eating a mixed diet

Question 14

Partial Pressure of O2 in alveolar air (equation)

Answer 14

PAO2=PiO2-[PaCO2/0.8]

Question 15

Partial pressure gradient for PaO2

Answer 15

Gases move from lungs to tissue (for PaCO2 tissue to lung)

Question 16

Why is the PP gradient for CO2 smaller than that of O2?

Answer 16

CO2 is twenty times O2 diffusion coefficient ie it is much more soluble in membranes

Question 17

Fick’s Law

Answer 17

The amount of gas to move across a sheet of tissue in unit time is proportional to the area of the sheet and inversely proportional to its thickness

Question 18

Respiratory tree

Answer 18

Trachea-> bronchi-> bronchioles-> terminal bronchioles-> respiratory bronchioles-> alveolar ducts-> alveolar sacs

Question 19

Components of the conducting zone of the respiratory tree

Answer 19

Trachea-> bronchi-> bronchioles-> terminal bronchioles

Question 20

Components of the transport and respiratory zone go the respiratory tree

Answer 20

Respiratory bronchioles-> alveolar ducts-> alveolar sacs

Question 21

Alveolus

Answer 21

Thin walled, inflatable sac
Wall made of type 1 alveolar cells
Function in gas exchange
Surrounded by pulmonary capillary

Question 22

When partial pressure increases, rate of transfer across alveolar membrane…

Answer 22

Increases

Question 23

When diffusion coefficient increases, rate of transfer across alveolar membrane…

Answer 23

Increases

Question 24

When surface area increases, rate of transfer across alveolar membrane…

Answer 24

Increases

Can be achieved via exercise (deeper breathing-> alveoli expand and pulmonary capillaries open up when cardiac output increases)
SA decreases with emphysema etc.

Question 25

When tissue thickness increases, rate of transfer across alveolar membrane…

Answer 25

Decreases

Thickness increases with pulmonary oedema, fibrosis, pneumonia etc.

Question 26

Non respiratory functions of the respiratory system

Answer 26

1. Route for water loss and heat elimination
2. Increases venous return (cardio)
3. LPS helps maintain acid-base balance (respiratory and renal)
4. Speech, singing etc.
5. Defence against foreign particles
6. Nose- organ of smell
7. removes/ modifies/ (in)activates materials passing through pulmonary circulation

Question 27

How does air flow match blood flow?

Answer 27

Local controls work on smooth muscle of airways and arterioles

Question 28

What happens when perfusion in alveoli is increased?

Answer 28

Decreased airway resistance-> increases air flow-> CO2 accumulates

Question 29

What happens when ventilation is increased?

Answer 29

Pulmonary vasodilation-> increases blood flow to match larger airflow-> Increased alveolar O2 conc

Question 30

Which pressure of a gas determines the pressure gradient?

Answer 30

Partial pressure