Gas Exchange

Question 1

What process do gasses move down their concentration gradients from high to low pressure?

Answer 1

Diffusion

Question 2

Are concentration gradients the same as pressure gradients?

Answer 2

Yes

Question 3

What changes as you go down the respiratory tree from the bronchioles to the alveoli?

Answer 3

• Airways branch into smaller and more numerous until terminating at a group of alveoli
• Each division result in an increase in number, a decrease in diameter and an increase in surface area

Question 4

What must the sum of the partial pressures or tensions of a gas be equal to?

Answer 4

The total pressure

Question 5

At sea level what does atmospheric pressure equal?

Answer 5

760 mmHg (barometric pressure)

Question 6

How can you work out the partial pressure of a gas if you are given the % of it in the air?

Answer 6

Pgas = fraction of gas (Fgas) (percentage) in the mixture x barometric pressure (760mmHg)

Question 7

What are the conducting airways?

Answer 7

• Bronchi containing cartilage and non-respiratory bronchioles
• They do not participate in gas exchange
• They form anatomic dead space

Question 8

What is anatomic dead space?

Answer 8

Conducting airways that are not involved in gas exchange so gas exchange of air does not occur until it reaches the lower bronchioles/alveoli

Question 9

What are respiratory airways?

Answer 9

• Bronchioles with alveoli where gas exchange occurs (from terminal bronchiole to alveoli)
• The region is around 5mm long and around 2500ml in volume

Question 10

What is the respiratory unit/gas exchange unit?

Answer 10

The basic physiological unit of the lung consisting of respiratory bronchioles, alveolar ducts and alveoli

Question 11

In adults how many alveolar sacs are there?

Answer 11

Around 300-400 million

Question 12

What shape are alveoli?

Answer 12

Polygonal in shape

Question 13

What types of epithelial cells are alveoli composed of?

Answer 13

Type 1 and type 2

Question 14

Why are alveoli ideal for gas exchange?

Answer 14

• They have a huge surface area and thin walls

- They also have good diffusion characteristics

Question 15

What are type 1 epithelial cells and how abundant are they?

Answer 15

• Primary site of gas exchange

- Occupy 97% of surface area of the alveoli

Question 16

What are type 2 epithelial cells and how abundant are they?

Answer 16

• Produce pulmonary surfactant (reduces surface tension)

- Occupies 3% of surface area

Question 17

What is the function of alveolar macrophages?

Answer 17

• Removal of debris

Question 18

What are the 2 different blood supplies of the lungs?

Answer 18

• Pulmonary circulation: brings deoxygenated blood from the hear to the lungs and oxygenated blood from the lungs to the heart and then rest of body
• Bronchial circulation: brings oxygenated blood to ling parenchyma (functioning part of the lung)

Question 19

What is the total blood volume in the pulmonary circulation?

Answer 19

500mls (10% of total)

Question 20

What is the distance between alveoli and red blood cells?

Answer 20

1-3 micrometres

Question 21

How quickly do RBC pass through capillaries?

Answer 21

In less than 1 second - sufficient time for CO2 and O2 gas exchange

Question 22

Where does O2/CO2 go in the pulmonary circuit?

Answer 22

• O2 enters blood

- CO2 leaves the blood

Question 23

Where does O2/CO2 go in the systemic circuit?

Answer 23

• O2 leaves the blood

- CO2 enters the blood

Question 24

Why is the pressure gradient for O2 much bigger than for CO2?

Answer 24

Because CO2 is more diffusible