Respiratory Physiology Lecture 1.3: The Alveoli

Question 1

What are alveoli?

Answer 1

Tiny, thin-walled, capillary rich sac in the lungs where the exchange of oxygen and carbon dioxide takes place

Question 2

Where does the exchange of gases take place in the lungs?

Answer 2

Alveoli

Question 3

Approximately how many alveoli are in the human lung?

Answer 3

~ 500 million

Question 4

Diameter of alveoli

Answer 4

~⅓ mm

Question 5

How many capillaries are in the lungs?

Answer 5

~280 billion capillaries

Question 6

What volume of blood does the lung capillaries have?

Answer 6

• At rest they contain 70 mL of blood
• 200 mL during physical activity

Question 7

What are the two types of alveolar cells?

Answer 7

• Type I alveolar cells
• Type II alveolar cells

Question 8

What type of alveolar cell is most abundant?

Answer 8

Type I

Question 9

Type I alveolar cells

Answer 9

• Most of the surface of the alveolar walls are lined by a continuous mono-layer of flat epithelial cells
• Do not divide
• Susceptible to inhaled or aspirated toxins

Question 10

Type II alveolar cells

Answer 10

• produce surfactant
• act as progenitor cells

Question 11

How much of alveolar cells is made up of Type II?

Answer 11

7% of alveolar surface

Question 12

What is the surfactant produced by Type II alveolar cells?

Answer 12

Detergent-like substance made of lipoproteins

Question 13

What does surfactant do?

Answer 13

reduces surface tension of alveolar fluid

Question 14

How do type II alveolar cells act as progenitor cells?

Answer 14

When there is injury to Type I cells, Type II cells can multiply and eventually differentiate into Type I cells

Question 15

size of capillaries

Answer 15

Capillaries are small (7 to 10 μM in diameter)

Question 16

What can pass through capillaries?

Answer 16

just enough space for a red blood cell to pass

Question 17

How long does it take for a RBC to pass through capillaries?

Answer 17

Each red blood cell spends about 0.75 seconds in the capillary network and during this time probably traverses 2 or 3 alveoli

Question 18

What network do the alveolar walls contain?

Answer 18

The alveolar walls also contain a dense network of capillaries and a small interstitial space (Connective tissue and interstitial fluids)

Question 19

How does gas exchange occur?

Answer 19

Transfer of O2 and CO2 occurs by diffusion through the respiratory membrane

Question 20

diameter of respiratory membrane

Answer 20

0.2 - 0.5 uM thick

Question 21

Another term for type I and type II alveolar cells?

Answer 21

Type I pneumocyte and Type II neumocyte

Question 22

What makes up the epthelium avelolar wall?

Answer 22

Type I and Type II pneumocytes`

Question 23

What are the layers of the respiratory membrane?

Answer 23

• Alveolar fluid (With surfactant)
• Alveolar epithelium
• Basement membrane of alveolar epithelium
• Interstitial space
• Basement membrane of capillary endothelium
• Capillary endothelium

Question 24

What are the layers of the respiratory membrane?

Answer 24

• Alveolar fluid (With surfactant)
• Alveolar epithelium
• Basement membrane of alveolar epithelium
• Interstitial space
• Basement membrane of capillary endothelium
• Capillary endothelium