Topic 13: Respiratory System - Overview + Pulmonary Ventilation

Question 1

What are the 3 processes involved in the exchange of air?

Answer 1

1) Pulmonary ventilation - inspiration and expiration
2) External Respiration
3) Internal Respiration

Question 2

What is the flow of air from the atmosphere to a cell? (4)

Answer 2

atmosphere to lungs to blood to cell

Question 3

Why does pulmonary ventilation occur?

Answer 3

• result of pressure gradients caused by changes in thoracic cavity volume (Boyle’s Law)

Question 4

What is Boyle’s Law? (2)

Answer 4

• gas volume is inversely proportional to pressure
• as volume increases, pressure decreases vice versa for the same number of molecules of air (gas amount is constant)

Question 5

What pressures are involved in pulmonary ventilation? (3)

Answer 5

1) Atmospheric pressure (Patm) - 760 mmHg (sea-lvl)
2) Intrapulmonary pressure (Ppul)
3) Intrapleural pressure (Pip)

Question 6

What is intrapulmonary pressure? (2)

Answer 6

• air pressure inside lungs
• between breaths is Patm

Question 7

What is intrapleural pressure? (3)

Answer 7

• fluid pressure in plural cavity
• always less than Ppul and usually less than Patm
• around 4 mm less than Patm (756 mmHg at rest)

Question 8

Why is intrapleural pressure less than atmospheric pressure? (2)

Answer 8

• thoracic walls recoil out and lungs recoil in
• but fluid holds them together, so Pip is slightly lower

Question 9

What are the four types of pulmonary ventilation?

Answer 9

• quiet inspiration
• forced inspiration
• quiet expiration
• forced expiration

Question 10

What is quiet inspiration? (3)

Answer 10

• active process where muscles contract
• at the start, atmospheric pressure = intrapulmonary pressure (760 mmHg)
• no air moves

Question 11

What occurs in quiet inspiration? (5)

Answer 11

1) diaphragm and external intercostals contract, increases volume of thoracic cavity
2) lungs resist expansion, decreases Pip (756 to 754)
3) higher pressure difference between Ppul and Pip pushes lungs out
4) lungs expand, decreasing Ppul (760 to 758 mmHg)
5) air moves down pressure gradient until Ppul = Patm

Question 12

What muscles are involved in forced inspiration? (5)

Answer 12

• diaphragm
• external intercostals
• sternocleidomastoids
• pectoralis minors
• scalenes
  they all contract and are therefore ACTIVE

Question 13

What occurs in forced Inspiration? (2)

Answer 13

• increased volume of thoracic cavity
• pressure gradient moves up and more air moves in

Question 14

What occurs in quiet expiration? (4)

Answer 14

• relax muscles so lungs go to resting size
• decrease thoracic cavity size (passive process)
• volume decreases and Pip increases (754 to 756 mmHg)
• therefore Ppul increases (760 to 762) and air moves down gradient

Question 15

What occurs in forced expiration? (5)

Answer 15

• laboured or impeded (ie. asthma) breathing
• relax diaphragm, external intercostals
• contract internal intercostals and abdominals (ACTIVE PROCESS)
• therefore increases intrapleural P, decreasing lung volume
• increases Ppul and air moves out