[6.7] the mechanism of breathing

Question 1

what is ventilation?

Answer 1

the process to maintain diffusion of gases across the alveolar epithelium by constantly moving air in and out of the lungs

aka breathing

Question 2

what is inspiration?

Answer 2

when air pressure of atmosphere is greater than air pressure inside lungs so air is forced into lungs

aka inhalation

Question 3

what is expiration?

Answer 3

when the air pressure in the lungs is greater than that of the atmosphere so air is forced out of lungs

aka exhalation

Question 4

what are the 3 sets of muscles which bring about the pressure changes within the lungs?

Answer 4

• diaphragm - sheet of muscle that separates thorax from abdomen
• intercostal muscles - lie between ribs. include:

> internal intercostal muscles - contraction leads to expiration

> external intercostal muscles - contraction leads to inspiration

Question 5

what happens during inspiration? (7)

Answer 5

• external intercostal muscles contract
• internal intercostal muscles relax
• ribs are pulled upwards and outwards
• diaphragm muscles contract so it moves downwards
• therefore, volume in thorax increases
• therefore pressure in thorax decreases
• once thoratic pressure is lower than atmospheric pressure, air is forced into the lungs down the pressure gradient

Question 6

what happens during expiration?

Answer 6

• external intercostal muscles relax, internal intercostal muscles contract
• ribs are pulled downwards and inwards
• diaphragm muscles relax so it moves upwards
• therefore, volume in thorax decreases
• therefore pressure in thorax increases
• once thoratic pressure is higher than atmospheric pressure, air is forced out of the lungs down the pressure gradient

Question 7

is inspiration and expiration passive or active?

Answer 7

• inspiration is an active process
• expiration is largely passive

> helped by the natural elastic recoil, which requires no energy input, of the lung tissue, rib cage and intercostal muscles

Question 8

describe a graph which shows pressure in thorax relative to atmospheric pressure against time

Answer 8

• during inspiration (breathing in), pressure is lower in thorax relative to atmospheric pressure
• during expiration (breathing out), pressure is higher in thorax relative to atmospheric pressure
• basically looks like ∿ but mirrored?

Question 9

what is pulmonary ventilation rate?

Answer 9

• the total volume of air that is moved into the lungs during 1 minute
• pulmonary ventilation rate (dm³ min⁻¹) = tidal volume (dm³) × breathing rate (min⁻¹)

> tidal volume is the volume of air normally taken in at each breath when the body is at rest. usually 0.5 dm³

> breathing rate is the number of breaths taken in 1 min. usually 12-20 in a healthy adult

Question 10

what is the equation for cardiac output?

Answer 10

stroke volume × heart rate