11.2 Mechanism of Breathing

Question 1

What does a spirometer do?

Answer 1

records the volume of air exchanged during both normal and deep breathing

Question 2

What is tidal volume?

Answer 2

the amount of air inhaled and exhaled at rest, normally about 0.5 L

Question 3

How is it possible to increase the amount of air inhaled and the amount exhaled?

Answer 3

by deep breathing

Question 4

What is vital capacity?

Answer 4

the maximum volume of air that can be moved in and out during a single breath

Question 5

Why is it called vital capacity?

Answer 5

because breathing is essential to life

Question 6

What can decrease vital capacity?

Answer 6

a number of respiratory disorders discussed in 11.4

Question 7

What is inspiratory reserve volume?

Answer 7

when you take a deep breath, a healthy person can increase the volume of inhaled air beyond the tidal volume by about 3 L, an amount called the inspiratory reserve volume

Question 8

What is expiratory reserve volume?

Answer 8

similarly to inspiratory reserve volume, people can forcefully exhale well beyond the normal tidal volume, usually about 1.5 L of air

Question 9

What is vital capacity the sum of?

Answer 9

tidal volume + inspiratory reserve volume + expiratory reserve volume

Question 10

What does inspiratory and expiratory reserve volumes depend on? How do these various factors affect the volumes? (3)

Answer 10

• age: decreasing after age 30
• gender: 10-20% lower in women
• physical activity: 20-30% higher in conditioned athletes

Question 11

How is the total percentage of tidal volume split during normal breathing?

Answer 11

• 70% of the tidal volume actually reaches the alveoli

- 30% remains in the airways

Question 12

What is residual volume?

Answer 12

even after a very deep exhalation, some air (about 1 L) remains in the lungs

Question 13

What happens to residual volume in some lung diseases?

Answer 13

it increases because the individual has difficulty emptying the lungs

Question 14

Describe the air remaining in the lungs as part of the residual volume.

Answer 14

air is not as useful for gas exchange because it has been depleted of oxygen

Question 15

What are the 3 facts that should be remembered to understand ventilation?

Answer 15

1. normally there is a continuous column of air from the pharynx to the alveoli

2.

• the lungs lie within the sealed-off thoracic cavity
• the rib cage forms the top and sides of the thoracic cavity
• the intercostal muscles lie between the ribs
• the diaphragm and connective tissue form the floor of the thoracic cavity

3. lungs adhere to the thoracic wall by way of the pleura and normally any space between the two pleurae is minimal due to the surface tension of the fluid between them

Question 16

Where do the lungs lie?

Answer 16

within the sealed-off thoracic cavity

Question 17

What does the rib cage consist of?

Answer 17

ribs joined to the vertebral column posteriorly and to the sternum anteriorly

Question 18

What does the rib cage form?

Answer 18

the top and sides of the thoracic cavity

Question 19

Where do the intercostal muscles lie?

Answer 19

between the ribs

Question 20

What do the diaphragm and connective tissue form?

Answer 20

the floor of the thoracic cavity

Question 21

How do the lungs adhere to the thoracic wall?

Answer 21

by way of the pleura

Question 22

Why is any space between the 2 pleurae normally minimal?

Answer 22

due to the surface tension of the fluid between them

Question 23

What is inspiration?

Answer 23

the active phase of ventilation because this is the phase in which the diaphragm and external intercostal muscles contract

Question 24

What shape is the diaphragm in its relaxed state?

Answer 24

dome-shaped

Question 25

What happens to the diaphragm, external intercostal muscles, and rib cage during deep inspiration?

Answer 25

• diaphragm contracts and lowers
• external intercostal muscles contract
• rib cage moves upward and outward

Question 26

Describe what happens during inspiration.

Answer 26

• following the contractions, the volume of the thoracic cavity increases and the lungs expand
• now the air pressure within the alveoli decreases, creating a partial vacuum
• because alveolar pressure is now less than atmospheric pressure outside the lungs, air naturally flows from outside the body into the respiratory passages and into the alveoli

Question 27

Why does air come into the lungs?

Answer 27

because the lungs have already opened up

• AIR DOES NOT FORCE THE LUNGS OPEN
• this is why “humans inhale by negative pressure”
• while inspiration is the active phase of breathing, the actual flow of air into the alveoli is passive

Question 28

What is expiration?

Answer 28

the passive phase of breathing, and no effort is required to bring it about

Question 29

Describe what happens during expiration.

Answer 29

• the elastic properties of the thoracic wall and lungs cause them to recoil
• the surface tension of the fluid lining the alveoli tends to draw them closed
• the abdominal organs press up against the diaphragm
• the rib cage moves down and inward

Question 30

What happens to the diaphragm and external intercostal muscles during expiration?

Answer 30

usually relaxed

Question 31

When can expiration be active?

Answer 31

when breathing is deeper and/or more rapid

Question 32

What does contraction of the internal intercostal muscles do to the rib cage?

Answer 32

can force the rib cage to move downward and inward, and the increased pressure in the thoracic cavity helps to expel air

Question 33

What is the normal adult resting breathing rate?

Answer 33

12-20 ventilations per minute

Question 34

What is the rhythm of ventilation controlled by?

Answer 34

a respiratory centre located in the medulla oblongata of the brain

Question 35

Describe how the respiratory centre controls inspiration and expiration.

Answer 35

stimulates inspiration by automatically sending impulses to the diaphragm by way of the phrenic nerve, and to the intercostal muscles by way of the intercostal nerves

when the respiratory centre temporarily stops sending neuronal signals to the diaphragm and the rib cage, the diaphragm relaxes and resumes its dome shape

expiration occurs

Question 36

What does the respiratory centre control?

Answer 36

the rate and depth of breathing

Question 37

What can the respiratory centre’s activity be influenced by?

Answer 37

nervous and chemical input

Question 38

What happens after forced inhalation?

Answer 38

stretch receptors in the alveolar walls send inhibitory nerve impulses via the vagus nerve to the respiratory centre, which temporarily inhibits the respiratory centre from sending out nerve impulses

Question 39

Describe the nervous control of breathing.

Answer 39

• respiratory centre automatically stimulates the external intercostal (rib) muscles and diaphragm to contract via the phrenic nerve
• after forced inhalation, stretch receptors send inhibitory nerve impulses to the respiratory centre via the vagus nerve
• usually, expiration automatically occurs because of the lack of stimulation from the respiratory centre to the diaphragm and intercostal muscles

Question 40

Why does expiration usually occur?

Answer 40

because of the lack of stimulation from the respiratory centre to the diaphragm and intercostal muscles

Question 41

Describe the chemical input influence on the respiratory centre.

Answer 41

• most of CO2 that enters the blood combines with water, forming an acid, which breaks down and gives off H+
• respiratory centre contains cells that are sensitive to the levels of both CO2 and H+ in the blood
• when either rises, respiratory centre increases the rate and depth of breathing
• respiration rate is also influenced by cells called CAROTID BODIES (in carotid arteries) and AORTIC BODIES (in aorta)
• when the concentration of blood oxygen decreases, these bodies communicate with the respiratory centre, and the rate and depth of breathing increase