Respiratory Physiology 1 and 2

Question 1

List the functions of the respiratory system

Answer 1

Gas exchange – Oxygen added to the blood from the air, carbon dioxide removed from the blood into the air.

Acid base balance – regulation of body pH (see renal lectures)

Protection from infection

Communication via speech

Question 2

Describe the difference between external and internal respiration.

Answer 2

Cellular/Internal respiration – biochemical process that releases energy from glucose either via Glycolysis or Oxidative Phosphorylation. Latter requires oxygen and depends on:

External Respiration – movement of gases between the air and the body’s cells, via both the respiratory and cardiovascular systems.

Question 3

Describe the difference between pulmonary and systemic circulation

Answer 3

The pulmonary circulation is opposite to the systemic circulation in it’s function and it’s terminology.

It delivers CO2 (to the lungs) and collects O2 (from the lungs) while the systemic circulation delivers O2 to peripheral tissues and collects CO2.

The pulmonary artery carries deoxygenated blood, while the pulmonary vein carries oxygenated blood.

Question 4

Identify points of gas exchange between the respiratory and cardiovascular systems

Answer 4

Gas exchange occurs at the alveoli.

Question 5

Identify the net volume of gas exchanged in the lungs and the importance of this

Answer 5

In the steady state, the net volume of gas exchanged in the lungs per unit time (250ml/min O2; 200ml/min CO2) is equal to the net volume exchanged in the tissues.

This prevents gas build up in the circulation which would hamper gas exchange and helps to ensure supply = demand

Question 6

Identify respiration rate at rest and max

Answer 6

Respiration rate is 12-18 breaths/min at rest,
Can reach 40 - 45 at max. exercising capacity in adults

Question 7

Describe the respiratory tract using features to show where they start and end

Answer 7

Question 8

Describe the gross anatomical features of the lung

Answer 8

Question 9

Describe the main anatomical features of the airways and Identify the different classes of airways.

Answer 9

Question 10

Describe how and why resistance to air flow varies across the respiratory tree.

Answer 10

Air in the conducting zone sits in dead space. Airway diameter, and therefore resistance to air flow, can be altered by activity of bronchial smooth muscle: Contraction decreases diameter = increases resistance, Relaxation increases diameter = decreases resistance.

Fewer trachea means there is more resistance in these airways.

Question 11

Two types of alveoli

Answer 11

Two types of alveoli:
Thin walled type I cells permit gas exchange

Specialised Type II cells secrete surfactant fluid
Type I makes up the bulk of the alveolar wall

Question 12

Describe what is meant by anatomical dead space

Answer 12

Air in the airways which do not participate in gas exchange as the walls of the airways are too thick.

Question 13

Describe the size of the surface area of alveoli.

Answer 13

The surface area of the alveoli is enormous (80m2) but extremely thin so fits in a volume of approx. 6 L (3 L in each lung)

Question 14

Name and explain the key terms used to describe the different lung volumes

Answer 14

TV - Tidal Volume. The volume of air breathed in and out of the lungs at each breath.
ERV - Expiratory Reserve Volume. The maximum volume of air which can be expelled from the lungs at the end of a normal expiration.
IRV - Inspiratory Reserve Volume. The maximum volume of air which can be drawn into the lungs at the end of a normal inspiration.
RV - Residual Volume. The volume of gas in the lungs at the end of a maximal expiration.

VC - Vital Capacity = tidal volume + inspiratory reserve volume + expiratory reserve volume.
TLC - Total Lung Capacity = vital capacity + the residual volume.
IC - Inspiratory Capacity = tidal volume + inspiratory reserve volume.
FRC - Functional Residual Capacity = expiratory reserve volume + residual volume.
FEV1:FVC = Fraction of forced vital capacity expired in 1 second.

Question 15

Describe the anatomy of the pleural cavity

Answer 15

The interior of the thorax and each lung is enclosed in two pleural membranes, the space between these are known as the pleural cavity. Pleural cavity contains a thin layer of serous pleural fluid, which lubricates and allows pleurae to move smoothly over each other during respiration.

Question 16

Describe the relationship between the parietal and visceral pleura and why this is important for inflation and deflation of the lung

Answer 16

Visceral pleural membrane: lines the outer surface of the lungs.
The parietal pleural membrane: lines inner surface of the ribs. Lungs are effectively stuck to the rib cage through the relationship of the pleural membranes. Visceral pleura is stuck to parietal pleura via the cohesive forces of the pleural fluid.

Question 17

Describe how the muscles of respiration act to increase and decrease thoracic volume

Answer 17

The diaphragm is involved in respiration and causes changes in thoracic volume.
During inspiration airways are pulled open by physical forces of inspiration.
Airways are compressed by physical forces during expiration.
At rest the diaphragm is relaxed.
During inspiration the diaphragm contracts, thoracic volume increases.
During expiration the diaphragm relaxes, thoracic volume decreases.

Question 18

Relate Boyle’s law to the mechanics of breathing, inspiration and expiration

Answer 18

Boyle’s Law states that the pressure exerted by a gas is inversely proportional to to its volume (P a 1/V).
Gases (singly or in mixtures) move from areas of high pressure to areas of low pressure.
Breathing Occurs because the thoracic cavity changes volume
Based on Boyles Law:
increase volume = decrease pressure
decrease volume = increase pressure
Gases always move from high pressure to low pressure so changes in thoracic cavity volume drive in airflow into the lungs during respiration.

Question 19

Describe which muscles are involved in respiration

Answer 19

Inspiration uses external intercostals muscles and the diaphragm
Expiration is passive at rest, but uses internal intercostal and abdominal muscles during severe respiratory load

Question 20

Describe relevant pressures

Answer 20

Intra-thoracic (Alveolar) Pressure (PA): pressure inside the thoracic cavity, (essentially pressure inside the lungs). May be negative or positive compared to atmospheric pressure.
Intra-pleural Pressure (Pip): pressure inside the pleural cavity, typically negative compared to atmospheric pressure (in healthy lungs at least!)
Transpulmonary pressure (PT): difference between alveolar pressure and intra-pleural pressure. Almost always positive because Pip is negative (in health). PT = Palv – Pip.

Question 21

State the mechanical factors that affect respiratory minute volume.

Answer 21

Elastic recoil of the chest wall pulls the chest wall outward, elastic recoil of the lung causes an inward pull.

Question 22

Explain why intrapleural pressure is always less than atmospheric pressure.

Answer 22

Intrapleural pressure is less than atmospheric due to the recoil of the lungs and the expansion of the chest pulling the two pleural membranes apart causing increase in volume in the cavity thus decreasing the pressure.

Question 23

Explain why intrapleural pressure is always less than alveolar pressure.

Answer 23

At rest alveolar pressure is the same as atmospheric pressure and intrapleural is less. During expiration intrapleural pressure becomes less negative whereas alveolar pressure becomes more positive. Conversely during inspiration alveolar pressure becomes negative (below atmospheric pressure) however intrapleural pressure becomes even more negative due to the cohesive forces in the pleural fluid.

Question 24

Describe what causes a pneumothorax

Answer 24

If the sealed pleural cavity is opened to the atmosphere, air flows in. The air moves from the higher P-atmos to the lower P-ip to equalise the pressure. The relationship between the two pleural membranes is lost and the affected lung becomes useless as it collapses to unstretched size.

Question 25

What is surfactant?

Answer 25

Detergent like fluid produced by Type II Alveolar cells

Question 26

State the role of pulmonary surfactant.

Answer 26

Surfactant reduces surface tension on alveolar surface membrane thus reducing tendency for alveoli to collapse.
Increases lung compliance (distensibilty)
Reduces lung’s tendency to recoil
Makes work of breathing easier

Question 27

When does surface tension occur?

Answer 27

Surface tension occurs where ever there is an air-water interface and refers to the attraction between water molecules

Question 28

Why is surfactant more effective in small alveoli

Answer 28

Is more effective in small alveoli than large alveoli because surfactant molecules come closer together and are therefore more concentrated.

Question 29

Relate the law of LaPlace to surfactant effectiveness.

Answer 29

The law of LaPlace states P=2T/r
T describes the surface tension of an area. Surfactant reduces surface tension causing pressure to be equalised in large and small alveoli.

Question 30

Describe surfactant production and it’s consequences on infants.

Answer 30

Surfactant production starts ~25 weeks gestation. Complete by ~36 weeks. (40 weeks = full term). Stimulated by thyroid hormones and cortisol which increase towards end of pregnancy.
Premature babies suffer Infant Respiratory Distress Syndrome (IRDS).

Question 31

Define the term compliance and factors that affect this

Answer 31

Definition: change in volume relative to change in pressure i.e. how much does volume change for any given change in pressure.
It represents the stretchability of the lungs (not the elasticity!)
HIGH COMPLIANCE = large increase in lung volume for small decrease in ip pressure
LOW COMPLIANCE = small increase in lung volume for large decrease in ip pressure
Affected by disease states/age
Is determined, in part, by action of surfactant.