Respiratory Function & Dysfunction

Question 1

List 5 defence mechanisms of the respiratory system.

Answer 1

1. Mucociliary defenses - mucous traps microbes, cilia beat to move them away from lungs.
2. Sneeze and cough reflex - stimulation of irritant receptors.
3. IgA - antibody found in respiratory secretions
4. Alveolar macrophages - engulf small particles
5. pulmonary microbiome

Question 2

What are the 3 processes involved in gas exchange (conditions that affect these factors impair gas exchange)

Answer 2

1. alveolar-capillary diffusion
2. ventilation
3. pulmonary perfusion

Question 3

Define ventilation and what it depends on.

Answer 3

The physical movement of air into and out of the lungs (=inspiration and expiration)
Depends on:
1. pressure gradients
2. airway resistance
3. lung and chest compliance

Question 4

Explain the physical and pressure related process associated with inspiration.

Answer 4

• Diaphragm and external intercostals contract
• Increases thoracic volume
• lungs are pulled open
• decreased pressure in the airways and alveoli pressure (Pa)
• Pa<Patm = air enters the lungs down a pressure gradient

Question 5

Explain the physical and pressure related process associated with exhalation.

Answer 5

• Inspiratory muscles relax
• Decreased thoracic volume
• elastic components recoil and the lungs are compressed
• Increased alveolar pressure
• Pa>Patm = air flows out down a pressure gradient

Question 6

What is the effect of bronchiole diameter on respiration?

Answer 6

1. Constriction of the bronchioles - parasympathetic stimulation (vagus nerve) = bronchoconstriction which increases airway resistance
2. Stimulation of the sympathetic system (B2 receptors) = bronchodilation which decreases airway resistance

Question 7

What is the role of elastic fibres in airway resistance?

Answer 7

Elastic fibres within bronchiole walls - stretch during inspiration (allow air flow in) and recoil during expiration (push air out).

NOTE: radiating elastic fibres pull outwards on bronchiole wall preventing complete collapse between breaths.

Question 8

How does chronic bronchitis contribute to airway resistance?

Answer 8

Thickening of airway walls with inflammation.

Question 9

How does cystic fibrosis contribute to airway resistance?

Answer 9

Airway occlusion from mucus accumulation.

Question 10

How does emphysema contribute to airway resistance?

Answer 10

Loss of elastic fibres need to keep airways open.

Question 11

Define lung compliance.

Answer 11

The effort required to expand the lungs and chest wall.

High compliance = the lungs expand easily

Low compliance = greater force is required to expand the lungs during inhalation.

Question 12

What are mechanisms causing decreased lung compliance (5)?

Answer 12

Conditions that decrease elasticity:
- scarring of the lungs (collagen is inelastic)
- e.g. pulmonary fibrosis.

Conditions that increase the water content of the lungs:
- filling of lung tissue with fluid makes the lungs stiff
- e.g. pulmonary edema

Conditions that impair diaphragm flattening or rib cage expansion:
- e.g. obesity, pregnancy, ascites, kyphosis

Conditions that cause lung collapse:
- e.g. pneumothorax (air enters the pleural cavity causing an increase in Pip)

Conditions that increase alveolar surface tension:
- causes alveolar collapse and difficulty expanding the lungs
- e.g., surfactant deficency

Question 13

What are some causes of neuromuscular dysfunction that impact ventilation?

Answer 13

1. CNS depression (opioid overdose)
2. Injury or lesion affecting the brainstem (stroke)
3. Disease of the motor neurons of the spinal cord (spinal cord injury, ALS)
4. Disease of the neuromuscular junction (myasthesia gravis)
5. disease of respiratory muscles (muscular dystrophy)

Question 14

What are 3 causes of impaired ventilation leading to restrictive or obstructive lung disease?

Answer 14

1. decrease in lung or chest compliance
2. neuromuscular dysfunction
   (1and 2 decrease lung expansion and inhalation) = RESTRICTIVE lung disease
3. increase in airway resistance
   (impaired lung emptying and exhalation) = OBSTRUCTIVE lung disease

Question 15

Describe alveolar-capillary diffusion.

Answer 15

O2 and CO2 move by diffusion across a pressure gradient between the alveoli and capillaries.

Question 16

Efficiency of alveolar-capillary diffusion depends on:

Answer 16

1. differences in partial pressure across the membrane
2. the diffusion distance (thickness of the membrane)
3. surface area available

Question 17

What are 3 causes of impaired alveolar-capillary diffusion?

Answer 17

1. loss of alveolar surface area (e.g. emphysema)
2. increased thickness of the respiratory membrane (e.g. pulmonary edema or fibrosis)
3. decreased pressure gradient (e.g. altitude)

Question 18

What is pulmonary perfusion?

Answer 18

The blood flow through the pulmonary capillary bed that is available for gas exchange.

Question 19

What are 3 causes of impaired pulmonary perfusion?

Answer 19

1. Occlusion/obstructed blood flow (e.g. PE or valve stenosis)
2. Hypotension (e.g. shock)
3. right-to-left-shunt (e.g. AVM or VSD shunt reversal

Question 20

What is ventilation/perfusion matching?

Answer 20

Optimal gas exchange requires that the areas of the lungs that are ventilated (V) are equally perfused (Q).

Question 21

What is a V/Q mismatch?

Answer 21

When ventilation and perfusion are mismatched = hypoxemia

Low V/Q (shunt) occurs in airway obstruction

High V/Q (wasted ventilation) occurs in pulmonary obstruction

Question 22

What is hypoxic vasoconstriction?

Answer 22

A compensatory mechanism in V/Q mismatch.

• A decrease in PaO2 (alveolar O2) stimulates the constriction of arterioles supplying the affected alveoli
• redirects blood to better ventilated areas

Question 23

Describe respiratory control.of br

Answer 23

• the medullary rhythmicity area (medulla oblongata) controls the basic rhythm of breathing. It receives inputs from the pons and sensory neurons. These inputs modify rate and depth of breathing.
• contains motor neurons that control respiratory muscles
• resting adult rhythm = inhale for 2 sec, exhale for 3 sec (=12 breaths/min)

Question 24

What are inputs that trigger signals from pons and sensory neurons to the medullary rhythmicity area to affect rate and depth of breathing?

Answer 24

1. Chemoreceptors (PO2, PCO2, pH)
2. baroreceptors (BP)
3. Lung stretch receptors (lung volume)
4. airway irritant receptors
5. proprioceptors (joints)
6. limbic system (emotions)
7. hypothalamus (body temp)
8. cerebral cortex (voluntary control)

Question 25

Describe the peripheral and central chemoreceptors that affect breathing.

Answer 25

1. peripheral:
   - located in the aortic arch (aortic bodies) and carotid sinuses (carotid bodies)
   - primarily detect decreased PaO2
   - large decrease in PaO2 <60mmHg (hypoxemia)
2. central:
   - located in the medulla oblongata
   - detect H+ in the CSF (indicates increased PaCO2). When PaCO2 increases, CO2 crosses into the CSF and is converted to H+ and HCO3.
   - small increase in PaCO2 > 45mmHG (hypercapnia)

Question 26

What is responsible for regulating respiratory drive?

Answer 26

CO2 levels.