Module 3 Section 3

Question 1

what is Poiseuille’s Law

Answer 1

determines the resistance to flow

Question 2

explain bronchoconstriction

Answer 2

• the airways are highly innervated with both sympathetic and parasympathetic inputs
• the activity of these fibres plays a key role in determining airway resistance
• at rest, parasympathetic activity is dominant and promotes bronchoconstriction
  -smooth muscle contraction in the bronchioles occurs because ventilator demand is low
• these fibres have a tonic activity to maintain a resting level of contraction or “tone”
• also occurs under the influence of local chemical controls and pathological factors

Question 3

what factors can play a role in bronchoconstriction

Answer 3

• histamine release
• excess mucus
• airway collapse
• oedema of the airway walls
• allergy-induced spasm of the airways caused by slow-reactive substance of anaphylaxis

Question 4

explain bronchodilation

Answer 4

• when not at rest, or during periods of sympathetic domination when body O2 demands are increased, sympathetic activity causes bronchodilation to allow maximum flow rates with minimum resistance
• sympathetic activity is two-fold, as it is mediated by both direct and indirect innervation

Question 5

explain direct and indirect innervation of bronchodilation

Answer 5

1. Direct: nerve terminals release NE, which activates B2-receptors on the bronchial smooth muscle cells
2. Indirect: E released from the adrenal medulla circulates through the pulmonary circulation to the airway smooth muscle

Question 6

what are other contributing factors of bronchodilation

Answer 6

• increased CO2 concentrations can also cause bronchodilation in an effort to increase ventilation and remove the excess CO2
• there are no pathological conditions that cause bronchodilation

Question 7

explain airway resistance and chronic pulmonary diseases

Answer 7

• chronic lung diseases are foten characterized by a narrowing of the lower airways, which results in an increased resistance
• a larger pressure gradient is necessary to maintain flow
• this can cause people with pulmonary diseases to need to work harder to breathe

Question 8

explain asthma

Answer 8

• a chronic inflammatory disease of the airways that causes difficulty breathing
• symptoms may include shortness of breathe, chest tightness, coughing, or wheezing

Question 9

what are the 3 ways airways can be impaired in asthmatic individuals

Answer 9

1. the airway walls are thickened due to histamine-induced oedema
2. thick mucus secretion physically blocks the airways
3. airway hyper-responsiveness causes spasms of smooth muscles in smaller airways, resulting in their constriction

Question 10

explain normal vs. asthmatic airways

Answer 10

• the triggers for these impairments is varied but frequently involves repeated exposure to allergens, irritants, or infection
• severe asthma attacks can narrow airways to the point that all airflow is blocked, leading to death

Question 11

explain chronic obstructive pulmonary disease

Answer 11

• COPD is a term used to cover both emphysema and chronic bronchitis and is usually caused by long-term cigarette smoking
• it is currently the 4th leading cause of death in Canada

Question 12

explain chronic bronchitis

Answer 12

• a long term inflammatory condition of the lower airways
• it is usually caused by chronic exposure to cigarette smoke, allergens, or air pollution
• the airways become narrowed due to oedema of the airway walls and secretion of a thick mucus

Question 13

explain emphysema

Answer 13

• this irreversible condition is characterized by the collapse of the smaller airways and breakdown of alveolar tissues
• in response to chronic exposure to cigarette smoke, alveolar macrophages release substances like trypsin as a defensive mechanism
• excess trypsin and other destructive enzymes destroy the lung tissue