Class notes Human anatomy and physiology

Week 10

Airway Anatomy:
1. Distribution of Cartilage and Smooth Muscle:
Airway Region Cartilage Smooth Muscle Notes
Trachea Most Abundant (C- Between cartilage Provides structure;
shaped) rings prevents collapse
during inspiration
Bronchi Present (plates Present between Transition from rigid
instead of full rings) cartilage plates to flexible
Bronchioles No cartilage Almost entirely Key site for
smooth muscle regulation of airway
diameter
Respiratory No cartilage Little smooth muscle Begin gas exchange;
Bronchioles (discontinues) dominated by alveoli

2. Site of Greatest Airflow resistance:
- Bronchioles:
- Contain smooth muscle capable of bronchoconstriction and bronchodilation
- Lack of cartilage support -> more prone to narrowing
- Resistance depends on radius -> small changes in diameter cause large changes in
resistance.
Airway Function and Dysfunction
1. Ventilation and Airway Resistance:
- Inspiration -> Resistance Decreases:
- Lung inflation pulls alveoli and bronchioles open
- Airway diameter increases -> airflow is easier
- Expiration -> Resistance Increases:
- Lungs recoil -> airways compress and narrow
- Smaller radius -> higher resistance
- Resistance is very high, airflow becomes turbulent, producing a wheeze
- Trapped air prevents fresh air entry -> impaired gas exchange.
2. Bronchoconstriction vs. Bronchodilation
- Sympathetic Pathway:
- Neurotransmitter: epinephrine and norepinephrine
- Effect: Bronchodilation
- Receptors: beta 2-adrenergic
- Parasympathetic:
- Neurotransmitter: Acetylcholine

, - Effect: Bronchoconstriction
- Receptors: Muscarinic
3. Mechanisms that increase airway resistance:
- 1. Smooth Muscle Contraction:
- Acute: asthma attack -> bronchoconstriction
- Chronic: smooth muscle hypertrophy from inflammation
- 2. Inflammation:
- Edema and vascular congestion within airway walls narrow the lumen
- 3. Obstruction of Lumen:
- From mucus, tumors, or foreign bodies
4. Clinical Methods to Reduce Airway Resistance:
- Bronchodilators:
- Mechanism:
- Stimulate B2 receptors -> relax smooth muscle -> bronchodilation
- Albuterol
- Inhaled Corticosteroids:
- Mechanism: decrease inflammatory response and edema
- Fluticasone, budesonide
5. Decreased Lung Compliance:
- Causes:
- Chronic inflammation
- Fibrosis/ scar tissue formation
- Consequences:
- 1. Increased work of breathing -> more ATP required -> inc. metabolic rate.
- 2. Incomplete inflation -> dec. alveolar expansion -> impaired gas exchange
- 3. Reduced elastic recoil -> active expiration required -> additional ATP use.
Partial Pressure
1. Concept of Partial pressure
- Definition:
- Pressure exerted by an individual gas within a mixture of gases.
- PP= Total pressure x fraction of gas
- @ Sea Level:
- Atmospheric pressure = 760mmHg
- Oxygen = 21% of air
2. Abbreviations for Respiratory Gases:
- PO2:
- Partial pressure of oxygen
- 160 mmHg
- Decreases @ higher altitudes
- FO2:
- Fraction of oxygen in air
- 0.21 (21%)
- Constant regardless of altitude




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