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Pulmonary Ventilation 1 (Muscles breathing (Diaphragm:
Contracts…
Pulmonary Ventilation 1
Muscles breathing
Diaphragm:
- Contracts inspiration: flattens, increase vol thoracic cavity
- Relaxes expiration: raise + decreasing voln thoracic cavity
Internal intercostal muscles
- Lower ribcage FORCED EXPIRATION
External intercostal muscles
- Raise rib cage NORMAL/QUIET INSPIRATION
Scalenes, pectoralis minor, sternocleidomastoid:
-
Breathing
Inspiration:
- diaphragm contracts (vertical)
- Parasternal and external intercostal muscles raise ribs
(lateral)
Expiration
- Voln decrease (vertically)
- External parasternal and intercostals relax (lateral) :QUIET
- Internal intercostals contract: FORCED (lowers ribs)
Controlling breathing
-
-
Central chemoreceptors
- Increase rate and depth with increase CO2
PO2 + PCO2
Pouiseuille's Law
Resistance to airflow
- Viscosity of gas inversely proportional to 4th power r
-
Law of Laplace
- Pressure directly proportional to surface tension and inversely proportional to radius of alveolus
- Small alveoli greater risk of collapse without surfactant
Physical properties
Elasticity
- Lungs return to initial size after stretch (recoil)
- Lungs stuck to thoracic wall, under elastic tension
- Tension increases during inspiration, reduced by elastic recoil during expiration
Surface tension
- Exerted by fluid secreted on the alveoli
- Fluid absorbed by active transport Na+, secreted active transport Cl-
- Raises pressure of alveolar air, acts to collapse alveolus
- CF: imbalance of fluid absorption and secretion
Lung compliance
- Lungs expand when stretched
- change in lung voln per change in transpulmonary pressue
- Ease with whcih lungs expand under pressure
- Reduced by factors that produce resistance to distention: infiltration of connective tissue proteins in PF
Surfactant:
- Secreted type 2 alveolar cells
- hydrophobic protein and phospholipids
- Reduces surface tension between water molecules, reduces number of H bonds between water molecules
- More concentrated as alveoli get smaller during expiration
- Prevents collapse of alveoli
- Allows residual volume air remain in lungs
Alveolar-arterial gradient
- measure of difference in alveolar conc of O2 and arterial conc of O2
- PAO2: alveolar gas equation: PiO2 - PaCO2/0.8
- PiO2 = inspired air delivered to patient
- PaCO2: partial pressure CO2 from blood gas