General definitions, anatomy of respiratory system, characteristics of bronchi and bronchioles, diffusion, lung blood supply, muscles of respiration, LaPlace's law, gas laws

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Biomedical Science
BMS 420
Charles Miller

29 October General Definitions C: Concentration or content (mL/dL) or mmol/L D: Diffusing capacity (mLO /mi2 x mmHg) P: Gas pressure or partial pressure (mmHg) – torr, mmHg, cmH O 2 Tension = partial pressure T: Temperature V: Gas volume CaO :2Arterial O c2ntent CvO :2Mixed venous O conte2t PB: Barometric pressure (atmospheric pressure) PaCO : 2rterial blood CO tens2on PaO :2Arterial blood O te2sion PAO 2 Alveolar O te2sion PCO :2Partial pressure of CO (in 2as or liquid [does not specify arterial or venous]) PO 2 Partial pressure of O (in2gas or liquid [does not specify arterial or venous]) Ppa: Mean pulmonary artery pressure Pppl: Pleural pressure PtO 2 Partial pressure for O in2tissue Anatomy of the Respiratory System – Quick Review Right lung with 3 lobes and left lung with 2 lobes Alveolar spaces are responsible for majority of the 4 liters or so lung volume Alveolar spaces separated by interstitium with collagen and potential space for fluids and cells Upper airways: nares to larynx Lower airways: trachea to alveoli Visceral pleura: thin membrane covering outside of lungs Parietal pleura: thin membrane lining lungs and diaphragm Pleural cavity: space between the two membranes and important in ventilation Characteristics of Bronchi and Bronchioles Bronchi: cartilage, diameter - > 1 mm, epithelium – pseudostratified/columnar, blood supply – bronchial, no alveoli Terminal bronchioles: no cartilage, diameter - <1 mm, epithelium – cuboidal, blood supply – bronchial, no alveoli Respiratory bronchioles: no cartilage, diameter - <1 mm, epithelium – cuboidal, blood supply – pulmonary, alveoli Dead space: no gas exchange – anatomical or physiologic (ventilation:perfusion mismatch) Length of respiratory bronchioles to alveoli is about 5 mm long Contains most of the lung volume (2.5 L) – terminal bronchioles ~ lung volume of 200 mL 70 – 80 m surface area at resting lung volume Type I cells – structural component of alveoli Type II cells – septal cells Responsible for creating surfactant (lowers surface tension, easier to inflate lungs) Only cells in fetal lungs – evolve into type I Repair alveoli Each cluster of alveoli is surrounded by elastic fibers and a network of capillaries Type I cells are thinner – easier to cross Admixture – oxygenated and deoxygenated blood in pulmonary veins, physiological shunt Type II cells occupy about 2 – 4% of surface area and found in “corners” of alveoli Diffusion 300 million alveoli Each alveoli is 1/3 mm (about 300 μm) in diameter 280 billion capillaries or 1000 per alveolus Surface area = 85 m 2 Note thin b
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