Physiology 1 Lungs

movement of air from the atmosphere to gas exchange surfaces within the lung

maintain adequate O2 supply and CO2 removal to and from respiring tissues

volume and rate of breathing

Minute volume(mL) = tidal volume(mL) x frequency(min^-1)

minute vol - the total volume of air inhaled in all breaths over one minute. tidal vol - the volume of air inhaled in each breath. frequency - number of breaths per minute

150mL

Alveolar min vol = (tidal vol - deadspace vol) x frequency

fluid filled space between membrane (pleura) that line the chest wall and each lung which reduces friction during breathing

diaphragm contracts volume of thoracic cavity increases alveolar pressure decreases below atmospheric pressure Parietal (chest) and visceral (lungs) pleura moves outwards

diaphragm relaxes, lungs recoil Visceral and parietal pleura moves inwards Volume in thoracic cavity decreases Alveolar pressure increases above atmospheric pressure

Pneumothorax (collapsed lung) because it destroys the negative pressure vacuum that normally holds the lung open against the chest wall.

𝐴𝑖𝑟𝑓𝑙𝑜𝑤 (𝑉) “= (Δ𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 (𝑃))/(𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑅)) ↑ΔP = ↑airflow ↑resistance = ↓airflow

𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑅) “∝ “ 1/𝑟𝑎𝑑𝑖𝑢𝑠^4 As an airway’s radius decreases, the resistance increases (and the airflow decreases) dramatically

Quantifies the relationship between the level of expansive force applied to the lung and the resulting change in volume

Transpulmonary pres. (Pt p) = Alveolar pres. (P alv) – Intrapleural pres (P ip) Transpulmonary pressure ≈ the level of force acting to expand the lung

𝐶𝑜𝑚𝑝𝑙𝑖𝑎𝑛𝑐𝑒 =Δ𝑉𝑜𝑙𝑢𝑚𝑒/Δ𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒

chest wall mechanics - e.g scoliosis, obesity ↓lung compliance alveolar surface tension - NRDS ↓lung compliance elastin fibres - COPD ↑lung compliance, Fibrosis ↓lung compliance

the presence of pulmonary surfactant secreted by type 2 pneumocytes

to equalise pressure & volume across varying alveoli prevent alveolar oedema reduces alveolar surface tension

multiplying total pressure by mole fraction.

alveolar collapse (atelectasis), reduced lung compliance, and difficulty breathing.

𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛=𝑃𝑎𝑟𝑡𝑖𝑎𝑙 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 ×𝑆𝑜𝑙𝑢𝑏𝑖𝑙𝑖𝑡𝑦 The partial pressure of gas dissolved in a liquid reflects the amount of gas that would dissolve (at equilibrium) if the liquid was placed in contact with a gas phase of equivalent partial pressure.

Large surface area wall = one cell layer thick richly innervated by capillaries for adequate blood supply

Matching of ventilation to perfusion(VQ coupling) as there is a maximum amount of O2 each unit of blood can carry.