RESPIRATORY PHYSIOLOGY
The Thorax and its contentsVentilation: Action of breathing with muscles and lungs Gas exchange: Between air and capillaries in the lungs. Between systemic capillaries and tissues of the body
Respiration
Gas ExchangeO2, CO2 Acid-base balanceCO2 +H2O←→ H2CO3 ←→ H+ + HCO3- Phonation Pulmonary defense Pulmonary metabolism and handling of bioactive materials
Inspiration: lung volume increases -> decrease in intrapulmonary pressure, to just below atmospheric pressure -> air goes in! Expiration: vice versa
Compliance: This the ability of the lungs to stretch during inspiration lungs can stretch when under tension. Elasticity: It is the ability of the lungs to recoil to their original collapsed shape during expiration Elastin in the lungs helps recoil
Inspiration – Active processDiaphragm contracts -> increased thoracic volume vertically.Intercostals contract, expanding rib cage -> increased thoracic volume laterally.More volume -> lowered pressure -> air in.Negative pressure breathing
Expiration – PassiveDue to recoil of elastic lungs.Less volume -> pressure within alveoli is just above atmospheric pressure -> air leaves lungs.Note: Residual volume of air is always left behind, so alveoli do not collapse.
Conducting zone: Includes all the structures that air passes through before reaching the respiratory zone. Mouth, nose, pharynx, glottis, larynx, trachea, bronchi.
Conducting zone Warms and humidifies until inspired air becomes: 37 degrees Saturated with water vapor Filters and cleans: Mucus secreted to trap particles Mucus/particles moved by cilia to be expectorated.
Respiratory zone Region of gas exchange between air and blood Respiratory bronchioles Alveolar ducts, Alveolar Sacs and Alveoli
Air duct
Air SacAlveoliAir sacsHoneycomb-like clusters~ 300 million.Large surface area (60–80 m2).Each alveolus: only 1 thin cell layer.Total air barrier is 2 cells across (2 mm) (alveolar cell and capillary endothelial cell).
Alveolar cells Alveolar type I: structural cells. Alveolar type II: secrete surfactant.
Respiratory Zone
Mechanical process that moves air in and out of the lungs.Diffusion of…O2: air to blood.C02: blood to air.Rapid:large surface area small diffusion distance. * Insert 16.1
Alveolar capillary interface
Alveolar capillary interfaceCellular Respiration
Oxygen: large “reservoir” attached to hemoglobin.So chemoreceptors are more sensitive to changes in PC02 (as sensed through changes in pH).Ventilation is adjusted to maintain arterial PC02 of 40 mm Hg.Chemoreceptors are located throughout the body (in brain and arteries).Affinity between hemoglobin and 02: pH falls -> less affinity -> more unloading (and vice versa if pH increases) temp rises -> less affinity -> more unloading exercise, fever
C02 transported in the blood: - most as bicarbonate ion (HC03-) - dissolved C02 - C02 attached to hemoglobin (Carbaminohemoglobin)
Carbonic anhydrase in RBC promotes useful changes in blood PC02
H20 + C02 -> H2C03 -> HC03-
high PC02
CA
H20 + C02 <- H2C03 <- HC03-
low PC02
CA
Normal blood pH: 7.40 (7.35- 7.45) Alkalosis: pH up Acidosis: pH down
H20 + C02 Hypoventilation: PC02 rises, pH falls (acidosis). Hyperventilation: PC02 falls, pH rises (alkalosis).H2C03
H+ + HC03-
Ventilation is normally adjusted to keep pace with metabolic rate, so homeostasis of blood pH is maintained.