Primary function of respiratory system is transport of O2 and CO2. This requires the four processes collectively known as respiration:
Cellular respiration is process of O2 use inside cells.
The conducting zone is composed of the primary bronchi and 23 orders of divisions of these tubes. The tubes less than 1mm in diameter are bronchioles,the smallest are terminal bronchioles. This series of branches is the bronchial tree.
As the tubes become smaller, the cartilage rings disappear, the epithelium thins as the type of epithelial cells change, and the muscle becomes relatively greater.
Respiratory zone includes branches of the terminal bronchioles called respiratory bronchioles. These have outward distensions or sacs. They branch into alveolar ducts which lead into alveolar sacs, which are basically clusters of alveoli, the chambers where most gas exchange occurs.
The respiratory membrane is formed of the walls of the alveoli, plus the walls of the capillaries that surround them. The alveolar walls contain Type I and II cells. The type I cells form most of the walls, and the gases diffuse through these cells. The type II cells secrete a fluid to keep the membrane moist. This fluid contains surfactant, which acts like a detergent to lower the surface tension of water and thus allow easier expansion of the tiny alveoli. Alveolar macrophages or dust cells protect the lungs against foreign particles.
Like the heart, the lungs have a double membrane around them, the pleura (parietal and visceral), with a pleural cavity between them filled with lubricating pleural fluid.
Breathing, aka pulmonary ventilation, consists of inspiration and expiration.
Pressure in the lungs is always spoken of relative to atmospheric pressure, measured in mmHg. 760 standard.
Intrapulmonary is pressure inside alveoli, intrapleural pressure is inside pleural cavity. Intrapulmonary pressure always equalizes with atm. pressure, intrapleural pressure is always negative relative to others. If this wasn't the case, the lungs would collapse.
Inspiration: Downward movement of diaphragm and expansion of ribcage enlarge volume of the lungs. Because as volume increases, pressure decreases, atmospheric air floods lungs. As the muscles relax, natural elasticity of lungs causes them to return to normal size, expiring air. Lung compliance is the ease with which lungs can be expanded. Lung elasticity is the ability of lungs to recoil after expansion.
Respiratory or lung volume includes:
Respiratory capacity includes:
Anatomical dead space is air in passageways that does not contribute to the exchange of gases
Alveolar dead space is air spaces in nonfunctional alveoli. Two combined are total dead space.
Nonrespiratory air movements include sneezing, coughing, laughing, crying.
Dalton's Law says that the total pressure exerted by a mixture of gases is equal to the sum of the pressures exerted by the component gases of the mixture.
Henry's Law says that gases will dissolve into liquids in proportion to their partial pressures. This is true of the reverse as well.
Composition of gas in alveoli not same as atm. More CO2, more humid, less O2.
Explain exchange due to different partial pressures of O2, CO2.
Partial pressure of O2 in pulmonary blood only about 40mmHg, compared to 104mm in alveoli. Diffusion occurs rapidly, reloading blood in about 0.25 sec. Local autoregulatory mechanisms ensure blood is sent to alveoli that have adequate ventilation.
Similar mechanism controls exchange of gases with tissues.
O2 can be transported by blood attached to hemoglobin or dissoblved in plasma. Not readily soluble, so only about 1.5% carried that way.
Oxy- vs. deoxyhemoglobin
Loading of one O2 molecule enhances loading of other 3. Same for unloading. Due to shape changes.
Oxygen-hemoglobin dissociation curve. Nonlinear relationship.
Only about 20% of bound O2 is unloaded to tissues on one systemic circuit. Difference between 100mmHg and 40mmHg ppO2.
Hemoglobin nearly completely saturated, even at relatively low ppO2 (70mmHg, normal atm. around 159). Allows high altitude existence.
Affininty declines with high temp. Unloading not efficient at low temps.
acidity (H+ conc.) decreases affinity (Bohr effect)
About 8% carried dissolved in plasma, 20-30% bound to globin in hemoglobin, 60-70% as bicarbonate ions in plasma. Bicarbonate ions mostly formed in rbcs, exit to plasma. More CO2 can be carried in deoxygenated blood, though the two gases do not compete for the heme groups.
Control of respiration
inspiratory and expiratory centers in medulla.
Rate of respiration can be affected by irritants, overstretching (Hering-Breuer reflex), hypothalamus (emotions), cortical (conscious) control, chemical factors (CO2 concentrations most important, low O2 also)