The Respiratory SystemI. Mechanics of Breathinga. Also known as Pulmonary ventilationb. Two phasesi. Inspiration (air flows in lungs)ii. Expiration ( air exits lungs)c. Pressure relationships in Thoracic Cavityi. Respiratory pressures described relative to atmospheric pressure1. Atmospheric pressure is pressure of air in the environment2. 760 mmHgii. Negative pressure (-4 mmHg) indicates pressure is lower 4 lower than atmospheric1. positive (+4) means the oppositeiii. Intrapulmonary Pressure1. Rises and falls with phases of breathing2. always eventually equalizes with atmospheric pressured. Pulmonary Ventilationi. Consist of inspiration and expirationii. Mechanical process that depends on volume changes in the Thoracic cavityiii. Pressure of gas varies inversely with its volume P1V1=P2V21. Means if pressure increases volume of the container must decrease and vice versaiv. Inspiration1. Action of Diaphragm*a. Diaphragm contracts and it moves downward increasing the amount of space in thoracic cavityb. *Remember more volume results in a lower pressurei. Pressure moves from high (environment) to low (inside lungs) thus inspiration c. Pressure only needs to drop a minimum of 1 mmHg for air to be forced inside lungsv. Expiration1. Diaphragm will relax and the elasticity of the lungs cause them to recoil a. Thoracic and lung volume decreasei. Volume decreases thus pressure increases slightly above atmospheric pressure pushing air from high (inside the lungs) to low (outside the lungs)2. Forced expirationa. Active process produced by contraction of abdominal wall musclesi. Transverse and obliqueii. Further decrease volume of thoracic cavity by depressing the rib cage e. Physical Factors Influencing Pulmonary Ventilationi. Airway resistance1. friction of gas on respiratory passages affects pulmonary ventilation2. The gas flow is given by this equationa. F (gas flow) = P (change in pressure)/ R ( Resistance)b. What this meansi. Gas flow decreases as resistance increasesii. Gas flow increases as pressure difference increases3. Airway diameters are large in conducting zone thus less resistance due to low viscosity of air4. You would think in areas with smaller diameter that there is more resistancea. However since the bronchioles branch they have huge cross sectional areab. Thus most resistance is found in medium size bronchiii. Surfactant1. a chemical used to decrease surface tension on alveoli2. Water tends to be adhesive to itself and would thus collapse the alveoli if this film was not present on lungsiii. Lung Compliance1. The stretchiness or distensibility of the lungs2. The higher lung compliance the easier it is to expand the lungs at any given transpulmonary pressure3. Determined by two factorsa. Distensibility of lung tissue b. Alveolar surface tension f. Respiratory Volumes i. Dead Space1. Gas that fills conducting respiratory passageways but never contributes to gas exchange in alveoli2. about 150 ml3. Tidal volume (air inspired) is 500ml this means only about 350 ml actually gets used in gas exchangeii. Alveolar ventilation1. Alveolar ventilation rate (AVR)a. Takes into account the volume of air wasted in the dead space and measures the flow of fresh gases in and out of the alveoli during a time intervali. AVR (ml/min) = frequency (breaths/min) X (Tidal volume- Dead space) b. Depth of breaths increasing gas exchange rather than fast shallow breathingII. Gas Exchanges between the Blood, Lungs and Tissuesa. External Respirationi. Partial Pressure gradients and Gas Solubilities1. Pressure gradients of O2 and CO2 drive diffusion of these gases across respiratory membranea. Oxygeni. Oxygen in alveoli is about 104 mmHg while in the deoxygenated blood it is only about 40 mmHgii. Flows from high (in alveoli) to low (in blood) until equilibrium is reachediii. Opposite happens in arterioles of systemic (flows from high in blood to low in tissues)b. Carbon Dioxidei. Diffuses in opposite directionii. From 40-45 mmHg in blood to 5 mmHg in alveoliiii. Thus high to low forces it from blood to lungs and out of bodyiv. Pressure gradient is less steep because CO2 is 20 times more soluble in plasma and alveolar fluid than CO2b. Internal Respirationi. Partial pressure and diffusion gradients for oxygen and CO2 are reversed1. Oxygen goes from high blood to low in tissues2. CO2 goes from high tissues to low in blood III. Transport of Respiratory Gases by Blooda. Travels mainly bound to hemoglobinb. Each hemoglobin can combine with four molecules of O2c. Loading of oxygen enhances the loading of more oxygen until saturatedi. And the opposite unloading facilitates unloading of more oxygend. O2 binding to Hemoglobin also regulated byi. Temperatureii. Blood Phiii. CO2iv. * Think exercise1. If you’re doing exercise temperature increases, blood Ph becomes more acidic (lactic acid build up), and increased CO2a. All facilitate oxygen to unload from hemoglobine. Oxygen hemoglobin dissociation curvei. Under normal condition Hb is 98% saturatedii. 100 ml of systemic blood contains about 20 ml of O2iii. Small drop in PO2 will cause a large increase in unloadingiv. Substantial amounts of O2 are still available in venous blood (venous reserve) not all is unloadedv. Most important thing to know is that relationship is not linear because as one oxygen unloads affinity of hemoglobin changes causing a more rapid unloading of more oxygenf. Carbon Dioxide Transporti. Two main forms1. bound to hemoglobin a. carbaminohemoglobinb. deoxygenated hemoglobin combines with CO2 more rapidly than oxygenated2. As bicarbonate in plasmaa. CO2 enters RBCsb. Where it is converted for transport as bicarbonate ions (HCO3-)i. Via enzyme carbonic anhydrasec. To counter negative charge of bicarbonate leaving RBCs, chloride moves into RBC’si. Called chloride shiftii. Influence of CO2 on blood Ph1. Bicarbonate can accept or release hydrogen ions to maintain blood phIV. Control of Respirationa. Controlled by changing levels of CO2, O2 and H+b. Two typesi. Central1. located in brain stem (ventrolateral medulla)2. CO2 accumulates in brain it forms carbonic acid then H+ dissociates lowering Ph 3. Lower Ph activates respiratory regulators to increase breathing rate and depth4. *Respond to CO2 levelsii. Peripheral1. in aortic arch and carotid arteries2. *Respond to O2 levelsThe Urinary SystemI. Nephronsa. Are the structural and functional units of the kidneysb. Consist ofi. Glomerulus1. collection of capillariesii. Renal tubuleiii.
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