The Respiratory System I Mechanics of Breathing a Also known as Pulmonary ventilation b Two phases Inspiration air flows in lungs i ii Expiration air exits lungs c Pressure relationships in Thoracic Cavity i Respiratory pressures described relative to atmospheric pressure 1 Atmospheric pressure is pressure of air in the environment 2 760 mmHg ii Negative pressure 4 mmHg indicates pressure is lower 4 lower than atmospheric 1 positive 4 means the opposite iii Intrapulmonary Pressure 1 Rises and falls with phases of breathing 2 always eventually equalizes with atmospheric pressure d Pulmonary Ventilation i Consist of inspiration and expiration ii Mechanical process that depends on volume changes in the Thoracic cavity iii Pressure of gas varies inversely with its volume P1V1 P2V2 1 Means if pressure increases volume of the container must decrease and vice versa iv Inspiration 1 Action of Diaphragm v Expiration a Diaphragm contracts and it moves downward increasing the amount of space in thoracic cavity b Remember more volume results in a lower pressure i 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 lungs 1 Diaphragm will relax and the elasticity of the lungs cause them to recoil a Thoracic and lung volume decrease i Volume decreases thus pressure increases slightly above atmospheric pressure pushing air from high inside the lungs to low outside the lungs 2 Forced expiration a Active process produced by contraction of abdominal wall muscles i Transverse and oblique ii Further decrease volume of thoracic cavity by depressing the rib cage e Physical Factors Influencing Pulmonary Ventilation i Airway resistance 1 friction of gas on respiratory passages affects pulmonary ventilation 2 The gas flow is given by this equation a F gas flow P change in pressure R Resistance b What this means i Gas flow decreases as resistance increases ii Gas flow increases as pressure difference increases 3 Airway diameters are large in conducting zone thus less resistance due to low viscosity of air 4 You would think in areas with smaller diameter that there is more resistance a However since the bronchioles branch they have huge cross sectional area b Thus most resistance is found in medium size ii Surfactant bronchi 1 a chemical used to decrease surface tension on alveoli 2 Water tends to be adhesive to itself and would thus collapse the alveoli if this film was not present on lungs iii Lung Compliance 1 The stretchiness or distensibility of the lungs 2 The higher lung compliance the easier it is to expand the lungs at any given transpulmonary pressure 3 Determined by two factors a Distensibility of lung tissue b Alveolar surface tension 1 Gas that fills conducting respiratory passageways but never contributes to gas exchange in alveoli 2 about 150 ml 3 Tidal volume air inspired is 500ml this means only about 350 ml actually gets used in gas exchange ii Alveolar ventilation 1 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 interval f Respiratory Volumes i Dead Space i AVR ml min frequency breaths min X Tidal volume Dead space b Depth of breaths increasing gas exchange rather than fast shallow breathing II Gas Exchanges between the Blood Lungs and Tissues a External Respiration i Partial Pressure gradients and Gas Solubilities 1 Pressure gradients of O2 and CO2 drive diffusion of these gases across respiratory membrane a Oxygen b Carbon Dioxide i Oxygen in alveoli is about 104 mmHg while in the deoxygenated blood it is only about 40 mmHg ii Flows from high in alveoli to low in blood until equilibrium is reached iii Opposite happens in arterioles of systemic flows from high in blood to low in tissues i Diffuses in opposite direction ii From 40 45 mmHg in blood to 5 mmHg in alveoli iii Thus high to low forces it from blood to lungs and out of body iv Pressure gradient is less steep because CO2 is 20 times more soluble in plasma and alveolar fluid than CO2 b Internal Respiration are reversed i Partial pressure and diffusion gradients for oxygen and CO2 1 Oxygen goes from high blood to low in tissues 2 CO2 goes from high tissues to low in blood III Transport of Respiratory Gases by Blood a Travels mainly bound to hemoglobin b Each hemoglobin can combine with four molecules of O2 c Loading of oxygen enhances the loading of more oxygen until saturated i And the opposite unloading facilitates unloading of more oxygen d O2 binding to Hemoglobin also regulated by i Temperature ii Blood Ph iii CO2 iv Think exercise 1 If you re doing exercise temperature increases blood Ph becomes more acidic lactic acid build up and increased CO2 a All facilitate oxygen to unload from hemoglobin e Oxygen hemoglobin dissociation curve i Under normal condition Hb is 98 saturated ii 100 ml of systemic blood contains about 20 ml of O2 iii Small drop in PO2 will cause a large increase in unloading iv Substantial amounts of O2 are still available in venous blood venous reserve not all is unloaded v 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 oxygen f Carbon Dioxide Transport i Two main forms 1 bound to hemoglobin a carbaminohemoglobin b deoxygenated hemoglobin combines with CO2 more rapidly than oxygenated 2 As bicarbonate in plasma a CO2 enters RBCs b Where it is converted for transport as bicarbonate ions HCO3 i Via enzyme carbonic anhydrase c To counter negative charge of bicarbonate leaving RBCs chloride moves into RBC s i Called chloride shift ii Influence of CO2 on blood Ph 1 Bicarbonate can accept or release hydrogen ions to maintain blood ph IV Control of Respiration a Controlled by changing levels of CO2 O2 and H b Two types i Central located in brain stem ventrolateral medulla 1 2 CO2 accumulates in brain it forms carbonic acid then H 3 Lower Ph activates respiratory regulators to increase dissociates lowering Ph breathing rate and depth 4 Respond to CO2 levels ii Peripheral in aortic arch and carotid arteries 1 2 Respond to O2 levels The Urinary System I Nephrons a Are the structural and functional units of the kidneys b Consist of i Glomerulus 1 collection of capillaries ii Renal tubule iii Glomerular capsule Bowmans capsule 1 encloses the capillaries of Glomerulus iv Glomerulus
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