Gas Exchange between Blood Air and Tissuesgases only move by diffusion down their concentration gradientsThere are no transport mechanisms for hemThe system is designed to create the gradients in the direction where the gas needs to goTop: Alveolar Air (Reservoir of air)Dry air 760 mmHg, PO2 – 150 mmHg PCo2 0.25Alveolar air has less PO2 and higher PCO2 because we have a one way ventilation systemHave a lot of CO2 because the lung is getting rid of the CO2 into the alveolar air and that CO2 is mixing with incoming air so at the end of exhalation you have a lot of CO2 and then you inhaleThe 100mmHG stays constant in the alveolar air for PO2 although the PCO2 changes from 40mmHgAppears that maintenance of alveolar PO2 is the point of the whole systemIncoming pulmonary venous blood from right side of heartPO2 = 40mmHgPCO2 = 46mmHgSame as what goes into the lungs and then there is gas exchange in the capillaries of the lungsBlood comes into the lungs with a PO2 of 40 and the Alveolar air has PO2 of 100 so the O2 moves down concentration gradient into the blood and the CO2 moves down concentration into alveolar airBlood going into the systemic arteriesHas the same concentration that comes out of the lungsAt capillaries in systemic systemBlood coming in at PO2 of 100 gives up O2 because the tissues only have PO2 of 60 and vice versa for CO2Exchange of oxygen between blood and tissues is efficientPathological VentilationPathological conditionsInvolve either poor ventilation of the alveoli or poor gas exchange or bothAll involve hypoxia (deficiency of oxygen) and hypercapnia (excessive CO2 levels in tissues)1. Emphysemachronic progressive destruction of alveolicaused by cigarette smokingsmoke causes chronic inflammation and destroys and causes scar tissue in the lungreduces surface area for gas exchangebronchioles are usually compressible and in a normal lung the elasticity of the lung tissues and the residual surface tension keeps the bronchioles open but when the surface tension is reduced then the bronchioles collapse (especially during expiration) this traps air in the lungs making it hard to breathventilation and gas exchange are bothalveolar PO2 may be normal or low and the PO2 coming out of the lung is low due to the destruction of alveolimost common form of COPD-5th leading cause of death2.Fibrotic lung diseaseenvironmental contaminantsloss of lung compliance- still scar tissue where there should be elastic tissuethickens the membrane (increase the distance over which diffusion has to occur)PO2 low3. Pulmonary edemaFluid in the interstitial spaces in the lungIf there is excessive fluid in the lungs this can infiltrate into the alveoli and fill the alveoli or increase the thicknessThis increases the distance by which diffusion occursAlveolar PO2 is normal but PO2 is normal but pulmonary vein PO2 goes downThis doesn’t affect CO2 as much because it is more soluble than O2Causes are the same as edema everywhereMain cause is high pulmonary blood pressurecauses of high pulmonary blood pressure- for test4. Asthmabronchiolar constriction increases the airway constriction and increases airway resistance decreasing airway ventilationHemoglobin98% of the oxygen in the blood is carried by hemoglobinbasic reaction is where Hb combines with O2 to form HbO24 units with 2 identical pairs (2 alpha and 2 beta)Each of these subunits has a porforin ring structure and nitrogen ions hold a ferrous iron ion in the center and this is where oxygen reversibly binds (each Hb can hold 4 oxygen molecules)Oxygen hemoglobin dissociation curvePlots the percent saturation of hemoglobin with oxygen 0-100Central solid curve: at low oxygen concentrations no oxygen bound, as you increase O2 you get increased amount bound, and the slope is the measure of the binding affinity. Slope suddenly increases because there binding of one oxygen increases the binding affinity of the other sites become even higher. Goes up until you saturate it and levels offAt 100mmHg hemoglobin is fully saturated. The average PO2 in systemic tissues at rest is about 40mmHg and at 40mmHg you are at the sloping part of the curve so that the affinity of oxygen is slightly reduced so hemoglobin can let go of oxygen at 40 in the tissues. Gives up about a quarter of what it carries (oxygen in blood only goes down 25%) This is important because means that blood has a reserve of oxygen. A person who has stopped breathing still has oxygen in their lungs so chest compressions are more effective1. Shift to right of curve:increase in PCO2 or a decrease in pH or an increase in temperature will decrease an affinity of hemoglobin for oxygen release more oxygen to tissues2. Shift to leftdecrease in PCO2, increase in pH or decrease in temperature will increase the affinity of hemoglobin for oxygen less oxygen to tissuesDPG* and Fetal HbRBCs have an inherent mechanisms in which they can fine tune and adjust the affinity of hemoglobin because they have DPG which can reduce the affinity of hemoglobin for oxygen by binding itWithout DPG the affinity of hemoglobin would be too highUnder conditions (hypoxia) where the body needs more oxygen delivered (anemia) or in high altitude then more DPG to bind to hemoglobinThis automatically happens because oxyhemoglobin inhibits the enzyme that produces DPG so in hypoxic conditions, there is less inhibition and DPG is released. This is like a negative feedback systemOn the right:During fetal life, a different form of hemoglobin is made. The fetal genes are 2 alpha and 2 GAMMAGamma cannot bind DPG so it is insensitive to lowering of affinity to oxygen and therefore the affinity is much higher for fetus than adults.This allows the fetal hemoglobin to strip oxygen off of hemoglobin of the maternal hemoglobin and comes back 100% saturated. Mother breathes more rapidly or deeply to compensateCarbon Dioxide Transport in BloodCO2 is transported alsoSource of CO2 is cellular respiration in tissues—on the right, 7% of the CO2 dissolved in the blood, the rest diffuses into the RBC (23% bound to hemoglobin (bound to free amino groups) and the remainder 70% combines with water in the cytoplasm by carbonic anhydride and forms carbonic acid and readily associates into bicarbonate ions and protons)Deoxyhemoglobin binds protons so it will bind these protons to prevent a decrease in pH. This accumulation of protons makes the inside of the RBC positive which attracts Cl- ions because there are Cl-/HCO3 exchangers in the RBC