BISC 307L 1st Edition Lecture 34 Current Lecture Gas Exchange between Blood Air and Tissues o o gases only move by diffusion down their concentration gradients o There are no transport mechanisms for hem o The system is designed to create the gradients in the direction where the gas needs to go o Top Alveolar Air Reservoir of air Dry air 760 mmHg PO2 150 mmHg PCo2 0 25 Alveolar air has less PO2 and higher PCO2 because we have a one way ventilation system Have 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 inhale The 100mmHG stays constant in the alveolar air for PO2 although the PCO2 changes from 40mmHg Appears that maintenance of alveolar PO2 is the point of the whole system o Incoming pulmonary venous blood from right side of heart PO2 40mmHg PCO2 46mmHg Same as what goes into the lungs and then there is gas exchange in the capillaries of the lungs Blood 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 air o Blood going into the systemic arteries Has the same concentration that comes out of the lungs o At capillaries in systemic system Blood coming in at PO2 of 100 gives up O2 because the tissues only have PO2 of 60 and vice versa for CO2 Exchange of oxygen between blood and tissues is efficient Pathological Ventilation o o Pathological conditions Involve either poor ventilation of the alveoli or poor gas exchange or both All involve hypoxia deficiency of oxygen and hypercapnia excessive CO2 levels in tissues o 1 Emphysema chronic progressive destruction of alveoli caused by cigarette smoking smoke causes chronic inflammation and destroys and causes scar tissue in the lung reduces surface area for gas exchange bronchioles 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 breath ventilation and gas exchange are both alveolar PO2 may be normal or low and the PO2 coming out of the lung is low due to the destruction of alveoli most common form of COPD 5th leading cause of death o 2 Fibrotic lung disease environmental contaminants loss of lung compliance still scar tissue where there should be elastic tissue thickens the membrane increase the distance over which diffusion has to occur PO2 low o 3 Pulmonary edema Fluid in the interstitial spaces in the lung If there is excessive fluid in the lungs this can infiltrate into the alveoli and fill the alveoli or increase the thickness This increases the distance by which diffusion occurs Alveolar PO2 is normal but PO2 is normal but pulmonary vein PO2 goes down This doesn t affect CO2 as much because it is more soluble than O2 Causes are the same as edema everywhere Main cause is high pulmonary blood pressure causes of high pulmonary blood pressure for test o 4 Asthma bronchiolar constriction increases the airway constriction and increases airway resistance decreasing airway ventilation Hemoglobin o o o o o 98 of the oxygen in the blood is carried by hemoglobin basic reaction is where Hb combines with O2 to form HbO2 4 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 o Oxygen hemoglobin dissociation curve Plots the percent saturation of hemoglobin with oxygen 0 100 Central 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 off At 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 effective 1 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 tissues 2 Shift to left decrease in PCO2 increase in pH or decrease in temperature will increase the affinity of hemoglobin for oxygen less oxygen to tissues DPG and Fetal Hb o o RBCs 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 it o Without DPG the affinity of hemoglobin would be too high o Under conditions hypoxia where the body needs more oxygen delivered anemia or in high altitude then more DPG to bind to hemoglobin o This 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 system o On the right During fetal life a different form of hemoglobin is made The fetal genes are 2 alpha and 2 GAMMA Gamma 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 compensate Carbon Dioxide Transport in Blood o o CO2 is transported also o Source 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 o Deoxyhemoglobin binds protons so it will bind these protons to prevent a decrease in pH This accumulation of protons makes the