Systems Physiology Lecture 22 Schematic of lung showing typical volumes and flows under ph partial pressure of physiological conditions. What is anatomic dead space Note: Anatomic dead space and conducting airways are the same thing. Ie. No alveoli thus no gas exchange in this space Total ventilation volume of air that fills both conducting and respiratory airways during a period of time The air that stays in the conducting airways is wasted air (anatomic dead space) because it does not participate in gas exchanges Ventilation of anatomic dead space (conducting airways) Note: the difference between tidal volume (500ml) and dead space volume End of expiration (left ) ( small column: anatomic dead space ? volume of conduction airway High partial pressure of O2 in the fresh, ambient atmospheric air that is about to be inhaled In step 2, person has now inspired, the very first gas to enter alveolar space is not fresh air, it is stale, stagnat dead space air, just before inspiration begins. The volume of fresh air that is now flowing into the alveoli is reduced by about 1/3. In step 3, both the stagnant dead space air and the freshly inspired ambient air mix with the previously existing alveolar air ( a lower P02 and a higher PC02 increases partial pressure of PC02 Partial pressure of gases that exist in the atmosphere is not the same when it enters the alveoli. The PC02 rises and the P02 falls As the freshly inspired air enters the conducting pathways it is moistened. Water vapor pressure drops the P02 Fresh air is constantly being shuttled between conducting airways and atmosphere ( occupies a useless space Exchange and transport of gases How is oxygen exchanged and transported? How is carbon dioxide exchanged and transported Partial pressure, contents and carrying External respiration and the physiology of 02 and C02 in the alveoli and blood Transport: how the freshly inhaled oxygen moves from the lungs to the tissues and how the C02 produced by tissues Exchange: define it Ratio of C02 produced to 02 consumed ( slight difference in these numbers How P02 and PC02 vary according to location in body Downhill P02 gradient between air and cells ? must exist in order for us to extract oxygen. Opposite with PC02 (greater than ambient air, reverse downhill gradient) External: 2 kinds of respiration: uptake of ambient air and its delivery to the cells Internal: cellular or biochemical respiration: the way mitochondria and other organelles use oxygen in processes Exchange of gases and the influence of width of diffusion barriers Top left panel: Red dots are oxygen. Barrier separating ambient oxygen from alveolar oxygen. First things that affects exchange ? consists of pulmonary epithelium, basement membrane, capillary endothelium Surface area affects the exchange of gases. It changes Inhale ( alveoli expands. SA expands. Expire ? vice versa. Width or thickness of barrier influences exchange. Thicker barrier will result in slower exchange than a thinner barrier Concentration/content of gas: the greater the content/concentration, the more rapid the exchange Possible to study respiration under what we call standard temperature and pressure saturated conditions Because of moisture, the barrier becomes thicker ? exchange of gas slows down Exchange and the influence of solubility of gases in blood and plasma Solubility of gas molecules in aqueous solutions affects exchange A 100mm Hg partial pressure in water [O2] in water = .15mmoles/liter [CO2] in water = 3.0 mmoles/liter Carbon dioxide is much more soluble than oxygen in water, plasma, or whole blood Exchange, transit distance of pulmonary capillary blood and diffusion under sea level baseline conditions Pulmonary capillaries suggest that the deoxygenated blood enters arteriole end of capillary and oxygenated leaves the veniolar At what length of the pulmonary capillary does steady equilibration Inspiration lowest thickness, expiration thickest Partial pressure of oxygen on the top c02 on the bottom correspondingly change. Inspiration p02 is the highest, expiration at its lowest. Opposite for PC02 lowest during inspiration highest during expiration Partial pressure of 0 to 100%, P02 is at its highest point within the first 1/3 of the capillary length, uptake of oxygen is very rapid, only requires a fraction of the length of the pulmonary capillary to be in equilibrium with alveoli and remains constant throughout the rest of length Exchange, transit distance along pulmonary capillary and diffusion under resting conditions at summit of Mount Everest Here after the total length of capillary, P02 barely reaches 27028%. Still well below the alveolar P02 This respiratory system is in trouble Exchange has slowed down and distance has increased ? due to fluid accumulation in alveoli (pneumonia conditions) Barometric pressure is 1/3 of barometric pressure in the room. The partial pressure driving oxygen has been reduced to a 1/3 of its level and the person has inflammation. Summary and gas exchange Partial pressure influence gas exchange Characteristics of diffusion barrier influence exchange Solubility of gases in aqueous media influence exchange 02 is less soluble than C02 in water (blood, plasma) Extra notes Respiratory quotient ? the ratio of C02 production to 02 consumption All the oxygen we are going to exchange from the alveoli to the pulmonary capillary, well oxygenated before it gets to the capillary Exchange, transit distance along pulmonary capillary and diffusion under resting conditions at summit of Mount Everest 02 is transported in physical solution and bound to protein the oxygen is transported in one of 2 different ways: some ends up in the plasma water, the only oxygen that exerts a partial pressure ? can only exert pressure if it is free and unbound <1% 99% enters the red cell, some of the oxygen entering red cell dissolves in the cytosol but does not get bound to hemoglobin. 98% + binds to reduced hemoglobin creating oxyhemoglobin and that is how it is transported to the tissues. Partial pressure of gases is caused only by the molecules that are free to collide with each other Transport of 02 in the circulation Role of hemoglobin (Hb vs Hb02) What is 02 carrying capacity What can we learn Structure and function of Hemoglobin A (HbA) Globin + 4 polypeptides Heme = iron-containing group Carries oxygen 98.5% oxygen bound to Hb, 1.5% dissolved in plasma Oxygenated Hb ? bright red Deoxygenated Hb ? dark red Also carries C02, H+, C0 The structure/function of hemoglobin Iron in ferrous state bound to molecular oxygen 2 different states ? bound and unbound with oxygen histamine amino acid on the blue structure relative to the same histamine locations on the red structure causes a movement about 8/10ths of an Angstrom ( movement takes it from tense state blue domed to a relaxed state red planar structure. Necessary for successful binding and transport in blood! Oxygen carrying capacity 15g Hb in each 100ml whole blood ( 15g/dl, 15g%, 15g/100ml 1.34 ml O2/g Hb when all four O2 binding sites are occupied (1.34 ml O2)(15g Hb) = 20.1 ml O2/100ml blood* *this is the oxygen carrying capacity men will have more hemoglobin than women Changes in Hb02 dissociation curve Ability of The oxygen and hemoglobin to separate or come together Each curve has hemoglobin saturation % vs P02 Top left panel: middle curve: us right now Yellow ? acidic conditions. Green ? basic Acid right, base left P50 - At a parital pressure of about 27mmHg of oxygen, there is 50% saturation of hemoglobin molecules Saturation: of all the hemoglobin molevules in the sample, what % of them are bound to all 4 molecules oxygen (some have 3,2, or even 1) Venous blood under acidic conditions still has 80% of hemoglobin saturation Effect on temperature: Red curve ? standard temp . yellow ? lower curve; hypothermia. Green ? elevated temp Acidosis and alkalosis can originate from 2 different sources Acidosis ? kidneys are failing to excrete protons ( metabolic acidosis Acidosis ? because kidneys are normal, but the lungs are not eliminationg pC02 ( respiratory alkalosis They will compensate for each other to maintain homeostasis Summary 02 transport 02 is transported both in solution and bound to Hb Dissociation curve describes relationship between P02 and Hb02 saturation P50 = P02 at which Hb is 50% saturated (around 27mmhg) Hypoxia/anemia affects above Transport of carbon dioxide CO2 is carried as gas dissolved in H20 CO2 is carried as bicarbonate ion (HC03) CO2 is carried bound to proteins as carbamino compounds Transport of C02 from systemic capillaries to the lungs C02 either becomes dissolved in available water space or bound 89% of C02 enters the red cell. 11% stays in solution in plasma, Of that 11 % 6 remains dissolved and generates the Pc02, 5% undergoes hydration reaction with water to produce weak acid bicarbonic acid. Bicarbonic acid will dissociate with produce carbonate and H+ ion ( third way is when 1% of C02 binds to protein to form carbamino compounds the smallest fraction makes a PC02, the largest fraction gets hydrated to form bicarbonic acid. carbonic anhydrase catalyzes this reaction producing more bicarbonate inside the cell than outside. Another fraction binds to hemoglobin that has just released its oxygen Hemoglobin is also a transporter of C02 Constituents of total Co2 in systemic blood The difference between the height of the curves is the addition of c02, of the additional co2 that?s added the vast majority is bicarbonate, then carbonyl compounds, and then finally dissolved C02 Shows arterial mixed venous blood, and v-a difference for C02 Summary and conclusions Exchange (diffusion) of gases depends on barriers and partial pressure gradients Gases are transported in the blood
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