BIO 251 1st Edition Lecture 19 Outline of Last Lecture I. Overview of respiration II. Structure of respiration III. Respiratory cycle IV. Airway resistance V. Volume, capacity, & ventilation VI. Control of respirationOutline of Current Lecture I. Review of respiration a. External b. internalII. Gas exchangea. Physical principles b. Oxygenc. Carbon dioxideIII. Gas transporta. Oxygenb. Carbon dioxideIV. Local control of respirationThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.V. Control of respirationa. Decreased arterial PO2 in regulating ventilation b. Increased arterial “ “c. Increased H+Current LectureI. Review of Respiration (Fig 16.1)a. External Respiration: Entire sequence of events involved in the exchange of O2 and CO2 between the external environment and the cells of the body.i. Ventilation: exchange of air between environment & lung air sacs (alveoli)ii. O2 and CO2 exchanged between alveoli and bloodiii. O2 and CO2 are transported by blood between lungs & tissueiv. Exchange of O2 and CO2 between blood and tissues across capillariesb. Internal Respiration: Intracellular metabolic processes which use O2 and produce CO2 and derive energy from nutrient moleculesII. Gas Exchangea. Physical Principlesi. Gas flows down its pressure gradientii. Every gas (such as oxygen) in a mixture of gases (such as air) has a partial pressure which is the relevant variable when determining pressure gradients for a specific gasiii. Partial pressure of oxygen (PO2) in dry atmospheric air at sea level1. atmospheric pressure = 760 mm Hg2. oxygen makes up 21% of air3. partial pressure of oxygen: .21 x 760 mm Hg = 160 mm Hgiv. Partial pressure of oxygen in alveoli is1. 100 mm Hg; this is fairly constant2. Less than 160 mm Hg becausea. water vapor, which exerts a partial pressure of 47 mm Hg, reduces PO2 to 150 mm Hgb. mixing of fresh inspired air with “old” air in lungs (lungs always have at least 1200 ml of air in them, even after max exhalation) further drops PO2 to 100 mm Hgv. Partial pressure of carbon dioxide (PCO2)1. 0.3 mm Hg in dry air2. 40 mm Hg in alveoli because of CO2 produced by tissues and brought to lungs by blood; this is fairly constantb. Oxygen (Fig 17.4)i. Pulmonary capillaries1. PO2 in alveoli is 100 mm Hg; in returning ("dexoygenated") blood of systemic circulation, it is usually about 40 mm Hg2. Hence a pressure gradient of 60 mm Hg exists, toward blood from alveoli, so O2 diffuses from alveoli into bloodii. Systemic capillaries1. PO2 in blood (after oxygenation in lungs) is 100 mm Hg (ie, just what it isin the alveoli); in tissue, PO2 is 40 mm Hg (although this varies quite a bit depending on amount of cellular metabolism)2. Pressure gradient of 60 mm Hg exists, toward tissues from blood, so O2 diffuses from blood to tissues.c. Carbon Dioxide (Fig 17.4)i. Pulmonary capillaries1. PCO2 in alveoli is 40 mm Hg; in returning ("dexoygenated") blood of systemic circulation, it is usually about 46 mm Hg2. Pressure gradient of 6 mm Hg exists, toward alveoli from blood, so CO2 diffuses from blood into alveoliii. Systemic capillaries1. PCO2 in blood (after visit to lungs) is 40 mm Hg (ie, just what it is in the alveoli); in tissue, PCO2 is about 46 mm Hg (although this varies quite a bit depending on amount of cellular metabolism)2. Pressure gradient of 6 mm Hg exists, toward blood from tissues, so CO2 diffuses from tissues to bloodIII. Gas Transport: Role of Hemoglobin (Hb)a. Oxygen-Hb binding (17.6 & 17.7)i. Most O2 in the blood is carried by Hb!ii. Each Hb molecule can bind up to 4 O2 molecules; when it is carrying 4 oxygens, it is said to be fully saturatediii. Percent Hb saturation is a measure of the extent to which the Hb present is combined with oxygen, and can vary from 0 to 100%iv. The saturation of Hb with oxygen depends on the PO2 of the blood; note that oxygen already bound to Hb does NOT contribute to PO2!!!v. The amount of O2 bound to Hb depends on the PO2 . Relationship between PO2and % Hb saturation is complex: Fig 17.81. in pulmonary capillaries, PO2 is about 100 mm Hg; a large change in PO2here results in only a small change in % Hb saturation. Hence PO2 can fall nearly 40% in lungs, but Hb still highly saturated. This facilitates loading of Hb with oxygen in lungs.2. in systemic capillaries, PO2 is about 40 mm Hg; a small change in PO2 here results in a large change in % Hb saturated. Hence when PO2 falls even a little in systemic capillaries, a large amount of O2 disassociates from Hb. This facilitates unloading of O2 from Hb in tissues.vi. Bottom line: Hb acts as oxygen storage location in the blood, allowing the blood to carry much more oxygen than it could otherwise. As oxygen diffuses from the alveoli into the blood, it is loaded by Hb very rapidly; this loaded oxygen does not contribute to the blood PO2, so more oxygen enters the blood and is picked up by Hb, and so on. As oxygen diffuses from the blood into the tissues, oxygen unloads from the Hb into the blood, where it continues to diffuse into the tissues.vii. Modification of O2-Hb binding curve (Fig 17.9-17.10)1. Increased metabolism leads to increase in tissue temperature, acidity and CO2. An increase in all these variables “right shifts” the O2-Hb curve, which results in more unloading of oxygen for a given PO2 (ie, Hb delivers more O2 to the tissues at lower PO2).2. Carbon monoxide “left shifts” the O2-Hb curve, so that less oxygen bindsCO 240 times more readily than it does O2. These factors result in rapid death when breathing CO.b. Carbon dioxide transported in the blood in 3 ways (Fig 17.11)i. Dissolved in blood1. About 10% of CO2 transported this way2. Dependent on PCO2ii. Bound to Hb1. About 30% of CO2 bound to globin portion of Hb (not heme portion as O2 does)2. Reduced Hb (ie, unoxygenated) has a greater affinity for CO2 than does oxygenated Hb, which facilitates Hb picking up CO2 in tissue capillariesiii. As bicarbonate (HCO3- ) dissolved in plasma1. 60% of CO2 converted to HCO3- and H+ by the enzyme carbonic anhydrase within red blood cells (this reaction uses water also)2. HCO3- then diffuses out of the red blood cells into the plasma, and Cl- diffuses into the red blood cells to restore the electrical gradient. This is called the chloride shift3. The H+ remaining in the red blood cells binds to Hb; again, deoxygenated Hb has a greater affinity for H+ than does