BSC 2086 1st Edition Lecture 18 Outline of Last Lecture I. Introduction to Gas ExchangeII. Pulmonary VentilationIII. Gas ExchangeOutline of Current Lecture I. Gas TransportII. Respiration ControlIII. Effects of AgingIV. Digestive Tract Current LectureI. Gas Transport a. Gas pickup and delivery i. Blood plasma cant transport enough O2 or CO2 to meet physiological needs ii. Red blood cells transport O2 to, and CO2 from, peripheral tissues1. Allow gases to diffuse in blood by removing O2 and CO2 from plasmab. Oxygen transport i. Oxyhemoglobin (HbO2) is made by O2 binding to iron ions in hemoglobin (Hb) molecules ii. Reversible reaction iii. Each RBC has about 280 million Hb molecules and each Hb molecule binds 4 oxygen molecules iv. This means 1.1 billion O2 molecules are transported in one RBCc. Hemoglobin saturationi. Percentage of heme units in a hemoglobin molecule that contain bound oxygenii. Hemoglobin is affected by environmental factors:1. PO2 of blood2. Blood pH3. Temperature4. Metabolic activity inside RBCsiii. Oxygen-Hemoglobin Saturation Curve1. Graph relating saturation of hemoglobin to partial pressure of oxygen a. High PO2 = more Hb saturation2. Hb changes shape each time an O2 molecule binds, therefore a curve is seen rather than a straight linea. Each time an O2 binds, it makes it easier for the next O2 to bind b. This allows Hb to bind O2 when O2 levels are lowc. Hb is about 90% saturated even at low PO2 (about 60 mmHg)3. Standardized for normal blood with a pH of 7.4 and at 37*C4. When pH drops or temperature rises more oxygen is released and the curve shifts to the right5. When pH rises or temperature drops less oxygen is released and the curve shifts leftiv. Oxygen Reserve: amount of oxygen released from capillaries to interstitialfluid depends on interstitial PO21. RBCs may reserve up to ¾ (venous O2 reserve)v. Carbon monoxide: CO from burning fuels1. Takes the place of O2 and binds strongly to Hb2. Carbon monoxide poisoning can result3. Treated by:a. Preventing further CO exposureb. Pure O2 airc. Blood transfusionvi. Hemoglobin and pH 1. Bohr effect: result of pH on hemoglobin-saturation curve 2. Caused by CO2a. CO2 is diffused into RBCs b. Carbonic anhydrase catalyzes reaction with H2O producing carbonic acid (H2CO3)i. Dissociates into hydrogen ion (H+) and bicarbonate ion (HCO3-)ii. Hydrogen ions diffuse out of RBC, lowering the pH3. At less Hb saturation equals more O2 release vii. Hemoglobin and temperature 1. Temperature increase means more release of oxygen by Hb2. Temperature decrease means Hb holds on more tightly to oxygena. Temperature effects are significant only in active tissues that are able to generate a lot of heatb. An example would be active skeletal muscles that generateheat, warms the blood, and causes release of more O2 from Hbviii. Carbon Dioxide Transport (CO2)1. Carbon dioxide generated as by product of aerobic metabolism (cellular respiration)2. CO2 in blood stream a. Converted to carbonic acidi. 70% of CO2 is transported as carbonic acid (H2CO3)1. this dissociates into H+ and bicarbonate (HCO3-)2. Most of the hydrogen ions will bind to hemoglobin forming HbH+ which acts as a pH 3. Bicarbonate ions move into the plasma by an exchange mechanism known as the chloride shift which takes Cl- ions without using ATPa. Produced by carbonic anhydrase in RBC b. Bound to Hb within RBCsi. 23% is bound to amino groups of globular proteins in Hb molecule forming carbaminohemoglobinc. Dissolved in plasma i. 7% is transported as CO2 dissolved in plasmaII. Respiration Controla. Respiratory Centers of Braini. When oxygen demand rises, cardiac output and respiratory rates increasedue to neural control (coordinated together)1. Have voluntary and involuntary components ii. Voluntary centers in the cerebral cortex affect the respiratory centers of the pons and medulla oblongata as well as the motor neurons that control the respiratory musclesiii. The respiratory center located in the reticular foramen of the medulla oblongata and pons1. Regulate respiratory muscles in response to sensory information via respiratory reflexes 2. Can be stimulated by caffeine and amphetamines b. Respiratory centers of Medulla Oblongatai. Set pace for respiration ii. Can be divided into: 1. Dorsal respiratory group (DRG)a. Inspiratory center stimulates the inspiratory musclesb. Functions in quiet and forced breathing2. Ventral respiratory group (VRG)a. Inspiratory and expiratory center activates the accessory inspiratory muscles and exhalation muscles b. Functions only in forced breathing c. Sudden infant death syndrome (SIDS)i. Disrupts the normal respiratory reflex pattern, which may result from problems between the pacemakers and respiratory centers d. Respiratory reflexesi. Respiratory centers modified by: 1. Chemoreceptors sensitive to PCO2, PO2, or pH of blood or cerebrospinal fluid 2. Baroreceptors in the aortic and carotid sinuses are sensitive to changes in blood pressure a. If there is a decrease in BP, it causes breathing to become harder and faster. A decrease in BP also means you don’t have enough RBC, therefore not enough oxygen in tissues 3. Stretch receptors respond to lung volume changes4. Irritating physical or chemical stimuli in the nasal cavity, larynx, or bronchial tree 5. Other sensations include pain, changes in body temperature, abdominal visceral sensations e. Chemoreceptor stimulationi. Increased depth and rate of respirationii. Subject to adaptation 1. Decreased sensitivity due to chronic stimulation 2. Chronic low PO2 and high PCO2 can reset chemoreceptors to the baseline which makes treatment difficult 3. They are also sensitive to pH drop due to lactic acid production from exerciseiii. Hypercapnia is an increase in arterial PCO21. Stimulates chemoreceptors in the medulla oblongata to restore homeostasis 2. A common cause of hypercapnia is hypoventilationa. CO2 build up in blood is caused by abnormally low respiration rate3. Hyperventilation, or excessive ventilation, results in abnormally low PCO2 (hypocapnia)a. Decrease in respiratory rate due to stimulated chemoreceptors f. Baroreceptor reflexesi. Carotid and aortic baroreceptor stimulation affects blood pressure and respiratory centersii. When the blood pressure falls, respiration increasesiii. When blood pressure rises, respiration decreasesiv. Hering-Breuer Reflexes 1. Involved in forced breathing2. Inflation reflexa. Prevents the overexpansion of lungs during forced inhalation by
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