BSC 2086 1st Edition Lecture 18 Outline of Last Lecture I Introduction to Gas Exchange II Pulmonary Ventilation III Gas Exchange Outline of Current Lecture I Gas Transport II Respiration Control III Effects of Aging IV Digestive Tract Current Lecture I 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 tissues 1 Allow gases to diffuse in blood by removing O2 and CO2 from plasma b 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 RBC c Hemoglobin saturation i Percentage of heme units in a hemoglobin molecule that contain bound oxygen ii Hemoglobin is affected by environmental factors 1 PO2 of blood 2 Blood pH 3 Temperature 4 Metabolic activity inside RBCs iii Oxygen Hemoglobin Saturation Curve 1 Graph relating saturation of hemoglobin to partial pressure of oxygen a High PO2 more Hb saturation 2 Hb changes shape each time an O2 molecule binds therefore a curve is seen rather than a straight line a 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 low c 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 C 4 When pH drops or temperature rises more oxygen is released and the curve shifts to the right 5 When pH rises or temperature drops less oxygen is released and the curve shifts left iv Oxygen Reserve amount of oxygen released from capillaries to interstitial fluid depends on interstitial PO2 1 RBCs may reserve up to venous O2 reserve v Carbon monoxide CO from burning fuels 1 Takes the place of O2 and binds strongly to Hb 2 Carbon monoxide poisoning can result 3 Treated by a Preventing further CO exposure b Pure O2 air c Blood transfusion vi Hemoglobin and pH 1 Bohr effect result of pH on hemoglobin saturation curve 2 Caused by CO2 a 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 pH 3 At less Hb saturation equals more O2 release vii Hemoglobin and temperature 1 Temperature increase means more release of oxygen by Hb II 2 Temperature decrease means Hb holds on more tightly to oxygen a Temperature effects are significant only in active tissues that are able to generate a lot of heat b An example would be active skeletal muscles that generate heat warms the blood and causes release of more O2 from Hb viii 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 acid i 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 ATP a Produced by carbonic anhydrase in RBC b Bound to Hb within RBCs i 23 is bound to amino groups of globular proteins in Hb molecule forming carbaminohemoglobin c Dissolved in plasma i 7 is transported as CO2 dissolved in plasma Respiration Control a Respiratory Centers of Brain i When oxygen demand rises cardiac output and respiratory rates increase due 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 muscles iii The respiratory center located in the reticular foramen of the medulla oblongata and pons b c d e 1 Regulate respiratory muscles in response to sensory information via respiratory reflexes 2 Can be stimulated by caffeine and amphetamines Respiratory centers of Medulla Oblongata i Set pace for respiration ii Can be divided into 1 Dorsal respiratory group DRG a Inspiratory center stimulates the inspiratory muscles b Functions in quiet and forced breathing 2 Ventral respiratory group VRG a Inspiratory and expiratory center activates the accessory inspiratory muscles and exhalation muscles b Functions only in forced breathing Sudden infant death syndrome SIDS i Disrupts the normal respiratory reflex pattern which may result from problems between the pacemakers and respiratory centers Respiratory reflexes i 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 changes 4 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 Chemoreceptor stimulation i Increased depth and rate of respiration ii 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 exercise iii Hypercapnia is an increase in arterial PCO2 1 Stimulates chemoreceptors in the medulla oblongata to restore homeostasis 2 A common cause of hypercapnia is hypoventilation a CO2 build up in blood is caused by abnormally low respiration rate 3 Hyperventilation or excessive ventilation results in abnormally low PCO2 hypocapnia a Decrease in respiratory rate due to stimulated chemoreceptors f Baroreceptor reflexes i Carotid and aortic baroreceptor stimulation affects blood pressure and respiratory centers ii When the blood pressure falls respiration increases iii When blood pressure rises respiration decreases iv Hering Breuer Reflexes 1 Involved in forced breathing 2 Inflation reflex a Prevents the overexpansion of lungs during forced inhalation by slowly inhibiting DRG and stimulating the expiratory center of VRG 3 Deflation reflex a Inhibits expiratory centers and
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