Lec 6 Respiratory Regulation 2024 PDF

‫ بسمـ هللا‬2024 – lec 6 Respiratory Regulation Introduction: The total amount of O 2 consumption and CO 2 production by the cells during muscle exercise can increase as much as 20-fold. Pulmonary ventilation and perfusion increase to supply the extra amounts of O 2 and removes the extra amounts of...

‫ بسمـ هللا‬2024 – lec 6 Respiratory Regulation Introduction: The total amount of O 2 consumption and CO 2 production by the cells during muscle exercise can increase as much as 20-fold. Pulmonary ventilation and perfusion increase to supply the extra amounts of O 2 and removes the extra amounts of CO 2. Regulation of ventilation during muscle exercise: Pulmonary ventilation is stimulated by a variety of neurogenic impulses reaching the respiratory centers in the brain stem. A- Blood gases o Pulmonary ventilation is so well matched with the metabolic demands. o During light to moderate exercise the arterial PO2 and PCO2 and H + values remain unchanged o Severe and sustained exercise, lactic acid accumulates in the blood and pH may drop to 7.2. The lactic acidosis causes hyperventilation. B- Muscle, tendon and joint receptors o Impulses from proprioceptors in muscles, tendons and joints stimulate the respiratory centers during movement of joints. C- Higher brain centers o As exercise begins, brain transmits motor impulses to the muscles and collateral impulses to stimulate RC, causing the immediate increase in ventilation. o Experienced athletes increase their respiration even before the start of exercise. (conditioned reflexes) D- Increased tissue metabolism and temperature: stimulate breathing by impulses reaching the RC from hypothalamus. E- Increased Venous Return: o stimulate cardiac mechanoreceptors in the right atrium which reflex stimulates respiration. F- Norepinephrine: released from the sympathetic nervous system stimulates RC  Oxygen supply to muscle could also increased by In addition to hyperventilation there is o An increase in rate of gas diffusion o Shift of O2 dissociation curve to the right o Increase cardiac output which ensure increased O2 supply to the tissues. Oxygen Diffusing Capacity of Athletes -The oxygen diffusing capacity is a measure of the rate at which oxygen can diffuse from the pulmonary alveoli into the blood. - This is expressed in terms of milliliters of oxygen that will diffuse each minute for each millimeter of mercury difference between alveolar partial pressure of oxygen and pulmonary blood oxygen pressure Oxygen transport by the blood O2 is transported in the blood in two forms: A- Physically dissolved. [0.3 ml/100 ml arterial blood] Determines PO2 that determined the direction of diffusion of O2 and O2 carried by hemoglobin. o PO2 in tissues during exercise is 20 mmHg. o PO2 in tissues during rest is 40 mmHg. o PO2 at the lung and in arterial blood is 100 mmHg. B- Attached in chemical combination with hemoglobin. In the whole blood volume (5 liters) pumped by heart per minute, the O2 present in physical solution supplied to tissues per min is 15 ml. In adult man the total tissue O2 requirements / minute is 250 ml. An additional form of O2 is transported by Hemoglobin O2 carried by hemoglobin is 19.5 ml of O2 /I00 ml arterial blood. (98% of transported O2) It constitutes the main supply for the O 2 need of the tissues.  Oxygen content, capacity and hemoglobin saturation O2 content is the volume of O2 carried by blood combined with hemoglobin / 100 ml blood. The O2 content depends on: 1. Amount of hemoglobin present. 2. O2 tension. 3. O2 affinity of hemoglobin. 4. Metabolic state of the organ Oxygen content, capacity and hemoglobin saturation -1 The O2 capacity is the maximum volume of O2 that can be carried by hemoglobin, when hemoglobin is fully saturated with O2.(19.5 ml of O2 /I00 ml arterial blood) - The percentage saturation of hemoglobin with O2, (% HbO2) equals: The hemoglobin O2 dissociation curves Represent the relationship between PO2 and % HbO2 saturation. At 100 mmHg PO2 , Hb is approximately 97% saturated At 60 mmHg PO2, Hb is approximately 90% saturated Consequently arterial PO2 can decrease from 100mmHg to 60 mmHg with little change in % HbO2 as at high altitudes The flat portion of the oxyhemoglobin dissociation curve means that Hb has high affinity to O2 (loading), and complete saturation with O2.  The hemoglobin O2 dissociation curves At 40 mmHg PO2 : o in tissues during rest, blood is 70% saturated. So, tissues take about 27% of O2 of arterial blood. o The curve becomes vertical. This means that Hb has low affinity to O2 (unloading), this allows easy and rapid desaturation of Hb and enables the tissues to extract large amounts of O2 from blood. At 20 mmHg PO2 : o in tissues during exercise, Hb is about 20% saturated with O2. o So, tissues take about 50% of O2 of arterial blood Factors that shift the oxyhemoglobin dissociation curve to the right ( during exercise) a. Increase of PCO2 b. Increase of temperature c. Decrease of pH and increase H+ concentration. d. Increase 2,3-diphosphoglycerate (2,3-DPG), it is an end product of the RBCs metabolism. It binds to hemoglobin, changing its conformation and facilitating the off-loading of O2 and shifting the oxyhemoglobin dissociation curve to the right. A right ward shift of the curve means that, at a given PO2 there is less O2 bound to hemoglobin and more O2 is available to the active muscle. Factors that shift the oxyhemoglobin dissociation curve to the Left A decrease in temperature and PCO2 and an increase in pH shift the curve to the left. A leftward shift means that there is more O2 bound to hemoglobin (Increased affinity of hemoglobin to O2) So, it gives its O2 with difficulty to tissues. this occurs at rest and during sleep. Carbon dioxide transport by the blood CO2 is present in two forms: A. Physically dissolved —3 ml CO2/100 ml. —It is responsible for the PCO2 in the blood. —The arterial PCO2 is 40 mmHg. Carbon dioxide and oxygen transport Carbon dioxide transport by the blood B. Chemical combination (bicarbonate, carbamino compounds) - Bicarbonate Some of the dissolved CO2 reacts with water forming carbonic acid which readily ionizes to bicarbonate and H+. This reaction is very slow in plasma, but several thousand times faster in red blood cells due to carbonic anhydrase enzyme. HCO3- present in RBCs as KHCO3 and in plasma as NaHCO3(alkaline reserve). - Carbamino compounds They are formed by the reaction of CO2 with terminal amine groups on hemoglobin and on plasma protein Tidal CO2 o It is CO2 which is given by tissues to 100ml blood. o At rest, the tidal CO2 is 4ml./100ml. blood. o Tidal CO2 is mainly carried in chemical combination, so that the pH of blood does not markedly change. o Hb plays an important role in ‫ تخزين‬buffering the tidal CO2.