Lecture 16: Oxygen Transport & CO2 Transport PDF

Lecture 16 How is O2 transported from the lung to skeletal muscle? - Transported through blood through hemoglobin (Hb) What percentage of O2 is transported in the blood bound to Hb? - Approximately 99% What is oxyhemoglobin? - Oxygen bound to Hb What is deoxyhemoglobin? - Oxygen...

Lecture 16 How is O2 transported from the lung to skeletal muscle? - Transported through blood through hemoglobin (Hb) What percentage of O2 is transported in the blood bound to Hb? - Approximately 99% What is oxyhemoglobin? - Oxygen bound to Hb What is deoxyhemoglobin? - Oxygen is not bound to Hb How many oxygen molecules are connected to Hb? - 4 oxygens are connected to 1 Hb Where does the last percentage of oxygen go? - The 1% goes to plasma What is the relationship between partial pressure of oxygen and Hb saturation? - Hb binds to oxygen very strong - When RBC goes through those capillaries in the alveoli, and oxygen diffuse in What is the percentage of Hb at rest after perfusing skeletal muscle? - 75% What is the oxyhemoglobin curve? - Describes the binding characteristics of oxygen to Hb - It shows the partial pressure of oxygen - 100 mmHg is important because of the partial pressure of oxygen in the capillaries in the alveoli and binds to oxygen is 100 - 100 is the highest in the body - Percentage of Hb saturated with oxygen - Not linear, steep and flatter section What is the partial pressure of oxygen at rest?* - 40 Why do we only drop off 25% of oxygen bound to Hb at rest? - There is no reason to dump all the oxygen since you don’t need as much during rest, don’t need a lot of ATP - Need to match the production to what we need What happens to the other 75%? - Oxygen is not bound to Hb and not used during rest What happens to the oxyhemoglobin dissociation curve with acute exercise? - Changes in PO2 - With exercise muscle PO2 is decreased and more oxygen is released from Hb - The rate of oxygen increases to meet the demand - After resting, the curve is steeper for the oxygen to be released, to drop off a lot of oxygen - Steeper curve, more oxygen being released - The curve is set up to utilize oxygen and drop off oxygen What happens to pH when exercising? - Declines - The blood becomes more acidic What happens to the oxyhemoglobin dissociation curve with pH? - Results in a rightward shift of the curve called the Bohr effect - The Bohr effect favors the off loading of oxygen to the tissues - The curve shifts for more oxygen to be released - 45% of oxygen is dropped off What happens when we make our blood more acidic? - We hold onto the oxygen more What happens to temperature during exercise? - Increases What happens to the oxyhemoglobin dissociation curve with temperature? - Results in a rightward shift - Favors the off loading of oxygen from Hb - Free to go into the skeletal muscle from Hb What causes a rightward shift in the oxyhemoglobin dissociation curve? - Decrease of PO2 - Decrease of pH - Increase of temperature - Those 3 factors allow the blood itself to regulate how much oxygen gets to the working skeletal muscle What is the relationship between myoglobin to hemoglobin? - Myoglobin oxygen binding protein found in skeletal muscle - Acts as a site for oxygen storage When does myoglobin release oxygen? - At very low PO2 What kind of exercise intensity needs to happen for myoglobin to drop off oxygen? - High intensity How is CO2 transported from the working skeletal muscle to the lung? - Gets it to the blood, to the lungs then the alveoli - Mostly not bound to Hb Where does CO2 go? - 10 % will dissolve in the plasma - 20% bound to Hb - 70% is transported by the bicarbonate system What is the bicarbonate system equation? - CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3- What happens to PCO2 when going to the left and right of the equation? - High: drives equation to the right, to the cell itself - Left: drives equation to the left, to the lungs What are the mechanisms of bicarbonate? - Buffers out H ions, combining with bicarbonate and blowing it out as carbon dioxide Can hydrogen unbind to an oxygen molecule? - No What happens when the PCO2 is high when transporting CO2 into the blood? - The CO2 in the 70% goes into the RBC, the reaction of CO2 and H2O is catalyzed by carbonic anhydrase, which causes carbonic acid to be formed to CO3 - Carbonic acid dissociates into the hydrogen ion and bicarbonate ion - The bicarbonate can’t be transported in the RBC, it has to be transferred through the plasma - Hydrogen ions binds to Hb - The bicarbonate ion is negatively charged and is taken out of the cell, to maintain the electoral chemically balance and needs to be replaced with someone to take its spot - With is chloride, the chloride shift occurs - Bicarbonate moves out if the RBC and chloride moves into RBC to maintain electrochemical balance - Decrease in pH, more acidic Where can bicarbonate be transported through? - Plasma What happens when the PCO2 is low when transporting CO2 into the blood? - Oxygen binds to Hb and releases H ions  - Chloride leaves RBC and bicarbonate enters RBC - Bicarbonate and hydrogen form carbonic acid - Carbonic acid dissociates to water and carbon dioxide - Oxygen increases Why is the bicarbonate system used? - To transfer the 70% of CO2 - A way of transporting CO2 but changes it into bicarbonate since only 10% can dissolve in the plasma itself - So it can go through the plasma What occurs from rest to work transitions? - Ventilation increases - Slight decrease in PO2 - Slight decrease in PCO2 - After the increase/decrease plateaus, around the first 1-2 minutes, then it is maintained - Where the perfect amount of oxygen is going to be released into the working skeletal muscle Why does PO2 slightly decrease when going from rest to work? - There is not enough O2 going to the skeletal muscle Why does PCO2 slightly decrease when going from rest to working? - Not getting CO2 fast enough How does temperature impact ventilation during prolonged steady state exercise? - Starts drifting What happens when you exercise in a hot environment during prolonged exercise? - Ventilation tends to drift upward - Little change in PCO2 - Higher ventilation not due to increased PCO2 Does ventilation increase linearly with increasing workload? - No What happens to ventilation with incremental exercise? - Linear curve increase, up to 50-70% VO2max Around the same time what happens to the pH? - Goes down Why does the pH go down with incremental exercise? - It goes down due to more H ions in the blood to buffer out H ions to breathe more - Therefore more ventilation What happens to ventilation when pH drops? - You start ventilating at higher rates What is the ventilatory threshold (Tvent)? - The inflection point where VE increases exponentially - To correspond to OBLA or lactic acid Why are there more hydrogen ions in the blood? - To break down ATP at super high rates How is the ventilatory threshold altered with chronic exercise training? - Higher - Utilized aerobic pathways - Not have a decrease in pH as quickly - Able to work at higher capacities What is the ventilatory response to exercise in a trained person? - Decrease in PO2 - Increase CO2 and decrease RBC transit time - pH maintained at a higher work rate - Tvent occurs at a higher work rate - Due to the lack of change, the heart gets larger and the cardiac output increases What is the ventilatory difference between a trained vs untrained individual during exercise? - They both have the same capillaries but have the small amount of blood going through it because the Hb isn’t binding to oxygen as well - Increased VO2max How is ventilation controlled? - Mechanisms in our body to make sure we match our oxygen with the needs if our body What are the two humoral inputs to the respiratory control center? - Central chemoreceptors - Peripheral chemoreceptors What are the neural inputs to the respiratory control center? - Efferent input - Afferent - It will help us breathe the exact way we need to What does the efferent input do? - Information leaving the brain - Motor cortex  - “Spill over”, signal going to the muscle need more oxygen - Most important in the regulation of ventilation during exercise What does the afferent input do in the skeletal muscle? - Muscle spindles, golgi tendon organs, joint pressure receptors, picking up movements and sent to the brain - H+ and potassium What chemical stimulus impacts the regulation of breathing most? - PCO2 - PCO2 is the largest driving force of ventilation to get oxygen to the working skeletal muscle and organs