hi everyone welcome to bite size med where we talk about quick bite-sized concepts in basic medical sciences for study and rapid review this video is on the respiratory changes in exercise the respiratory response to exercise is an amalgamation of a bunch of physiology concepts so if during this video you feel like you need help on any of the concepts i talk about you can check links in the description box below during exercise the exercising muscles have a high oxygen demand and from increased tissue metabolism more carbon dioxide is produced for more oxygen to get in and to get rid of the excess carbon dioxide alveolar ventilation has to increase and it does if there's increased ventilation where oxygen is entering the capillary and carbon dioxide is leaving you'd expect the arterial oxygen to increase and carbon dioxide to reduce but that doesn't happen both of them stay normal now the reason for this is not clear the increased ventilation and the efficiency of gas exchange might be so good that the arterial oxygen and carbon dioxide get maintained this is arterial the increased carbon dioxide produced from tissue metabolism increases the venous carbon dioxide and from oxygen consumption the venous oxygen reduces so arterial oxygen and carbon dioxide stay normal but venous carbon dioxide increases and venous oxygen reduces the increased carbon dioxide is cleared out by increased alveolar ventilation before it can reach the arteries one stimulus for increased ventilation comes from the muscle and joint proprioceptors they stimulate the dorsal respiratory group of neurons in the medulla this group controls inspiration so stimulation of it would increase inspiration now we know what happens to the oxygen and carbon dioxide but what happens to the ph during moderate exercise it's maintained but during strenuous exercise from increased metabolism there's more lactic acid production lactic acid is a product of anaerobic metabolism this lactic acid increases hydrogen ions so there's low ph and strenuous exercise to meet the oxygen demand the cardiac output increases the cardiac output from the right heart therefore also increases and that's pulmonary circulation so pulmonary blood flow increases the ventilation perfusion ratio is the ratio of air coming in per minute to blood coming in per minute now normally this is not uniform while standing ventilation is low at the apex than at the base and perfusion is much lower at the apex than at the base so at the apex with lower perfusion than ventilation the ratio is higher and at the base with higher perfusion than ventilation the ratio is lower the perfusion is pulmonary blood flow so if pulmonary blood flow is increasing perfusion is higher and the vq ratio becomes more uniform so the tissues are producing more carbon dioxide from anaerobic metabolism there's more lactic acid production which lowers the ph and there's a high temperature of the exercising muscles all of this shifts the oxygen dissociation curve to the right and right releases so there's more oxygen release so the p50 which is the partial pressure at which 50 percent of hemoglobin is saturated will increase more oxygen is needed to get to 50 saturation there's low affinity for oxygen and there's more oxygen released to the tissues which are the muscles and they have a high oxygen demand so this demand is met by shifting the oxygen dissociation curve to the right if this video helped you give it a thumbs up share and subscribe thanks for watching and i'll see you in the next one