2Gas Exchange at the Muscles Now we have considered how our respiratory and cardio-vascular system brings air into our lungs, exchange oxygen and carbon dioxide in the alveoli, and transport oxygen to the muscles (and CO2 away from them).All that remains is for us to consider the delivery of oxygen to the muscles from the capillary blood.This gas exchange between the tissue and the blood in the capillaries is known as – internal respiration.
3The Arterial-venous Oxygen Difference At rest, the oxygen content of arterial blood is about 20ml of oxygen per 100 ml of blood.This value drops to 15 or 16ml of O2 per 100ml as the blood passes through the capillaries into the venous system.This difference in oxygen content between arterial and venous blood is referred to as the arterial-venous oxygen difference (a-VO2diff).Why? Oxygen is being used!!!!
4ARTERIOVENOUS OXYGEN DIFFERENCE a-vO2 diffthis expresses the difference between the oxygen carried by blood in arteries and veinsand represents the amount of oxygen delivered to working tissue in the capillary systema-vO2 diff - AT RESTvenule capillary arterioleblood flow15ml O2per 100ml blood20ml O2per 100ml blooda-vO2 diff = 5mlper 100ml bloodAt rest, the oxygen content of arterial blood is about 20ml of oxygen per 100 ml of blood.The value drops to 15 or 16ml of oxygen per 100ml as the blood passes through the capillaries into the venous system.This difference in oxygen content between arterial and venous blood is referred to as the arterial-venous oxygen difference (a-VO2diff).It reflects the 4-5 ml of oxygen per 100 ml of blood taken up by the tissues.The amount of oxygen taken up is proportional to its use for oxidative energy production. Thus as the rate of oxygen use increases, the a-vO2 diff also increases.a-vO2 diff - DURING INTENSE EXERCISEvenule capillary arterioleblood flow5ml O2per 100ml blood20ml O2per 100ml blooda-vO2 diff = 15mlper 100ml blood
5The Arterial-venous Oxygen Difference It reflects the 4-5 ml of oxygen per 100 ml of blood taken up by the tissues.The amount of oxygen taken up is proportional to its use for oxidative energy production. Thus as the rate of oxygen use increases, the a-vO2 diff also increases.
6The Arterial-venous Oxygen Difference E.g. during intense exercise the a-vO2 diff in contracting muscles can increase to 15 to 16 ml per 100ml of blood. During such an effort, the blood unloads more oxygen to the active muscles because the PO2 in the muscles is drastically lower than in arterial blood.
7Key PointThe a-vO2 diff increases from a resting value of about 4 to 5 ml per 100 ml of blood up to values of 15 to 16 ml per 100 ml of blood during exercise.This increase reflects an increase extraction of oxygen from arterial blood by active muscle, thus decreasing the oxygen content of the venous blood.
8Factors Influencing Oxygen Delivery and Uptake. The rates of oxygen delivery and uptake depend on the three major variables.The oxygen content of blood.The amount of blood flow.The local conditions.As we begin to exercise, each of these variables must be adjusted to ensure increased oxygen delivery to our active muscles.
9Factors Influencing Oxygen Delivery and Uptake. We have discussed in class that under normal circumstances haemoglobin is 98% saturated with oxygen.Any reduction in the blood’s normal oxygen carrying capacity would hinder oxygen delivery and reduce cellular uptake of oxygen.
10Factors Influencing Oxygen Delivery and Uptake. Exercise causes increased blood flow through the muscles. As more blood carries oxygen through the muscles, less oxygen must be removed from each 100 ml of blood (assuming the demand remains unchanged).Thus increasing blood flow improves oxygen delivery and uptake.
11Factors Influencing Oxygen Delivery and Uptake. Many local changes in the muscle during exercise affect oxygen delivery and uptake.Muscle activity increases muscle acidity because of lactate production.Muscle temperature and carbon dioxide concentration both increase because of increased metabolism.All of these increase oxygen uploading from haemoglobin molecule, facilitating oxygen delivery and uptake by the muscles.
12Factors Influencing Oxygen Delivery and Uptake. During maximal exercise,however, when we push our bodies to the limit, changes in any of these areas can impair oxygen delivery and restrict out abilities to meet oxidative demands.