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Transport of oxygen and carbon dioxide Session format At the end of this lecture the student will be able to: understand how O2 and CO2 are transported around the body. describe the structure, function and location of RBC, haemoglobin and myoglobin. describe the oxygen dissociation curve for haemoglobin. understand the Bohr effect. Recap The cardiovascular system is composed of the heart, blood and The main job of the cardiovascular system is to transport respiratory gases (O2 and CO2) around the body. This is in the form of oxygenated and deoxygenated blood. Q: Which blood has the highest concentration of CO2; oxygenated or deoxygenated blood? Recap During exercise the demand for oxygen Especially at the This is because O2 is required for the production of (Energy). The energy is used for muscular contraction and hence movement of the body. During exercise the cardiac output is increased by increasing Recap Remember that: Heart rate is the amount of heart beats per minute. Stroke volume is the amount of blood ejected from the heart with each beat. Cardiac output is the total amount of blood pumped out of the heart in one minute. Cardiac output = Recap Sympathetic activity = Parasympathetic activity = Increase in heart rate is due to an increase in sympathetic activity. Accompanied by a decrease in parasympathetic activity. Hormonal control by adrenaline and Recap Blood is shunted away from certain organs during exercise and redirected to the working muscles. “Supply and Demand” This is achieved through vasoconstriction and vasodilation of the Q: Will the blood vessels supplying the working muscles vasodilate or vasoconstrict during exercise? Transport of O2 Oxygen picked up by the blood at the lungs ( ) must be transported to the tissues. Oxygen is transported in the blood in two forms: – physically dissolved in the blood ( – bound to haemoglobin ( ) ) Very little O2 is dissolved in the plasma of the blood as it poorly soluble. Due to the small amount of O2 dissolved in the blood there must be an additional mechanism of transporting oxygen from the lungs to the tissues. Transport of O2 This mechanism is (Hb) Haemoglobin - iron bearing protein molecule contained within red blood cells (RBC). 280 million haemoglobin molecules crowded into each RBC. Men have more haemoglobin than women. Due to male testosterone increasing RBC production. Haemoglobin has the ability to form a reversible combination with oxygen. Q: What does reversible mean? Transport of O2 When not combined to O2, haemoglobin is referred to as reduced haemoglobin. When combined with O2, it is called Hb + Haemoglobin O2 Oxygen HbO2 Oxyhaemoglobin Transport of O2 The haemoglobin molecule has four atoms of iron. Each of the four iron atoms has the ability to combine with . Each Hb molecule can carry up to 4 molecules of O2. Hb is considered to be fully saturated when all iron atoms combine with a molecule of O2. Transport of O2 The percent haemoglobin saturation (%Hb) is a measure of the extent to which Hb in the blood is combined with O2. Can vary from 0 to 100% 100% = all of the haemoglobin molecules within the blood are fully saturated with O2. Healthy individuals = Hb Influenced by PO2 of the blood. PO2 = partial pressure of Oxygen. Caused by movement of dissolved oxygen in the blood. Transport of O2 Gases (O2 and CO2) move down partial pressure gradients. PO2 is high at the (pulmonary capillaries). PO2 is low at the (systemic capillaries). When PO2 is high oxygen combines readily with haemoglobin, until the haemoglobin becomes saturated. Called oxygenation When the PO2 is low haemoglobin releases O2 to the tissues. Called deoxygenation Transport of O2 Because of the difference in PO2 at the lungs and the tissues, Hb automatically loads up on oxygen at the lungs (oxygenation) and unloads it at the tissues (deoxygenation). The relationship between PO2 and % haemoglobin saturation is known as the: Oxygen -Haemoglobin Dissociation Curve S - shaped curve (see graph) Oxygen - Haemoglobin Dissociation Curve 100 80 % sat of Hb 60 40 20 0 0 20 40 60 PO2 80 100 Transport of O2 Note: from the Oxygen haemoglobin dissociation curve that the % saturation of haemoglobin is higher at the lungs and lower at the tissues. Oxygen is attaching to haemoglobin at the lungs Oxygen is unloading The Bohr effect Oxygen - haemoglobin curve shown previously is at normal conditions (pH 7.4, tissue Temp of 37oC). Any increase in acidity, temperature or concentration of carbon dioxide causes the dissociation curve to shift downwards and to the right. In other words the haemoglobin releases oxygen more readily. Known as the The Bohr Effect 100 80 % sat of Hb rightward shift due to increased carbon dioxide, acidity and temp. 60 40 20 CO2, acidity, Temp 0 0 20 40 60 PO2 80 100 Carbon Monoxide Carbon Monoxide (CO) is a poisonous gas. Found in such things as motor car fumes. Carbon Monoxide and Oxygen compete for the same binding sites on Haemoglobin. CO is times more likely to attach to haemoglobin than O2. Therefore if CO is present oxygen is transported in the blood. Death can occur due to oxygen starvation of the tissues. Myoglobin Myoglobin is an iron containing protein. Found in skeletal and muscle It’s function is as a storage site for . Similar to haemoglobin - combines reversibly with oxygen. Each myoglobin molecule contains 1 iron atom, in contrast to haemoglobin which contains 4 atoms. High concentration of myoglobin in slow twitch muscle fibres (generate ATP aerobically). Myoglobin Facilitates (helps) the transfer of oxygen to the tissues. Especially during beginning of exercise and during During rest and moderate levels of exercise the myoglobin stays attached to the oxygen. Unlike haemoglobin, myoglobin is not affected by acidity, carbon dioxide and temperature. Therefore does not display the Transport of Carbon dioxide (CO2) Remember - gases flow a pressure gradient. When blood flows through the tissue capillaries CO2 diffuses down its pressure gradient from the tissue cells into the blood. The blood then becomes . CO2 is produced as a by product of metabolism (energy production). Transport of Carbon dioxide (CO2) CO2 is transported in the blood in three ways: – physically dissolved (10%) – bound to haemoglobin (30%) – as bicarbonate ( ) When CO2 combines with haemoglobin the product is known as carbomino-haemoglobin (HbCO2). The unloading of O2 at the tissues facilitates the picking up of CO2 by Haemoglobin. Transport of Carbon dioxide (CO2) By far the most important means of transporting CO2 from the tissues to the lungs is as a bicarbonate (HCO3-). 60% of the CO2 is converted to a bicarbonate. The chemical reaction takes place in the It is essential both at rest and during exercise that O2 and CO2 are transported around the body. This is achieved through various mechanisms within the blood.