Transport of oxygen and carbon dioxide

Session format At the end of this lecture the student will be able to: understand how O 2 and CO 2 are transported around the body. understand how O 2 and CO 2 are transported around the body. describe the structure, function and location of RBC, haemoglobin and myoglobin. describe the structure, function and location of RBC, haemoglobin and myoglobin. describe the oxygen dissociation curve for haemoglobin. describe the oxygen dissociation curve for haemoglobin. understand the Bohr effect. understand the Bohr effect.

Recap The cardiovascular system is composed of the heart, blood and The cardiovascular system is composed of the heart, blood and The main job of the cardiovascular system is to transport respiratory gases (O 2 and CO 2 ) around the body. The main job of the cardiovascular system is to transport respiratory gases (O 2 and CO 2 ) around the body. This is in the form of oxygenated and deoxygenated blood. This is in the form of oxygenated and deoxygenated blood. Q: Which blood has the highest concentration of CO 2 ; oxygenated or deoxygenated blood? Q: Which blood has the highest concentration of CO 2 ; oxygenated or deoxygenated blood?

Recap During exercise the demand for oxygen During exercise the demand for oxygen Especially at the Especially at the This is because O 2 is required for the production of (Energy). This is because O 2 is required for the production of (Energy). The energy is used for muscular contraction and hence movement of the body. The energy is used for muscular contraction and hence movement of the body. During exercise the cardiac output is increased by increasing During exercise the cardiac output is increased by increasing

Recap Remember that: Heart rate is the amount of heart beats per minute. Heart rate is the amount of heart beats per minute. Stroke volume is the amount of blood ejected from the heart with each beat. 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 is the total amount of blood pumped out of the heart in one minute. Cardiac output = Cardiac output =

Recap Sympathetic activity = Sympathetic activity = Parasympathetic activity = Parasympathetic activity = Increase in heart rate is due to an increase in sympathetic activity. Increase in heart rate is due to an increase in sympathetic activity. Accompanied by a decrease in parasympathetic activity. Accompanied by a decrease in parasympathetic activity. Hormonal control by adrenaline and Hormonal control by adrenaline and

Recap Blood is shunted away from certain organs during exercise and redirected to the working muscles. Blood is shunted away from certain organs during exercise and redirected to the working muscles. “Supply and Demand” “Supply and Demand” This is achieved through vasoconstriction and vasodilation of the This is achieved through vasoconstriction and vasodilation of the Q: Will the blood vessels supplying the working muscles vasodilate or vasoconstrict during exercise? Q: Will the blood vessels supplying the working muscles vasodilate or vasoconstrict during exercise?

Transport of O 2 Oxygen picked up by the blood at the lungs ( ) must be transported to the tissues. Oxygen picked up by the blood at the lungs ( ) must be transported to the tissues. Oxygen is transported in the blood in two forms: Oxygen is transported in the blood in two forms: –physically dissolved in the blood ( ) –bound to haemoglobin ( ) Very little O 2 is dissolved in the plasma of the blood as it poorly soluble. Very little O 2 is dissolved in the plasma of the blood as it poorly soluble. Due to the small amount of O 2 dissolved in the blood there must be an additional mechanism of transporting oxygen from the lungs to the tissues. Due to the small amount of O 2 dissolved in the blood there must be an additional mechanism of transporting oxygen from the lungs to the tissues.

Transport of O 2 This mechanism is (Hb) This mechanism is (Hb) Haemoglobin - iron bearing protein molecule contained within red blood cells (RBC). Haemoglobin - iron bearing protein molecule contained within red blood cells (RBC). 280 million haemoglobin molecules crowded into each RBC. 280 million haemoglobin molecules crowded into each RBC. Men have more haemoglobin than women. Men have more haemoglobin than women. Due to male testosterone increasing RBC production. Due to male testosterone increasing RBC production. Haemoglobin has the ability to form a reversible combination with oxygen. Haemoglobin has the ability to form a reversible combination with oxygen. Q: What does reversible mean? Q: What does reversible mean?

Transport of O 2 When not combined to O 2, haemoglobin is referred to as reduced haemoglobin. When not combined to O 2, haemoglobin is referred to as reduced haemoglobin. When combined with O 2, it is called When combined with O 2, it is called Hb + O 2 HbO 2 Haemoglobin OxygenOxyhaemoglobin Haemoglobin OxygenOxyhaemoglobin

Transport of O 2 The haemoglobin molecule has four atoms of iron. The haemoglobin molecule has four atoms of iron. Each of the four iron atoms has the ability to combine with. Each of the four iron atoms has the ability to combine with. Each Hb molecule can carry up to 4 molecules of O 2. Each Hb molecule can carry up to 4 molecules of O 2. Hb is considered to be fully saturated when all iron atoms combine with a molecule of O 2. Hb is considered to be fully saturated when all iron atoms combine with a molecule of O 2.

Transport of O 2 The percent haemoglobin saturation (%Hb) is a measure of the extent to which Hb in the blood is combined with O 2. The percent haemoglobin saturation (%Hb) is a measure of the extent to which Hb in the blood is combined with O 2. Can vary from 0 to 100% Can vary from 0 to 100% 100% = all of the haemoglobin molecules within the blood are fully saturated with O % = all of the haemoglobin molecules within the blood are fully saturated with O 2. Healthy individuals = Hb Healthy individuals = Hb Influenced by PO 2 of the blood. Influenced by PO 2 of the blood. PO 2 = partial pressure of Oxygen. Caused by movement of dissolved oxygen in the blood. PO 2 = partial pressure of Oxygen. Caused by movement of dissolved oxygen in the blood.

Transport of O 2 Gases (O 2 and CO 2 ) move down partial pressure gradients. Gases (O 2 and CO 2 ) move down partial pressure gradients. PO 2 is high at the (pulmonary capillaries). PO 2 is high at the (pulmonary capillaries). PO 2 is low at the (systemic capillaries). PO 2 is low at the (systemic capillaries). When PO 2 is high oxygen combines readily with haemoglobin, until the haemoglobin becomes saturated. Called oxygenation When PO 2 is high oxygen combines readily with haemoglobin, until the haemoglobin becomes saturated. Called oxygenation When the PO 2 is low haemoglobin releases O 2 to the tissues. Called deoxygenation When the PO 2 is low haemoglobin releases O 2 to the tissues. Called deoxygenation

Transport of O 2 Because of the difference in PO 2 at the lungs and the tissues, Hb automatically loads up on oxygen at the lungs (oxygenation) and unloads it at the tissues (deoxygenation). Because of the difference in PO 2 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 PO 2 and % haemoglobin saturation is known as the: The relationship between PO 2 and % haemoglobin saturation is known as the: Oxygen -Haemoglobin Dissociation Curve S - shaped curve (see graph) S - shaped curve (see graph)

Oxygen - Haemoglobin Dissociation Curve % sat 60 of Hb PO 2

Transport of O 2 Note: from the Oxygen haemoglobin dissociation curve that the % saturation of haemoglobin is higher at the lungs and lower at the tissues. 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 attaching to haemoglobin at the lungs Oxygen is unloading Oxygen is unloading

The Bohr effect Oxygen - haemoglobin curve shown previously is at normal conditions (pH 7.4, tissue Temp of 37 o C). Oxygen - haemoglobin curve shown previously is at normal conditions (pH 7.4, tissue Temp of 37 o C). Any increase in acidity, temperature or concentration of carbon dioxide causes the dissociation curve to shift downwards and to the right. 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. In other words the haemoglobin releases oxygen more readily. Known as the Known as the

The Bohr Effect rightward shift due to increased 80 rightward shift due to increased carbon dioxide, acidity and temp. carbon dioxide, acidity and temp. % sat 60 of Hb CO2, acidity, Temp PO 2

Carbon Monoxide Carbon Monoxide (CO) is a poisonous gas. Carbon Monoxide (CO) is a poisonous gas. Found in such things as motor car fumes. Found in such things as motor car fumes. Carbon Monoxide and Oxygen compete for the same binding sites on Haemoglobin. Carbon Monoxide and Oxygen compete for the same binding sites on Haemoglobin. CO is times more likely to attach to haemoglobin than O 2. CO is times more likely to attach to haemoglobin than O 2. Therefore if CO is present oxygen is transported in the blood. Therefore if CO is present oxygen is transported in the blood. Death can occur due to oxygen starvation of the tissues. Death can occur due to oxygen starvation of the tissues.

Myoglobin Myoglobin is an iron containing protein. Myoglobin is an iron containing protein. Found in skeletal and muscle Found in skeletal and muscle It’s function is as a storage site for. It’s function is as a storage site for. Similar to haemoglobin - combines reversibly with oxygen. Similar to haemoglobin - combines reversibly with oxygen. Each myoglobin molecule contains 1 iron atom, in contrast to haemoglobin which contains 4 atoms. 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). High concentration of myoglobin in slow twitch muscle fibres (generate ATP aerobically).

Myoglobin Facilitates (helps) the transfer of oxygen to the tissues. Facilitates (helps) the transfer of oxygen to the tissues. Especially during beginning of exercise and during Especially during beginning of exercise and during During rest and moderate levels of exercise the myoglobin stays attached to the oxygen. 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. Unlike haemoglobin, myoglobin is not affected by acidity, carbon dioxide and temperature. Therefore does not display the Therefore does not display the

Transport of Carbon dioxide (CO 2 ) Remember - gases flow a pressure gradient. Remember - gases flow a pressure gradient. When blood flows through the tissue capillaries CO 2 diffuses down its pressure gradient from the tissue cells into the blood. When blood flows through the tissue capillaries CO 2 diffuses down its pressure gradient from the tissue cells into the blood. The blood then becomes. The blood then becomes. CO 2 is produced as a by product of metabolism (energy production). CO 2 is produced as a by product of metabolism (energy production).

Transport of Carbon dioxide (CO 2 ) CO 2 is transported in the blood in three ways: CO 2 is transported in the blood in three ways: –physically dissolved (10%) –bound to haemoglobin (30%) –as bicarbonate ( ) When CO 2 combines with haemoglobin the product is known as carbomino-haemoglobin (HbCO 2 ). When CO 2 combines with haemoglobin the product is known as carbomino-haemoglobin (HbCO 2 ). The unloading of O 2 at the tissues facilitates the picking up of CO 2 by Haemoglobin. The unloading of O 2 at the tissues facilitates the picking up of CO 2 by Haemoglobin.

Transport of Carbon dioxide (CO 2 ) By far the most important means of transporting CO 2 from the tissues to the lungs is as a bicarbonate (HCO 3 - ). By far the most important means of transporting CO 2 from the tissues to the lungs is as a bicarbonate (HCO 3 - ). 60% of the CO 2 is converted to a bicarbonate. 60% of the CO 2 is converted to a bicarbonate. The chemical reaction takes place in the The chemical reaction takes place in the It is essential both at rest and during exercise that O 2 and CO 2 are transported around the body. This is achieved through various mechanisms within the blood. It is essential both at rest and during exercise that O 2 and CO 2 are transported around the body. This is achieved through various mechanisms within the blood.