Hemoglobin – Blood Cells

by Paul Moss, PhD

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    00:01 Now, red cells are packed with haemoglobin. Haemoglobin consists of four protein chains and each of those carries a pocket for a molecule called HAEM.

    00:19 Now, these four protein chains vary slightly during our development in embryonic, fetal times You have slightly different forms of haemoglobin. but I'm not going to go into that today but in the adult, the 4 proteins consists of two alpha chains and two beta chains as represented on the right.

    00:41 and haem contains iron. Iron is critical for the carriage of oxygen within haemoglobin.

    00:51 In fact much of the iron within your body is found within your haemoglobin.

    00:55 We'll be discussing that later in the lecture series.

    01:01 and one thing we just need to consider is how haemoglobin can take up and release oxygen and it releases oxygen to the tissues. On the right you'll see a graph, it is called an oxygen dissociation curve and on the x-axis, we will see the partial pressure of oxygen, basically how much oxygen there is around. And on the y-axis the percentage saturation of haemoglobin at that given partial pressure of oxygen.

    01:39 You'll see the dark green line representing haemoglobin.

    01:43 of course as the oxygen concentration goes up the saturation goes up.

    01:49 You can see it's not exactly a linear line, it is not a straight line, it is what we call a sigmoid curve, it starts and then it accelerates. That's because when one globin molecule binds oxygen it helps the others to bind, it's a cooperative interaction and the haemoglobin can almost readily grab the oxygen. Another important point I want you to look at on that slide is the amount of saturation of haemoglobin within arterial blood and venous blood.

    02:24 So in the right you'll see the dotted line showing arterial blood.

    02:27 So it's a p02 of around 100 millimetres of mercury which is what we see in arterial blood, haemoglobin is almost completely saturated whereas if we look at blood coming back to the heart, venous blood, the partial pressure of oxygen is around 40 millimetres of mercury and at that point, the haemoglobin is around 75% percent saturated. It's around 25% of its capacity of oxygen carriage has been lost as it's gone around the body. There's still quite a lot of oxygen still remaining in venous blood even though when we take it of course it looks very blue compared to red blood from arteries but there is excess capacity to release more oxygen, perhaps if there is intense exercise. So we have some capacity to increase oxygen delivery.

    03:20 There are molecules within red cells such as 2-3-Diphosp hoglycerate which can shift this curve slightly to the left or the right so the body can regulate how much oxygen it releases into the tissues and we often find patients who have chronic anaemias who have low levels of haemoglobin and red cells that their 2-3-DPG levels are such that they can release more oxygen into the tissues to help their bodies cope with metabolism. Finally on that slide there is a dotted green-line above the haemoglobin curve and that is myoglobin You can see there the myoglobin curve there's not sigmoid and it has much more avidity for oxygen than haemoglobin.

    04:10 Haemoglobin needs to release oxygen into the tissues.

    04:17 Well it's not just about getting oxygen to tissues, of course you know from your biochemistry lectures on respiration that carbon dioxide is formed and so haemoglobin helps carbon dioxide to be transferred to the lungs and out of the body. So carbon dioxide diffuses from tissues into red cells and there is an enzyme carbonic anhydrase which generates the carbonic acid, that dissociates into bicarbonate ion and a proton. The protons are buffered by haemoglobin. So haemoglobin has an important role in buffering the production of that acidic proton. So as well as helping with oxygen delivery, haemoglobin helps with removal of carbon dioxide from tissues.

    About the Lecture

    The lecture Hemoglobin – Blood Cells by Paul Moss, PhD is from the course Hematology: Basics.

    Included Quiz Questions

    1. It holds on to oxygen very tightly compared to myoglobin.
    2. It consists of 2 alpha and 2 beta chains.
    3. Iron is a major constituent of haem.
    4. It is not the major form of haemoglobin present at birth
    5. Each globin chain carries a molecule of haem
    1. 4 molecules, 2 alpha chains and 2 beta chains
    2. 4 molecules, 2 alpha chains and 2 gamma chains
    3. 4 molecules, 2 alpha chains and 2 delta chains
    4. 3molecules, 1 alpha chains and 2 beta chains
    5. 3 molecules, 2 alpha chains and 1 beta chains
    1. In the absence of 2,3-BPG, hemoglobin's affinity for oxygen decreases
    2. Myoglobin is a hyperbolic shape in oxygen dissociation curve.
    3. Hemoglobin A has a sigmoid shape in oxygen dissociation curve.
    4. Increase in 2,3 DPG within the red cells can shift the red cell dissociation curve to the right.
    5. When there is a left shift of the oxygen dissociation curve, there is a decrease in the 2,3 DPG.
    1. The protons generated are buffered by the haemoglobin.
    2. Hemoglobin helps in the diffusion of carbon dioxide from tissue to the red cell.
    3. Hemoglobin helps in generation of H2CO3.
    4. Hemoglobin helps in dissociation of H2CO3 into HCO3+ and H+
    5. Hemoglobin is not involved in the transport of CO2

    Author of lecture Hemoglobin – Blood Cells

     Paul Moss, PhD

    Paul Moss, PhD

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