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Erythrocytes – Blood Cells

by Paul Moss, PhD
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    00:01 Hello in the second lecture in our series on haematology we're going to look at the physiology and function of some of the major blood cells, and the learning outcomes that we'll be getting from this lecture are as follows: We will look at red cell production and how that's regulated by erythropoietin, and we will explore how red cells contain haemoglobin and how that helps them to carry oxygen to tissue.

    00:29 We will look at the subsets of white cells which play specific roles in protection against infection and we will explore how lymphocytes mediate the function of the immune system and find out how neutrophils are critical in the first line of defence against bacteria and fungi.

    00:48 In this lecture we are not going to focus on platelets because they're the subject of a later lecture on blood clotting.

    00:57 Let's look at red cells in a little bit more detail, by far the most common cell within the blood.

    01:07 Red blood cells derive of course from a nucleated cell within the bone marrow and the first cell that is committed to forming red cells is the erythroblast and there are rare forms of leukaemia in fact derived from these cells.

    01:23 Red cells are packed with haemoglobin and they carry oxygen to tissue.

    01:29 The reason that we've evolved red cells is that it allows haemoglobin to be packaged effectively within these blood cells rather than being free within the blood, the major production of red cells is through this hormone called erythropoietin and we'll explore the regulation of erythropoietin in some detail.

    01:52 On the right, you'll see a lovely scanning electron micrograph of red cells and you'll see that classic biconcave disc structure of the red cell which allows it to be flexible and flow through the capillaries as well as diffusing oxygen into tissue.

    02:14 Now, haematologists can't stop making blood films and there you’ll see a blood film on the right and you'll see how red cells look down the microscope and you'll see the characteristic pale centre because of their shape. They are around seven microns in diameter and highly flexible structures with the biconcave shape.

    02:39 Now, some red cells in the blood are very young, because they've just come out of the bone marrow and we call those reticulocytes. They carry a lot of RNA and that RNA gradually gets degraded over 2-3 days and the final red cell then becomes apparent.

    03:02 So you'll see on the left reticulocytes can live for two or three days normally within the blood.

    03:07 Around 2% of the red cells are reticulocytes and we can detect them by staining what we call the supravital staining with this wonderful dye called brilliant cresyl blue and you'll see on the right those cells with the intense blue stain, those are reticulocytes.

    03:28 There's an awful lot in that picture and many more of them we'd find in your own blood I'm sure.

    03:34 Now as well as being physiologically important, reticulocytes are important clinically because they can give us a guide as to the type of anaemia that we may be dealing with in a patient.

    03:46 Because if the reticulocyte count has increased, it shows that the patient's bone marrow is very active and pouring out a lot of red cells into the blood, whereas if we can't find many reticulocytes, it means that there's a problem with the production of red cells from the bone marrow.

    04:05 So when we discuss anaemia in later lectures, you can see why the reticulocyte count is a very useful test for trying to understand the etiology of the anaemia.

    04:18 Now, the production of red cells is described by the term erythropeoisis.

    04:26 And again, it's represented by those green cells.

    04:30 Erythroblasts are the first precursors and those differentiate into normoblast.

    04:38 Normoblasts have a nucleus but then as they themselves differentiate, the nucleus is ejected and at that stage, the reticulocytes can be released into the blood.

    04:50 Now we don't know why the nucleus is ejected in red cell production but it may be that that allows more room for haemoglobin production and that has been selected during evolution as a very effective way to increase oxygen transport within the blood.

    05:12 Now the regulation of this process of haemopoiesis is really controlled through this protein called erythropoietin or EPO. This hormone EPO is produced largely from the kidney.

    05:29 Again very surprising finding, the kidney should be regulating our blood production.

    05:36 But if cells in the kidney detect that the blood is hypoxic in any way, they will then release erythropoietin into the blood. Erythropoietin circulates to the bone marrow and it stimulates the production of red cells. As you could probably imagine, EPO or erythropoietin levels are increased in people who are short of oxygen. For instance, those who live at high altitude or patients who have lung disease or perhaps, smoke. You'll see on the right there, a representation of stimuli to hypoxia, factors such as anaemia, or low atmospheric oxygen tension.

    06:22 That hypoxia is detected by the kidney and erythropoietin is produced.

    06:31 Erythropoietin stimulates haemopoiesis through a number of mechanisms.

    06:35 It increases the differentiation pathway through erythropoiesis to make more erythropoietic cells.

    06:43 It accelerates cell division and it accelerates release of cells into the blood.

    06:51 That can usually address the hypoxia. Of course, the negative feedback loop is established.

    06:59 Erythropoietin is actually a very useful molecule for clinical therapy and we can use it to stimulate haemopoiesis in patients with some forms of anaemia.


    About the Lecture

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


    Included Quiz Questions

    1. They are useful in determining the relative activity of erythropoiesis in the marrow.
    2. They contain a nucleus that is lost soon after release into blood.
    3. Increased presence of reticulocytes indicates anaemia.
    4. They are detected by red stain on supravital staining.
    5. They exist for around 10 days before maturing to erythrocytes.

    Author of lecture Erythrocytes – Blood Cells

     Paul Moss, PhD

    Paul Moss, PhD


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