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Blood Structure – Blood Formation

by Paul Moss, PhD
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    00:01 Now let's just consider the environment in which this haemopoiesis takes place and specifically consider the stem cell niche.

    00:13 Blood is made in the bone marrow. We don't know why this evolved, but it seems to be a highly effective strategy for the generation of blood. Now haemopoietic bone marrow or bone marrow that's making blood is present in almost all bones in children, but as we get older, it gets more restricted.

    00:33 Its in our vertebra or pelvis and in our proximal long bones, and stem cells are supported within the bone marrow in a niche on microenvironment. We can have a closer look of that on the right.

    00:49 On the top right in dark green, we see the cortical bone and up against it on the top right of the stem cells, the progenitor cells and bone cells such as osteoblasts directly support the survival of haemopoietic stem cells.

    01:11 As these stem cells give rise to haemopoiesis, we see waves of differentiated haemopoietic cells, which flow through the bone marrow and into that grey central longitudinal vein and you will see in that diagram, haemopoietic islands and erythropoietic islands for haemopoiesis.

    01:36 You'll see just to the bottom there, a megakaryocyte a very large cell with multiple nuclei that's releasing platelets into the central longitudinal vein, On the right, we will see some of the cells that support bone marrow function - adipocytes or fat cells. They comprise a great proportion of the bone marrow and if you take a biopsy of bone marrow, you'll see a lot of empty space occupied by fat cells.

    02:05 And just at the bottom right the extracellular matrix fibres, which provide the structural support for the bone marrow and also bind molecules such as chemokines which are critical in guiding the migration of cells in and out of the bone marrow.

    02:26 I want to finish this lecture by talking about the structure of the spleen which is a fascinating organ.

    02:35 Normally under your left rib, you shouldn't feel your spleen, it is well tucked away.

    02:41 This consists of two major types of tissue: the red pulp and the white pulp.

    02:47 The red pulp is where the red cells in our blood undergo a quality control and I will explain that in a minute.

    02:56 Whereas the white pulp is part of our immune system and the spleen has a very important role in scanning the blood for evidence of bacterial infection.

    03:07 The blood system in the spleen is really quite fascinating because it has a unique open system which is not contained within capillaries. Let me explain.

    03:19 Look at that diagram on the right. At the bottom, we have the blood coming in through the trabecular artery and into the central artery and around it in grey and green,you will see lots of lymphocytes.

    03:38 It is coded there as PALS, the periarteriolar lymphatic sheath.

    03:43 That is the massive lymphoid tissue which is screening the blood for the presence of bacteria and starting and initiating antibody responses against those. That is a good example of the white pulp activity of spleen.

    04:01 But those arteries go into capillaries, which break down and lose their wall structure and red cells end up in things called venous sinuses, which you can see represented higher up in the structure.

    04:18 Here red cells very slowly migrate in very large sinuses in the presence of many macrophages.

    04:28 The macrophages scan the red cells for any evidence of dysfunction or residual bits of iron from their release from the bone marrow, and they remove old and damaged red cells from the blood.

    04:43 Finally these red cells, now clear and the healthy ones are released back into the splenic vein and enter the blood system.

    04:55 It's a very remarkable open system of blood circulation within the spleen.

    05:03 So In summary, we have seen in this lecture, blood cells are derived from rare stem cells within the bone marrow. A wide range of different cell types are made, which help to carry oxygen, fight infection and repair damaged blood vessels.

    05:22 As we shall see, inherited or acquired disorders can affect any of these different cells and lead to a wide range of different clinical complications.

    05:33 I hope you have enjoyed this introduction to blood.


    About the Lecture

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


    Included Quiz Questions

    1. Red cells make up most of the volume of blood.
    2. Fresh frozen plasma is used to treat blood clotting disorders.
    3. Blood flows in a closed circulation in all organs except the spleen.
    4. Serum is the liquid that is left after blood clots.
    5. The amount of blood in your body is approximately 70ml/kg.

    Author of lecture Blood Structure – Blood Formation

     Paul Moss, PhD

    Paul Moss, PhD


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    By Subhabrata G. on 10. September 2017 for Blood Structure – Blood Formation

    good becoz it will definitely help me in my up coming exam of ut-3 thanks Dr. Paul Moss