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Haemopoiesis (blood cell development) in bone marrow

Medical Sciences Asked on August 29, 2021

I am currently studying the textbook Hoffbrand’s Essential Haematology, eighth edition, by A. Victor Hoffbrand and David P. Steensma. Chapter 1 Haemopoiesis says the following:

During normal childhood and adult life, the marrow is the only source of new blood cells. The developing cells are situated outside the bone marrow sinuses; mature cells are released into the sinus spaces, the marrow microcirculation and so into the general circulation.

I don’t understand this description. The authors state that the developing cells are situated outside the bone marrow sinuses. Presumably, the bone marrow sinuses are deeper within the bone, right? If so, then this description would be implying that the developing cells are located on the outer regions of the bone, away from the sinuses, and then are released from the outer region into the sinus space, and then into marrow microcirculation and general circulation. But isn’t this path of circulation leading towards the exterior of the bone? So it sounds like the authors are saying that the developing cells start on the outer regions of the bone, then are released deeper into the bone (into the sinuses), and then are taken via marrow microcirculation and general circulation back towards the outer parts of the bone, which is where they came from in the first place. Am I misunderstanding something here?

I would greatly appreciate it if people would please take the time to clarify this.

EDIT

I found a slide that seems to agree with the textbook description:

enter image description here

2 Answers

It's really simple, your misunderstanding just comes from mixing macro- and microanatomy.
Macroscopically, all of bone marrow is located inside the bone, in the medullar cavity.
Microscopically, bone marrow tissue consists of different cells, some of which are endothelial cells that comprise sinuses, and alongside them (or outside of them, if you will; in the bone marrow's stroma) you find all other cell types.

I'll attach this wiki page as reference just in case, your textbook is a much better option though I suppose, this was just a clarification question.

Correct answer by practiZ on August 29, 2021

enter image description here

Image source: cancer .gov.

Bone marrow is a semi-solid tissue found within the spongy or cancellous (denoting bone tissue with a meshlike structure containing many pores, typical of the interior of mature bones) portions of bones. As you can see in the image above the hematopoiesis occur at the ends of long bones where red bone marrow is present. In red bone marrow the ratio of stem cells to fat cells are more in comparison to yellow bone marrow which is present in shaft of long bones of adults.

Look at the image below:.

bone marrow sinuses

Image source: flipper.diff.org

This is a microstructure of bone marrow sinuses with the hematopoietic stem cells near by. These hematopoietic stems cells traverse the walls of sinuses once they are differentiated and mature and then comes into circulation. These sinuses are just lined by endothelial cells, they ultimately forms connection between arterioles and venules. For megakaryocyte, it extends cytoplasmic process inside the sinus which ultimately breaks down to form platelets.

the HSC in bone marrow

Image source:frontiersin.org

Here is another image showing how HSC clinging to endosteum differentiate and matures as it moves toward the sinuses which then ultimately traverse through the sinus wall.

Answered by Sikander on August 29, 2021

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