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