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What cell type is the main constituent of yellow bone marrow?




 Haematopoietic stem cells


Key Learning Point

Yellow bone marrow is made of fat



Bones are made of outer compact bone and inner cancellous bone, which forms the medullary cavity. The cavity is traversed by trabeculae of cancellous (spongy) bone. Inside the cavity are blood vessels and bone marrow.

Yellow marrow (most abundant) is predominantly fat, made of adipocytes, plus some fibroblasts. Red marrow is the site of active haematopoiesis - it contains haematopoietic stem cells and all developing lymphoid and myeloid cells.

Chondrocytes are found in catrilage and repsonsible for secretion of the collaen matrix.

Fibroblasts are also responsible for collagenous secretion and contribution to the extracellular matrix. 

Haematopoetic stem cells are found in bone marrow as oare megakaryoctes. Stem cells are the common ancestor of all haematologic cells produced and can differentiate into numerous cell lineages. Megakarocytes are the precursor to platelets.



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