Site of RBC formation in 20 year old healthy male is
A i.e. Flat bonesThe marrow of the long bones except for the proximal humerus and tibia (Guyton) / upper humerus & femur (Ganong) becomes inactive (fatty) and produces no more red blood cells after about age 20 years. Beyond this age most RBC are produced in marrow of membranous flat bones such as veebrae, sternum, ribs & iliaQ.ErythropoesisIt stas in 3rd week of intra uterine life. Upto middle trimester of gestation blood is formed out of medullary cavity (extramedullary erythropoesis).It is one of the largest and most active organ approaching weight & size of liver. Active cellular marrow is called red marrow, inactive fatty marrow is K/a yellow marrowNormally 75% marrow cells belong to white blood producing myeloid series & only 25% are maturing RBCs. Even though in circulation RBCs are 500 times more than WBCs d/t the fact that average life span of WBCs is sho and RBC is long.Cellularity & RBC production after 15 years onward is Veebrae > sternum > rib > femur shaft > tibia shaftBefore bihAgeSite3weks - 3 months(Intra vascularphase)Mesoderm of yolk sacQwithin the blood vessel.3-5 months (Hepaticphase)Liver (main), spleen &lymph nodesQ5-9 months(Myeloid phase)Red bone marrowQ* All marrow of long& flat bones is red atthis stageAfter bihAgeSiteBih -5 yearsRed bone marrowQ(myeloid phase)* All marrow of long & flat bone is red at this stage.5-20 yearsRed bone marrowQ of all flat & long bones * There is gradual decrease of red marrow in long bonesand so gradually increasing production from flat bones>20 years- Red marrow of flat membranous bones such asveebrae, sternum, ribs & iliamQ. - Very little production in upper humerus, tibia & femur
Flat bones
Long bones
Liver
Yolk sac