Blood is a special connective tissue consisting of a fluid matrix, plasma, and formed elements. The process of formation of blood is called Hemopoiesis. It takes place in red bone marrow found in the epiphysis of long bones.flat bones(ribs and cranial bones), vertebrae and pelvis.

Bone marrow is a semi-solid tissue which may be found within the spongy or cancellous portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production or hematopoiesis. It is composed of hematopoietic cells, marrow adipose tissue, and supportive stromal cells.

Granulocytes are a category of white blood cells characterized by the presence of granules in their cytoplasm. Granulocytes are produced via granulopoiesis in the bone marrow.

Erythropoiesis is the process which produces red blood cells, which is the development from erythropoietic stem cell to mature red blood cell. this usually occurs within the red bone marrow. In the early fetus, erythropoiesis takes place in the mesodermal cells of the yolk sac. By the third or fourth month, erythropoiesis moves to the liver. After seven months, erythropoiesis occurs in the bone marrow.

Hematopoiesis is the formation of blood cellular components. In developing embryo, blood formation occurs in aggregates of blood cells in the yolk sac called, blood islands. As development progresses, blood formation occurs in the spleen, lymph nodes, and liver. 

Red blood cells, most white blood cells, and platelets are produced in the bone marrow, the soft fatty tissue inside bone cavities

The platelet plug, also known as the hemostatic plug or platelet thrombus, is an aggregation of platelets formed during the earlier stage of hemostasis in response to blood vessel wall injury.  After platelets are recruited and begin to accumulate around the breakage, their “sticky” nature allows them to adhere to each other. This forms a platelet plug, which prevents more blood from leaving the body as well as any outside contaminants from getting in. The plug provides a temporary blockage of the break in the vasculature. As such, platelet plug formation occurs after vasoconstriction of the blood vessels but before the creation of the fibrin mesh clot, which is the more permanent solution to the injury. The result of the platelet plug formation is the coagulation of blood. It can also be referred to as primary hemostasis.

Blood cell formation also called Hematopoiesis, or Hemopoiesis is a continuous process by which the cellular constituents of blood are replenished as needed. It occurs in the bone marrow.

Spleen is the blood bank of human body as it has the capacity to store considerable amount blood, that can be released in a situation of emergency (about a cup).

The nucleus is absent in red blood cells in order to accomodate more space for haemoglobin. It also allows the cell to maintain its biconcave shape which aids diffusion.