The skeletal system contributes to endocrine regulation, protection, support, movement, calcium storage and blood cell production. The skeletal system consists of 206 bones in the adult human body, all divided into two main divisions. One division, the axial skeleton consisting of 80 bones, runs along the midline of the body and the other division, the appendicular skeleton which has 126 bones. Compact bone, or cortical bone, makes up 80 percent of the human skeleton, which is dense and filled with minerals and organic nutrients. It is the main bone in longer bones such as the arms and legs. Spongy bone, or spongy bone, is much lighter than compact bone; spongy bone provides the body with support and flexibility. Spongy bone can transform into compact bone thanks to osteoblasts. Bone marrow is normally red or yellow, but at birth all bone marrow starts out red, and over time half of it turns yellow. The large quantities of fat cells are the cause of the yellow coloring of the bone marrow; the body then uses these cells during starvation to obtain needed energy. Red marrow, usually found in flatter bones, such as the hip bones, signals its importance for the reproduction of blood cells. The skeleton of an embryo is primarily made of cartilage; the cartilage is then replaced by bone over the years, through a process called ossification. The two types of ossification are intramembranous ossification which develops membranous bone and endochondral ossification which develops cartilaginous bone. Cartilage is located in places like your ears and nose, cartilage is also found near the ribs so it grows every time you breathe. Joints consist of three different types of fibrous joints, cartilaginous joints, and ball and socket joints..... .middle of paper ......blood cells, or leukocytes, There are two major classes of white blood cells; Granular leukocytes and agranular leukocytes. Granular leukocytes have three subdivisions: neutrophils, eosinophils and basophils. Neutrophils neutralize bacteria that invade the body, eosinophils digest viruses bound to antibodies in the blood, and basophils release histamine to intensify allergic reactions and help protect the body against parasites. Platelets, small cell fragments, form blood clots to stop bleeding; platelets gather at a wound and attempt to become a barrier between the inside and outside of the body. Once blood comes into contact with air, a clot begins to form, platelets sense this air and begin to separate. Platelets are made in the bone marrow and are produced by the separation of platelet-rich plasma from the