The skeletal system helps in 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% of the human skeleton, which is dense and full of organic minerals and nutrients. It is the primary bone for longer bones such as those in the arms and legs. Cancellous bone, or spongy bone, is much lighter than compact bone; Cancellous bone provides the body with support and flexibility. Cancellous bone can transform into compact bone through osteoblasts. The bone marrow is normally red or yellow, however at birth all the bone marrow starts to be red and over time half of it turns yellow. Large quantities of fat cells are the cause of the yellow coloration of the bone marrow; the body then uses those cells during starvation for the required 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 made up mainly 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 found in places like the ears and nose, cartilage is also found near the ribs to expand every time you breathe. Joints are made up of three different types of fibrous joints, cartilaginous joints and ball-and-socket joints..... .center of paper......blood cells, or leukocytes, There are two main classes of white blood cells; Granular leukocytes and agranular leukocytes. Granular leukocytes have three subdivisions, they are neutrophils, eosinophils and basophils. Neutrophils neutralize bacteria that invade the body, eosinophils digest viruses that have been bound by antibodies in the blood, and basophils release histamine to intensify allergic reactions and help protect the body from parasites. Platelets, small fragments of cells, form blood clots to stop bleeding; platelets collect in a wound and try to become a barrier between the inside and outside of the body. Once the blood comes into contact with the air, a clot begins to form, the platelets sense the air and begin to move apart. Platelets are produced in the bone marrow and are produced by the separation of platelet-rich plasma from the bone marrow