Skeletal System

The skeletal system is composed of every bone and joint in the human body. This includes cartilage and ligaments as well. The skeleton can also be divided into the axial skeleton and the appendicular skeleton.The axial skeleton is formed by the vertebral column, the rib cage and the skull. The appendicular skeleton, which is attached to the axial skeleton, is formed by the pectoral girdles, the pelvic bone and the bones of the upper and lower limbs. The skeleton has six primary functions. They are support, protection, movement, mineral homeostasis, blood cell production, and storage.

The skeletal system is the framework of the body which supports the body and maintains it’s shape. The pelvis, along with ligaments and muscle, provide a floor for the pelvic structures. Without the rib cages, costal cartilages, and intercostal muscles, the lungs would collapse. The skeleton supports the softer tissue and provides a point of attachment for skeletal muscles. Some bones provide leverage for movement. Most bones are connected to other bones at flexible joints, which allow the skeletal framework a high degree of flexibility and movement. The bones are attached to tendons of the skeletal muscle and the ligaments of the joints. They then act as levers and pulleys to aid the contraction of the skeletal muscles into movement.

Bones store 99% of the bodies calcium and 85% of the bodies phosphorous, along with some magnesium and fluoride. This is why the skeletal system provides mineral homeostasis in the body. Calcium homeostasis is regulated by your bones and changes in this regulation can result in hypercalcemia or hypocalcemia. Calcium released from the bone is regulated by parathyroid hormone.The process of bone resorption by the osteoclasts releases stored calcium into the systemic circulation and is an important process in regulating calcium balance. As bone formation actively fixes circulating calcium in its mineral form, removing it from the bloodstream, resorption actively unfixes it thereby increasing circulating calcium levels. These processes occur in tandem at site-specific locations.

Low calcium in the body can result in osteoporosis. Osteoporosis is the weakening of bones due to loss of bone density. This results in fragile bones that can fracture from a small fall. Osteoporosis occurs when calcium usage in the body outpaces calcium deposition. Your body withdraws calcium from your bones to make your muscles move and for nerves to carry messages between the brain and every part of the body. In addition, calcium is used to help blood vessels move blood throughout the body and to help release hormones and enzymes that affect almost every function in the human body. This is why osteoporosis occurs. Your body needs calcium so bad that when you get enough from your diet your body takes it from your bones no matter the consequences. This is because the consequence for not having enough calcium in the bloodstream is the stoppage of your heart, and your body would prefer having weak bones.

Blood cell production is another major function of the skeletal system. All types of blood cells are made in bone including platelets. This production occurs in the bone marrow. There are two types of bone marrow, yellow and red (also known as myeloid tissue). Bone marrow contains two types of stem cells. Hematopoietic stem cells can produce all blood cells and are found in red bone marrow. Mesenchymal stem cells can produce fat, cartilage and bone and are usually found in the yellow bone marrow. Hematopoiesis is governed by a number of cytokines that promote the survival, proliferation, and differentiation of hematopoietic stem cells and progenitor cells. Stem cell factor is a hematopoietic cytokine that triggers its biologic effects by binding to its receptor.

Mesenchymal stem cells produce osteoblasts, chondrocytes, and adipocytes. Osteoblasts are primarily responsible for bone formation. They have only one nucleus and function by secreting a substance called osteoid, which is also known as the bone matrix. This substance is then mineralized with substances like calcium