Types of Bones and Bone Structures
Muscles are attached to bones and use the bones as an anchor from which to exert forces that result in limb movement. Bones provide for functional structure in the respiratory system such as: (a) bones in the face providing a nasal cavity passageway and (b) bones of the thorax are shaped to allow expansion of the chest cavity during inspiration.
- Long bones: longer than they are wide, act as levers. Examples in the upper extremity include the humerus, radius and ulna.
- Short bones: are short cubed shaped bones, found in the wrist and ankle. In the wrist there are 8 total in two rows.
They articulate with each other, as well as provide attachment points for ligaments.
- Flat bones: have broad surfaces for the protection of organs and attachment of muscles. In the skull, there are 8 bones that protect the brain and brain stem.
- Irregular bones: have a unique shape and provide both protection and multiple attachment points for muscles. Examples include the vertebra, which protects the spinal cord.
Bones: Calcium Storage: Calcium is stored primarily in bones and is released into the blood in response to hormones. Calcium is needed for bone development, blood clotting, normal muscle and nerve activity.
- Calcium Release into the Bloodstream
Calcium is stored in bone as a mineral salt with phosphate. Calcium is released from the bone in response to parathyroid hormone (PTH).
- Calcium Deposition in Bone
Calcium is stored in the bone as a mineral salt, along with phosphate, in response to decreased PTH levels and increased calcitonin (CT) release from the thyroid gland.
Bone Structure: bone is a complex array of osteocytes, canals and blood vessels.
Bone is relatively hard and lightweight and is primarily made of calcium phosphate. Bone can either be: (a) spongy - has an open meshwork which contains bone marrow or (b) compact – is dense; it forms the surface of bones and makes up approximately 80% of the bone mass.
- Bone Matrix
Bone matrix is made up of Osteons, which are long narrow cylinders containing both Haversian and Volkmann canals. Haversian canals surround blood vessels and nerves inside the bone. Volkmann’s canals connect the individual osteons to each other and to the periosteum. The periosteum provides the blood supply and houses the osteoclasts for bone resorption.
- Bone Marrow
The bone marrow is the site of red blood cells, white blood cell and platelet production.
B-Cells and T-Cells are produced in the bone marrow and then circulate to other lymphoid organs to be stimulated by antigens.
Joint Structure and Cartilage: Joints facilitate movement between bones by providing a meeting point between the bones and providing lubrication.
- Types of joints: Joints are separated into two categories: (a) fibrous – no synovial cavity containing synovial fluid, i.e.- sutures between bones of the skull and (b) synovial – in which there is a space between the articulating bones and the space is filled with synovial fluid which lubricates the joint, i.e.- knee joint.
- Types of cartilage: Cartilage is a type of dense connective tissue composed of cells called chondrocytes, which produce and maintain the cartilage. Cartilage contains no blood vessels; nutrients diffuse through the cartilage matrix. Cartilage is found between bones, in the nose, throat and in the spinal column.
- Hyaline cartilage: such as articular cartilage, line bones in joints and also provide a site for bone growth
(growth plate).
- Elastic cartilage: such as in the walls of the larynx (voice box), keeps tubes permanently open. It is made with elastin bundles to provide elasticity and yet be stiff.
- Fibrocartilage: such as between intervertebral disks, is located in sites that require great tensile strength. It is also found at sites connecting tendons and ligaments to bone.
- Ligaments and tendons: connect muscle to bone or bones together.
- Ligaments are short bands of tough fibrous tissue, composed mainly of collagen fibers. Ligaments connect bones to other bones to form a joint, i.e.- ilio-femoral ligament of the hip joint.
- Tendons are a tough band of fibrous tissue that connects muscle to bone or muscle to muscle, i.e. – Achilles tendon. Tendons are designed to withstand tension and stretch. The origin of a tendon is where it joins to a muscle and collagen fibers from the muscle itself extend directly into the tendon.
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