Osteomyoamare

Introduction to bones draft

The skeletal system includes the bones of the skeleton and the cartilage, ligaments and other connective tissues that stabilize and interconnect the bones. There are five primary functions of this body system:

• Support. The skeletal system acts as an anchor for the rest of the body, providing a structural framework for the attachment of soft tissues and organs
• Storage of Minerals and Lipids. Minerals and lipids play a vital role in physiological function, and the homeostatic regulation of these is the key to their function. The calcium bone salts are an invaluable tool to maintain normal calcium and phosphate levels in the blood. The bones of the skeleton store energy in the form of lipids in areas of yellow bone marrow.
• Blood Cell Production. Red blood cells (erythrocytes), white blood cells (leukocytes) and other blood elements are produced from hematopoietic stem cells in red marrow which fills the internal cavity of many bones.
• Protection. Many soft tissues and organ systems are surrounded by skeletal elements. The ribs protect the heart and lungs, the cranium protects the brain, the vertebrae encase the spinal cord and the pelvis cradles the digestive and reproductive organs.
• Leverage. Many bones have a role in translating the force generated by skeletal muscle into mechanical leverage against other bones.

Classification of Bones

The bones in the body can be separated into six broad categories according to their shape.

• Long Bones are categorised by their tubular shaft (diaphysis) with a rounded end (epiphysis) on each end. They are always longer than they are wide, and grow from each end, elongating the shaft. The femur, the long bone o the thigh, is the largest and heaviest bone in the human body.
• Short Bones are short and boxy being approximately as wide as they are tall. The carpal (wrist) and tarsal (ankle) bones are the only short bones in the human body.
• Flat Bones have thin wide surfaces and serve mostly as protective structures. The cranial (scalp) bones are an example of flat bones.
• Irregular Bones have complex shapes other than that of the other bones. The vertebrae are irregular bones.
• Sesamoid Bones are generally small, flat and have an apex at one end. These bones form by the thickening of a muscle tendon until it finally ossifies. The patella is the biggest sesamoid bone in the body, however sesamoid bones can arrise spontaneously in the hand and foot.

Bone Markings and Features

Elevations or projections appear on bones where ligaments and tendons attach and where other bones articulate at joints. Depressions, grooves and tunnels indicate the path of a nerve or vessel alongside or penetrating the bone. Some of the various features of bones are described in the following table.

Common Bone Features

General Description	Anatomical Term	Definition
Process formed where tendons and ligaments attach	Crest	A prominent ridge
	Line	A linear elevation
	Protuberance	A projection of bone
	Spine	A projecting "spine like" part
	Trochanter	A large, rough, blunt projection
	Tuberocity	A small, rough, blunt projection
	Tubercle	A small, smooth eminence
Processes formed where bones articulate with each other	Head	The expanded articular surface of an epiphysis.
	Condyle	A smooth, rounded articular process
	Epicondyle	An eminence superior to a condyle
	Malleolus	A rounded process
	Trochlea	A spool like articular process, acts like a pulley
	Capitulum	A small round articular head
	Facet	A small, flat articular surface

Bone Development

The process of bone formation is ossification; this is the formation on bone from other tissues. The major forms of ossification exist, endochondrial and intramembranous.

Endochondrial Ossification

Endochondrial bone formation is the ossification of existing cartilaginous structures. During development most bones begin as cartilage frames of the final bone. This cartilage is hardened during ossification and results in the boney structures observed in an adult. This process can be described through five generalised steps.

• Step 1. As the cartilage enlarges the chondrocytes near the center of the bone increase greatly in size. The internal matrix is reduced to a series of struts that take up calcium salts and ossify. The chondrocytes are then surrounded by cartilage and, deprived of nutrients, die, leaving large cavities in the calcified structure.
• Step 2. Blood vessels are now able to penetrate into these spaces, and cells on the outside of the bone begin to differentiate into osteoblasts (cells of the bone), and bone begins to form on the outside of the bone.
• Step 3. The Blood vessels are then able to fully penetrate the bone forming the Primary ossification center.
• Step 4. As the bone enlarges, osteoclasts (destructive bone cells) begin to erode the center of the bone, forming the medullary cavity.
• Step 5. The final step in this process is the formation of articular cartilage to protect the newly formed bone during articulation.

Intramembranous Ossification

Intramembranous bone formation is the formation of bone without a cartilage scaffold. This is the main process by which bone repair occurs, and is also used to form the bones of the face. This process can be summarised into the following.

• Mesenchyme cell in the membrane become osteochondral progenitor cell
• Osteochondral progenitor cell specialized to become osteoblast
• Osteoblast produce bone matrix and surrounded collagen fiber and become osteocyte
• As the result process trabeculae will develop
• Osteoblast will trap trabeculae to produce bone
• Trabeculae will join together to produce spongy cell
• Cells in the spongy cell will specialize to produce red bone marrow
• Cells surrounding the developing bone will produce periosteum
• Osteoblasts from the Periosteum on the bone matrix will produce compact bone