The Skeleton System

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Bones also provide the body with leverage, something essential to movement.


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In addition to providing structure, the bones manufacture red blood cells and store minerals. The skeletal system is comprised of all the bones in the body as well as their associated cartilage and joints. We will focus on the primary or major bones in the body associated with gross movements.

Bones are divided into four basic types or classifications figure 2. Bone classification is based primarily on the shape of the bone. Long bones are longer than they are wide and are primarily found in the appendages arms and legs. Long bones include the femur, tibia, fibula, radius, ulna, and humerus.

Long bones are slightly curved for strength and designed to absorb stress at several points. They consist of a long, thin part called the diaphysis , or shaft, and two bulbous-type ends called the epiphysis. Short bones are basically cube shaped and are about as wide as they are long. Examples are the bones found in the wrist and ankle. Flat bones are thin and generally flat.

The Skeletal System

They offer considerable protection and a great deal of surface area for muscles to attach. Examples of flat bones are the cranial bones, which protect the brain, and the scapula shoulder blade. Irregular bones include many of the bones that do not fall into the other three categories.

They have complex shapes and include bones like the vertebrae. A bone is made of many parts, with the proportions of each part depending on the size and shape of the bone.

Skeletal System Physiology

Generally, bones are composed of spongy and compact bone, periosteum and endosteum , and a medullary cavity figure 2. The periosteum is a dense, white, fibrous sheath that covers the surface of the bone and is where muscles and tendons attach. The medullary cavity of the bone is a cavity in the center of the bone filled with yellow, fatty marrow. The endosteum is the layer of cells that line the medullary cavity. The rigid part of the bone is made of spongy and compact bone. The spongy bone is less dense and contains spaces so blood vessels and other nutrients can be supplied to the bone.

The compact part of the bone contains few spaces and provides protection and strength. They consist of a long, thin part called the diaphysis, or shaft, and two bulbous-type ends called the epiphysis. Generally, bones are composed of spongy and compact bone, periosteum and endosteum, and a medullary cavity figure 2. The process through which bone grows in the body is called ossification.

Bones, in particular long bones, have cartilaginous growth plates located at either end called epiphyseal plates.

Initially, these plates are not completely hardened and are where growth occurs in the bone. These fragile growth plates can be damaged in growing children or teens and affect bone development. As a person matures, the epiphyseal plates harden, and growth stops between the ages of 21 and Children have large amounts of organic material in their bones, making their bones softer and more pliable. As we age, we have larger proportions of inorganic material, which causes bones to become brittle and more fragile. The structures in bones are in a continuous state of being built up and broken down.

When exercise is combined with adequate rest and nutrition, healthy bones become thicker and stronger. Exercise helps build and promote healthy bone tissue and reduces the risk of bone disease such as osteoporosis. The human skeleton consists of bones and is divided into two parts: The axial skeleton consists of the bones found around the axis the imaginary midline of the body and includes the skull, vertebral column, sternum, and ribs. The appendicular skeleton refers to the bones associated with the appendages and includes the bones in the arms, shoulders, legs, and hips figure 2.

An articulation joint is the point of contact between bones or cartilage and bones. Joints are classified as immovable, slightly movable, or freely movable. The amount of movement possible at a joint depends on the way in which the bones fit together, the tightness of the tissue that surrounds the joints and the position of ligaments, muscles, and tendons. Ligaments are dense, regular, connective tissue that attach bone to bone at movable joints and help to protect the joint from dislocation.

The vertebral column, or backbone of the human skeleton, is typically made up of 26 bones called vertebrae figure 2. These vertebrae are divided into five sections. The part of the vertebral column found in the neck is called the cervical spine and contains seven smaller vertebrae. The part of the vertebral column found behind the rib cage is called the thoracic spine and consists of 12 midsized vertebrae.

Introduction to Human Skeletal System:

The lower back area of the vertebral column is called the lumbar spine and consists of five large vertebrae. Below the lumbar spine is the sacrum, which is one bone made up of five fused sacral vertebrae. The coccyx, or tailbone, is made up of four vertebrae fused into one or two bones.

Composition of the Skeletal System

A fibrocartilaginous tissue, called an intervertebral disc, is found between each vertebra. This tissue can be injured through trauma or overuse, especially in the weight-bearing lumbar area or in the delicate cervical area of the spine. Osteoporosis, on the other hand, develops in previously constructed bones. Arthritis is a group of more than inflammatory diseases that damage joints and their surrounding structures. Arthritis can attack joints, joint capsules, the surrounding tissue or parts throughout the body. It usually affects the joints of the neck, shoulders, hands, lower back, hips or knees.

Treatment depends on the type of arthritis," Wei said.

Skeletal System: Facts, Function & Diseases

Also common is scoliosis, a side-to-side curve in the back or spine, often creating a pronounced "C" or "S" shape when viewed on an x-ray of the spine. This condition is typically becomes evident during adolescence, the Merck Manuals noted. Two to 3 percent of the population — an estimated 6 to 9 million people in the United States — suffers from scoliosis, according to the American Association of Neurological Surgeons. About 90 percent of people will experience lower back pain at some point in their lives, according to Dr.

James Nace of LifeBridge Health. One of the much rarer diseases of the skeletal system is bone cancer. It may originate in the bones or spread there from another part of the body. The American Cancer Society estimates around 3, new cases will be diagnosed for bones and joint cancer and around 1, people will die from it in in the United States.

Bone cancer accounts for less than 0. Cancers that metastasize — originate from other parts of the body and then spread to the bones — are much more common than primary bone cancer. Bone cancer is a malignancy arising in the bones and supporting structures such as cartilage, according to Dr. While leukemia is a cancer that primarily affects the blood, the skeletal system is involved as the cancer starts in the marrow of the bone. With this type of cancer, abnormal white blood cells multiply uncontrollably, affecting the production of normal white blood cells and red blood cells, according to the American Cancer Society.

Bursitis is a disorder that most commonly affects the shoulder and hip joints, Nace said. It is caused by an inflammation of the bursa, small fluid-filled bags that act as lubricating surfaces for muscles to move over bones. The skeletal system is also susceptible to breaks, strains and fractures. While bones are meant to protect the body's vital organs, it takes about 10 to 16 pounds of pressure to break an average bone. Bones such as the skull and femur are much tougher to break. Orthopedics is the medical specialty responsible for treating entire skeletal system.

In the United States, orthopedic surgeons have typically completed four years of undergraduate education and four years of medical school. They then undergo residency training in orthopedic surgery. The American Board of Orthopaedic Surgery oversees the certification process for this specialty. Many go on to further specialize in specific areas, such as the spine, hand or sports injuries.


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