Human Body - Skeletal System

Human Skeletal

Skeletal System : Introduction 

Inside every person is a skeleton, a sturdy framework of 206 bones. The skeleton protects the body's organs, supports the body, and provides attachment points for muscles to enable body movement. The human skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors muscles, and protects organs such as the brain, lungs and heart. Bones also produce blood cells and act as a storage site for minerals such as calcium and phosphorus.

All humans are born with over 300 bones. But some bones, such as those in the skull and lower spine, fuse (join together) during growth, thereby reducing the number. The skeletal system is made up of living material, with networks of blood vessels running throughout. Living mature bone is about 60 percent calcium compounds and about 40 percent collagen (a fibrous protein). Hence, bone is strong, hard, and slightly elastic. Although mature bones consist largely of calcium, most bones in the human skeleton began as cartilage. Cartilage is a type of connective tissue that contains collagen and elastin fibers.

The biggest bone in the body is the femur in the thigh and the smallest is the stapes bone in the middle ear. In an adult, the skeleton comprises around 30-40% of the total body weight, and half of this weight is water.

Skeletal System

Fused bones include those of the pelvis and the cranium. Not all bones are interconnected directly: there are three bones in each middle ear called the ossicles that articulate only with each other. The hyoid bone, which is located in the neck and serves as the point of attachment for the tongue, does not articulate with any other bones in the body, being supported by muscles and ligaments.

Individual bones meet at areas called joints and are held in place by connective tissue. Cartilage lines the surface of many joints and helps reduce friction between bones. The connective tissues linking the skeleton together at the joints are ligaments and tendons. Both are made up of collagen, but serve different functions. Ligaments link bones together and help prevent dislocated joints. Tendons link bone to muscle. Because the bones making up the human skeleton are inside the body, the skeleton is called an endoskeleton. Some animals, such as the crab, have an external skeleton called an exoskeleton.

Structure : Skeletal System

The human skeletal system is divided into two main groups: the axial skeleton and the appendicular skeleton. The axial skeleton includes bones associated with the body's main axis, the spine. This includes the spine, the skull, and the rib cage. The appendicular skeleton is attached to the axial skeleton and consists of the bones associated with the body's appendages—the arms and legs. This includes the bones of the pectoral girdle (shoulder area), the pelvic girdle (hip area), and the arms and legs.

• Axial skeleton

There are 28 bones in the skull. In adults, the bones of the cranium (part of the skull that encloses the brain) are flat and interlocking at their joints. In infants, cartilage fills the spaces between the cranial bones. Known as soft spots or fontanelles, these spaces allow the skull bones to move slightly during birth. This makes birth easier and helps prevent skull fractures. Eventually, the fontanelles are replaced by bone. In addition to protecting the brain, skull bones also support and protect the organs responsible for sight, hearing, smell, and taste.

Skeletal Muscles

The skull rests atop the spine, which encases and protects the spinal cord. The spine, also called the spinal column or backbone, consists of 33 stacked vertebrae, the lower ones fused. The spinal column helps to support the weight of the body and protects the spinal cord. Disks of cartilage lie between the bony vertebrae of the back and provide cushioning, like shock absorbers. The vertebrae of the spine are capable of only limited movement, such as bending and some twisting.

Twelve pair of ribs (a total of 24) extend forward from the vertebrae of the upper back. Most of the ribs (the first seven pair) attach in the front of the body via cartilage to the long, flat breastbone, or sternum. These ribs are called true ribs. The next three pair of ribs, called false ribs, do not attach to the sternum. They are connected by cartilage to the ribs above them. The lower two pair of ribs that do not attach in the front are called floating ribs. Ribs give shape to the chest and support and protect the body's major organs, such as the heart and lungs. The rib cage also provides attachment points for connective tissue, to help hold organs in place.

• Appendicular skeleton. 

The appendicular skeleton joins with the axial skeleton at the shoulders and hips. Forming a loose attachment with the sternum is the pectoral girdle, or shoulder. Two bones, the clavicle (collar bone) and scapula (shoulder blade) form one shoulder. The major advantage to the loose attachment of the pectoral girdle is that it allows for a wide range of shoulder motions and greater overall freedom of movement.

Unlike the pectoral girdle, the pelvic girdle, or hips, is strong and dense. Each hip, left and right, consists of three fused bones—the ilium, ischium, and pubic. The pelvic girdle is bowl-shaped, with an opening at the bottom. In a pregnant woman, this bony opening is a passageway through which her baby must pass during birth. The pelvic girdle of women is generally wider than that of men, which helps to ease birth. The pelvic girdle protects the lower abdominal organs, such as the intestines, and helps supports the weight of the body above it.

Ligament

The arms and legs, appendages of the body, are very similar in form. The upper arm bone, the humerus, is the long bone between the elbow and the shoulder. It connects the arm to the pectoral girdle. In the leg, the thigh bone, or femur, is the long bone between the knee and hip that connects the leg to the pelvic girdle. The humerus and femur are sturdy bones, especially the femur, which is the longest bone in the body.

At the elbow the humerus attaches to a set of parallel bones—the ulna and radius—the bones of the forearm. These bones attach to the eight small carpal bones of the wrist. The hand is made up of 19 bones.

Similarly, in the leg, the femur attaches to a set of bones of the lower leg, the fibula and tibia. The tibia, or shin bone, is larger than the fibula and forms the joint behind the patella (kneecap) with the femur. At the ankle joint, the fibula and tibia connect to the seven tarsal bones forming the ankle and heel. These, in turn, are connected to the 19 bones that make up the foot.

Functions of the Skeletal System

• Support : 

The skeletal system is made up of bones and cartilages. There are 206 bones in the body and these bones and cartilages help provide the support and points of attachment to many soft tissues, muscles and ligaments in the body. There are different types of bones like the long bones, short bones, flat bones, irregular bones and sesamoid bones. The skeletal system functions also include providing rigidity and body shape. It helps supporting the weight of muscles and internal organs, without which the body would collapse.

Tendon

• Protection :

The skeleton protects many vital organs:

• The skull protects the brain, the eyes, and the middle and inner ears.
• The vertebrae protects the spinal cord.
• The rib cage, spine, and sternum protect the lungs, heart and major blood vessels.
• The clavicle and scapula protect the shoulder.
• The ilium and spine protect the digestive and urogenital systems and the hip.
• The patella and the ulna protect the knee and the elbow respectively.
• The carpals and tarsals protect the wrist and ankle respectively.

• Helping in Movement :

The bone joint act as levers and anchors for the muscles. The point of origin of the muscle is called the anchor and the bone acts as lever. There are three types of joints, viz. fixed joint or Synarthroses like the skull bones, the slightly movable or Amphiarthroses like the symphysis pubis and the freely movable or Diarthroses. The freely movable joints are divided into four groups. The first, ball and socket joint like the hip joint, the hinge joint in the anatomy of elbow, the pivot joint of the radius and ulna and the gliding joint are seen in the carpal joint of wrist.

• Storage of Minerals :

Bone matrix can store calcium and is involved in calcium metabolism, and bone marrow can store iron in ferritin and is involved in iron metabolism. However, bones are not entirely made of calcium,but a mixture of chondroitin sulfate and hydroxyapatite, the latter making up 70% of a bone.

• Production of Red Blood Cells :

The red blood cells as well as the white blood cells are produced in the red marrow of the bones. After birth and in early childhood, the red blood morrow is red in color. Then, in adulthood, half of the bone marrow turns yellow, as it consists of fat cells. The long bones consist of yellow marrow and the red marrow is found in the flat bones of hip, skull and shoulder blades. You may also find red marrow in the vertebrae and the end of the long bone. In extreme conditions, the body can convert some of the yellow bone marrow to red bone marrow.

• Chemical Energy Storage :

Bone cells release a hormone called osteocalcin, which contributes to the regulation of blood sugar (glucose) and fat deposition. Osteocalcin increases both the insulin secretion and sensitivity, in addition to boosting the number of insulin-producing cells and reducing stores of fat.

Human Body Muscles and Human Anatomy

Interesting Facts About Skeletal System

• There are 206 bones in an adult human body.
• A baby is born with 300 bones. But throughout the growth years, many of the bones of the skull and spine fuse together.
• Bones do not move on their own, they need the help of the muscles attached to the bones.
• Bones have life. They’re made up of living cells that is why they can grow and repair themselves.
• The longest bone, about one-quarter of a person’s overall height, is the femur bone. It’s located in the leg.
• The smallest bone in the body is the stirrup bone, located deep inside the ear. It is just a little larger than a grain of rice.
• The largest bone in the body is the pelvic bone.
• Collar bone is the most frequently broken bone in a human body. It is also known as clavicle.
• Hyoid bone is the only bone that is not connected to any other bone. It is located in the throat of a human’s body.
• Most bones consist of two types of bone tissues, namely compact hard bones and spongy bone.
• More than half of the bones in the body are located in the hands and feet together.
• Humans and giraffes have the same number of bones in their necks. It is just that giraffes have a much longer vertebra.
• Bones are filled with a substance called bone marrow that is critical for the production of red and white blood cells.
• There are two types of bone marrow. Red marrow produces blood cells while yellow marrow produces fatty cells.
• At birth, all bone marrow is red.
• The ears and the end of the nose don't have bones. These parts of the body are given their shape by cartilage.
• Cartilage is lighter and flexible than bone, allowing movement and the ability to bend.
• Cartilage degrades faster than bone that is why many human remains are found without a nose or ears.
• Cartilage contains no blood vessels or nerve cells.
• Embryos contain cartilage, not bones.
• In adults, the skeleton makes up for 15-20 percent of total body weight.

Posted in: Human Body