Read the text carefully to obtain detailed understanding of it. The complete set of bones in the body is called the skeleton

The complete set of bones in the body is called the skeleton. The skeleton is the framework which supports and gives shape to the body. It also protects the organs inside. Without the skeleton we would not be able to move or even to stand. The human skeleton is made up of 206 bones. The functions of the skeleton are to provide support, give our bodies shape, and provide protection to other systems and organs of the body, to provide attachments for muscles, to produce movement and to produce red blood cells.

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. The biggest bone in the body is the femur and the smallest is the stapes bone in the middle ear. In an adult, the skeleton comprises around 13% of the total body weight and half of this weight is water.

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.

Formation

Early in gestation, a foetus has a cartilaginous skeleton from which the long bones and most other bones gradually form throughout the remaining gestation period and for years after birth in the process called endochondrial ossification. At birth a newborn baby has approximately 231 bones, whereas on average an adult human has 206 bones. The difference comes from a number of small bones that fuse together during growth, such as the sacrum and coccyx of the vertebral column. The sacrum (the bone at the base of the spine) consists of five bones which are separate at birth but fuse together into a solid structure in later years. An infant is born with bones of cartilage, called epiphyseal plates, between segments of bone to allow further growth. Longitudinal bone growth ends when the bone of the epiphysis and diaphysis fuses. This process, called epiphyseal plate closure, happens at about 18 years of age in females and 21 years of age in males.

The axial skeleton and the appendicular skeleton

There are 206 bones in the adult human skeleton. These bones are organized into a longitudinal axis, the axial skeleton, to which the appendicular skeleton is attached.

The axial skeleton (80 bones) is formed by the vertebral column (26), the thoracic cage (12 pairs of ribs and the sternum), and the skull (22 bones and 7 associated bones). The axial skeleton transmits the weight from the head, the trunk, and the upper extremities down to the lower extremities at the hip joints, and is therefore responsible for the upright position of the human body. The 633 skeletal muscles acting on the axial skeleton position the spine, allowing for small movements in the thoracic cage for breathing, and the head, where they control the minute and complex facial movements.

The appendicular skeleton (126 bones) is formed by the pectoral girdles (4), the upper limbs (60), the pelvic girdle (2), and the lower limbs (60). Their functions are to make locomotion possible and to protect the major organs of locomotion, digestion, excretion, and reproduction.

Functions

The skeleton has six main functions:

Support

The skeleton provides the framework which supports the body and maintains its shape. The pelvis and associated ligaments and muscles provide a floor for the pelvic structures. Without the ribs, costal cartilages, and the intercostal muscles the lungs would collapse.

Movement

The joints between bones permit movement, some allowing a wider range of movement than others, e.g. the ball and socket joint allows a greater range of movement than the pivot joint at the neck. Movement is powered by skeletal muscles, which are attached to the skeleton at various sites on bones. Muscles, bones, and joints provide the principal mechanics for movement, all coordinated by the nervous system.

Protection

The skeleton protects many vital organs:

• The skull protects the brain, the eyes, and the middle and inner ears.

• The vertebrae protect 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.

Blood cell production

The skeleton is the site of haematopoiesis, which takes place in red bone marrow. Marrow is found in the centre of long bones.

Storage

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.

Endocrine regulation

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.

Gender-based differences

There are many differences between the male and female human skeletons. Most prominent is the difference in the pelvis, owing to characteristics required for the processes of childbirth. The shape of the female pelvis is flatter, more rounded and proportionally larger to allow the head of a foetus to pass. Men tend to have slightly thicker and longer limbs and digit bones (phalanges), while women tend to have narrower rib cages, smaller teeth, less angular mandibles, less pronounced cranial features such as the brow ridges and external occipital protuberance (the small bump at the back of the skull), and the carrying angle of the forearm is more pronounced in females. Females also tend to have more rounded shoulder blades.

2. True or false statements. Make true with "T", false with "F". Correct the false statements.

1._______The biggest bone in the body is the femur and the smallest is the stapes bone in the middle ear.

2._______The skeleton comprises around 33% of the total body weight and half of this weight is water.

3._______The hyoid bone, which is located in the pelvis and serves as the point of attachment for the tongue.

4._______The sacrum (the bone at the base of the cranium) consists of five bones which are separate at birth but fuse together into a solid structure in later years.

5._______Longitudinal bone growth ends when the bone of the epiphysis and diaphysis begins.

6._______Epiphyseal plate closure happens at about 19 years of age in females and 22 years of age in males.

7._______There are three bones in each middle ear called the ossicles.

8._______The appendicular skeleton is formed by the pelvic girdle.

9._______The skeleton has seven main functions.

10._______Without the ribs, costal cartilages, and the intercostal muscles the lungs would not collapse.

11._______The rib cage, spine, and sternum protect the lungs, heart and major blood vessels.

12._______There are no differences between the male and female human skeletons.

3. Here are the answers to some questions from the text. What are the questions?

1. The biggest bone in the body is the femur.

2. It is powered by skeletal muscles, which are attached to the skeleton at various sites on bones. It holds a baby when a woman is pregnant.

3. No, there aren't. There are not 213 bones in the adult human skeleton. There are 206 bones in the adult human skeleton.

4. It is formed by the pectoral girdles.

5. They protect the digestive and urogenital systems and the hip.

6. Yes, it is. The skeleton is the site of haematopoiesis

7. The skeleton has six main functions.

8. They release a hormone called osteocalcin.

9. No it doesn't. Chondroitin sulfate doesn't increase both the insulin secretion and sensitivity. Osteocalcin increases both the insulin secretion and sensitivity.

10. The difference comes from a number of small bones that fuse together during growth.

11. Because it allows the head of a foetus to pass.

4. What do the following numbers refer to?

231,22, 633, 126, 2, 60, 70, 12, 13.