Bones

Bones are composed of several kinds of tissues, and thus they are the organs of the skeletal system.

Because bones are rigid structures, they provide support and protection for softer tissues, and they act together with skeletal muscles to make body movements possible. They also house the tissue that produces blood cells, and they store inorganic salts.

The shapes of individual bones are closely related to their functions. Projections provide places for the attachment of muscles, tendons, and ligaments; openings serve as passageways for blood vessels and nerves; and the ends of bones are modified to form joints with other bones.

Bones can be classified according to their shapes - long, short, flat, or irregular.

Long bones have long longitudinal axes and expanded ends. Examples are the arm and leg bones.

Short bones are somewhat cube like, with their lengths and widths roughly equal. The bones of the wrists and ankles are examples of this type.

Flat bones are platelike structures with broad surfaces, such as the ribs, scapulae, and bones of the skull.

Irregular bones have a variety of shapes and are usually connected to several other bones. Irregular bones include the vertebrae that comprise the backbone and many of the facial bones.

In addition to these four groups of bones, some authorities recognize a fifth group called the round or sesamoid bones. The bones of this group are usually small, and they often occur within tendons adjacent to joints, where the tendons undergo compression. The kneecap (patella) is an example of a very large sesamoid bone.

Functions of Bones

Skeletal parts provide shape, support, and protection for body structures. They also act as levers that aid body movements, house tissues that produce blood cells and store various inorganic salts.

Bones give shape to structures such as the head, face, thorax, and limbs. They also provide support and protection. For example, the bones of the feet, legs, pelvis, and backbone support the weight of

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the body. The bones of the skull protect the eyes, ears, and brain. Those of the rib cage and shoulder girdle protect the heart and lungs, while bones of the pelvic girdle protect the lower abdominal and internal reproductive organs.

Although the number of bones in a human skeleton is often reported to be 206, the actual number varies from person to person. Some people lack certain bones, while others have extra ones. For example, the flat bones of the skull usually grow together and become tightly joined along irregular lines called sutures. Occasionally extra bones called wormian or sutural bones develop in these sutures. Also, extra small, round sesamoid bones may develop in tendons, where they function to reduce friction in places where tendons pass over bony prominences.

Post-text assignments

1 List four groups of bones, based upon their shapes, name an example from each group.

2 Build medical terms. Choose them from the list below:

1 Abnormal condition of porous bones. 2 Inflammation of bone and bone marrow. 3 Dead bone tissue. 4 A disease in which there is enlargement of the bones of the head, hands and feet resulting from a tumor of the putuitary gland that causes overproduction of growth hormone. 5 An instrument for recording muscular contractions.

(a – ...graph; b – osteomyel...; c – ...porosis; d – sequestrum; e –

...megalia)

3 Match the descriptions and functions listed in column 1 with		the
bones listed in column II (Drawings 1, 2):
I	II
1) coronoid process	a) ethmoid bone
2) cribriform plate	b) frontal bone
3) foramen magnum	c) mandible
4) mastoid process	d) maxillary bone
5) palatine process	e) occipital bone
6) sella turcica	f) temporal bone

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7) supraorbital notch	g) sphenoid bone
8) temporal process	h) zygomatic bone
9) acromion process	i) femur
10) deltoid tuberosity	j) fibula
11) greater trochanter	k) humerus
12) lateral malleolus	l) radius
13) medial malleolus	m) scapula
14) olecranon process	n) sternum
15) radial tuberosity	o) tibia
16) xiphoid process	p) ulna

Unit 2

Pre-text assignments

1 Learn the key words and phrases:

joint, junction, lever system, to bend, to straighten, rigid structure, fibrous joints, cartilaginous joints, synovial joints, immovable, slightly movable, freely movable joints

2 Build medical terms:

1 Inflammation of joints. 2 Inflammation of bone and joints. 3 Abnormal condition of pus in a joint. 4 Any of various immovable articulations, or joints (as in suture joints of the skull). 5 A freely movable joint; any articulation, as of the hip, permitting free movement in any direction. 6 Neuralgic pain in a joint or joints.

(a – synarthr...; b – ...itis; c – ...arthritis; d – arthro...osis; e – dia…osis; f – arthr...ia)

Joints of the Skeletal System

Joints are the junctions between the bones of the skeletal system. That is, a joint occurs wherever two or more bones come together. Most joints function in lever systems that make movements possible by bending or straightening. Others, however, are relatively rigid structures that help hold bones in place or enable bones to grow.

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Wherever two or more bones meet, a joint is formed. Such joints, or articulations, represent the functional junctions between bones. They bind various parts of the skeletal system together, allow bone growth to occur, permit certain parts of the skeleton to change shape during childbirth, and enable body parts to move in response to skeletal muscle contractions.

Classification of Joints

Although joints vary considerably in structure and function, they can be classified according to the type of tissue that binds the bones together at eachjunction. On this basis, three general groups can be identified - fibrous joints, cartilaginous joints, and synovial joints.

Joints can also be grouped according to the amount of movement possible at the bony junctions. In this scheme, joints are classified as immovable (synarthrotic), slightly movable (amphiarthrotic), and freely movable (diarthrotic).

Types of Joint Movements

Movements at synovial joints are produced by actions of skeletal muscles. Typically, one end of a muscle is attached to a relatively immovable or fixed part on one side of a joint, and the other end of the muscle is fastened to a movable part on the other side. When the muscle contracts, its fibers pull its movable end (insertion) toward its fixed end (origin), and a movement occurs at the joint.

Post-text assignments

1 Give full answers to the following questions:

1How would you explain to an athlete why damaged joint ligaments and cartilages are so slow to heal following an injury?

2Compared to the shoulder and hip joints, in what way is the knee joint poorly protected, and thus especially vulnerable to injuries?

3Based upon your knowledge of joint structures, which do you think could be most satisfactorily replaced by a prosthetic device, a hip joint or a knee joint? Why?

4If a patient's lower arm and elbow were immobilized by a cast for sevcral weeks, what changes would you expect to occur in the bones of the arm?

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