7.1 Tissues and Organs of the Skeletal System

The _____ system is composed of bones, cartilages, and ligaments joined tightly to form a strong, flexible framework for the body.

______, the forerunner of most bones in embryonic and childhood development, covers many joint surfaces in the mature skeleton.

_____ hold bones together at the joints.

_____ are structurally similar to ligaments but attach muscle to bone; they are considered part of the muscular system.

Functions of the Skeleton

The skeleton plays at least six roles:

1) _____. Bones of the limbs and vertebral column ____ the body; the mandible and maxilla ____ the teeth; and some viscera are ____ by nearby bones.

2) ______. Bones enclose and ____ the brain, spinal cord, heart, lungs, pelvic viscera, and bone marrow.

3) ______. Limb ______, breathing, and other _____ are produced by the action of muscles on the bones.

4)______. The skeleton stores calcium and phosphate ions and releases them into the tissue fluid and blood according to the body's physiological needs.

5)__-___ ____. Bone tissue buffers the blood against excessive pH changes by absorbing or releasing alkaline phosphate and carbonate salts.

6)______. Red bone marrow is the major producer of blood cells, including cells of the immune system.

Bones and Osseous Tissue

Bone, or ____ tissue, is a _____ tissue in which the matrix is hardened by the deposition of ___ _____ and other minerals. The hardening process is called mineralization or _____. (Bone is not the hardest substance in the body; that distinction goes to tooth enamel.)

Osseous tissue is only ____ of the tissues that make up a ____. Also present are blood, bone marrow, cartilage, adipose tissue, nervous tissue, and fibrous connective tissue.

The word ___ can denote an organ composed of all these tissues, or it can denote just the osseous tissue.

General Features of Bones

Bones have a wide variety of shapes _____ with their varied protective and locomotor functions.

Most of the cranial bones are in the form of thin curved plates called ___ bones, such as the paired parietal bones that
form the dome of the top of the head.

The sternum (breastbone), scapula (shoulder blade), ribs, and hip bones are also ___ bones.

The most important bones in body movement are the ____ bones of the limbs—the humerus, radius, and ulna of the arm and forearm; the femur, tibia, and fibula of the thigh and leg; and the metacarpals, metatarsals, and phalanges of the hands and feet. Like crowbars, long bones serve as rigid levers that are acted upon by skeletal muscles to produce the major body ____.

The wrists and ankles have a total of 30 ____ bones (carpal and tarsal bones), which are approximately equal in length and width and which produce relatively limited ____ movements.

The patella is also a ____ bone. Many bones, however, do not fit any of these categories and are collectively considered _____ bones i.e.the vertebrae

General Features of Bones

Figure 7.1 shows the general anatomy of a long bone. Much of it is composed of an outer shell of dense white osseous tissue called ____ (dense) bone.

The shell encloses a space called the medullary (MED-you-lerr-ee) cavity, or marrow cavity, which contains ____ _____.

At the ends of the bone, the central space is occupied by a more loosely organized form of osseous tissue called _____ (cancellous) bone. A narrow zone of spongy bone also occurs just inside the compact bone of the shaft and in the middle of most flat, irregular, and short bones.

The skeleton is about ____ compact bone and ___ spongy bone by weight.

Spongy bone is always enclosed by more durable ____ bone.

General Features of Bones

The principal features of a long bone are its shaft, called the ____, and an expanded head at each end called the _____.

The diaphysis provides ____, and the epiphysis is enlarged to strengthen the joint and provide added ____ ____ for the attachment of tendons and ligaments.

The joint surface where one bone meets another is covered with a layer of hyaline cartilage called the ____ cartilage. Together with a lubricating fluid secreted between the bones, this cartilage enables a joint to move far more ___ than it would if one bone rubbed directly against the other.

Blood vessels penetrate into the bone
through minute holes called _____ ____; we will trace where they go when we consider the histology of bone.

General Features of Bones

Externally, a bone is covered with a sheath called the ____. This has a tough, outer fibrous layer of ____ and an inner osteogenic layer of bone-forming cells described later in the chapter.

Some collagen fibers of the outer layer are continuous with the tendons that bind muscle to bone, and some penetrate into the bone matrix as perforating fibers.

The periosteum thus provides strong _____ and continuity from muscle to tendon to bone. The osteogenic layer is important to the growth of bone and healing of fractures.

There is no periosteum over the ____ cartilage.

A thin layer of reticular connective tissue called the _____ lines the internal marrow cavity, covers all the honeycombed surfaces of ____ ____, and lines the canal system, described later, in compact bone.

General Features of Bones

In children and adolescents, an _____ plate of hyaline cartilage separates the marrow spaces of the epiphysis and diaphysis.. On X-rays, it appears as a transparent line at the end of a long bone.

The epiphyseal plate is a zone where the bones grow in ____. In adults, the
epiphyseal plate is depleted and the bones can grow no longer, but an epiphyseal line marks where the plate used to be.

Figure 7.2 shows a ___ bone of the cranium. It has a sandwich-like construction with __ layers of compact bone enclosing a middle layer of spongy bone.

The spongy layer in the cranium is called _____. A moderate blow to the skull can fracture the outer layer of compact bone, but the diploe may ___ the impact and leave the inner layer of compact bone unharmed.

Both surfaces of a flat bone are covered with ____, and the marrow spaces amid the spongy bone are lined with _____.

8.1 Overview of the Skeleton

The skeleton (fig. 8.1) is divided into two regions: the ___ skeleton and ____ skeleton.

The ___ skeleton, which forms the central supporting axis of the body, includes the skull, auditory ossicles, hyoid bone, vertebral column, and thoracic cage (ribs and sternum).

The ____ skeleton includes the bones of the upper limb and pectoral girdle and the bones of the lower limb and pelvic girdle.

Bones of the Skeletal System

It is often stated that there are ___ bones in the skeleton, but this is only a typical adult count, not an invariable number.

At birth there are about __, and even more bones form during childhood. With age, however, the number ____ as separate bones gradually ____. For example, each side of a child's pelvic girdle has three bones—the ilium, ischium, and pubis—but in adults, these are fused into a single hip bone on each side.

The fusion of several bones, completed by late adolescence to the mid-__s, brings about the average adult number of 206.

Bones of the Skeletal System

This number varies even among adults. One reason is the development of ____ bones—bones that form within some tendons in response to strain.

The ___ (kneecap) is the largest of these; most of the others are small, rounded bones in such locations as the hands and feet.

Another reason for adult variation is that some people have ___ bones in the skull called sutural (SOO-chur-ul), or ____, bones.

Anatomical Features of Bones

Bones exhibit a variety of ridges, spines, bumps, depressions, canals, pores, slits, cavities, and articular surfaces.

It is important to know the names of these bone markings because later descriptions of joints, ___ attachments, and the routes traveled by nerves and blood vessels are based on this ____.

Anatomical Features of Bones

You will probably study both ______ skeletons (dried bones held together by wires and rods to show their spatial relationships to each other) and ________ bones (bones taken apart so their surface features can be studied in more detail).

Rotate your forearm, cross your legs, palpate your skull and wrist, and think about what is happening beneath the surface or what you can feel through the skin.