Chapter 7
Skeletal Tissue Review
Answer Key
Directions: Answer the following questions as completely as possible. You may use your book
or your notes to help you.
1. Describe the microscopic structure of bone and cartilage.
The microscopic structure of compact bone is centered on the osteon. Concentric layers
of calcified matrix surround the osteon. The bone cells are located in small spaces in the
lamellae called lacunae. The cells are connected to the other cells and the osteon by
small canals called canaliculi. In cancellous bone, the structure is based on the
trabeculae. Bone cells are found in the trabeculae. The microscopic structure of cartilage
consists of many collagenous fibers embedded in a firm gel rather than a calcified matrix.
Cartilage is more flexible.
2. Describe the structure of a long bone.
The long bone contains six structures:
The diaphysis is the main shaft of the bone
The epiphyses are the two ends of the bone
The articular cartilage is a thin layer of cartilage that covers the joint surfaces.
The periosteum is a dense, white, fibrous membrane that covers the bone.
The medullary cavity is a tube like hollow space in the diaphysis.
The endosteum is a thin epithelial layer that lines the medullary cavity.
3. Explain the functions of the periosteum.
The function of the periosteum is to cover the bone and provide an attachment point for
muscle tendon fibers. It contains bone-forming and bone-destroying cells and contains
the blood vessels that supply the bone.
4. Describe the two principal chemical components of extracellular bone.
The two components are inorganic salts and organic matrix. Inorganic salts consist of
calcium and phosphate crystals called hydroxyapatite. The organic matrix consists of a
mixture of protein and polysaccharides.
5. List and discuss each of the major anatomical components that together constitute an
osteon.
An osteon consists of lamellae, which are concentric cylinder-shaped layers of calcified
matrix; lacunae, which are spaces in which the bone cells lie; and canaliculi, which are
small canals radiating in all directions from the lacunae.
6. Compare and contrast the three major types of cells found in bone.
The three major cell types found in bone are osteoblasts, osteoclasts, and osteocytes.
Osteoblasts are small cells that synthesize and secret osteoid. Osteoclasts are large,
multinucleated cells responsible for the active erosion of bone minerals. Osteocytes are
mature, nondividing osteoblasts that have become surrounded by matrix.
7. Discuss and discriminate between the sequence of steps characteristic of fracture healing.
Vascular damage occurring immediate after a fracture results in a hemorrhage and the
pooling of blood that forms the fracture hematoma. As the hematoma resorbs, a bone
callus forms, which serves to bind the ends of the broken bone together and stabilizes the
fracture. If the fracture is properly aligned and immobilized, the callus tissue will be
actively modeled and replaced with normal bone.
8. Compare and contrast the basic structural elements of bone and cartilage.
Both bone and cartilage have a matrix that consists of collagen fiber. Both tissues consist
of more extracellular substances than cells. In bone, however, the fibers are embedded in
a calcified matrix, whereas in cartilage they are embedded in a more flexible material.
Bone is a vascular tissue and cartilage has no blood vessels in it.
9. Compare the structure and function of the three types of cartilage.
Hyaline cartilage: is semitransparent and has a bluish cast. Hyaline cartilage forms
articular cartilage of bones, costal cartilage, the rings of the trachea and bronchi, and the
tip of the nose.
Elastic cartilage: Have fewer collagen fibers and a large number of elastic fibers.
Yellowish in color and is found in the external ear, the epiglottis, the Eustachian tube,
and the nasal cavity.
Fibrocartilage: Have a small quantity of matrix and an abundance of fibrous elements. It
is strong and rigid. Found in the symphysis pubis, intervertebral disks.
10. Cancer treatment may generate a need for a bone marrow transplant. Osteoporosis is a
condition characterized by an excessive loss of calcium in bone. These two conditions
are disruptions or failures of two bone functions. Identify these two functions and
explain what their normal functioning should be.
Hematopoiesis: This bone function is responsible for the formation of blood cells. This
function is carried out by the myeloid tissue or bone marrow.
Mineral Storage: Normally this bone function is responsible for maintaining the
homeostatic level of blood calcium. If there is too much calcium in the blood, calcium is
stored in the bone. If there is too little calcium in the blood calcium is removed from the
blood.
11. Compare and analyze bone formation in intramembranous and endochondral ossification.
In intramembranous ossification, groups of cells in the membrane differentiate into
osteoblasts. They secrete matrix material and collagenous fibers. The Golgi apparatus of
these osteoblasts secrete a compound called mucopolysaccharide, and the endoplasmic
reticulum secretes collagen. Large amounts of ground substance accumulate around each
osteoblast, and numerous collagen fibers become embedded in the ground substance.
This constitutes the organic matrix. As the matrix calcifies, the trabeculae join in a
network to form spongy bone. Eventually, the spongy bone will be covered by plates of
compact bone.
In endochondral ossification, the pattern of the bone has been formed by cartilage. This
cartilage model develops a periosteum, which produces a ring or collar of bone. Soon
after the collar of bone appears, the cartilage begins to calcify. A primary ossification
center forms when blood vessels enter the rapidly changing cartilage at the midpoint of
the diaphysis. Ossification progresses from the diaphysis toward each epiphysis, and the
bone grows in length. Secondary ossification centers appear in the epiphyses, and growth
begins toward the diaphysis until bone length is complete. A layer of cartilage called the
epiphyseal plate remains between the epiphysis and the diaphysis. The epiphyseal plate
allows the bone to grow in length by thickening, and ossification occurs on the side
nearest the diaphysis.
12. How does the mechanism of cartilage growth differ from bone growth?
There are two forms of cartilage growth: interstitial and appositional. Interstitial growth
occurs when the cartilage cells in the substance of the tissue mass divide and begin to
secrete additional matrix. This is possible because of the soft and pliable nature of the
matrix. Appositional growth occurs when the cells in the inner layer of the
perichondrium begin to divide and secrete matrix on the surface of the cartilage, causing
an increase in size.
Bone growth can occur by apposition in intramembranous bone when the cells of the
periosteum add matrix to the outside of the bone. In endochondral bone, a type of
interstitial growth occurs when the epiphyseal plate lays down more cartilage, and
ossification occurs from the diaphysis of the bone outward, adding length to the bone.