CHAPTER 6

1) Which of the following is NOT a major function of the skeletal system?

a) communication

3) What is another name for the shaft of a long bone?

a) diaphysis

6) What is the region of long bone found between the diaphysis and the epiphysis called?

c) metaphysis

74) Like other _____, bone tissue contains an abundant extracellular matrix that surrounds widely separated cells.

d) connective tissues

21) Which type of fracture is considered a partial fracture and is only seen in children?

d) greenstick

28) An archeologist and an anthropologist are studying two skeletons from an ancient tomb that had apparently been looted in an earlier time. Both skeletons are females and both are approximately the same height. However, the anthropologist is absolutely certain that one skeleton is the remains of someone from the privileged class while the other skeleton is the remains of a servant or slave. How could the anthropologist be so sure of the economic status of the individuals based solely on their skeletal remains?

A person who is from the privileged class probably has better nutrition but doesn't have to do as much physical labor (exercise) as a person from the servant or slave class. The anthropologist probably notes a difference in bone density in the two skeletons—especially on parts of bones where muscles attached. The skeleton of the servant probably has more density than the skeleton of the privileged class at those points. It is also possible that the servant suffered from malnutrition during life. If so, her skeleton might show evidence of rickets or osteopenia.

27) Patient X has a tumor of the parathyroid glands that causes a hypersecretion of PTH from these glands. Predict the effect this hypersecretion would have on the skeletal system and on the secretion of calcitonin from the thyroid gland.

High levels of PTH would cause high levels of osteoclast activity, thus removing calcium from bones. Bones would become weak and soft. Excess phosphate would be lost from the kidneys. High levels of calcium ions in blood may disrupt nerve and muscle function. Calcitonin levels would probably be high, trying to restore homeostasis by increasing deposition of calcium into bone.

29) Describe the signs and symptoms of osteoporosis and describe the risk factors for developing osteoporosis.

In osteoporosis, bone resorption outpaces bone deposition so that bone mass is depleted, sometimes to the point of spontaneous fracture. Pain and height loss may occur as vertebrae shrink. Postmenopausal women are especially at risk due to dramatically reduced estrogen levels after menopause. Family history may play a role, as does ethnicity (white and Asian women have a higher rate of disease), inactivity, cigarette smoking, excessive alcohol consumption, and a diet low in calcium and vitamin D.

16) Briefly describe the steps in bone deposition.

Solution: during bone deposition, osteogenic cells develop into osteoblasts. The osteoblasts secrete collagen fibers and other organic substances to begin formation of matrix. Within the spaces between fibers, calcification occurs to form a solid matrix that eventually surrounds the osteoblast and some extracellular fluid. The osteoblast in its new lacuna is isolated and becomes an osteocyte. The osteocyte continues to secrete matrix but at a lower level.

69) Briefly describe the major differences between compact and spongy bone.

Spongy bone is light, which reduces the overall weight of a bone so that it moves more readily when pulled by a skeletal muscle. The trabeculae of spongy bone tissue support and protect the red bone marrow. Compact bone, usually found in the exterior of bone, is heavy and dense and made up of osteons. Its function is to resist breakage and provide support of the body.

47) Briefly describe what is happening in each step of fracture repair shown in the diagram.

The diagram illustrates repair of a bone fracture. In step one, there is formation of a fracture hematoma. In step two, a fibrocartilaginous callus is formed. In step three, a bony callus is formed. In step four, bone remodeling begins.

44) Briefly describe what is happening in each of the numbered stages of intramembranous ossification as observed in a child's skull shown in the diagram below.

The diagram is depicting intramembranous ossification in a child's skull. Stage1 involves the development of an ossification center. During stage 2, calcification begins. In stage 3, trabeculae begin to form. Finally, in stage 4, the periosteum develops.

26) Briefly describe the processes by which bone increases in length and diameter.

The only means by which bone can increase in length (interstitial growth) is by activity at the epiphyseal plate. Until full height is reached, the plate consists of layers of chondrocytes, which generate matrix that is then calcified and replaced by bone matrix secreted by osteoblasts on the diaphyseal side of the plate. Around ages 18-20 the cartilage is replaced completely by bone and no more lengthwise growth can occur. Bone increases in diameter via appositional growth as new bone matrix is laid down by osteoblasts in the periosteum.

68) List and briefly describe the six main functions of the skeletal system.

The skeletal system is used for support for the soft tissues of the body and as attachment sites for tendons of most skeletal muscles. The skeletal system also functions in protection for the internal organs. The skeletal system assists in movement working together with the muscle system. Skeletal system aids in mineral (calcium and phosphorus) homeostasis by storing several minerals and releasing them into the bloodstream on demand. Within some bones is red bone marrow that produces blood cells. Bones also contain yellow bone marrow which is a storage site for energy in the form of triglycerides.

66) Briefly, explain how blood calcium level is regulated.

When blood Ca2+ levels drop, PTH is secreted from the parathyroid glands. PTH increases the activity of osteoclasts to increase bone resorption, which ultimately increases Ca2+ in blood. PTH also acts on the kidneys to prevent Ca2+ loss in the urine. PTH also stimulates the production of calcitriol, which acts on the GI tract to increase absorption of Ca2+ from the intestinal lining. When blood Ca2+ level increases, it causes the synthesis and release of calcitonin from the thyroid gland. Calcitonin, inhibits osteoclasts and stimulates osteoblastic activity to increase Ca2+ deposition into bones which promotes bone formation.

70) Which of the following selections correctly lists the sequence of events that occur during intramembranous ossification?

a) Ossification center develops > Calcification > Formation of trabeculae > Development of new periosteum.

67) Hypersecretion of human growth hormone during childhood results in

a) giantism.

30) Which of the following hormones is the most important for Ca2+ regulation?

a) parathyroid hormone

7) What is the fibrous covering on the surface of bone that is involved in thickening of the bone called?

a) periosteum

25) Describe the steps in bone repair.

after the break in the bone occurs, blood vessels in that area are damaged and blood surrounds the fracture. The blood solidifies to form a clot, which reduces bleeding. White blood cells migrate into the area to remove bacteria and damaged cells. Osteoclasts migrate in to remove dead bone matrix. Secondly, fibroblasts migrate into the fracture to form a plate of cartilage to prevent further movement and damage at the fracture site. Thirdly, osteoblasts invade to replace the cartilage with bone matrix in the form of spongy bone. Lastly, the bone matrix will be remodeled as compact bone replaces spongy bone.

24) An increase in bone growth is promoted by which hormones?

b) calcitonin and calcitriol

2) Which region of a long bone articulates with other bones?

b) epiphysis

10) What are bone-dissolving cells called?

b) osteoclasts

8) Which of following selections lists bone cells in the order from unspecialized stem cell to highly specialized mature bone cell?

b) osteogenic cells, osteoblasts, osteocytes

18) Which of the following two minerals are needed in large quantities when bones are growing?

c) calcium and phosphorous

20) During adulthood, which of the following does NOT significantly contribute to bone remodeling and growth?

c) epinephrine

13) How are osteons in compact bone tissue aligned?

c) parallel to the length of the diaphysis.

71) During endochondral ossification in a fetus, bones initially develop as a cartilage model surrounded by a connective tissue covering called the

c) perichondrium.

4) Which a layer of hyaline cartilage reduces friction between bones involved in a joint?

d) articular cartilage

12) What are the extracellular fluid filled extensions of the lacunae called?

d) canaliculi

11) Which of the following structures contain osteocytes?

d) lacunae

65) Which of the following conditions results when the articular cartilages in a joint degenerate to the point where the bony ends of articulating bones touch?

d) osteoarthritis

9) Which of the following are considered to be bone-building cells?

d) osteoblasts

23) Bone mass reduction is promoted by which hormone?

d) parathyroid hormone

19) Which of the following correctly lists the order of the four zones of cartilage found within the growth plate starting at the epiphysis and extending to the diaphysis?

d) resting cartilage, proliferating cartilage, hypertrophic cartilage, calcified cartilage

17) Briefly describe the steps in bone resorption.

during bone resorption, an osteoclast attaches tightly to the endosteum or periosteum of the bone and forms a leak proof seal at the edges. Then it releases protein-digesting lysosomal enzymes and several amino acids into the sealed pocket. The enzymes digest collagen fibers and other organic substances while the acids dissolve the bone materials. Working together several osteoclasts carve out a small tunnel in the old bone. The degraded bone proteins and extracellular matrix minerals enter an osteoclast by endocytosis, cross the cell in vesicles, and undergo exocytosis on the side opposite the ruffled border. Now in the interstitial fluid, the products of bone resorption diffuse into nearby blood capillaries. Once a small area of bone has been resorbed, osteoclasts depart and osteoblasts move in to rebuild bone in that area.

14) Which of the following statements about bone remodeling is FALSE?

e) It occurs at a faster rate in compact bone than spongy bone.

72) Which of the following substances are stored in the structure of adult bones for use by other tissues in the body?

e) More than one of these substances is stored in bone.

75) Calcium is involved in all of the following important body functions EXCEPT

e) being the primary cation that regulates osmotic balance in cells.

15) Which of the following activities has the greatest effect on bone remodeling and bone deposition?

e) both c and d (running and jumping)

5) Which layer of hyaline cartilage allows the diaphysis to grow in length?

e) epiphyseal plate

64) Which of the following is the correct sequence of steps in the repair of a bone fracture?

e) fracture hematoma, fibrocartilaginous callus formation, bony callus formation, bone remodeling

73) Which of the following hormones are more important post-puberty for bone growth?

e) sex hormones

22) About 25% of all stress fractures involve which bone?

e) tibia