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Chapter Summary

Introduction (page 196)

Individual bones are the organs of the skeletal system. A bone contains very active tissues.

Bone Structure (page 196)

Bone structure reflects its function.

1. Bone classification

Bones are grouped according to their shapes—long, short, flat, irregular, or round (sesamoid).

2. Parts of a long bone a. Epiphyses at each end are covered with articular cartilage and articulate with other bones.

b. The shaft of a bone is called the diaphysis.

c. Except for the articular cartilage, a bone is covered by a periosteum.

d. Compact bone has a continuous matrix with no gaps.

e. Spongy bone has irregular interconnecting spaces between bony plates.

f. Both compact and spongy bone are strong and resist bending.

g. The diaphysis contains a medullary cavity filled with marrow.

3. Microscopic structure a. Compact bone contains osteons cemented together.

b. Central canals contain blood vessels that nourish the cells of osteons.

c. Perforating canals connect central canals transversely and communicate with the bone's surface and the medullary cavity.

d. Diffusion from the surface of thin bony plates nourishes cells of spongy bones.

Bone Development and Growth (page 200)

1. Intramembranous bones a. Certain flat bones of the skull are intramembranous bones.

b. They develop from layers of connective tissues.

c. Osteoblasts within the membranous layers form bone tissue.

d. Mature bone cells are called osteocytes.

e. Primitive connective tissue gives rise to the periosteum.

2. Endochondral bones a. Most of the bones of the skeleton are endochondral.

b. They develop as hyaline cartilage that is later replaced by bone tissue.

c. Primary ossification center appears in the diaphysis, whereas secondary ossification centers appear in the epiphyses.

d. An epiphyseal plate remains between the primary and secondary ossification centers.

3. Growth at the epiphyseal plate a. An epiphyseal plate consists of layers of cells: resting cells, young dividing cells, older enlarging cells, and dying cells.

b. The epiphyseal plates are responsible for lengthening.

c. Long bones continue to lengthen until the epiphyseal plates are ossified.

d. Growth in thickness is due to intramembranous ossification beneath the periosteum.

e. The action of osteoclasts forms the medullary cavity.

4. Homeostasis of bone tissue a. Osteoclasts and osteoblasts continually remodel bone.

b. The total mass of bone remains nearly constant.

5. Factors affecting bone development, growth, and repair a. Deficiencies of vitamin A, C, or D result in abnormal development.

b. Insufficient secretion of pituitary growth hormone may result in dwarfism; excessive secretion may result in gigantism, or acromegaly.

c. Deficiency of thyroid hormone delays bone growth.

d. Male and female sex hormones promote bone formation and stimulate ossification of the epiphyseal disks.

Bone Function (page 205)

1. Support and protection a. Bones shape and form body structures.

b. Bones support and protect softer, underlying tissues.

2. Body movement a. Bones and muscles function together as levers.

b. A lever consists of a rod, a pivot (fulcrum), a resistance, and a force that supplies energy.

c. Parts of a first-class lever are arranged resistancepivot-force; of a second-class lever, pivot-resistanceforce; of a third-class lever, resistance-force-pivot.

3. Blood cell formation a. At different ages, hemopoiesis occurs in the yolk sac, the liver, the spleen, and the red bone marrow.

b. Red marrow houses developing red blood cells, white blood cells, and blood platelets.

4. Inorganic salt storage a. The intercellular material of bone tissue contains large quantities of calcium phosphate in the form of hydroxyapatite.

b. When blood calcium ion concentration is low, osteoclasts resorb bone, releasing calcium salts.

c. When blood calcium ion concentration is high, osteoblasts are stimulated to form bone tissue and store calcium salts.

d. Bone stores small amounts of sodium, magnesium, potassium, and carbonate ions.

e. Bone tissues may accumulate lead, radium, or strontium.

Skeletal Organization (page 209)

1. Number of bones a. Usually a human skeleton has 206 bones, but the number may vary.

b. Extra bones in sutures are called sutural bones.

2. Divisions of the skeleton a. The skeleton can be divided into axial and appendicular portions.

b. The axial skeleton consists of the skull, hyoid bone, vertebral column, and thoracic cage.

c. The appendicular skeleton consists of the pectoral girdle, upper limbs, pelvic girdle, and lower limbs.

Skull (page 213)

The skull consists of twenty-two bones, which include eight cranial bones, thirteen facial bones, and one mandible.

1. Cranium a. The cranium encloses and protects the brain and provides attachments for muscles.

b. Some cranial bones contain air-filled sinuses that help reduce the weight of the skull.

c. Cranial bones include the frontal bone, parietal bones, occipital bone, temporal bones, sphenoid bone, and ethmoid bone.

2. Facial skeleton a. Facial bones form the basic shape of the face and provide attachments for muscles.

b. Facial bones include the maxillary bones, palatine bones, zygomatic bones, lacrimal bones, nasal bones, vomer bone, inferior nasal conchae, and mandible.

3. Infantile skull a. Incompletely developed bones, connected by fontanels, enable the infantile skull to change shape slightly during childbirth.

b. Proportions of the infantile skull are different from those of an adult skull, and its bones are less easily fractured.

Vertebral Column (page 225)

The vertebral column extends from the skull to the pelvis and protects the spinal cord. It is composed of vertebrae separated by intervertebral disks. An infant has thirty-three vertebral bones, and an adult has twenty-six. The vertebral column has four curvatures—cervical, thoracic, lumbar, and pelvic.

1. A typical vertebra a. A typical vertebra consists of a body, pedicles, laminae, spinous process, transverse processes, and superior and inferior articulating processes.

b. Notches on the upper and lower surfaces of the pedicles on adjacent vertebrae form intervertebral foramina through which spinal nerves pass.

2. Cervical vertebrae a. Cervical vertebrae comprise the bones of the neck.

b. Transverse processes have transverse foramina.

c. The atlas (first vertebra) supports the head.

d. The dens of the axis (second vertebra) provides a pivot for the atlas when the head is turned from side to side.

3. Thoracic vertebrae a. Thoracic vertebrae are larger than cervical vertebrae.

b. Their long spinous processes slope downward, and facets on the sides of bodies articulate with the ribs.

4. Lumbar vertebrae a. Vertebral bodies of lumbar vertebrae are large and strong.

b. Their transverse processes project posteriorly at sharp angles, and their spinous processes are directed horizontally.

5. Sacrum a. The sacrum, formed of five fused vertebrae, is a triangular structure that has rows of dorsal sacral foramina.

b. It is united with the coxal bones at the sacroiliac joints.

c. The sacral promontory provides a guide for determining the size of the pelvis.

6. Coccyx a. The coccyx, composed of four fused vertebrae, forms the lowest part of the vertebral column.

b. It acts as a shock absorber when a person sits.

Thoracic Cage (page 231)

The thoracic cage includes the ribs, thoracic vertebrae, sternum, and costal cartilages. It supports the pectoral girdle and upper limbs, protects viscera, and functions in breathing.

1. Ribs a. Twelve pairs of ribs are attached to the twelve thoracic vertebrae.

b. Costal cartilages of the true ribs join the sternum directly; those of the false ribs join indirectly or not at all.

c. A typical rib has a shaft, head, and tubercles that articulate with the vertebrae.

2. Sternum a. The sternum consists of a manubrium, body, and xiphoid process.

b. It articulates with costal cartilages and clavicles.

Pectoral Girdle (page 233)

The pectoral girdle is composed of two clavicles and two scapulae. It forms an incomplete ring that supports the upper limbs and provides attachments for muscles that move the upper limbs.

1. Clavicles a. Clavicles are rodlike bones that run horizontally between the sternum and shoulders.

b. They hold the shoulders in place and provide attachments for muscles.

2. Scapulae a. The scapulae are broad, triangular bones with bodies, spines, heads, acromion processes, coracoid processes, glenoid cavities, supraspinous and infraspinous fossae, superior borders, axillary borders, and vertebral borders.

b. They articulate with the humerus of each upper limb and provide attachments for muscles of the upper limbs and chest.

Upper Limb (page 234)

Limb bones provide the frameworks and attachments of muscles and function in levers that move the limb and its parts.

1. Humerus a. The humerus extends from the scapula to the elbow.

b. It has a head, greater tubercle, lesser tubercle, intertubercular groove, anatomical neck, surgical neck, deltoid tuberosity, capitulum, trochlea, epicondyles, coronoid fossa, and olecranon fossa.

2. Radius a. The radius is located on the thumb side of the forearm between the elbow and wrist.

b. It has a head, radial tuberosity, styloid process, and ulnar notch.

3. Ulna a. The ulna is longer than the radius and overlaps the humerus posteriorly.

b. It has a trochlear notch, olecranon process, coronoid process, head, styloid process, and radial notch.

c. It articulates with the radius laterally and with a disk of fibrocartilage inferiorly. 4. Wrist and hand a. The wrist includes eight carpals that form a carpus.

b. The palm has five metacarpals.

c. The five fingers have fourteen phalanges.

Pelvic Girdle (page 239)

The pelvic girdle consists of two coxae that articulate with each other anteriorly and with the sacrum posteriorly. The sacrum, coccyx, and pelvic girdle form the pelvis. The girdle provides support for body weight and attachments for muscles and protects visceral organs.

1. Os coxae

Each coxa consists of an ilium, ischium, and pubis, which are fused in the region of the acetabulum.

a. Ilium

(1) The ilium, the largest portion of the coxa, joins the sacrum at the sacroiliac joint.

(2) It has an iliac crest with anterior and posterior superior iliac spines and iliac fossae.

b. Ischium

(1) The ischium is the lowest portion of the coxa.

(2) It has an ischial tuberosity and ischial spine.

c. Pubis

(1) The pubis is the anterior portion of the coxa.

(2) Pubis bones are fused anteriorly at the symphysis pubis.

2. Greater and lesser pelves a. The lesser pelvis is below the pelvic brim; the greater pelvis is above it.

b. The lesser pelvis functions as a birth canal; the greater pelvis helps support abdominal organs.

3. Differences between male and female pelves a. Differences between male and female pelves are related to the function of the female pelvis as a birth canal.

b. Usually the female pelvis is more flared; pubic arch is broader; distance between the ischial spines and the ischial tuberosities is greater; and sacral curvature is shorter.

Lower Limb (page 242)

Bones of the lower limb provide the frameworks of the thigh, leg, and foot.

1. Femur a. The femur extends from the hip to the knee.

b. It has a head, fovea capitis, neck, greater trochanter, lesser trochanter, linea aspera, lateral condyle, and medial condyle.

2. Patella a. The patella is a flat, round, or sesamoid bone in the tendon that passes anteriorly over the knee.

b. It controls the angle of this tendon and functions in lever actions associated with lower limb movements.

3. Tibia a. The tibia is located on the medial side of the leg.

b. It has medial and lateral condyles, tibial tuberosity, anterior crest, and medial malleolus.

c. It articulates with the talus of the ankle.

4. Fibula a. The fibula is located on the lateral side of the tibia.

b. It has a head and lateral malleolus that articulates with the ankle but does not bear body weight.

5. Ankle and foot a. The ankle and foot consists of the tarsus, metatarsus, and five toes.

b. It includes the talus that helps form the ankle, six other tarsals, five metatarsals, and fourteen phalanges.

Life-Span Changes (page 247)

Aging-associated changes in the skeleton are apparent at the cellular and whole-body levels.

1. Incremental decrease in height begins at about age thirty.

2. Gradually, bone loss exceeds bone replacement.

a. In the first decade following menopause, bone loss occurs more rapidly in women than in men or premenopausal women. By age 70, both sexes are losing bone at about the same rate.

b. Aging increases risk of bone fractures.

Critical Thinking Questions

1. What steps do you think should be taken to reduce the chances of bones accumulating abnormal metallic elements such as lead, radium, and strontium in bones?

2. Why do you think incomplete, longitudinal fractures of bone shafts (greenstick fractures) are more common in children than in adults?

3. When a child's bone is fractured, growth may be stimulated at the epiphyseal disk. What problems might this extra growth cause in an upper or lower limb before the growth of the other limb compensates for the difference in length?

4. Why do elderly persons often develop bowed backs and appear shorter than they were in earlier years?

5. How might the condition of an infant's fontanels be used to evaluate skeletal development? How might the fontanels be used to estimate intracranial pressure?

6. Why are women more likely than men to develop osteoporosis? What steps can reduce the risk of developing this condition?

7. How does the structure of a bone make it strong yet lightweight?

8. Archeologists discover skeletal remains of humanlike animals in Ethiopia. Examination of the bones suggests that the remains represent four types of individuals. Two of the skeletons have bone densities that are 30% less than those of the other two skeletons. The skeletons with the lower bone mass also have broader front pelvic bones. Within the two groups defined by bone mass, smaller skeletons have bones with evidence of epiphyseal plates, but larger bones have only a thin line where the epiphyseal plates should be. Give the age group and gender of the individuals in this find.

Shier-Butler-Lewis: I II. Support and Movement I 7. Skeletal System I I © The McGraw-Hill

Human Anatomy and Companies, 2001

Physiology, Ninth Edition

Review Exercises

Part A

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

2. Sketch a typical long bone, and label its epiphyses, diaphysis, medullary cavity, periosteum, and articular cartilages.

3. Distinguish between spongy and compact bone.

4. Explain how central canals and perforating canals are related.

5. Explain how the development of intramembranous bone differs from that of endochondral bone.

6. Distinguish between osteoblasts and osteocytes.

7. Explain the function of an epiphyseal plate.

8. Explain how a bone grows in thickness.

9. Define osteoclast.

10. Explain how osteoclasts and osteoblasts regulate bone mass.

11. Describe the effects of vitamin deficiencies on bone development.

12. Explain the causes of pituitary dwarfism and gigantism.

13. Describe the effects of thyroid and sex hormones on bone development.

14. Explain the effects of exercise on bone structure.

15. Provide several examples to illustrate how bones support and protect body parts.

16. Describe a lever, and explain how its parts may be arranged to form first- , second- , and third-class levers.

17. Explain how upper limb movements function as levers.

18. Describe the functions of red and yellow bone marrow.

19. Explain the mechanism that regulates the concentration of blood calcium ions.

20. List three substances that may be abnormally stored in bone.

21. Distinguish between the axial and appendicular skeletons.

22. Name the bones of the cranium and the facial skeleton.

23. Explain the importance of fontanels.

24. Describe a typical vertebra.

25. Explain the differences among cervical, thoracic, and lumbar vertebrae.

26. Describe the locations of the sacroiliac joint, the sacral promontory, and the sacral hiatus.

27. Name the bones that comprise the thoracic cage.

28. List the bones that form the pectoral and pelvic girdles.

29. Name the bones of the upper limb.

30. Name the bones that comprise the coxa.

31. List the major differences that may occur between the male and female pelves.

32. List the bones of the lower limb.

33. Describe changes in trabecular bone and compact bone with aging.

34. List factors that may preserve skeletal health.

Part B

Match the parts listed in column I with the bones listed in column II.

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  • Wendy Yang
    Why do elderly persons often develop bowed backs and appear shorter than they were in earlier years?
    6 years ago
  • macario
    How might the condition of an infant's fontanels be used to evaluate skeletal development?
    3 years ago
  • Teppo
    What steps can be taken to reduce the chance of bones accumulating matellic elements?
    1 year ago

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