174 Chapter 11 Answers: Skeletal System

11.2 Introduction to the Skeletal System: Review Questions and Answers

1. What is the skeletal system? How many bones are there in the adult skeleton? The skeletal system is the organ system that provides an internal framework for the human body. In adults, the skeleton contains 206 bones.
2. Describe the composition of bones. Bones are made of dense connective tissues, mainly the tough protein collagen. Bones also contain blood vessels, nerves, and other tissues. Bones are hard and rigid due to deposits of calcium and other mineral salts within their living tissues.
3. Besides bones, what other organs are included in the skeletal system? Besides bones, the skeletal system includes cartilage and ligaments.
4. Identify the two major divisions of the skeleton. The two major divisions of the skeleton are the axial skeleton, which includes the skull, spine, and rib cage; and the appendicular skeleton, which includes the appendages and the girdles that attach them to the axial skeleton.
5. List several functions of the skeletal system. Answers may vary. Sample answer: Functions of the skeletal system include supporting the body, giving the body shape, protecting internal organs, allowing the body to move, producing blood cells, storing minerals, helping maintain mineral homeostasis, and producing endocrine hormones.
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7. If a person has a problem with blood cell production, what type of bone tissue is most likely involved? Explain your answer. Red marrow, because that is where blood cells are produced in the bone.
8. What are three forms of homeostasis that the skeletal system regulates? Briefly explain how each one is regulated by the skeletal system. The skeletal system helps maintain mineral homeostasis by regulating the level of calcium and other minerals in the blood by storing or releasing them from bones as needed. This process also helps maintain homeostasis in blood pH because the minerals are basic. Bones also regulate blood glucose and fat deposition through the secretion of the endocrine hormone osteocalcin.
9. What do you think would happen to us if we did not have ligaments? Explain your answer. Answers may vary. Sample answer: Ligaments hold bones together and keep them in place, so without ligaments we would be a pile of bones and internal organs inside a bag of skin.
10. What is a joint? How is cartilage related to joints? Identify one joint in the human body and describe its function. Answers may vary. Sample answer: A joint is an area where two or more bones meet. Cartilage covers the ends of bones at joints, creating a smooth surface for the bones to move over. The elbow is a joint in the human body that allows the bones to move like a lever in order to bend and straighten the arm.

11.3 Divisions of the Skeletal System: Review Questions and Answers

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3. What are the advantages of an S-shaped vertebral column?The advantages of an S-shaped vertebral column include allowing it to absorb shocks and to distribute the weight of the body.
4. What is the rib cage? What is its function?  What types of ribs are there?The rib cage includes 12 thoracic vertebrae, the sternum, and 12 pairs of ribs. Its function is to hold and protect the organs of the upper part of the trunk, including the heart and lungs.
5. Explain the advantage of having some ribs that are not attached directly to the sternum. Answers may vary. Sample answer: The false ribs and floating ribs are not attached directly to the sternum. This allows them to move more easily to accommodate the movements of breathing.
6. What is the shoulder girdle? Why does it allow considerable upper limb mobility? The shoulder girdle attaches the upper limbs to the trunk of the body. It includes a right and left clavicle and a right and left scapula. The shoulder girdle allows considerable upper limb mobility because it is connected to the axial skeleton only by muscles.
7. Describe some of the similarities between the upper limbs and the lower limbs. Answers may vary. Sample answer: Both the upper limbs and lower limbs have 30 bones. Also, both limbs have one bone in the top of the limb and two bones in the bottom of the limb. Finally, both the hands and feet have 14 phalanges.
8. Describe the pelvic girdle and the bones it contains. The pelvic girdle is the part of the skeleton that attaches the legs to the trunk of the body and supports the organs of the abdomen. It consists of two halves that are fused together in adults. Each half consists of three bones: the ilium, pubis, and ischium.

11.4 Structure of Bone: Review Questions and Answers

1. Describe osseous tissue. Osseous tissue is the main tissue in bones. It is a type of connective tissue consisting mainly of a collagen matrix that is mineralized with calcium and phosphorus crystals.
2. Why are bones hard, but not brittle? Bones are hard but not brittle because they are made of a combination of flexible collagen and mineral crystals.
3. Compare and contrast the compact and spongy bone. The two main types of osseous tissue are compact bone tissue and spongy bone tissue. Both types consist of the same kinds of cells, but the cells have different arrangements in the two types of bone. As a result, compact bone is smooth and dense, whereas spongy bone is porous and light. Compact bone makes up the outer layer of bones, whereas spongy bone is found inside many bones.
4. What non-osseous tissues are found in bones? Non-osseous tissues found in bones include nerves, blood vessels, bone marrow, and periosteum.
5. List four types of bone cells and their functions. Four types of bone cells are osteoblasts, which form new organic bone matrix and mineralize it; osteoclasts, which break down bone; osteocytes, which regulate the formation and breakdown of bone; and osteogenic cells, which form new bone cells.
6. Identify six types of bones. Give an example of each type. The six types of bones are long bones such as limb bones, short bones such as wrist bones, sesamoid bones such as the patella, sutural bones in skull sutures, and irregular bones such as vertebrae.
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8. Compare and contrast yellow bone marrow and red bone marrow. Answers may vary. Sample answer: Yellow and red bone marrow are both found in the marrow cavity of bones, but yellow marrow is mostly fat and red marrow produces blood cells. All marrow in newborns is red, but much of it changes to yellow marrow in adults.
9. Which type of bone cell divides to produce new bone cells? Where is this cell type located? Osteogenic cells, which are located in the periosteum covering the bone.
10. Where do osteoblasts and osteocytes come from? How are they related to each other? Osteoblasts are produced by osteogenic cells. Osteocytes, in turn, arise from osteoblasts that have become trapped in bone matrix.
11. Which type of bone is embedded in tendons? Sesamoid bone.

11.5 Bone Growth, Remodeling, and Repair: Review Questions and Answers

1. Outline how bone develops starting early in the fetal stage, and through the age of skeletal maturity. Early in the development of a human fetus, the skeleton is made almost entirely of cartilage. The relatively soft cartilage gradually turns into hard bone in the process called ossification. It begins at a primary ossification centre in the middle of bone and later also occurs at secondary ossification centres in the ends of bone. Ossification of some bones continues through childhood, until the late teens or early twenties when skeletal maturity occurs. After that, bones can no longer grow in length because the areas of ossification have met and fused.
2. Describe the process of bone remodeling. When does it occur? Bone remodeling is the process in which osteoclasts resorb bone and osteoblasts make new bone to replace it. It occurs continuously throughout life, with about ten per cent of bone mass being remodeled each year in adults.
3. What purposes does bone remodeling serve? Bone remodeling serves several purposes. It shapes the skeleton, repairs tiny flaws in bones, and helps maintain mineral homeostasis in the blood.
4. Define bone repair. How long does this process take? Bone repair is the natural process in which a bone repairs itself following a bone fracture. This process may take several weeks.
5. Explain how bone repair occurs. In the process of bone repair, periosteum (the connective tissue covering bone) produces precursor cells that develop into osteoblasts. Then the osteoblasts form new bone matrix to heal the fracture.
6. Identify factors that may affect bone repair. Bone repair may be affected by diet, age, pre-existing bone disease, or other factors.
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8. If there is a large region between the primary and secondary ossification centres in a bone, is the person young or old? Explain your answer. If there is a large region between the primary and secondary ossification centres in a bone, the person is young, mostly likely well under 18 years of age. This is because as a person grows older, the primary and secondary ossification centres grow towards each other and eventually meet and fuse around the ages of 18 to 25.
9. If bones can repair themselves, why are casts and pins sometimes necessary in the process? Answers may vary. Sample answer: Bones can repair themselves, but casts and pins are sometimes needed to hold the pieces of the broken bone together in the right positions so that they can fuse together correctly.
10. When calcium levels are low, which type of bone cell causes the release of calcium to the bloodstream? Osteoclasts.
11. Which tissue and bone cell type are primarily involved in bone repair after a fracture? After a bone fracture, the periosteum produces cells that develop into osteoblasts, which form new bone tissue.
12. Describe one way in which hormones are involved in bone remodeling. Answers will vary. Sample answer: Growth hormone regulates the rate at which osteoblasts create new bone during bone remodeling.

11.6 Joints: Review Questions and Answers

1. What are joints? Joints are locations at which bones of the skeleton connect with one another.
2. What are two ways that joints are commonly classified? Joints can be classified structurally or functionally, but there is significant overlap between the two types of classifications.
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4. How are joints classified structurally? The structural classification of joints depends on the type of tissue that binds the bones to each other at the joint. There are three types of joints in the structural classification: fibrous, cartilaginous, and synovial joints.
5. Describe the functional classification of joints. The functional classification of joints is based on the type and degree of movement that they allow. There are three types of joints in the functional classification: immovable, partly movable, and movable joints.
6. How are movable joints classified? Movable joints are classified according to the type of movement they allow.
7. Name the six classes of movable joints. Describe how they move and give an example of each. The six classes of movable joints are pivot, hinge, saddle, plane, condyloid, and ball-and-socket joints. A pivot joint allows one bone to rotate around another. A hinge joint allows back and forth movement like the hinge of a door. A saddle joint allows two different types of movement. For example, the thumb is a saddle joint that permits the thumb to move toward and away from the index finger and also to cross over the palm toward the little finger. A plane joint allows two bones to glide over one another. A condyloid joint is one in which an oval-shaped head on one bone moves in an elliptical cavity in another bone, allowing movement in all directs except rotation around an axis. A ball-and-socket joint allows the greatest range of movement of any movable joint. It allows forward and backward as well as upward and downward motions. It also allows rotation in a circle.
8. Which specific type of moveable joint do you think your knee joint is? Explain your reasoning. Answers may vary. Sample answer: I think the knee joint is a hinge joint like the elbow because it allows back and forth movement like a hinge.
10. Explain the difference between cartilage in a cartilaginous joint and cartilage in a synovial joint. Cartilage in a cartilaginous joint actually holds the bones together, whereas in a synovial joint, the cartilage covers the ends of the bones which are held together by ligaments.
11. Why are fibrous joints immovable? Fibrous joints are immovable because they are made of dense connective tissue rich in collagen fibres, which does not allow movement.
12. What is the function of synovial fluid? Synovial fluid cushions the ends of bones.

11.7 Disorders of the Skeletal System: Review Questions and Answers

1. Create a brochure or poster about osteoporosis to educate others about this disease.  Include information about:
   1. A definition of osteoporosis Osteoporosis is an age-related disorder in which bones lose mass, weaken, and break more easily than normal bones. The basic cause of osteoporosis is an imbalance between bone formation and bone resorption in bone remodeling that results in a net loss of bone mass.  In simpler terms, osteoporosis occurs when the creation of new bone doesn’t keep up with the loss of old bone.This may occur as a side effect of other disorders or certain medications.
   2. Causes Osteoporosis causes bones to become weak and brittle — so brittle that a fall or even mild stresses such as bending over or coughing can cause a fracture. Osteoporosis-related fractures most commonly occur in the hip, wrist or spine.
   3. Dangers of living with the disease Osteoporosis is dangerous because it often leads to bone fractures. Osteoporosis itself is rarely fatal and generally doesn’t even cause symptoms, but complications of fractures often are debilitating and may lead to death.
   4. Canadian osteoporosis statistics
   5. Risk factors Risk factors for osteoporosis include older age, female sex, European or Asian ancestry, family history of osteoporosis, short stature and small bones, smoking, alcohol consumption, lack of exercise, vitamin D deficiency, poor nutrition, and consumption of soft drinks.
   6. Diagnosis Osteoporosis is diagnosed by measuring a patient’s bone density and comparing it with the normal level of peak bone density of a young adult reference population of the same sex as the patient.
   7. Treatment Osteoporosis is often treated with medications such as bisphosphonates that may slow or even reverse bone loss. The only way to prevent osteoporosis is to eliminate risk factors that can be controlled through changes of behavior, such as undertaking weight-bearing exercise if you have been sedentary.
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3. Why is it important to build sufficient bone mass in your young adult years? Answers may vary. Sample answer: Osteoporosis results from the loss of bone mass after the peak years of the 30s. If sufficient bone mass is not developed before and during that time, your peak bone mass will start out lower and you will be at greater risk for osteoporosis as bone mass declines in your later years.
4. Explain the difference in cause between rheumatoid arthritis and osteoarthritis. Rheumatoid arthritis is an autoimmune disease that arises when the body’s immune system attacks the joints. Osteoarthritis, on the other hand, is caused by mechanical stress on the joints with insufficient repair of cartilage.
5. Debunk the myth: Osteoarthritis is caused by physical activity, so people who are equally active are equally susceptible to it. False, because OA is generally caused by insufficient repair of cartilage, which does not happen equally in the general population, therefore exercise would not necessarily have the same effect on joints in different individuals.
6. Explain how we know that estrogen generally promotes production of new bone. Estrogen protects the adult skeleton against bone loss by slowing the rate of bone remodeling and by maintaining a focal balance between bone formation and resorption.

13.8 Case Study Conclusion and Chapter 13 Summary: Review Questions and Answers

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2. Why does the rib cage need to be flexible? Why can it be flexible? Answers may vary. Sample answer: The rib cage needs to be flexible because it needs to expand and contract with breathing movements. It is able to be flexible because true ribs are attached to the sternum by cartilage, which creates partly movable joints. Also, false ribs and floating ribs are attached by cartilage to true ribs or to muscles in the abdominal wall, respectively. This also allows them the flexibility to move as the person breathes.
3. In general, what do “girdles” in the skeletal system do? Answers may vary. Sample answer: The shoulder and pelvic girdles both function to connect the limbs to the axial skeleton.
4. Would swimming be more effective as an exercise for preventing osteoporosis or as a treatment for osteoarthritis? Explain your answer. Answers may vary. Sample answer: Swimming is likely more of an effective treatment for osteoarthritis than a way to prevent osteoporosis, because it is not a weight-bearing exercise. That means it is gentle on the joints, which is needed when a person has osteoarthritis because they have lost cartilage that cushions the joints. To prevent osteoporosis, weight-bearing exercise such as running or weight training is needed because it causes stress on the bones which stimulates bone building. This helps prevent the loss of bone mass that occurs in osteoporosis.
5. Explain why some of the vertebrae become misshapen in the condition called dowager’s hump (or kyphosis). Answers may vary. Sample answer: A dowager’s hump is typically caused by osteoporosis, which is a disorder involving the loss of bone mass. This causes compression fractures in the thoracic vertebrae, because the bones are brittle and fracture easily even without a major injury. These compression fractures result in the misshapen vertebrae seen in a dowager’s hump.
6. Explain why osteoarthritis often involves inflammation in the joints. Osteoarthritis often involves inflammation in the joints because the cartilage in the joints breaks down. As cells lining the joint attempt to remove these breakdown products, inflammation results.
7. Osteoporosis can involve excess bone resorption, as well as insufficient production of new bone tissue. What are the two main bone cell types that carry out these processes, respectively? Osteoclasts carry out bone resorption and osteoblasts produce new bone tissue.
8. Describe two roles that calcium in bones play in the body. Answers may vary. Sample answer: Calcium helps make bones hard in order to support and protect the body. Also, bones serve as a storage site for calcium, so that calcium can be released from bones when the level of calcium in the blood is too low.