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# 21.2: The Skeletal System

Difficulty Level: At Grade Created by: CK-12

## Lesson 21.2: True or False

Name___________________ Class______________ Date________

Write true if the statement is true or false if the statement is false.

_____ 1. Cartilage is a type of dense connective tissue.

_____ 2. One of the functions of the skeleton is to produce blood cells.

_____ 3. When blood levels of minerals are too high, bones release some of the minerals back into the blood.

_____ 4. The basic structure of bones is bone matrix.

_____ 5. There are three types of specialized cells in human bones.

_____ 6. Osteoclasts make new bone cells.

_____ 7. Bones are dynamic, living tissues.

_____ 8. Compact bone makes up the dense outer layer of bone.

_____ 9. Periosteum is soft connective tissue.

_____ 10. Early in the development of a human fetus, the skeleton is made entirely of bone.

_____ 11. A joint is a place where two or more bones of the skeleton meet.

_____ 12. There are four main types of joints.

_____ 13. Immovable joints are also known as synovial joints.

_____ 14. Of all the movable joints, a ball-and-socket joint has the greatest range of motion.

_____ 15. Despite their hardness and strength, bones can suffer from injury and disease.

Name___________________ Class______________ Date________

Read these passages from the text and answer the questions that follow.

Types of Joints

There are three main types of joints: immovable, partly movable, and movable.

• Immovable joints allow no movement because the bones at these joints are held securely together by dense collagen. The bones of the skull are connected by immovable joints.
• Partly movable joints allow only very limited movement. Bones at these joints are held in place by cartilage. The ribs and sternum are connected by partly movable joints.
• Movable joints allow the most movement. Bones at these joints are connected by ligaments. Movable joints are the most common type of joints in the body, so they are described in more detail next.

Movable Joints

Movable joints are also known as synovial joints. This is because the space between the bones is filled with a thick fluid called synovial fluid that cushions the joint.

There are a variety of types of movable joints, which are illustrated below. The joints are classified by how they move. For example, a ball-and-socket joint, such as the shoulder, has the greatest range of motion, allowing movement in several directions. Other movable joints, including hinge joints such as the knee, allow less movement.

Types of Movable Joints in the Human Skeleton. Movable joints can move in a variety of ways. Try moving each of the joints indicated in the diagram. Can you tell how their movements differ? Other joints in the human skeleton that are not depicted here include saddle, elipsoid, and plane joints. (Skeleton image copyright 3drenderings, 2010, used under license from Shutterstock.com. Joints images courtesy of Produnis and under GNU-FDL 1.2. Composite created by CK-12 Foundation.)

Questions

1. What are the differences among the three main types of joints?

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2. What is the function of synovial fluid?

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3. Name three types of movable joints.

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4. What are other joints in the human skeleton not depicted in the figure?

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5. Try moving each of the joints indicated in the diagram. Can you tell how their movements differ?

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## Lesson 21.2: Multiple Choice

Name___________________ Class______________ Date________

Circle the letter of the correct choice.

1. How many bones does the human skeleton consist of?
1. 203
2. 206
3. 216
4. 235
2. Bone matrix consists of tough fibers made of
1. carbohydrate.
2. fat.
3. protein.
4. none of the above.
3. Osteoblasts secrete
1. calcium.
2. water.
3. hormones.
4. collagen.
4. Which of the following makes up the dense outer layer of bone?
1. compact bone
2. spongy bone
3. bone marrow
4. periosteum
5. Which of the following produces blood cells?
1. compact bone
2. spongy bone
3. bone marrow
4. periosteum
6. A person reaches skeletal maturity
1. in the early teens.
2. in the late teens or early twenties.
3. in the mid twenties.
4. in the late twenties or early thirties.
7. The main difference between osteoblasts and osteoclasts is that
1. osteoblasts make new bone cells and osteoclasts dissolve bone material.
2. osteoclasts make new bone cells and osteoblasts dissolve bone material.
3. osteoblasts make new bone from cartilage and osteoclasts make cartilage from bone.
4. osteoblasts make new bone cells and osteoclasts regulate bone mineral homeostasis.
8. The ribs and sternum are connected by
1. immovable joints.
2. partly moveable joints.
3. movable joints.
4. none of the above.

## Lesson 21.2: Vocabulary I

Name___________________ Class______________ Date________

Match the vocabulary word with the proper definition.

Definitions

_____ 1. process in which mineral deposits replace cartilage and change it into bone

_____ 2. type of bone cell that regulates mineral homeostasis by directing the uptake of minerals from the blood and the release of minerals back into the blood as needed

_____ 3. band of fibrous connective tissue that holds bones together

_____ 4. soft connective tissue in spongy bone that produces blood cells

_____ 5. dense outer layer of bone that is very hard and strong

_____ 6. type of bone cell that dissolves minerals in bone and releases them back into the blood

_____ 7. place where two or more bones of the skeleton meet

_____ 8. rigid framework of bone that consists of tough protein fibers and mineral crystals

_____ 9. light, porous inner layer of bone that contains bone marrow

_____ 10. human body system that consists of all the bones of the body as well as cartilage and ligaments

_____ 11. type of bone cell that makes new bone cells and secretes collagen

_____ 12. tough, fibrous membrane that covers the outer surface of bone

Terms

a. bone marrow

b. bone matrix

c. compact bone

d. joint

e. ligament

f. ossification

g. osteoblast

h. osteoclast

i. osteocyte

j. periosteum

k. skeletal system

l. spongy bone

## Lesson 21.2: Vocabulary II

Name___________________ Class______________ Date________

Fill in the blank with the appropriate term.

1. Cartilage is a type of dense ___________________ tissue.

2. The skeleton provides attachment surfaces for __________________.

3. The skeleton maintains ________________ homeostasis.

4. When mineral levels in the blood are too high, bones absorb some of the minerals and store them as mineral ___________________.

5. Bone matrix is crisscrossed by blood vessels and ___________________.

6. Osteoclasts dissolve minerals in bone ___________________.

7. Bone marrow is found inside the pores of ________________ bone.

8. Early in the development of a human fetus, the skeleton is made entirely of ______________________.

9. By birth, several areas of cartilage remain in the skeleton, including the ends of the ___________________ bones.

10. With the help of muscles, joints work like mechanical ___________________.

11. The surfaces of bones at joints are covered with a smooth layer of cartilage that reduces ___________________ at the points of contact between the bones.

12. Immovable joints allow no movement because the bones at these joints are held securely together by dense ___________________.

## Lesson 21.2: Critical Writing

Name___________________ Class______________ Date________

Thoroughly answer the question below. Use appropriate academic vocabulary and clear and complete sentences.

Describe the three types of bone problems.

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Date Created:
Feb 23, 2012