Chapter 6: Bones

Question 1

What is skeletal cartilage?

Answer 1

It is made up of highly resilient, molded cartilage tissue consisting of mostly water. It contains no blood vessels or nerves.
The perichondrium is the layer of dense connective tissue surrounding the cartilage like a girdle. It helps cartilage resist outward expansion. Contains blood vessels for delivery of nutrients to cartilage.

Question 2

How do bones grow?

Answer 2

Appositional growth which entails the cartilage-forming cells that secrete against external face of existing cartilage. The new matrix is laid down on surface of the cartilage.

Interstitial growth is when chondrocytes within lacunae divide and secrete new matrix, expanding cartilage from within. The new matrix made within cartilage.

Question 3

What are the functions of bones?

Answer 3

1. Support: For body and soft organs
2. Protection: Protect brain, spinal cord, and vital organs.
3. Movement: The levers for muscle action.
4. Mineral and growth factor storage: Calcium and phosphorus, and growth factors reservoir.
   Blood cell formation
5. Hematopoiesis: occurs in red marrow cavities of certain bones.
6. Triglyceride (fat) storage: Fat, used for an energy source, is stored in bone cavities.
7. Hormone production: Osteocalcin secreted by bones helps to regulate insulin secretion, glucose levels, and metabolism.

Question 4

What are the five classifications of bone types?

Answer 4

1. Long bones: Longer than they are wide(humerous)
2. Short bones: Cube-shaped bones (in wrist and ankle)
3. Sesamoid bones: Form within tendons (patella) and vary in shape.
4. Flat bones: Thin, flat, slightly curved (Sternum, scapulae, ribs, most skull bones)
5. Irregular bones: complicated shapes(vertebrae and hip bones)

Question 5

Structurally what are bones made up of?

Answer 5

Bones have nervous tissue, cartilage, fibrous connective tissue, muscle cells, and epithelial cells in its blood vessels. They contain two levels of structure gross and
microscopic.

Question 6

What is spongy bone?

Answer 6

Made up of a honeycomb of small, needle-like or flat pieces of bone called trabeculae.

Question 7

What is compact bone?

Answer 7

Dense outer layer on every bone that appears smooth and solid.

Question 8

What do the short, flat, and irregular bones have in common structurally?

Answer 8

Consist of thin plates of spongy bone covered by compact bone. The periosteum covers outside of compact bone. The endosteum covers inside portion of compact bone. Bone marrow is scattered throughout spongy bone. Hyaline cartilage covers area of bone that is part of a movable joint.

Question 9

What are the structures of the long bone?

Answer 9

• All long bones have a shaft (diaphysis), bone ends (epiphyses), and membranes.
• Diaphysis: tubular shaft that forms long axis of bone
• Consists of compact bone surrounding central medullary cavity that is filled with yellow marrow
• Epiphyses: ends of long bones that consist of compact bone externally and spongy bone internally

Question 10

What are the two membranes of bone?

Answer 10

The periosteum and endosteum

Question 11

What is the periosteum?

Answer 11

A white, double-layered membrane that covers external surfaces.

Question 12

What is the fibrous layer?

Answer 12

An outer layer consisting of dense irregular connective tissue.

Question 13

What is osteogenic layer?

Answer 13

An inner layer bone and contains primitive osteogenic stem cells.

Question 14

Bones are anchoring points for ________ and _______.

Answer 14

Tendons; ligaments

Question 15

Where is red bone marrow found?

Answer 15

Red marrow is found within trabecular cavities of spongy bone. In adults, red marrow is located in heads of femur and humerus. It is the most active areas like flat bones and some irregular bones (such as the hip bone).

Question 16

What are the four major cells of bones?

Answer 16

1. Osteogenic cells
2. Osteoblasts
3. Osteocytes
4. Osteoclasts

Question 17

What are osteogenic cells?

Answer 17

The active stem cells in periosteum and endosteum. When stimulated, they differentiate into osteoblasts or bone-lining cells. Some of them remain as osteogenic stem cells.

Question 18

What are osteoblasts?

Answer 18

Bone-forming cells that secrete unmineralized bone matrix called osteoid. An osteoid is made up of collagen and calcium-binding proteins.

Question 19

What are osteocytes?

Answer 19

Mature bone cells in lacunae that no longer divide. They maintain bone matrix and act as stress or strain sensors. They also respond to mechanical stimuli such as increased force on bone or weightlessness.

Question 20

What are osteoclasts?

Answer 20

Derived from same hematopoietic stem cells that become macrophages. When active, cells are located in depressions and perform bone resorption. Also helps seal off area from surrounding matrix.

Question 21

Flat Bones Consist of a Layer of ___________ Sandwiched between two thin Layers of _________.

Answer 21

Spongy bone; compact bone

Question 22

What is ossification?

Answer 22

The process of bone tissue formation. Formation of bony skeleton begins in month 2 of development, and postnatal bone growth occurs until early adulthood. Bone remodeling and repair are lifelong process.

Question 23

What is endochondral ossification?

Answer 23

When bones form by replacing hyaline cartilage. They are referred to as cartilage bones and form most of the skeleton. Forms essentially all bones inferior to base of skull, except clavicles. Begins late in month 2 of development and starts at primary ossification center in center of the shaft.

Question 24

What is intramembranous ossification?

Answer 24

When bones form from a fibrous membrane. These bones are referred to as membrane bones.

Question 25

What are the main steps of endochondral ossification?

Answer 25

1: Bone collar forms around diaphysis of cartilage model.
2: Central cartilage in diaphysis calcifies, then develops cavities.
3: Periosteal bud invades cavities, leading to formation of spongy bone. Bud is made up of blood vessels, nerves, red marrow, osteogenic cells, and osteoclasts.
4: Diaphysis elongates, and medullary cavity forms
Then Secondary ossification centers appear in epiphyses.
5: Epiphyses ossify
Lastly, Hyaline cartilage remains only in epiphyseal plates and articular cartilages.

Question 26

What are the main steps of intramembranous ossification?

Answer 26

It begins within fibrous connective tissue membranes formed by mescenchymal cells. It forms the bones of the skull and the clavicles.

1. Ossification centers are formed when mescenchymal cells cluster and become osteoblasts.
2. Osteoid is secreted and then calcified.
3. Woven bone is created when osteiod is laid down around the blood vessels resulting in trabeculae.
4. Lamellar bone replaces woven bone and then red bone marrow appears.

Question 27

What happens for postnatal bone growth?

Answer 27

• Long bones grow lengthwise by interstitial (longitudinal) growth of epiphyseal plate.
• Bones increase thickness through appositional growth.
• Bones stop growing during adolescence
• Some facial bones continue to grow slowly through life

Question 28

What are the steps to long bone epiphyseal plate growth?

Answer 28

1. Resting (quiescent) zone: Area of cartilage on epiphyseal side of epiphyseal plate that is relatively inactive.
2. Proliferation (growth) zone: New cells formed move upward, pushing epiphysis away from diaphysis, causing lengthening.
3. Hypertrophic zone: Cartilage lacunae enlarge and erode, forming interconnecting spaces.
4. Calcification zone: Surrounding cartilage matrix calcifies; chondrocytes die and deteriorate.
5. Ossification (osteogenic) zone: Ultimately replaced with spongy bone and medullary cavity enlarges as spicules are eroded.

Question 29

What is bone remodeling?

Answer 29

• Bone remodeling consists of both bone deposit and bone resorption.
• Occurs at surfaces of both periosteum and endosteum.
• Remodeling units: packets of adjacent osteoblasts and osteoclasts coordinate remodeling process.

Question 30

What is bone resorption?

Answer 30

• Osteoclasts also phagocytize, emineralized matrix and dead osteocytes.
• Osteoclast activation involves PTH (parathyroid hormone) and immune T cell proteins.

Question 31

What is bone deposit?

Answer 31

• New bone matrix is deposited by osteoblasts.
• Osteoid seam: band of unmineralized bone matrix that marks area of new matrix.
• Calcification front: abrupt transition zone between osteoid seam and older mineralized bone.
• Mechanical signals for increased concentrations of calcium and phosphate ions for hydroxyapatite formation.
• Matrix proteins bind and concentrate calcium for the appropriate amount of enzyme alkaline phosphatase for mineralization.

Question 32

Why do bones remodel?

Answer 32

1. Hormonal controls
2. Negative feedback loop that controls blood Ca2+ levels
3. Calcium functions in many processes, such as nerve transmission, muscle contraction, blood coagulation, gland/nerve secretions, and cell division.
4. Parathyroid hormone (PTH): produced by parathyroid glands in response to low blood calcium levels. Stimulates osteoclasts to resorb bone. PTH secretion stops when homeostatic calcium levels are reached.
5. Calcitonin: produced in the thyroid gland in response to high levels of blood calcium levels.
6. Leptin: hormone released by adipose tissue may play role in bone density regulation by inhibiting osteoblasts.
7. Serotonin: neurotransmitter regulates mood and sleep; also interferes with osteoblast activity.

Question 33

What are the different types of bone fractures?

Answer 33

Position of bone ends after fracture..

1. Nondisplaced: ends retain normal position
2. Displaced: ends are out of normal alignment

Completeness of break..

1. Complete: broken all the way through
2. Incomplete: not broken all the way through

Whether skin is penetrated..

1. Open (compound): skin is penetrated
2. Closed (simple): skin is not penetrated