Chapter 6

Question 1

Hyaline cartilage

Answer 1

• Provide support with flexibility and resilience
• Most abundant; made of collagen fibers
• Includes: Articular cartilages (at ends of bones), Costal cartilages (connect ribs to sternum), Respiratory cartilages (larynx and respiratory passageways), Nasal Cartilages (support external nose)

Question 2

Elastic cartilage

Answer 2

• Resemble hyaline cartilages, but contain more elastic fibers
• Able to stand up to repeated bending
• Ear and epiglottis

Question 3

Fibrocartilage

Answer 3

• Highly compressible with great tensile strength
• Parallel rows of chondrocytes alternating with thick collagen fibers
• Menisci of the knee and discs between vertebrae

Question 4

Explain how cartilage grows

Answer 4

• Appositional growth: New matrix secreted from the perichondrium against the external face of the existing cartilage tissue
• Interstitial growth: Chondrocytes in lacunae divide and secrete new matrix, expanding cartilage from within

Question 5

Axial skeleton

Answer 5

Forms the long axis of the body

-Bones of skull, vertebral column, and rib cage

Question 6

Appendicular skeleton

Answer 6

Consists of the bones of the upper and lower limbs and the girdles (shoulder and hip bones)

Question 7

Long bones

Answer 7

• Longer than they are wide
• Shaft plus two expanded ends
• All limb bones expect the patella, wrist, and ankle are long bones

Question 8

Short bones

Answer 8

• Roughly cube shaped
• Wrist and ankle
• Sesamoid bones: special type of short bone formed in a tendon (patella)

Question 9

Flat bone

Answer 9

• Thin, flattened, and usually a bit curved

- Sternum, scapulae, ribs, most skull bones

Question 10

Irregular bones

Answer 10

• Complicated shapes that fit none of the other classes

- Vertebrae and hip bones

Question 11

Functions of bones

Answer 11

• Support: framework, cradle organs
• Protection: surround important features
• Movement: skeletal muscles use bones as levels to move body
• Mineral and growth factor storage: reservoir for minerals, stores important growth factors
• Blood cell formation: (hematopoiesis) occurs in red marrow of certain bones
• Hormone production: osteoclacin

Question 12

Gross anatomy of a flat bone

Answer 12

• Thin plates of spongy bone covered by compact bone
• Covered outside by periosteum and inside by endosteum
• No shaft of epiphyses
• Bone marrow, but no marrow cavity
• Covered by hyaline cartilage where they form moveable joints

Question 13

Gross anatomy of a long bone

Answer 13

• Diaphysis (shaft): long axis of bone, collar of compact bone, medullary cavity, and yellow marrow cavity
• Epiphyses (bone ends): outer shell of compact bone, interior contains spongy bone; articular (hyaline) cartilage covers joint surface; epiphyseal line (remnant of epiphyseal plate which lengthens the bone) or metaphysis
• Membranes:
  
  • Periosteum covers the external surface of the entire bone except joint surfaces–outer fibrous layer (dense irregular connective tissue) and inner osteogenic layer (primitive stem cells)–richly supplied with nerve fibers and blood vessels–perforating (Sharpey’s) fibers secure periosteum to bone
  • Endosteum covers internal bone surfaces–trabeculae of spongy and canals of compact bone

Question 14

Red marrow

Answer 14

Typically found in trabecular cavities of spongy bone in long bones and diploe of flat bones–red marrow cavities

Question 15

Yellow marrow

Answer 15

Found in the medullary cavity, can convert to red blood cells

Question 16

Function of bone markings

Answer 16

Serve as sites of muscle, ligament, and tendon attachment, as joint surfaces, or as conduits for blood vessels and nerves

Question 17

Histology of compact bone

Answer 17

• Osteon (Haversian system): structural unit of compact bone, group of hollow tubes of bone matrix; each matrix tube is a called a lamella and contains collagen fibers
• Canals and canaliculi: Central or Haversian canal runs through the core of each osteon; Perforating Volksmann’s canals connect blood and nerve supply of medullary cavity to central canals; Osteocytes in lacunae; Canaliculi connect lacunae to each other and the central canal
• Interstitial and Circumferential lamellae: interstitial lie between intact osteons and incomplete lamellae, fill gaps or remnant of osteons; circumferential resist twisting of long bone

Question 18

Histology of spongy bone

Answer 18

Trabeculae with irregularly arranged lamellae and osteocytes interconnected by canaliculi; no osteons are present

Question 19

Chemical composition of bone

Answer 19

Organic components: bone cells and osteoid (ground substance and collagen fibers)
Inorganic components: mineral salts, which account for hardness and resistance to compression

Question 20

Osteogenic cells

Answer 20

• Mitotically active stem cells found in the periosteum and endosteum
• Can differentiate into other cells

Question 21

Osteoblasts

Answer 21

• Bone forming cells that secrete the bone matrix
• Actively mitotic
• Includes collagen and calcium-binding proteins to make up osteoid
• Play a role in matrix calcification

Question 22

Osteocytes

Answer 22

• Mature bone cells in lacunae

- Monitor and maintain bone matrix, act as stress or strain sensors, and respond to mechanical stimuli

Question 23

Bone lining cells

Answer 23

• Flat cells found on bone surfaces where bone remodeling is not going on
• Help maintain matrix
• External surface: periosteal cells
• Internal surface: endosteal cells

Question 24

Osteoclasts

Answer 24

• Giant, multinucleate cells located at sites of bone resorption
• Located in resorption bay with ruffled border, which increase surface area for enzymatically degrading the bones

Question 25

Intramembranous ossification

Answer 25

• Develops from fibrous membrane and the bone is called a membrane bone
  1. Ossification centers appear in the fibrous connective tissue membrane
  2. Osteoid secreted within the fibrous membrane and calcifies
  3. Woven bone and periosteum form
  4. Lamellar bone replaces woven bone and red marrow appears

Question 26

Endochondral ossification

Answer 26

• Develops by replacing hyaline cartilage and the resulting bone is called a cartilage, or endochondral, bone
  1. Bone collar forms around the diaphysis of the hyaline cartilage model
  2. Cartilage in the center of the diaphysis calcifies and then develops cavities
  3. The periosteal bud invades the internal cavities and spongy bone forms
  4. The diaphysis elongates and a medullary cavity forms
  5. Epiphyses ossify

Question 27

Process of long bone growth

Answer 27

• Occurs at the epiphyseal plate
• Side facing epiphysis contains resting cartilage cells
• Area proximal to the resting cartilage is arranged in four zones: proliferation, hypertrophic, calcification, and ossification (region of earliest stage of growth to region where bone is replacing cartilage)

Question 28

Remodeling functions of osteoblasts

Answer 28

In bone deposit, the osteoid seam marks areas of new matrix deposits by osteoblasts

Question 29

Remodeling functions of osteocytes

Answer 29

Packets of adjacent osteoblasts and osteoclasts called remodeling units coordinate bone remodeling

Question 30

Remodeling functions of osteoclasts

Answer 30

In bone resorption, they move along a bone surface, digging depressions or grooves as they break down the bone matrix

Question 31

How do hormones and physical stress regulate bone remodeling?

Answer 31

Hormones: parathyriod hormone (PTH), when levels of calcium decline, PTH stimulates osteoclasts to resorb bone and release calcium into blood
Mechanical stress: bone grows or remodels in response to the demands placed on it

Question 32

Steps of fracture repair

Answer 32

1. Hematoma forms
2. Fibrocartilaginous callus forms
3. Bony callus forms
4. Bone remodeling occurs

Question 33

Osteoporosis

Answer 33

Refers to a group of diseases in which bone resorption outpaces bone deposit, sex hormones help maintain health and normal density of the skeleton; can be treated with calcium, vitamin D supplements, exercise, and hormone replacement therapy

Question 34

Osteomalacia

Answer 34

Includes a number of disorders in which the bones are poorly mineralized; osteiod produced, but calcium slats are not adequately deposited
-Rickets is the analogous disease in children

Question 35

Paget’s disease

Answer 35

Characterized by excessive and haphazard bone deposit and resorption; bone is hastily made and has a abnormally high ration of spongy to compact bone

Question 36

Development of bone throughout life

Answer 36

• At birth: well ossified bones except epiphyses
• After birth: secondary ossification centers develop
• Bone formation exceeds bone resorption in children and adolescents
• Young adults: nearly all bones ossified, skeletal growth ceases, formation and resorption are in balance
• Old age: resorption predominates