Chapter 7 - Skeletal System

Question 1

Bone Classification by Shape

Answer 1

• Long bones: long longitudinal axes and expanded ends
• Short bones: equal lengths and widths
  ○ Sesamoid is a special type
• Flat bones: platelike structures with broad surfaces
• Irregular bones: a variety of shapes mostly connected to several other bones

Question 2

2 Types of Bone in a Long Bone

Answer 2

• Compact bone: dense bone tissue which cells are organized into osteons
• Spongy bone: bone consisting of bars and plates(trabeculae) separated by space

Question 3

Parts of a Long Bone

Answer 3

• Epiphysis: expanded end made of spongy bone
  
  • Diaphysis: shaft which is composed of compact bone
  • Metaphysis: between diaphysis and epiphysis
  • Articular cartilage: covers epiphysis
  • Periosteum: covers the bone
  • Medullary cavity; hollow cavity in the diaphysis
  • Endosteum: lines the medullar cavity
    Bone marrow: red or yellow which lies in the
    
    • medullary cavity or in spongy bone spaces

Question 4

Bone Structure

Answer 4

• Osteocytes: mature bone cells
  
  • Lacuna: chambers occupied by osteocytes
  • Canaliculi: tiny passageways through which cell processes of osteocytes exchange nutrients and wastes
  • Bone matrix is collagen fibers which makes it resilient and inorganic salts(calcium, phosphorous, magnesium) which hardens it

Question 5

Structure of Compact Bone

Answer 5

• composed of osteons which are osteocytes surrounded by lamellae
  ○ Function as weight bearing pillars which resist compression
  ○ Central canal contains blood vessels and nerves
  - Perforating canals line horizontal to join adjacent canals

Question 6

Osteocytes, Osteoblasts, Osteoclasts

Answer 6

• Osteocytes: mature bone cells that maintain the bony matrix
• Osteoblasts: build or secrete bony matrix around themselves which turns them eventually into osteocytes as part of bone remodeling
• Osteoclasts: break down bone matrix as part of bone remodeling
  
  • Release minerals stored in bones when they break it down

Question 7

structure of Spongy Bone

Answer 7

• Composed of osteocytes and ECM which lie in the trabeculae; thin columns of bone
• Get nutrients from substances diffusing into the canaliculi that lead to the surface

Question 8

Blood Cell Formation

Answer 8

• Hematopoiesis is the process of blood cell formation which begins in the yolk sac which is outside the embryo
  
  • Later its developed in the liver and spleen
  • After maturation its formed in bone marrow

Question 9

Bone Marrow and the 2 types

Answer 9

A soft like mass of connective tissue
- Composed of red marrow which forms red and white blood cells as well as blood platelets
- Yellow marrow stores fat and replaces red marrow as someone ages

Question 10

Function of Bone: inorganic salt storage

Answer 10

• Salts account for over 70% of the ECM
  ○ are mostly hydroxyapatite; types of calcium phosphate
  ○ Magnesium ions
  ○ Sodium ions
  ○ Potassium ions
  - Carbonate ions

Question 11

Regulation of Calcium

Answer 11

• When calcium is low, detected by parathyroid cells which releases parathyroid hormone to stimulate osteoclasts to break down bone tissue in order to release calcium salts into the blood
• When there is high blood calcium, thyroid cells detect the change and secrete calcitonin which stimulates osteoblasts to form bone tissue and inhibits osteoclast activity

Question 12

Types of Bone Development

Answer 12

• Intramembranous bones: originate within sheetlike layers of connective tissue
  ○ Occurs for flat, clavicles, sternum and some facial bones
  • Endochondral bones: originate as a mass of hyaline cartilage which is later replaced by bone tissue called endochondral bones
    Occurs for long bones and most of the skeleton inferior to the skull

Question 13

Intramembranous Bones

Answer 13

• Skull
  
  • Clavicle
  • Sternum
    
    • Facial bones like mandible, maxillae, zygomatic bones

Question 14

Process of Intramembranous Ossification

Answer 14

• During osteogenesis, mesenchyme; layers of embryonic connective tissue, appear at the site of future bones
  
  • Mesenchymal cells within enlarge and differentiate into osteoblasts
  • These began to form bony matrix around themselves
  • Dense networks of blood vessels supply these connective tissues
  • Osteoblasts then become completely surrounded by ECM and secluded within lacunae forming osteocytes
  • ECM encloses the osteoblasts which gives rise to canaliculi
    Mesenchyme on the outside of the bones form the periosteum

Question 15

Endochondral Bones

Answer 15

• Begin as hyaline cartilage
• All bones of skeleton besides carpals and tarsals

Question 16

Process of Endochondral Ossification

Answer 16

• Chondrocytes enlarge and the lacunae grow
• The ECM breaks down and the chondrocytes die which allows osteoblasts to invade the area and deposit bone matrix
• They form spongy bone first and then compact bone until they are encased and become osteocytes

Question 17

Endochondral Long Bone Ossification

Answer 17

• areas in the center of diaphysis is the primary ossification center which is where bone tissue first replaces the cartilage
• Bone tissue replacement starts from there and moves towards the ends of the bone
• Osteoblasts from the periosteum deposit the compact bone around the primary ossification center
• Secondary ossification centers develop in the epiphyses and produce spongy bone in all directions from it
• As spongy bone is deposited in the diaphysis and the epiphysis, a epiphyseal plate separates the two ossification centers

Question 18

Homeostasis of Bone Tissue

Answer 18

Bone Remodeling: the re-shapement or remodeling of bones by osteoblasts and osteoclasts which occurs throughout life
- (10-20% of skeleton replaced each year)

• Bone resorption: removal of bone by osteoclasts
• Bone deposition: formation of bone by osteoblasts

Question 19

Fracture Classification: Cause

Answer 19

• Traumatic: fracture caused by injury
• Spontaneous or pathologic: fracture caused by disease

Question 20

Fracture Classification: nature of wound

Answer 20

• simple is closed where the fracture is protected by uninjured skin
• Compound is open where the fracture is exposed to the outside through an opening in the skin

Question 21

Types of Fractures(6)

Answer 21

• Greenstick: incomplete break on the convex surface of the bend in the bone
• Fissured: incomplete longitudinal break
• Comminuted: complete and fragments the bone
• Transverse: complete and break occurs at a right angle to the axis of the bone
• Oblique: complete break which occurs at an angle other than a right angle
• Spiral: caused by excessive twisting of a bone

Question 22

Steps in Fracture Repair

Answer 22

• Hematoma: large blood clot forms right after the fracture
• Cartilaginous(soft) callus: osteoblasts invade and produce spongy bone, phagocytes remove debris and fibrocartilage is produced
• Bony(hard) callus: cartilaginous callus breaks down and osteoblasts invade filling it with hard callus
• Bone remodeling: bone restored close to original shape and osteoclasts remove excess bone

Question 23

Fragility Fractures

Answer 23

fracture occurring after a fall from less than standing height

• During bone remodeling, osteoclasts remove more bone than osteoblasts deposit
• Signs of low bone density; osteoporosis
• Elderly people are vulnerable to osteoporosis

Question 24

Prevention of Fragility Fractures

Answer 24

• Get 30 mins of exercise per day, including weight bearing exercise
• Get enough calcium and Vitamin D
  Do not smoke or drink alcohol

Question 25

Factors Affecting bone development, growth and repair

Answer 25

• Vitamin D: calcium absorption
• Vitamin A: osteoblast and clast activity
• Vitamin C: collagen synthesis
• Growth hormone: stimulates cartilage cell deficiency
• Calcitonin hormone: causes replacement of cartilage in epiphyseal plates
• Parathyroid hormone: stimulates osteoclast and the breakdown of bone
• Sex hormones(testosterone and estrogen): promote bone formation
  
  • Estrogen is more effective
    Physical stress: stimulates bone growth