14 - Bones & Skeletal Tissue

Question 1

What is the skeletal system composed of?

Answer 1

• bones
• cartilage
• joints
• ligaments

Question 2

What are the 3 types of cartilage & where are they found?

Answer 2

• Hyaline cartilage - everything else is hyaline
• Elastic cartilage - flexible, places start w/ E
  ○ Ex. External ear, epiglottis, Eustachian (auditory) tube
• Fibrocartilage - thick fibers, support
  ○ Ex. Pubic symphysis, in knee joint & intervertebral discs

Question 3

What are the 2 ways that cartilage grow?

Answer 3

• appositional - surface b/w existing cartilage & perichondrium, adds protuberance to surfaces
• interstitial - expand cartilage from within, chondrocytes divide & secrete matrix

Question 4

How does cartilage calcify?

Answer 4

• chondrocytes hypertrophy & secrete enzymes
• calcium phosphate is deposited & matrix crystalizes - no O2 can get through
• chondrocytes die (leaves spaces)
• calcified cartilage does not equal bone

Question 5

What are the 2 membranes of bones?

Answer 5

• periosteum - fibrous lyaer & osteogenic (cellular) layer
  
  • secured to underlying bone by Sharpey’s fibers
  • need to keep muscles attached
• endosteum - on internal surfaces of bone, contains osteogenic cells
  
  • constantly changing bone

Question 6

Describe the anatomy of Compact bone

Answer 6

• Haversian system (osteon) - structural unit
• Central (haversian) canal - contains blood vessels & nerves
• Lamellae - “tree trunks”, concentric rings, Interstitial lamellae & Circumferential lamellae
• Perforating (Volkmann’s) canals
• Lacunae - small cavities that contain osteocytes
• Canaliculi - hairlike canals that connect lacunae to each other and to the central canal - like holding hands

Question 7

Describe the anatomy of Spongey Bone

Answer 7

• have trabeculae - irregularly arranged lamellae, osteocytes & canacliculi
• No osteons
• capillaries in endosteum supply nutrients

Question 8

Describe the structure of short, irregular & flat bones

Answer 8

• like aero chocolate bar
• spongey bone covered by compact bone
• bone marrow b/w trabeculare
• hyaline cartilage covers articulation points

Question 9

Describe the structure of a Long bone

Answer 9

• Diaphysis (shaft)
  ○ Compact bone collar surrounds medullary cavity
  ○ Medullary cavity (adults) contains fat = yellow marrow
• Epiphyses (expanded ends)
  ○ Spongey bone interior (red marrow)
  ○ Epiphyseal line (aka metaphysis) is adult remnant of growth plate
  ○ Articular (hyaline) cartilage on joint surface
• NOTE: bone is vascularized

Question 10

What are the 5 organic cells of bone?

Answer 10

• osteogenic (osteoprogenitor) cells - stem cells
• osteoblast - synthesize osteoid
• ostocytes - mature bone cells in lacunae
• bone lining cells - mature cells on bone surfaces that maintain bone matrix
• osteoclasts - macrophages that break down bone matrix

Question 11

What is Osteoid?

Answer 11

• organic bone matrix secreted by osteoblasts
• ground susbtance, collagen fibers & calcium-binding proteins
• provides tensile strength & flexibility

Question 12

What is the Inorganic part of Bone?

Answer 12

• hydroxyapatites (mineral salts) -> mainly calcium phosphate

Question 13

What is Osteogenesis?

Answer 13

• bone tissue formation

Question 14

What are the 2 types of bone formation?

Answer 14

• Endochondral ossification - Bone forms by replacing hyaline cartilage model
• Intramembranous ossification - Bone develops from fibrous membrane

Question 15

What are the steps in Endochondral ossification?

Answer 15

1. fibroblasts differentiate to osteoblasts & lay down matrix, bone collar
2. chondrocytes in center hypertrophy, calcify matrix & die to develop cavities
3. blood supply of periosteal bud, osteoclasts erode cartilage, osteoblasts secrete osteoid
4. diaphysis elongates, sencondary ossification centers in epiphysis
5. epiphyses calcify, hyaline only in epiphyseal plates & articular cartilages

Question 16

What are the steps in Intramembranous Ossification?

Answer 16

1. ossification centers in fibrous CT membrane
2. osteoid secreted w/in membrane & calcifies
3. woven bone (trabeculae) & periosteum form
4. Lamellar bone replaces woven bone (just deep to periosteum) & red marrow appears

Question 17

What is Interstitial growth?

Answer 17

• increase length of long bones
• proliferation zone (epiphyseal size) -> Hypertonic zone -> Calcification zone -> Ossification zone (Diaphysis side)

Question 18

What is Appositional growth?

Answer 18

• increase thickness & remdelling of all bones by osteoblasts & osteoclasts on bone surfaces
• osteoclasts on endosteum break down bone
• increases shaft diameter while amount of bone stays same

Question 19

How osteoid calcifies

Answer 19

• proteins of osteoid bind Ca2+
• Osteoblasts release vesicles containing alkaline phosphatase
• Cuts phosphate ions off osteoid proteins, increase local [Pi]
• When [ ]’s of Ca2+ & Pi are high enough, calcium phosphate crystals form & encourage hydroxyapatite crystal formation

Question 20

What do osteoclasts secrete for bone resorption?

Answer 20

• Lysosomal enzymes - digest organic matrix
• Protons -> HCl -> converts calcium salts into soluble forms

Question 21

What are the 2 controls of Bone Remodelling?

Answer 21

• hormonal mechanisms - maintain blood Ca2+, if & when
• mechanical & gravitational forces - where

Question 22

What hormones regulate bone growth?

Answer 22

• GH - protein synthesis & cell growth
• Thyroid hormone (T3 & T4) - modulate activity of GH
• testosterone & estrogens - promote growth spurts

Question 23

When blood Ca2+ is low what happens?

Answer 23

• PTH released
• osteoclast activity increases, osteoblast activity decreases
• Ca2+ absorbed from intestine
• decrease in urinary Ca2+ excretion

Question 24

When blood Ca2+ level is high what happens?

Answer 24

• Calcitonin released
• osteoclast activity is inhibited
• inhibit Ca2+ reabsorption in kidneys

Question 25

What is Wolff’s law?

Answer 25

• A bone grows or remodels in response to forces or demands placed upon it
• Ex. Handedness, arm bones stronger in dominant hand

Question 26

How are fractures classified?

Answer 26

1. nondisplaced vs. displaced
2. complete vs. incomplete
3. compound (open) vs. simple (closed)

Question 27

What are the events in repair of a bone fracture?

Answer 27

1. formation of fracture hematoma
2. formation of internal callus & external callus
3. external callus replaced w/ bone
4. remodelling over time & completion of repair