Chapter 7 Bone Tissue

1
Chapter 7Bone Tissue

• Dynamic tissue that continually remodels itself
• Bone
• connective tissue with a matrix hardened by
  minerals
• bones make up the skeletal system
• Functions of the skeletal system
• support, protection, movement, blood formation,
  mineral reservoir

2
Shapes of Bones
3
Structure of a Long Bone

• Parts of a long bone are the
• Epiphyses (ends)
• Diaphysis (shaft)
• Medullary (marrow) cavity
• Endosteum - contains osteoprogenitor cells
• Periosteum - membrane around the bone
• fibrous layer
• osteogenic layer
• Articular cartilage - hyaline cartilage covers
  the surface of joints

4
HISTOLOGY OF BONE

• Bone consists of widely separated cells
  surrounded by large amounts of matrix
• Four principal types of cells
• 1. osteoprogenitor cells - unspecialized can
  divide
• 2. osteoblasts - form bone, secrete collagen
• 3. osteocytes former osteoblasts, strain
  sensors that detect stress in the bone and talk
  to osteoblasts on the bone surface
• 4. osteoclasts - reabsorb bone

5
BONE HISTOLOGY (cont.)

• Matrix contains some calcium carbonate, calcium
  phosphate but mostly hydroxyapatite, which is the
  PRIMARY salt that makes bone hard.
• Matrix is deposited in a framework of collagen
  fibers, - calcification or mineralization
• salts confer hardness on bone
• collagen fibers give tensile strength
• Matrix (Bone) composition 25 water,
  25 protein fibers and 50 minerals

6
Compact Bone

• Bone may be categorized as compact or spongy
• Dense bone tissue consists of osteons (Haversian
  systems) basic structural unit
• cylinders of tissue formed from layers (lamellae)
  
• central canal holding a blood vessel
• osteocytes connected to each other and by tiny
  canals called canaliculi

7
Histology of Compact Bone
8
Blood Vessels of Compact Bone
9
Spongy Bone

• Spongelike appearance called trabeculae
• spaces filled with red bone marrow
• Provides strength with little weight
• trabeculae develop along bones lines of stress
• Spongy bone have few osteons, why?

10
Spongy Bone Structure and Stress
11
Primary Ossification Center Marrow Space

• A process called ossification (osteogenesis)
  forms skeleton of embryo
• cells differentiate into osteoblasts and
  osteoclasts
• Begins during the 6 or 7 th week of embryonic
  life and continues throughout adulthood

12
Metaphysis Secondary Ossification Center

• Metaphysis is cartilagenous material that remains
  as growth plate between medullary cavity
  secondary ossification centers in the epiphyses.

13
The Fetal Skeleton at 12 Weeks
14
Epiphyseal PlatesFuse in Adults
15
Bone Growth and Remodeling

• Grow and remodel themselves throughout life
• athletes or history of manual labor have greater
  density mass of bone
• Most bone is formed by Endochondral ossification
  (IN- outward)
• Step 1 Cartilage forms
• Step 2 Cartilage grows
• Step 3 Bone replaces the cartilage from the
  inside center outward.

16
Hormonal Bone Growth

• Hormonal Regulation of Bone Growth
• Human Growth Hormone (GH) stimulate bone
  deposition, in addition to thyroid hormone,
  parathyroid hormone, and calcitonin
• variation of these hormones can lead to either
  gigantism or dwarfism
• At puberty the sex hormones stimulate sudden
  growth and modify the skeleton
• thyroid hormone - promotes growth and maturity
• calcitonin - thyroid gland - promotes bone
  formation, inhibits osteoclast activity
• parathyroid hormone - promotes bone resorption,
  increase activity of osteoclasts

17
Mineral Resorption

• Bone is the major reservoir for calcium (Ca)
• Blood level of calcium ions is very important in
  cardiac, nerve, enzyme, blood
• If blood levels get to low, the body will pull
  from the bones

18
BONE HOMEOSTASIS

• Remodeling
• Replacement of old bone tissue with new bone
  tissue
• Destroyed by osteoclasts (clubbed) and is
  constructed by osteoblasts (built)
• Increased _____ activity/ decreased _____
  activity causes bone loss
• Increased _____ activity/ decreased _____
  activity causes bone creation

19
Example of Bone Remodeling

• Dental braces reposition teeth, creating greater
  pressure on the bone on one side of the tooth and
  less on the other side
• increased pressure stimulates osteoclasts
  decreased pressure stimulates osteoblasts to
  remodel jaw bone

20
Fractures

• Stress fracture is a break caused by abnormal
  trauma to a bone
• car accident, fall, athletics, etc
• Pathological fracture is a break in a bone
  weakened by some other disease
• bone cancer or osteoporosis

21
Types of Bone Fractures (Table 7.3)
22
Healing of Fractures

• Normally healing takes 8 - 12 weeks (longer in
  elderly)
• Stages of healing
• fracture hematoma (1)
• granulation tissue (2)
• callus formation (3)
• remodeling (4) occurs over next 6 months
• Electrical stimulation is used on fractures that
  take longer than 2 months to heal
• Silica- Horsetail herb, repairs fractures

23
Healing of Fractures
1 2
3 4
24
Fracture and Repair
25
Bone Diseases

• Abnormal softness of the bones is called rickets
  in children and osteomalacia in adults
• Paget's disease massive osteoclastic resorption
  and extensive bone formation
• Osteoporosis most common bone disease
• Bones lose mass become brittle
• risk of fracture of hip, wrist vertebral column
• lead to fatal complications such as pneumonia,
  why?
• widows (dowagers) hump is deformed spine
• Best treatment is prevention -- exercise
  calcium intake (1,500 mg/day) while young old

26
Effects of OsteoporosisLumbar Normal
Abnormal
27
Nutrition for good bones

• Vitamins
• A - controls activity of osteoblasts and
  osteoclasts, rarely toxic in high dosage
• D - promotes removal of Calcium from the bone
  (1,500 mg maximum)
• C - maintains the matrix
• Minerals
• calcium and phosphorus - make matrix hard
• magnesium - deficiency inhibits osteoblast
• manganese - inhibit formation of new bone,
  supports ligaments (Boneless chickens)

28
EXERCISE AND BONE

• Response to mechanical stress increases
  deposition of mineral salts and production of
  collagen fibers (aids osteoporosis)
• Removal of mechanical stress weakens bone through
  demineralization
• Weight-bearing activities help build and retain
  bone mass