Introduction to Bones

1
Introduction to Bones

• Chapter 6
• Biology 2121

2
Bone Tissue

• (1). Osseous Tissue
• Matrix
• 25 Collagen 25 Water 50 Mineral Salts
• (2). Mineral Salts
• Calcium phosphate calcium hydroxide
• hydroxyapatite
• (3). Cell Types
• Osteogenic
• Osteoblasts
• Osteocytes
• Osteoclasts

3
Bone Tissue

• Compact Bone
• Osteons
• Canals
• Volkmanns
• Haversian
• Lamellae
• Lacunae
• Canaliculi

4
Bone Tissue

• Spongy Bone
• Trabeculae
• Short, Flat , irregular bones
• Comparison with compact bone
• Weight
• Bone marrow
• Red bone marrow
• Hips , ribs, sternum, vertebrae, epiphysis of
  long bones
• Hematopoiesis in adults

5
Blood Supply

• (1). Arteries
• Periosteal
• Nutrient
• Metaphyseal
• Epiphyseal
• (2). Veins
• Nutrient
• Epiphyseal
• Metaphyseal
• Periosteal

6
General Structure of Bones Long Bones

• (1). Diaphysis
• (2). Epiphyses
• (3). Metaphyses
• Epiphyseal plate and line
• (4). Periosteum
• Sharpeys fibers
• (5). Medullary Cavity
• (6). Endosteum

7
Bone Formation

• Bone forms by a process called ossification or
  osteogenesis
• Embryo Mesenchymal stem cells
• Template Hyaline cartilage
• Types
• 1. Intramembranous ossification
• 2. Endochondral ossification

8
Intermembranous Formation
1. Development of Ossification Center
2. Calcification
9
Intramembranous Ossification
3. Trabeculae and Periosteum formation
4. Compact bone formation and appearance of Red
Marrow
10
Endochondrial Formation
1
2-3

• 2. Growth of the Cartilage Model
• Interstitial growth
• Appositional growth
• 3. Development of the primary ossification center
  
• Periosteum
• Periosteal Bud

• Development of the Cartilage Model
• Hyaline cartilage
• Perichondrium
• Bone Cavity and collar

11
5. Articular Cartilage formation - Epiphyseal
Plate
4 - 5

• 4. Development of the Medullary Cavity and
  Secondary Ossification Center
• Diaphysis
• Wall replaced by compact bone

12
Growth of Bone Length

• Growth of cartilage is downward from the
  epiphyseal plate Ossification chases cartilage
  growth!
• Zones
• 1. Resting (cartilage)
• 2. Proliferation growing cartilage
• 3. Hypertrophic
• Mature chondrocytes (enlarged)
• 4. Ossification
• Dead chondrocytes (calcified extracellular
  matrix)
• New bone forming

13
Growth in Thickness

• (1). Appositional Growth
• (2). Steps
• Osteoblasts secrete collagen and matrix
• Ridges fold and fuse forming a tunnel that
  encloses a BV
• Osteoblasts deposit bone and extracellular matrix
  forming lamellae
• Osteon forms with central haversian canal

14
Bone Remodeling

• (1). Bone continually renews itself throughout a
  lifetime
• (2). Bone resorption followed by bone deposition
• (3). Rate
• At any time, 5 of total bone mass remodeled
• Compact bone 4 per year
• Spongy bone 20 per year
• (4). Bones
• Distal Femur replaced every 4 months
• Shaft of Femur some parts not replaced

15
Bone Resorption

• (1). Multinucleated cells - move along a bone
  surface and dig resorption bays
• (2). Lysosomal enzymes digest the organic matrix
• (3). Hydrochloric acid makes calcium salts
  soluble
• (4). Broken down old matrix is released into the
  interstitial fluid and then into the blood
• Animation

16
Bone Deposit

• (1). Calcification front
• (a). formed between osteoid seam (unmineralized
  matrix) and older bone
• (2). Takes about 1 week before calcification of
  new bone takes place
• (3). Calcium and phosphate ions
• (a). crystals of hydroxyapatite form
• (4). Alkaline phosphatase (produced by
  osteoblasts)

17
Factors Affecting Bone Growth and Remodeling

• (1). Minerals
• Ca, P, F, Mg, Fe, Mn
• (2). Vitamins
• C collagen osteoblasts into osteocytes
• K and B12
• (3). Hormones
• Insulin growth factors (IGF) and HGH
• T3 and T4
• Androgens

18
Calcium Homeostasis

• (1). 99 calcium in body stored bone
• (2). Nerve and muscle cells depend on Ca
• Blood Clotting Enzymes
• (3). Levels in blood
• 9-11 mg/100ml
• (4). Role of PTH
• Bone resorption and kidneys
• (5). Role of Calcitonin

19
Homeostatic Disorders

• (1). Osteoporosis
• Bone resorption outpaces bone deposit
• Ca lost in urine, feces, sweat than absorbed
• Bone Mass declines
• Risks
• Estrogen declines osteoblast decline (females)
  decline in matrix
• Smoking low vitamin D alcohol
• (2). Rickets and Osteomalacia
• Ca salts not deposited in matrix caused by lack
  of Vitamin D
• Soft bones
• (3). Osteomyelitis
• (4). Osteoarthritis

20
Rickets and Pagets Disease
Rickets children
Pagets Osteomalacia (adult rickets)