22) Bone form and Function

• • Bones are adapted to their function and vary in size, shape and structure
• Bones are classified by their structure:

  • Flat (membranous)
  • Long (endochondral) 
  • Mixed composition (eg scapular)
• Examples of membranous (flat) bones are:

  • Calvarial (top of skull)
  • Facial Bones
• During embryonic development Neural crest cells differentiate into:

  • neurones
  • pigment cells
  • muscles
  • calvarial bones (formed by osteoprogenitor cells)
• Appositional growth is when new bone tissue is added on top of existing bones (grow in width)
• 1. some neural crest cells transform into mesenchymal cells 
  2. These cells can condense and arregate at regions where bones develop. 

  ⤷ They then differentiate into osteoprogenitor cells

  3. Osteoprogenitor cells differentiate into osteoblasts, stimulating osteogenesis! (bone formation)
• Steps in bone growth:

  1. Proliferation
  2. Differentiation
  3. Osteoprogenitor
  4. Apoptosis
• Most long (endochondral bones) originate from somites

  somites ⟶ mesenchyme ⟶ Cartilage (BONES)
• What is Osstification?

  Process that transforms tissues into bones
• Differentiation steps in Endochondral ossification:

  1. Mesenchymal (Stem cell) condensation
  2. Formation of Chondrocytes
  3. Formation of Perichondrium
  4. Hypertrophy of chondrocytes
  5. Vascular invasion of cartilage
  6. Death of Chondrocytes + Replaced by bones formed by blood-derived osteoblasts

  
• In order for bone to form, blood and osteoblasts must enter 
• Joints form where two long bones meet, allowing movement between them.
• Growth is regulated by hormones and signalling, limiting or overproducing amounts lead to dwarfism
• 6 Types of Joints:

  1. Plane
  2. Saddle
  3. Hinge
  4. Pivot
  5. Ball and Socket
  6. Elipsoid
• Distruction of cartilage leads to osteoarthritis
• Bones can also be:

  • Compact (cortical)
  • Trabecular (Spongy or Cancellous)
  • Or composed of both
• Osteoblasts are bone-forming cells taht secrete bone matrix
• osteoclasts are cells that break down bone

  • This process is catabolic
• Functions of bones:

  • Weight bearing and protection
  • Articulation of joints
  • Hearing
  • Calcium ion homeostasis
  • Hematopoeisis
• Calcium plays a critical role in

  • Muscle contraction
  • Enzymatic reactions
  • Mitosis
  • Blood clotting
  • Cell signalling Pathways