Normal Tissues

Anatomy

Bone

  • Organic phase mainly type I collagen, with proteoglycans, osteocalcin and osteonectin
  • Hydroxyapatite gives compressive strength, collagen gives tensile strength
  • Osteoblasts (mesenchymal origin) form osteoid
  • Osteocytes sense load within lacunae linked by canaliculi
  • Osteoclasts (haematopoietic origin) resorb bone in Howship lacunae
  • Cortical bone forms osteons around Haversian canals
  • Cancellous bone is trabecular with higher turnover
  • Woven bone is immature and disorganised, lamellar bone mature and stress oriented

Articular cartilage

  • No blood vessels, nerves or lymphatics, nourished by diffusion from synovial fluid
  • Type II collagen and aggrecan, whose charged glycosaminoglycans attract water and resist compression
  • Superficial zone collagen parallel to the surface, resisting shear
  • Middle zone collagen oblique
  • Deep zone collagen perpendicular, with the highest proteoglycan content
  • Tidemark and calcified cartilage anchor to subchondral bone

Meniscus

  • Fibrocartilage, mainly type I collagen
  • Circumferential fibres resist hoop stress, radial tie fibres resist longitudinal splitting
  • Peripheral portion vascular from the perimeniscal plexus, inner portion avascular

Tendon

  • Type I collagen in fibrils, fibres and fascicles with aligned tenocytes
  • Surrounded by paratenon or a synovial sheath
  • Direct insertion through four zone fibrocartilage, or indirect via Sharpey fibres

Ligament

  • More type III collagen and elastin than tendon, with less regular fibres
  • Mechanoreceptors contribute to proprioception

Skeletal muscle

  • Multinucleated fibres wrapped by endomysium, perimysium and epimysium
  • Sarcomere between Z lines, with thin actin and thick myosin filaments
  • Calcium from sarcoplasmic reticulum binds troponin, exposing actin binding sites
  • Type I fibres slow twitch and oxidative for endurance
  • Type II fibres fast twitch and glycolytic for power

Peripheral nerve

  • Endoneurium surrounds axons, perineurium fascicles and epineurium the nerve
  • Schwann cell myelin allows saltatory conduction between nodes of Ranvier

Pathology

Normal Tissues, histology of the zones of articular cartilage
Histology of the zones of articular cartilage. Image by Catherine A. Bautista, Hee Jun Park, Courtney M. Mazur, Roy K. Aaron, Bahar Bilgen, Wikimedia Commons, CC0.
  • Tendon heals through inflammatory, proliferative and remodelling phases, never regaining full strength
  • Ligaments fail at insertions in children and in midsubstance in adults
  • Seddon classifies nerve injury as neurapraxia, axonotmesis and neurotmesis
  • Wallerian degeneration occurs distally, with regeneration at about 1 mm per day

Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.