The Skeletal System:Macro and Micro Anatomy

I. Macroanatomy of the Human Skeleton

A. Classification: according to shape and type of osseous tissue:

  1. Shape: long, short, flat, and irregular Diagram
  2. Type: compact (dense, smooth, and homogenous) and spongy

B. Bone Surface Markings (Depressions and Processes or Projections) Diagram

  1. Depressions: (Openings allowing blood vessels and nerves to pass)
    1. Fissure - narrow, slitlike opening
    2. Foramen - round or oval opening through the bone
    3. Fossa - shallow and may serve as an articular surface
    4. Sulcus/meatus/canal - canal-like passageway
    5. Groove - furrow
  2. Processes: (Site of muscle and ligament attachment)
    1. Tuberosity - large rounded projection
    2. Crest - narrow ridge of bone
    3. Trochanter - very large, blunt, irregulary shaped process
    4. Line - narrow ridges of bone; less prominent than crest
    5. Tubercle - small rounded projection
    6. Epicondyle - raised area above a condyle
    7. Spine - sharp, slender, often pointed
  3. Processes: (Forms joints)
    1. Head - bony expansion carried on a narrow neck
    2. Facet - smooth and nearly flat articular surface
    3. Condyle - rounded articular projection
    4. Ramus - armlike bar of a bone

C. Axial and Appendicular Skeleton

  1. Axial skeleton (80) - Skull, Thoracic Cage, and Vertebral Column
      • Cranium (8): occipital (1), parietal (2), frontal (1), temporal (2), sphenoid (1), and ethmoid (1)
        • Sutures: coronal, sagittal, lambdoid, squamous
      • Fascial (14): nasal (2), zygomatic (2), maxilla (2), palatine (2), lacrimal (2), inferior concha (2), vomer (1), and mandible (1)
      • Auditory Ossicles (6)
      • Hyoid Bone (1)
    2. Thoracic Cage (25): RIBS AND STERNUM
      • Sternum (1)
      • Ribs (24): True (14), False (6), and Floating (4)
      • Vertebrae (24): Cervical (7), Thoracic (12), and Lumbar (5)
      • Sacrum (1)
      • Coccyx (1)
  2. Appendicular skeleton (126) - Arms, Legs, Pectoral Girdle, and Pelvic Girdle

II. Microanatomy of the Human Skeleton

A. Bone and Bone Structure Diagram

  1. Functions
    1. Support
    2. Protection
    3. Movement
    4. Storage (Fat and Calcium)
    5. Hematopoeisis
  2. Gross Anatomy of Long Bones:
    1. Diaphysis
    2. Proximal epiphysis and distal epiphysis
    3. Medullary cavity
    4. Endosteum
    5. Periosteum.
    6. Articular cartilage.
  3. Short, irregular, and flat bones
    1. Consist of thin plates of periosteum
    2. Perisoteum covered compact bone on the outside
    3. Endosteum covers spongy bone within.
  4. Hematopoietic tissue (red marrow) is located within the cavities of spongy bone of long bones and in the diploe of flat bones.
  5. NOTE: Newborns/infants have mostly red marrow in their medullary cavities but it is replaced with fat or yellow marrow as they age. Red marrow also can be found in the epiphysis of diploe flat bones (sternum) as well as in hip (irregular) bones. The yellow marrow may revert back to red under certain conditions (ex: anemia).

B. Microscopic Structure of the Bone Diagram Diagram

  1. Compact bone is made up of many structural units called osteons (haversian system)
  2. An osteon is an elongated cylinder orientated along the axis of the bone and made up of concentric circles of bone matrix (lamella)
  3. Running through the central core of the osteon is the haversian canal which contains nerve fibers and blood vessels.
  4. The canals running at right angles to the long axis of the bone and connecting vascular and nerve supplies of periosteum to those in haversian canals and medullary cavities is called volkman's canals
  5. Spider-shaped osteocytes (mature bone cells) lie in spaces (lacunae) and hair- like canals (canaliculi) connect the lacunae to each other and to the central canal.
  6. Between intact osteons lie incomplete lamellae called interstitial lamellae which fills gaps between forming or remodeling osteons. Lamellae that lie just deep to the periosteum and extend around the bone are called circumferential lamellae.

C. Composition:

  1. Organic components
  2. Inorganic components

D. Osteogenesis (ossification)

  1. Overview:
  2. Intramembranous Ossification: Diagram
  3. Endochondral Ossification: Diagram

E. Bone Growth: DIAGRAM

  1. Longitudinal Growth
  2. Appositional Growth

F. Bone Remodeling and Repair

  1. Bone Remodeling
  2. Bone repair (of fracture)
  3. Repair Process: Diagram
    1. Hematoma formation - blood vessels in bone tear and hemorrhage, resulting in a mass of clotted blood.
    2. Fibrocartilaginous callus formation -(granulation tissue formation) capillaries grow into hematoma and phagocytic cells invade area (to clean up debris). Fibroblasts and osteoblasts migrate to fracture. Fibroblasts secrete collagen fibers and/or differentiate into chondroblasts that secrete a cartilage matrix. Osteoblasts form spongy bone. Mass of repair tissue is referred to as a fibrocartilaginous callus. An internal callus connects bone ends and an external callus protrudes from outer bone surface
    3. Bony callus formation - osteoblasts and osteoclasts continue to migrate inward and multiply rapidly in fibrocartilaginous callus. The tissue is now called the bony callus.
  4. Remodeling - the shaft is reconstructed to resemble original unbroken bone. Reconstruction is mediated by hormonal cues.
  5. Fracture types:

G. Clinical Terms