lecture 10, bone structure and composition

components of long bone

• each of these bones is composed of a

  1. diaphysis

  2. the medullary cavity of the diaphysis (hollow)

  3. epiphysis

  4. epiphyseal plate

  5. epiphyseal line

  6. endosteum

  7. periosteum membrane

  8. articular cartilage

diaphysis

• the shaft/body of the bone

• composed of compact bone

the medullary cavity of the diaphysis (hollow)

• contains red bone marrow in a child

• contains yellow bone marrow in an adult

• contains fat

• lined by endosteum

  • lines the cavity

  • “outer” “bone”

epiphysis

• these are the proximal and distal entities (end part of long bone)

  • epiphysial plate: growth plate (cartilage, in between epiphysis and diaphysis, found in kids/teen)

  • epiphysial line: ossified remnant of growth plate (in adults, bone stops growing)

epiphyseal plate

• composed of hyaline cartilage

• bone growth in length occurs at this plate

• bone growth is called endochondral ossification

epiphyseal line

• replaces the epiphyseal plate when growth is finished

• appears as a line because it is the junction of the diaphysis and the epiphysis

endosteum

• connective tissue

• very delicate (but it inside a hard long bone)

• lines the internal surfaces of bone and canals (points of contact for delivery, allows for more access to nutrients)

• contains osteoblasts and osteoclasts

• “wallpaper”

periosteum membrane

• composed of fibrous connective tissue

• allows the bone to grow in diameter via intramembranous ossification

• is a double membrane that covers the entire bone surface (except for the joint)

• the outer layer is dese irregular connective tissue (good for movement)

• the inner layer is osteogenic

  • bone forming and consists of osteoblasts (build it bigger) and osteoclasts (hollows out) increase size of cavity when bone grows

articular cartilage

• hyaline cartilage that functions to prevent friction

• found on the epiphyseal surfaces of long bone

tissues of the skeletal system

• there are two primary tissues of the skeletal system

  1. bone

  2. cartilage

bone

• bone is either compact (dense) or spongy (holes)

• osteoprogenitor cells (like stem cells of the bone world, unspecialized) are cells that give rise to one of the following three cells

  1. osteoblasts: build the matrix

  2. osteocytes: maintain the matrix

  3. osteoclasts: resorb (breakdown) the matrix (because want it fresh)

• the cells of the connective tissue are separated by a matric that consists of

  • collagen fibers for flexibility

  • ground substances: hydroxyapatite crystals for strength → made from insoluble calcium phosphate salts

    • gives bone its characteristic strength

    • insoluble → otherwise bones would liquidify

  • water

compact bone is found on the exterior surface of all bones

• it is composed of individual structural units called osteons or Haversian systems

• an osteon is composed of

  • osteocytes found within special spaces called lacunae

  • lamellae which are concentric circles of bone matrix

    • osteocytes are present between the lamellae

  • canaliculi connect cells and blood vessels (connection)

  • Haversian canals contain blood vessels and the nerves

    • lined with endosteum

  • Volkmann’s canals are found at a right angle to blood vessels found in Haversian canals

    • these connect the periosteum to the endosteum providing blood supply to the medullary cavity and the Haversian canals

spongy bone is not organized into osteons

• plates of bone are called trabeculae

  • irregularly arranged lamellae containing osteocytes

    • osteocytes are located in lacunae and are connected by canaliculi

• found in epiphyses of long bone as well as in flat bones such as the skull and the ribs

• the spaces of the spongy bone contain red bone marrow

  • these spaces produce blood cells and provide a blood supply to developing osteocytes

    • stem cells → get you what you need

(compact bone is like an and aero bar, hard chocolate on top and bottom and bubbles in between)

hyaline cartilage

• the cells of the cartilage are chondrocytes and are found within lacunae

• the matrix is composed of

  • collagen fibers

  • ground substance consisting of chondroitin sulfate and hyaluronic acid

  • water (more water in cartilage than in bone)

• avascular tissue

  • harder to heal

  • look ugly when healed (sometimes)

articulations and joints

• points of contact between two or more bones

  • these can be classified on either structure or function

1. functional classification

   • this is based on degree of movement

     a. synarthrotic: immovable joints

     • ex. sutures

     b. amphiarthrotic: slightly moveable joints

     • ex. pubic symphysis (not free but ex. when jump it moves slightly)

     c. diarthrotic: freely moveable joints

     • ex. hip, knee, elbow, shoulder

structural classification is based on

• the presence of the absence of a joint cavity and the type of tissue connecting two bones

• there are three structural classifications of joints

  1. fibrous joints

     • no joint cavity, composed of fibrous connective tissue

     • ex. sutures on the skull

     • fibers create the joint

     • fibrous characteristic because don’t need to move

  2. cartilaginous joints

     • no joint cavity, composed of cartilage

     • ex. pubic symphysis and intervertebral disks

     • jump → compress down, but then come back up

  3. synovial joints

     • contain a joint cavity filled with synovial fluid

     • bones are held together by a joint cavity and associated ligaments

     • all diarthrotic joints are synovial joints (freely move)

     • ex. knee, shoulder, hip, elbow

synovial joints

• all contain

  1. articular cartilage

     • hyaline cartilage located on the ends of the bones

     • reduces friction

  2. joint cavity

     • contains synovial fluid

  3. joint capsule

     • contains an outer layer of fibrous connective tissue that attached to the periosteum

     • an inner synovial membrane which secretes synovial fluid

       • needs to come from the inner membrane (secretes it)

four primary types of synovial joints

• grouped according to the shape of articulating bones

1. gliding (plane)

   • flat surfaces

   • ex. sacroiliac joint

2. hinge

   • concave and convex surface

   • ex. elbow, knee

   • ligament and cartilage

3. pivot

   • ex. odontoid process of the axis

   • ability to pivot

   • on the axis of C2 that goes up to C1

4. ball and socket

   • head of femur and the acetabulum (hip)

   • head of the humerus and the glenoid fossa (shoulder)

   • allows for a large freedom of movement

   • can move a lot in different directions