Osteoclast

-

  • An osteoclast is a type of bone cell that resorbs bone tissue.
  • This function is critical in the maintenance and repair of compact bones in the mammalian skeleton.
  • Kolliker discovered osteoclasts in 1873.
  • An osteoclast is a large multinucleated cell and human osteoclasts on bone typically have five nuclei and are about 150-200 μm in diameter.
  • In bone, osteoclasts are found in pits in the bone surface, which are called resorption bays, or Howship's Lacunae.
  • Osteoclasts are characterized by a cytoplasm with a homogeneous, "foamy" appearance.
  • This appearance is due to a high concentration of vesicles and vacuoles.
  • These vacuoles include lysosomes filled with acid phophatase.
  • This permits characterization of Osteoclasts by their staining for high expression of tartrate resistant acid phosphatase (TRAP) and cathepsin K.

  • Osteoclast rough endoplasmic reticulum is sparse, and the Golgi complex is extensive.
  • Osteoclasts, large irregular cells with multiple nuclei, fill much of their cytoplasm with mitochondria to supply the energy required for these cells to resorb bone.
  • They usually lie directly against the bone matrix on endosteal, periosteal, and Haversian system bone surfaces, but unlike osteocytes, and presumably osteoblasts, they can move from one site of bone resorption to another.
  • Osteoclasts appear to form by fusion of multiple bone-marrow-derived mononuclear cells.
  • When they have finished their bone resorbing activity, they may divide to reform multiple mononuclear cells.

  • One of the most distinctive features of osteoclasts is the complex folding of their cytoplasmic membrane where it lies against the bone matrix at sites of bone resorption.
  • This ruffled or brushed border appears to play a critical role in bone resorption, possibly by increasing the surface area of the cell relative to the bone and creating a sharply localized environment that rapidly degrades bone matrix.
  • The fluid between the brush border and the bone matrix probably has a high concentration of hydrogen ions and proteolytic enzymes: the acidic environment could demineralize bone matrix, and the enzymes could degrade the organic bone matrix.

  • In cancellous bone, osteoclasts resorbing the bone surface create a characteristic depression called a Howship's lacuna.
  • In cortical bone, several osteoclasts lead the osteonal cutting cones that remodel dense cortical bone. 



Comments

  1. Unknown12 November 2018 at 22:34

    Could you please provide sources for this information?

    ReplyDelete

Post a Comment

Popular posts from this blog

Hanging Cast

-
Image
Indications 1.      For displace fracture of the humeral shaft with shortening, and also for oblique and spiral fractures –(Caldwell, 1933)  2.      Used for comminuted humeral fracture, distal humeral shaft fracture. ·       Cast must be lightweight and must extend from at least 1 inch proximal to the fracture site to wrist, with elbow at right angle & forearm in neutral rotation. ·        Arm must lie dependent to provide a traction force. ·        Patient must sleep erect or semi-erect to avoid supporting elbow when seated. ·        Erect position is maintained during the day as much as possible. ·     There should be no support under the elbow, and nothing should compress the arm against the body (such as clothing). It is frequently exchanged for functional bracing 1 to 2 weeks after injury. Correction Of Angulation: 1.      Sling must be securely fixed at the wrist by a loop made of plaster or other material.      To c
Read more

Skeletal Traction: Common sites

-
Image
1. Olecranon Site: 1.25 inches (3 cm) distal to the tip of olecranon just deep to the subcutaneous border of upper end of the ulna. Direction:  Medial to lateral at right angles to the longitudinal axis of ulna. Avoid: Ulnar nerve injury. 2. Second & Third Metacarpals Site:  About 1 inch (2-2.5 cm) Proximal to the distal end of Second metacarpal Direction:  The wire traverses 2nd and 3rd metacarpals transversely at right angles to the longitudinal axis of the radius. 3. Greater trochanter (upper end of femur ) Site: On the latera
Read more

SOMI Brace

-
Image
Sternal-Occipital-Mandibular Immobiliser  (SOMI) Brace  Cervico-Thoracic Orthoses (CTOs) provide greater motion restriction from C5-C7 spine from the increased leverage on the person’s body. The upper cervical spine has less motion restriction. CTOs are used in minimally unstable fractures . All CTO’s tend to control flexion better than extension . Parts 1. The SOMI is a rigid, 3-poster CTO that has an padded anterior chest plate extending to the xiphoid process, as well as two padded shoulder extension which hook over tops of the shoulder. 2. From these shoulder extension two Straps which cross in the interscapular region, pass downward and around the chest wall to attach to the lower part of the chest plate. 3. There are three adjustable uprights , which pass upward from the chest plate, two to the padded occipital support and one to the mandibular support. 4. A removable chin piece attaches to the chest plate with
Read more