Histology of Bone Cells Notes

Module Overview

  • Course Code: IMP-07-10212

  • Credit Hours: 8 crh

  • Year/Semester: 2024 / 2025, Year 1-Semester 2

  • Module Name: Musculoskeletal & Skin

Lecture Objectives

At the end of this lecture students should be able to:

  1. Define the general structure of bone.

  2. Describe the microscopic structure of different types of bone cells.

  3. Correlate the structure and function of bone cells.

  4. Describe medical applications related to bone cells.

Bone Structure

  • Definition: Bone is a strong type of connective tissue characterized by its solid and hard matrix, composed of cells and a matrix.

  • Components:

    • Bone Cells

    • Bone Matrix

    • Connective Tissue covering

Histological Preparation Methods

  1. Decalcified Compact Bone:

    • Treated with formic or nitric acids to remove calcium.

    • Soft specimens embedded in paraffin, cut, and stained by Hx & E.

  2. Ground Compact Bone:

    • Bones are ground until thin and transparent.

Types of Bone Cells

  1. Osteogenic Cells

    • Origin: UMCs and pericytes.

    • Location: Inner osteogenic layer of periosteum and endosteum.

    • Function: Divide and differentiate into osteoblasts under good oxygen; may become chondroblasts under low oxygen.

  2. Osteoblasts

  • Origin: Derived from osteogenic cells in good O2.

  • Location: Inner osteogenic layer of periosteum and endosteum.

  • Function:

Synthesize and secrete organic components of the bone matrix.

  1. Deposit calcium in the matrix via alkaline phosphatase.

  2. Differentiate into osteocytes when surrounded by bony matrix.

  1. Osteocytes

    • Origin: Derived from osteoblasts.

    • Location: Lacunae in calcified matrix.

    • Function:

      • Maintain bone matrix integrity.

      • Release alkaline phosphatase for matrix calcification.

      • Inhibit osteoclast activity.

  2. Osteoclasts

    • Origin: Bone marrow precursors.

    • Location: Bone surfaces in endosteum and marrow cavities.

    • Function:

      • Responsible for bone resorption and remodeling.

      • Secrete hydrolytic enzymes to digest organic components of bone matrix.

      • Regulate calcium levels in blood under hormonal control.

Structural Differences of Bone Cells

Cell Type

Origin

Shape

Cytoplasm

Nucleus

Function

Osteoblast

Osteogenic cells

Large oval/cuboidal

Deeply basophilic

Single eccentric vesicular

Bone formation

Osteocyte

Osteoblasts

Oval, in lacunae

Pale basophilic

Central and oval

Maintains bone matrix

Osteoclast

Bone marrow precursors

Large irregular motile

Foamy acidophilic

Multinucleated

Bone resorption

Medical Applications

  1. Osteopetrosis:

    • Genetic disease marked by lack of osteoclast ruffled border, leading to inadequate bone resorption, increased bone thickness, reduced bone marrow space, and anemia.

  2. Osteoporosis:

    • Condition in immobilized patients and postmenopausal women where bone resorption exceeds formation, resulting in decreased bone mineral density and increased fracture risk.

Conclusion

  • The exploration of bone cells, their structure, and function is vital for understanding various bone-related medical conditions and treatments.