Bones and Skeletal Tissues Study Notes

Bones and Skeletal Tissues

Chapter Overview

  • Introduction to the skeletal system and its organized structures.
  • Discussion on the histology of bone and cartilage.
  • Classification of bones and their various features.

Histology of Cartilage

  • Perichondrium: the dense layer of connective tissue that surrounds cartilage, providing nutrients and supporting the cartilage structure.
  • Types of Cartilage:
    • Hyaline Cartilage: most common type, providing support with some flexibility; found in ribs and nose.
    • Elastic Cartilage: contains elastic fibers, allowing it to return to its original shape; found in the ear and epiglottis.
    • Fibrocartilage: highly durable, found in intervertebral disks and the pubic symphysis, providing strength and support.

Key Components of Cartilage

  • Chondrocyte: the cell type found in cartilage and resides within small spaces called lacunae.
  • Matrix: the extracellular component that provides structure and support to cartilage, rich in collagen fibers.

Bone Anatomy

Gross Anatomy

  • Compact Bone: forms the dense outer layer; appears smooth and solid.
  • Spongy Bone: has a honeycomb appearance; consists of trabeculae filled with bone marrow, lacking osteons.

Classification of Bone Shapes

  • Bones are classified into four primary shapes:

    1. Long Bones: longer than they are wide (e.g., femur).
    2. Short Bones: approximately cube-shaped (e.g., carpals in wrist).
    3. Flat Bones: thin, flat structures (e.g., sternum).
    4. Irregular Bones: complex shapes that do not fit into other categories (e.g., vertebrae).

  • Sesamoid Bones: embedded within tendons (e.g., patella) and vary in number among individuals.

Bone Structure

Anatomy of a Long Bone

  • Epiphyses: the end parts of a long bone, which form joints with neighboring bones.
  • Diaphysis: the shaft or central part of a long bone.
  • Medullary Cavity: the hollow part of the diaphysis that contains bone marrow.
  • Articular Cartilage: cartilage covering the surfaces of bones at joints to facilitate smooth movement.
  • Periosteum: a dense layer of vascular connective tissue enveloping the bones except at the surfaces of the joints; serves as the attachment point for tendons and ligaments.
  • Endosteum: a thin membrane lining the medullary cavity of bones.

Bone Development

Ossification Processes

  • Ossification (Osteogenesis): the process of bone tissue formation that begins in embryonic development and continues through childhood and adolescence.
  • Types of Ossification:
    1. Endochondral Ossification: cartilage is replaced by bone, primarily in long bones.
    2. Intramembranous Ossification: bone develops from fibrous membranes (e.g., flat bones of the skull).

Stages of Endochondral Ossification

  1. Formation of a bone collar around the diaphysis of the hyaline cartilage model.
  2. Cavitation of the hyaline cartilage model.
  3. Invasion of the internal cavities by the periosteal bud and spongy bone formation.
  4. Formation of the medullary cavity as ossification continues; secondary ossification centers appear in the epiphyses.
  5. Ossification of the epiphyses; hyaline cartilage remains only at the epiphyseal plates and articular cartilages.

Growth in Length and Width

  • Epiphyseal Plates: areas of growth in the long bones; consist of different zones (resting, proliferation (growth), hypertrophic, calcification, and ossification).
  • Appositional Growth: increase in bone thickness due to the deposition of new bony matrix by osteoblasts on the external surface and bone resorption by osteoclasts on the endosteal surface.

Bone Remodeling

  • About 5-7% of bone mass is recycled each week with spongy bone replaced every 3-4 years and compact bone every 10 years.
  • Bone Remodeling Units: packets of osteoblasts and osteoclasts that coordinate the remodeling process which includes both bone deposition and resorption.

Hormonal Regulation of Bone Growth

  • Growth Hormone: stimulates epiphyseal plate activity in the growth phase.
  • Thyroid Hormones: modulate the effort of growth hormone,
    ensuring proportional growth.
  • Sex Hormones: testosterone and estrogen promote growth spurts and lead to the closure of the growth plates at puberty.

Bone Repair

  • Fracture Types:
    • Comminuted: bone fragments into three or more pieces.
    • Compression: bone is crushed, common in porous bones.
    • Spiral: ragged break from twisting forces.
    • Greenstick: an incomplete fracture; common in children.
    • Healing Process: includes stages such as hematoma formation, fibrocartilaginous callus formation, and bony callus formation, until the complete bone remodeling occurs.

Summary

  • The human skeleton is essential for structure, support, and protection of vital organs, along with facilitating movement through collaboration with muscular systems.
  • Understanding skeletal tissues and their functions is crucial for fields such as medicine, physical therapy, and sports science.