Chapter 7A Skeletal system (003)

Chapter 7: Skeletal System - Bone Structure and Function

7.1 Learning Objectives

• Components of the Skeletal System:

  • Understand the major parts of the skeletal system, including bones, cartilage, ligaments, and other connective tissues.

  • Identify the various types of bones and their significance.

  • Describe different types and locations of cartilage in the skeletal system.

  • Engage with the Anatomy and Physiology Review (APR) video focusing on bone cells and the process of bone formation.

7.1 Introduction to the Skeletal System

Components of the Skeletal System

• Bones: The primary organs of the skeletal system, providing a rigid framework that shapes the body and supports movement.

• Cartilage: A flexible yet sturdy connective tissue that supports and cushions joints, allowing them to move smoothly and absorb shock.

• Ligaments: Strong bands of dense connective tissue that attach bones to other bones, providing stability to joints.

Types of Bone

• Compact Bone:

  • Also referred to as cortical bone.

  • Comprises about 80% of the total bone mass; it has a dense and solid structure that contributes to strength and support.

• Spongy Bone:

  • Also known as cancellous or trabecular bone.

  • Accounts for around 20% of the total bone mass; it is characterized by a porous, lattice-like structure that is found internally within compact bones, aiding in weight reduction while still providing support.

7.1 Cartilage

• Definition: A semirigid connective tissue that offers greater flexibility compared to bone, making it essential for movement and joint function.

• Types of Cartilage:

  • Hyaline Cartilage: Provides smooth surfaces for joint movement and flexibility, found in the respiratory system and the embryonic skeleton.

  • Fibrocartilage: Tough and durable, this type absorbs compressive forces and is found in intervertebral discs and pubic symphysis.

Ligaments and Tendons

• Ligaments: Connect bones to other bones, ensuring joint stability.

• Tendons: Connect muscles to bones, facilitating movement by transmitting the force from muscle contraction to the skeleton.

7.2 General Functions of Bones

• Support and Protection: The skeletal system provides a framework that supports the body’s structure and protects vital organs like the heart, lungs, and brain.

• Levers for Movement: Bones act as levers when muscles contract, allowing for a wide range of movements.

• Hematopoiesis: Blood cell production, particularly red blood cells, occurs in the red bone marrow, predominantly found in the ends of long bones and within flat bones.

• Storage: Bones store essential minerals, such as calcium and phosphate, critical for various physiological functions, as well as energy reserves in the form of fat.

7.2 Classification of Bones by Shape

• Major Classes of Bones:

  • Long Bones: Typically longer than they are wide; examples include the femur and humerus.

  • Short Bones: Approximately equal in length and width; examples include the carpals and tarsals.

  • Flat Bones: Thin and flattened; examples include the skull bones and sternum.

  • Irregular Bones: Complex shapes that do not fit into the above categories; examples include vertebrae and pelvic bones.

7.2c Gross Anatomy of Bones

Regions of a Long Bone

• Diaphysis: The long central shaft that provides structural support; it is primarily composed of compact bone with a hollow medullary cavity.

• Medullary Cavity: A hollow space within the diaphysis that contains bone marrow, which can be red (producing blood cells) in children, and yellow (fat storage) in adults.

• Epiphysis: The rounded ends of long bones that help form joints; they are covered with articular cartilage for smooth movement.

• Articular Cartilage: A smooth, slippery tissue covering the ends of bones in joints, reducing friction and absorbing shock.

• Periosteum: A dense layer of vascular connective tissue enveloping the bones, which provides nourishment and serves as an attachment site for tendons and ligaments.

• Endosteum: A thin layer of connective tissue that lines the internal surfaces of bone, containing bone cells that are involved in growth and repair.

7.2d Bone Marrow

• Types of Bone Marrow:

  • Red Bone Marrow: Responsible for hematopoiesis, consisting primarily of hematopoietic stem cells, mainly found in the axial skeleton and proximal ends of long bones in adults.

  • Yellow Bone Marrow: Comprised mostly of adipose tissue; it can revert to red marrow in instances of high demand for blood cell production, such as severe blood loss.

7.2e Microscopic Anatomy of Bone

Bone Composition

• Cell Types:

  • Osteoprogenitor Cells: Stem cells located in the periosteum; they differentiate into osteoblasts when needed.

  • Osteoblasts: Responsible for synthesizing and secreting osteoid, the organic component of the bone matrix.

  • Osteocytes: The most abundant bone cells; they maintain bone matrix health and communicate stresses or damage to other bone cells.

  • Osteoclasts: Large, multinucleated cells that break down bone tissue, playing a crucial role in bone resorption and remodeling.

Bone Matrix Composition

• Organic Components: Composed of collagen fibers and ground substance, known as osteoid, which provide tensile strength.

• Inorganic Components: Primarily hydroxyapatite crystals that give bone its hardness and rigidity.

Bone Formation and Resorption

• Formation: Involves osteoblasts secreting osteoid that subsequently mineralizes into bone matrix.

• Resorption: Osteoclasts break down bone matrix, releasing stored minerals into the bloodstream, a vital process for maintaining mineral balance in the body.

7.2e Compact and Spongy Bone Microscopic Structure

• Compact Bone: Organized into structural units known as osteons (Haversian systems), featuring concentric lamellae surrounding a central canal that houses blood vessels and nerves.

• Spongy Bone: Characterized by trabecular structures that create a lightweight framework, surrounded by bone marrow, providing space for blood cell production and storage.