6A

Chapter 6A: Bones and Skeletal Tissues

Copyright Information

  • Marieb Human Anatomy & Physiology Twelfth Edition

  • Chapter 6A: Bones and Skeletal Tissues

  • Prepared by: Ashley Spring, Ph.D., Eastern Florida State College

  • Copyright © 2025 Pearson Education, Inc. All Rights Reserved

Importance of Understanding Bone Anatomy

  • Understanding bone anatomy and the process of bone remodeling is essential for effectively working with patients suffering from bone diseases, such as osteoporosis.

Learning Outcomes

Learning Outcome 6.1: Types of Cartilage

  • Describe the functional properties of the three types of cartilage tissue.

  • Locate the major cartilages of the adult skeleton.

  • Explain how cartilage grows.

Cartilage’s Role in the Skeleton

  • The human skeleton initially consists of cartilage, which is later replaced by bone in most areas except those requiring flexibility.

  • Skeletal Cartilage:

    • Composed of highly resilient and molded cartilage tissue primarily consisting of water.

    • Contains no blood vessels or nerves.

    • Perichondrium:

    • A dense connective tissue layer that surrounds cartilage, helping it resist outward expansion.

    • It contains blood vessels to provide nutrients to cartilage.

    • Cartilage itself is made up of chondrocytes, which are enclosed within small cavities known as lacunae within a jelly-like extracellular matrix.

Cartilage Structure, Types, and Locations

Three Types of Cartilage

  1. Hyaline Cartilage:

    • Provides support, flexibility, and resilience.

    • Most abundant type of cartilage.

    • Contains only collagen fibers.

    • Locations:

      • Articular (joints)

      • Costal (ribs)

      • Respiratory (larynx and respiratory passages)

      • Nasal (external nose)

  2. Elastic Cartilage:

    • Similar to hyaline cartilage but contains both collagen and elastic fibers.

    • Locations:

      • External ear

      • Epiglottis

  3. Fibrocartilage:

    • Composed of thick collagen fibers providing tensile strength.

    • Locations:

      • Menisci of knee

      • Pubic symphysis

      • Intervertebral discs

Growth of Cartilage

  • Cartilage grows in two ways:

    1. Appositional Growth:

    • New matrix is laid down on the surface of existing cartilage.

    • Cartilage-forming cells in the perichondrium secrete matrix against the external face.

    1. Interstitial Growth:

    • New matrix is formed within cartilage.

    • Chondrocytes within lacunae divide and secrete new matrix, causing expansion from within.

  • Growth of cartilage ends during adolescence.

Learning Outcomes

Learning Outcome 6.2: Functions of Bones

  • Describe the functions of the skeleton and of bone tissue.

Functions of Bones

  • The human skeleton has seven crucial functions:

    1. Support:

    • Provides structure for body and soft organs.

    1. Protection:

    • Safeguards the brain, spinal cord, and vital organs.

    1. Anchorage:

    • Serves as levers for muscle action.

    1. Mineral Storage:

    • Major minerals stored include calcium and phosphorus.

    1. Blood Cell Formation (Hematopoiesis):

    • Occurs within red bone marrow found in certain bones.

    1. Triglyceride Storage:

    • Serves as an energy source stored in bone cavities.

    1. Hormone Production:

    • Osteocalcin hormone regulation aids in insulin secretion, glucose homeostasis, and energy expenditure.

Learning Outcomes

Learning Outcome 6.3: Bone Classification

  • Name the major regions of the skeleton and describe their relative functions.

  • Compare and contrast the four bone classes and provide examples of each class.

Classification of Bones

  • The human skeleton consists of 206 named bones, classified into two groups:

    1. Axial Skeleton:

    • Comprises the long axis of the body, including:

      • Skull

      • Vertebral Column

      • Rib Cage

    1. Appendicular Skeleton:

    • Contains bones of upper and lower limbs and girdles attaching limbs to the axial skeleton.

Classification by Shape

  1. Long Bones:

    • Longer than wide, with a medullary cavity extending the length of the shaft.

    • Example: Most limb bones.

  2. Short Bones:

    • Cube-shaped bones.

    • Example: Wrist and ankle bones.

    • Sesamoid Bones:

      • Forms within tendons, example: Patella.

      • Vary in size and number.

  3. Flat Bones:

    • Thin, flat, and slightly curved.

    • Example: Sternum, ribs, most cranial bones.

  4. Irregular Bones:

    • Have complicated shapes.

    • Example: Vertebrae and hip bones.

Learning Outcomes

Learning Outcome 6.4: Bone Structure

  • Describe the gross anatomy of a typical flat bone and a long bone.

  • Indicate the locations and functions of red and yellow bone marrow, articular cartilage, periosteum, and endosteum.

  • Indicate the functional importance of bone markings.

Bone Structure Overview

  • Bones are considered organs containing various types of tissues:

    • Dominantly made up of bone (osseous) tissue.

    • Also includes nervous tissue, cartilage, dense connective tissue, muscle cells, and epithelial cells within blood vessels.

  • Three Levels of Structure:

    • Gross

    • Microscopic

    • Chemical

Gross Anatomy of Bone

  • Compact Bone:

    • Dense outer layer of every bone, appearing smooth and solid.

  • Spongy Bone:

    • Comprises small, needle-like or flat pieces of bone called trabeculae; contains open spaces filled with red or yellow bone marrow.

Structure of Short, Irregular, and Flat Bones

  • Consist of thin plates of spongy bone (diploe) covered by compact bone.

  • Compact bone is sandwiched between connective tissue membranes:

    • Periosteum:

    • Covers external surface of compact bone except at joints.

    • Endosteum:

    • Covers internal portion of compact bone.

  • Bone Marrow:

    • Scattered throughout spongy bone with no defined marrow cavity.

  • Articular Cartilage:

    • Covers the area of moving joints.

Structure of a Typical Long Bone

  • All long bones have:

    • Diaphysis:

    • Tubular shaft forming the long axis of the bone, consists of compact bone surrounding a central medullary cavity filled with yellow bone marrow.

    • Epiphyses:

    • Ends of long bones made up of compact bone externally and spongy bone internally.

      • Articular Cartilage:

      • Covers joint surfaces.

      • Epiphyseal Line:

      • The remnant of the childhood epiphyseal plate where bone growth occurs.

Membranes of Long Bones

  1. Periosteum:

    • Double-layered membrane covering the external surfaces of bones except joints.

    • Fibrous Layer:

      • Outer layer consisting of dense irregular connective tissue with Sharpey’s fibers anchoring it to bone matrix.

    • Osteogenic Layer:

      • Inner layer next to bone housing primitive osteogenic stem cells that generate most bone cells.

      • Contains many nerve fibers and blood vessels that enter the shaft via nutrient foramen openings.

      • Serves as anchoring points for tendons and ligaments.

  2. Endosteum:

    • Delicate connective tissue membrane covering internal bone surfaces, lining canals that pass through compact bone, and coverings trabeculae of spongy bone.

    • Similar to the periosteum, contains osteogenic cells.

Hematopoietic Tissue in Bones

  • Red Bone Marrow:

    • Found within trabecular cavities of spongy bone and diploë of flat bones (e.g., sternum).

    • In newborns, all medullary cavities and spongy bones contain red bone marrow.

    • In adults, red bone marrow is located in the heads of the femur and humerus, while the most active areas for hematopoiesis are flat bone diploë and some irregular bones (e.g., hip bone).

    • Yellow Bone Marrow:

    • Can convert to red bone marrow if the person becomes anemic.

Bone Markings

  • Bone markings are sites of muscle, ligament, and tendon attachment on the bone’s external surfaces, areas for joint formation, or conduits for blood vessels and nerves.

  • Categorized into three types:

    1. Projections:

    • Sites of muscle and ligament attachment.

    1. Surfaces:

    • Areas forming joints.

    1. Depressions and Openings:

    • Allow passage for blood vessels and nerves.

Summary of Bone Markings

  • Projections: Sites of muscle and ligament attachment.

    • Examples include:

    • Tuberosity: Large rounded projection, may be roughened.

    • Crest: Narrow ridge of bone, typically prominent.

    • Trochanter: Very large, blunt, irregularly shaped process found on femur.

    • Additional terms: Epicondyle, Tubercle, Process, Spinous Process.

  • Surfaces that Help Form Joints:

    • Examples include:

    • Head: Bony expansion carried on a narrow neck.

    • Facet: Smooth, nearly flat articular surface.

    • Condyle: Rounded articular projection often articulating with a corresponding fossa.

  • Depressions and Openings for Passage of Blood Vessels and Nerves:

    • Examples include:

    • Groove: Furrow or narrow slitlike opening.

    • Meatus: Canal-like passageway.

    • Foramen: Round or oval opening in a bone.

    • Fossa: Shallow, basin-like depression, often serving as an articular surface.

Conclusion

  • Understanding the structure and functions of bones and cartilage is crucial for the study of human anatomy and physiology, especially in contexts of health and disease.