Bones: Shape and Structure – Fundamentals of Anatomy & Physiology

Bones: Shape and Structure

Introduction

This study guide covers the major functions of the skeletal system and the classification of bones by shape and structure. Understanding these foundational concepts is essential for students of Anatomy & Physiology, as bone morphology relates directly to function and clinical significance.

Functions of the Skeletal System

Overview of Skeletal System Functions

The skeletal system is a complex framework that supports the body and facilitates movement. It consists of bones, cartilages, ligaments, and other connective tissues.

• Support: Provides structural support for the entire body and forms the framework for the attachment of soft tissues and organs.

• Storage of Minerals and Lipids: Bones store minerals such as calcium and phosphorus, which are essential for physiological processes. Yellow bone marrow stores lipids as an energy reserve.

• Blood Cell Production: Red bone marrow produces red blood cells, white blood cells, and platelets through the process of hematopoiesis.

• Protection: Bones protect vital organs, such as the brain (skull), heart and lungs (rib cage), and spinal cord (vertebrae).

• Leverage: Bones act as levers that muscles pull on to produce movement.

Classification of Bones

Bone Classification by Shape

Bones are classified according to their shape and structure, which reflects their functional roles in the body. The main bone shapes are:

• Sutural Bones (Wormian bones): Small, flat, irregularly shaped bones found between the flat bones of the skull. Their number and location vary among individuals.

• Irregular Bones: Have complex shapes that do not fit into other categories. Examples include spinal vertebrae and pelvic bones.

• Short Bones: Boxy in appearance. Examples are carpal bones (wrist) and tarsal bones (ankle).

• Flat Bones: Thin bones with parallel surfaces. Examples include bones of the skull roof, sternum, ribs, and scapulae.

• Long Bones: Long and slender bones found in the arms, legs, palms, soles, fingers, and toes.

• Sesamoid Bones: Usually small, round, and flat bones found within tendons near joints, such as the patella (kneecap). Their number and location can vary between individuals.

Table: Classification of Bones by Shape

Bone Type	Description	Examples
Sutural (Wormian)	Small, flat, irregularly shaped; found between skull bones	Sutures of the skull
Irregular	Complex shapes	Vertebrae, pelvic bones
Short	Boxy, approximately equal dimensions	Carpals, tarsals
Flat	Thin, parallel surfaces	Skull roof, sternum, ribs, scapulae
Long	Long and slender	Humerus, femur, radius, ulna, tibia, fibula
Sesamoid	Small, round, flat; within tendons	Patella

Bone Markings (Surface Features)

Overview of Bone Markings

Bones have various surface features called bone markings that serve as sites for muscle, tendon, and ligament attachment, as well as passages for nerves and blood vessels.

• Projections: Areas where muscles, tendons, and ligaments attach or where bones articulate with other bones.

• Openings and Depressions: Allow the passage of blood vessels and nerves.

Bone Structure

Structure of a Long Bone

Long bones have a distinct anatomy that supports their function in movement and weight-bearing.

• Diaphysis: The shaft of the bone, composed of a thick wall of compact bone surrounding a central medullary (marrow) cavity.

• Epiphysis: The expanded ends of the bone, consisting mostly of spongy (trabecular) bone.

• Metaphysis: The region where the diaphysis and epiphysis meet.

Structure of Flat Bones

Flat bones, such as those in the skull, have a unique structure that provides protection and surface area for muscle attachment.

• Composition: Consist of spongy bone (called diploë in the cranium) sandwiched between two layers of compact bone (cortex).

• Function: Protect internal organs and provide broad surfaces for muscle attachment.

Example: Parietal Bone Structure

• Outer and Inner Tables: Layers of compact bone.

• Diploë: Central layer of spongy bone.

Additional info: The structure of bones is closely related to their function. For example, the spongy bone in epiphyses helps absorb shock and reduce weight, while compact bone in the diaphysis provides strength for weight-bearing.