The Skeletal System: Bone Types and Functions

Skeletal System Overview

Introduction

The skeletal system is crucial for various bodily functions, not just structural support. It interacts with multiple organ systems to maintain homeostasis.

Protection

• The cranium, formed by bones, protects the brain.

• The vertebrae protect the spinal cord within the vertebral canal.

• The ribs and sternum protect the heart and lungs within the thoracic cavity.

Blood Cell Production

• Red bone marrow within bones is responsible for producing red and white blood cells.

Learning Objectives

• Review the learning objectives independently.

Divisions of the Skeletal System

The skeletal system is divided into two main divisions:

Axial Skeleton

• Bones along the body's vertical axis.

• Includes the sacrum, vertebrae, rib cage, sternum, and skull.

Appendicular Skeleton

• All the bones of the limbs (arms and legs) and girdles.

• Pectoral girdle (shoulder girdle): Includes the scapula (shoulder blade) and clavicle (collarbone).

• Pelvic girdle (hip girdle): Includes the bones of the pelvis.

Bone Classification by Shape

Bones are classified into five main types based on their shape:

Long Bones

• Longer than they are wide.

• Examples: Humerus, radius, ulna, femur, tibia, fibula, and bones in the hands (phalanges) and feet.

• The key is the proportion (length vs. width), not the overall size.

Short Bones

• Width and length are roughly equal.

• Examples: Trapezoid (wrist), bones in the midfoot.

Flat Bones

• Provide protection.

• Examples: Sternum (protects the mediastinum and heart), frontal bone (protects the frontal lobe of the brain).

Irregular Bones

• Have irregular shapes that don't fit other categories.

• Examples: Vertebrae, ethmoid bone, sphenoid bone.

Sesamoid Bones

• Short bones found within a tendon.

• Example: Patella (kneecap), which is encapsulated within the quadriceps tendon.

• The patella alters the angle of pull of the quadriceps muscle group, providing a mechanical advantage during knee extension.

• Vary in number between individuals and can also be found in the feet.

Suture Bones

• Small bones found within suture joints in the skull.

• Classified by position rather than shape.

Functions of the Skeletal System

Support

• Provides a rigid framework for the body.

Protection

• Protects vital organs like the brain (cranium), spinal cord (vertebrae), heart (sternum), and lungs (rib cage).

Movement

• Works with the muscular system to enable movement.

• Skeletal muscles attach to bones via tendons.

• Muscle contraction pulls on the skeletal system, causing movement at joints.

• The skeletal and muscular systems are often referred to as the musculoskeletal system due to their interdependence.

Mineral Homeostasis

• Bones serve as a reservoir for minerals, especially calcium and phosphorus.

• Calcium is essential for blood clotting, nerve function, and muscle contraction.

Blood Cell Production (Hemopoiesis)

• Hemopoiesis is the production of all blood cells, while erythropoiesis is the specific production of red blood cells.

• Occurs in the red bone marrow, specifically within the epiphyses of long bones.

Fat Storage

• Occurs in the yellow bone marrow.