Skeletal System: Structure, Function, and Growth (Study Guide)

Skeletal System Overview

Functions of the Skeletal System

The skeletal system provides the framework for the body, supports movement, and protects vital organs. It also serves as a reservoir for minerals and is involved in blood cell production.

• Support: The skeleton supports the body and maintains its shape.

• Protection: Bones protect internal organs (e.g., skull protects the brain, rib cage protects the heart and lungs).

• Movement: Bones act as levers for muscles to produce movement.

• Mineral Storage: Bones store minerals such as calcium and phosphorus.

• Blood Cell Production (Hematopoiesis): Occurs in the red bone marrow.

• Not a Function: Communication is not a function of the skeletal system.

Bone Tissue Types and Structure

Types of Bone Tissue

Bones are composed of different types of tissue, each adapted for specific functions.

• Compact Bone: Dense and strong, adapted to support weight and withstand tension stresses.

• Spongy Bone: Less dense, found at the ends of long bones and in the interior of other bones.

• Irregular Bone: Bones with complex shapes (e.g., vertebrae).

• Trabecular Bone: Another term for spongy bone.

Bone Marrow

• Yellow Bone Marrow: Contains a large percentage of fat.

• Red Bone Marrow: Site of hematopoiesis (blood cell formation).

Bone Classification

• Long Bones: Longer than they are wide (e.g., femur, humerus).

• Short Bones: Approximately equal in length and width (e.g., carpals).

• Flat Bones: Thin and broad (e.g., sternum, skull).

• Irregular Bones: Complex shapes (e.g., vertebrae).

• Sesamoid Bones: Embedded in tendons (e.g., patella).

Bone Growth and Development

Epiphyseal Plate and Bone Lengthening

The epiphyseal plate (growth plate) is responsible for the longitudinal growth of long bones during childhood and adolescence.

• Epiphyseal Plate: Allows the diaphysis (shaft) of the bone to increase in length until early adulthood.

• Epiphyseal Line: Remnant of the epiphyseal plate in adults after growth has ceased.

Bone Thickness and Appositional Growth

• Appositional Growth: The process by which bones increase in thickness. New bone tissue is added to the surface of existing bone.

• Equation: $\text{Bone Thickness} \propto \text{Appositional Growth}$

Stimuli for Bone Growth

• Growth Hormone: The most important stimulus for epiphyseal plate activity during infancy and childhood.

• Thyroid Hormone: Modulates the activity of growth hormone.

• Parathyroid Hormone: Regulates calcium levels and bone remodeling.

Bone Cells and Their Functions

Types of Bone Cells

• Osteoblasts: Cells responsible for secreting the bone matrix and forming new bone.

• Osteocytes: Mature bone cells that maintain bone tissue; formed when osteoblasts become surrounded by their own matrix.

• Osteoclasts: Cells responsible for bone resorption (breaking down bone tissue).

• Osteogenic Cells: Stem cells that differentiate into osteoblasts.

Bone Remodeling and Resorption

• Osteoclasts: Accomplish bone resorption, breaking down bone matrix for remodeling and calcium release.

• Parathyroid Hormone: Increases osteoclast activity to release calcium ions into the bloodstream.

Bone Structure and Anatomy

Osteon and Haversian Canal

• Osteon: The structural unit of compact bone, consisting of concentric lamellae surrounding a central canal.

• Haversian Canal: Runs through the core of each osteon and contains blood vessels and nerve fibers.

Periosteum and Osteogenic Layer

• Periosteum: A protective tissue covering bones; contains an inner osteogenic layer.

• Osteogenic Layer: Consists primarily of osteogenic cells that contribute to bone growth and repair.

Cartilage Growth

Appositional vs. Interstitial Growth

• Appositional Growth: Growth by addition of new matrix on the surface of existing cartilage.

• Interstitial Growth: Chondrocytes in the lacunae divide and secrete matrix, allowing cartilage to grow from within.

Prevention of Osteoporosis

Dietary Requirements

• Calcium and Vitamin D: Adequate intake is essential for bone health and prevention of osteoporosis.

Axial vs. Appendicular Skeleton

Classification of Bones

• Axial Skeleton: Includes the skull, vertebral column, and rib cage.

• Appendicular Skeleton: Includes the shoulder, hip, and upper and lower limbs. The skull is not part of the appendicular skeleton.

Summary Table: Key Bone Cell Functions

Cell Type	Main Function
Osteoblast	Secretes bone matrix, forms new bone
Osteocyte	Maintains bone tissue
Osteoclast	Resorbs (breaks down) bone matrix
Osteogenic Cell	Stem cell for bone formation

Example Applications

• Clinical: Growth hormone deficiency in childhood can result in stunted bone growth and short stature.

• Archaeology: Classification of bones by shape and size helps identify species and age.

• Health: Adequate calcium and vitamin D intake is crucial for bone strength and prevention of osteoporosis.

Additional info: The study notes expand on the brief multiple-choice questions by providing definitions, explanations, and context for each concept, making the guide suitable for exam preparation and self-study.