Bones and Bone Structure: Study Notes for ANP College Students

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Chapter 6: Bones and Bone Structure

Introduction to Bone Structure

Bones are dynamic organs that provide support, protection, leverage for movement, storage of minerals, and house bone marrow for blood cell production. Understanding their structure and classification is fundamental in anatomy and physiology.

Classification of Bones by Shape

Flat Bones: Thin, parallel surfaces; found in the skull, sternum, ribs, and scapulae. They protect soft tissues and provide surface area for muscle attachment.
Sutural Bones (Wormian Bones): Small, flat, irregular bones between skull bones; variable in number and size.
Irregular Bones: Complex shapes with short, flat, notched, or ridged surfaces; examples include vertebrae and pelvic bones.
Long Bones: Long and slender; found in limbs (e.g., femur, humerus, phalanges). The femur is the largest and heaviest bone.
Short Bones: Boxlike in appearance; found in wrists (carpals) and ankles (tarsals).
Sesamoid Bones: Small, round, and flat; develop inside tendons near joints (e.g., patella).

Classification of Bones by Shape

Bone Markings

Bone markings are surface features that serve as sites for muscle, tendon, and ligament attachment, or as passages for nerves and blood vessels.

Projections: Sites of muscle and ligament attachment (e.g., trochanter, crest, spine, tubercle, tuberosity).
Projections for forming joints: Head, neck, facet, condyle, trochlea.
Depressions: Sulcus (groove), fossa (shallow depression).
Openings: Foramen (rounded passageway), canal (duct/channel), fissure (slit), meatus (canal-like passage), sinus (air-filled cavity).

Bone Markings Part 1 Bone Markings Part 2

Gross Anatomy of Bones

Long Bone Structure

Diaphysis: Shaft; composed of compact bone surrounding the medullary cavity.
Epiphysis: Expanded ends; mostly spongy bone covered by compact bone.
Metaphysis: Region where diaphysis and epiphysis meet; contains the growth plate in children.
Medullary Cavity: Central cavity containing bone marrow.

Structure of a Long Bone and Flat Bone

Flat Bone Structure

Composed of two layers of compact bone with spongy bone (diploë) in between.

Microscopic Structure of Bone

Types of Bone Cells

Osteogenic Cells: Stem cells that differentiate into osteoblasts.
Osteoblasts: Immature bone cells that secrete organic components of the matrix (osteoid).
Osteocytes: Mature bone cells that maintain the bone matrix; reside in lacunae and communicate via canaliculi.
Osteoclasts: Large, multinucleate cells that resorb (break down) bone matrix using acids and enzymes.

Matrix Composition: Collagen fibers (provide flexibility and strength) and hydroxyapatite (calcium phosphate + calcium hydroxide; provides hardness).

Types of Bone Cells

Compact Bone Structure

Osteon (Haversian System): The structural unit of compact bone; consists of concentric lamellae around a central canal containing blood vessels and nerves.
Lamellae: Layers of bone matrix.
Lacunae: Small spaces housing osteocytes.
Canaliculi: Tiny channels connecting lacunae for nutrient and waste exchange.
Perforating (Volkmann's) Canals: Transverse canals connecting osteons and medullary cavity to the periosteum.

Structure of Compact Bone Osteon and Trabecular Bone Osteons of Compact Bone Organization of Osteons and Lamellae

Spongy Bone Structure

Trabeculae: Network of struts and plates; no osteons present.
Spaces between trabeculae contain red bone marrow (site of hematopoiesis).
Provides strength with minimal weight.

Structure of Spongy Bone

Periosteum and Endosteum

Periosteum: Outer membrane covering bone except at joints; consists of an outer fibrous layer and inner cellular layer. Provides attachment for tendons and ligaments via perforating fibers.
Endosteum: Thin membrane lining the medullary cavity and trabeculae of spongy bone; contains osteogenic cells, osteoblasts, and osteoclasts.

Periosteum and Endosteum

Mechanical Properties of Bone

Bones are strong under compression but weaker under tension and shear forces.
Collagen fibers provide flexibility; mineralized matrix provides compressive strength.

Forces on Bone Shaft

Paranasal Sinuses

Air-filled spaces in the skull (frontal, maxillary, sphenoid, ethmoid).
Functions: Lighten the skull, aid in phonation, and can become inflamed (sinusitis).

Summary Table: Types of Bone Cells

Cell Type	Function
Osteogenic Cell	Stem cell; produces osteoblasts
Osteoblast	Forms new bone matrix
Osteocyte	Maintains bone matrix
Osteoclast	Resorbs bone matrix

Key Equations

Hydroxyapatite Formation:

Additional info: Bone remodeling is regulated by hormones such as parathyroid hormone (PTH), which stimulates osteoclast activity, and calcitonin, which inhibits osteoclasts and promotes bone formation by osteoblasts.