Bones, Bone Structure, and Joints: Study Guide for BIOL 237 Exam 2

Bones and Bone Structure

Bone Classifications

Bones are classified based on their shape and function. Understanding these classifications is essential for identifying bone types and their roles in the skeletal system.

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

• Short Bones: Nearly equal in length and width; found in wrists and ankles (e.g., carpals, tarsals).

• Flat Bones: Thin, often curved; provide protection (e.g., skull, ribs, sternum).

• Irregular Bones: Complex shapes; do not fit other categories (e.g., vertebrae, pelvis).

• Sesamoid Bones: Small, round, embedded in tendons (e.g., patella).

Compact vs. Spongy Bone

Bones contain two main types of tissue: compact and spongy bone, each with distinct structures and functions.

• Compact Bone: Dense, forms the outer layer; composed of osteons (Haversian systems).

• Spongy Bone: Porous, found at ends of long bones and inside flat bones; composed of trabeculae.

• Location: Compact bone is found in diaphysis; spongy bone in epiphysis.

Functional Unit of Bone

The functional unit of compact bone is the osteon, which consists of concentric lamellae surrounding a central canal.

Parts of a Long Bone

Long bones have distinct anatomical regions, each with specific functions.

• Diaphysis: Shaft; provides strength.

• Epiphysis: Ends; contains spongy bone.

• Metaphysis: Region between diaphysis and epiphysis; site of growth plate.

• Medullary Cavity: Central cavity; contains bone marrow.

• Periosteum: Outer covering; contains nerves and blood vessels.

• Endosteum: Lines the medullary cavity.

Bone Marrow

• Red Bone Marrow: Produces blood cells; found in children and adults (in flat bones).

• Yellow Bone Marrow: Stores fat; increases with age, replaces red marrow in long bones.

Hydroxyapatite

Hydroxyapatite is the mineral component of bone, providing hardness and strength. Its chemical formula is:

$Ca_{10}(PO_4)_6(OH)_2$

It is essential for bone rigidity and resistance to compression.

Bone Cells

• Osteoblasts: Build new bone matrix.

• Osteoclasts: Break down bone matrix.

• Osteocytes: Mature bone cells, maintain bone tissue.

Bone Growth

• Appositional Growth: Increase in bone diameter by adding new layers to the surface.

• Intramembranous Ossification: Bone forms directly from mesenchyme; produces flat bones (e.g., skull).

• Endochondral Ossification: Bone forms from cartilage model; produces most bones (e.g., long bones).

Hormones Affecting Bone Growth

• Calcitonin: Lowers blood calcium; inhibits osteoclasts.

• Parathyroid Hormone (PTH): Raises blood calcium; stimulates osteoclasts.

• Growth Hormone: Stimulates bone growth.

• Sex Hormones: Promote bone growth and closure of growth plates.

Blood Calcium Regulation

Three systems maintain normal blood calcium:

• Skeletal System

• Digestive System

• Urinary System

Bone Disorders

• Pituitary Dwarfism: Short stature due to low growth hormone.

• Gigantism: Excess growth hormone before epiphyseal closure.

• Acromegaly: Excess growth hormone after epiphyseal closure; enlarged hands, feet, face.

• Osteoporosis: Severe bone loss, increased fracture risk.

• Osteopenia: Mild bone loss.

The Skeleton

Bone Identification and Structures

Students should be able to identify bones and their anatomical features from the bones list.

Skull Sutures and Fontanels

• Sutures: Immovable joints between skull bones (e.g., coronal, sagittal, lambdoid, squamosal).

• Fontanels: Soft spots in infant skull; allow for growth and flexibility.

Sinuses

Sinuses are air-filled cavities in skull bones; they lighten the skull and aid in voice resonance.

Vertebral Issues

• Kyphosis: Excessive thoracic curvature.

• Lordosis: Excessive lumbar curvature.

• Scoliosis: Lateral curvature.

Rib Articulation

Ribs articulate with thoracic vertebrae and the sternum.

Pelvic Anatomy

The ischial tuberosity is the part of the pelvis you sit on.

Male vs. Female Skeleton

• Male: Larger, heavier, narrower pelvis.

• Female: Smaller, lighter, wider pelvis for childbirth.

Joints

Types and Classification of Joints

Joints are classified by structure and function.

• Fibrous Joints: No movement; bones joined by fibrous tissue (e.g., sutures).

• Cartilaginous Joints: Limited movement; bones joined by cartilage (e.g., intervertebral discs).

• Synovial Joints: Freely movable; contain synovial fluid (e.g., knee, shoulder).

Synovial Joint Structure

• Articular Cartilage: Hyaline cartilage; covers bone ends, reduces friction.

• Joint Capsule: Encloses joint; contains synovial membrane.

• Synovial Fluid: Lubricates and nourishes joint.

• Ligaments: Connect bone to bone, stabilize joint.

Knee Joint

The knee is a complex synovial joint, containing menisci, ligaments (ACL, PCL, MCL, LCL), and articular cartilage.

Joint Movements

• Adduction: Movement toward midline.

• Abduction: Movement away from midline.

• Flexion: Decreases angle between bones.

• Extension: Increases angle between bones.

• Rotation: Bone turns around its axis.

Forms of Arthritis

• Osteoarthritis: Degenerative; wear and tear.

• Rheumatoid Arthritis: Autoimmune; inflammation.

• Gout: Uric acid crystal accumulation.

Table: Joint Classification and Examples

Type	Structural Classification	Example	Movement
Fibrous	Suture	Skull	Immovable
Cartilaginous	Symphysis	Pubic symphysis	Slightly movable
Synovial	Ball-and-socket	Shoulder, hip	Freely movable
Synovial	Hinge	Knee, elbow	Freely movable

Additional info:

• Articular cartilage is hyaline cartilage.

• Fontanels allow for rapid brain growth in infants.

• Sinuses also help humidify and filter inhaled air.