Skeletal Anatomy and Functions

Bone is dynamic, Cartilage heals slowly (avascular)

Skeleton Types

Exoskeleton: external support structure in arthropods

Endoskeleton: internal support structure in vertebrates

Skeleton Functions

• Support

• Protection

• Movement/leverage

• Mineral storage (Ca²⁺, phosphate)

• Blood cell production (hematopoiesis)

• Fat storage (yellow marrow)

Axial Skeleton

Protects vital organs

• Skull

• Vertebral column

• Ribs

• Sternum

• Hyoid bone

Appendicular Skeleton

Movement and locomotion

• Limbs

• Pectoral girdle

• Pelvic girdle

Macroscopic Bone Structure

• Long bone: epiphysis → growth plate → metaphysis → diaphysis

Epiphysis

ends of bone

Diaphysis

shaft

Metaphysis

region between epiphysis and diaphysis

Epiphyseal plate (growth plate)

cartilage region for longitudinal growth

Compact (cortical) bone

• Dense outer layer

• Strong and protective

Spongy (cancellous/trabecular) bone

• Porous inner bone

• Contains trabeculae

• Houses marrow

Red marrow

• Hematopoiesis

• Produces RBCs, WBCs, platelets

Yellow marrow

• Fat storage

• Can convert back to red marrow if needed

Periosteum

• Connective tissue covering bone

• Contains blood vessels and nerves

• Important for repair and osteoblast differentiation

Tendons vs Ligaments

• Tendons: muscle → bone

• Ligaments: bone → bone

Bone Matrix

• Collagen → flexibility/tensile strength

• Hydroxyapatite (calcium phosphate) → hardness/compression resistance

Osteon (Haversian System)

Functional unit of compact bone

Lamellae

• Concentric rings of matrix

Lacunae

• Spaces containing osteocytes

Canaliculi

• Tiny channels connecting osteocytes

• Permit nutrient/waste exchange

Central (Haversian) canals

• Longitudinal blood vessels/nerves

Volkmann’s canals

• Transverse connecting canals

Osteoblasts

• Build bone

• Secrete matrix

Osteoclasts

• Break down bone

• Bone resorption

Osteocytes

• Mature bone cells

• Maintain bone tissue

Ossification

Process of bone formation

Endochondral Ossification

• Bone replaces cartilage

• Forms long bones

• Most common type

Intramembranous Ossification

• Bone develops directly from mesenchyme

• Forms flat bones of skull

Growth Plate

• Cartilage area where long bones lengthen

• Closes after puberty

Wolff’s Law

Bone remodels according to stress placed on it

Parathyroid Hormone (PTH)

Raises blood calcium

• Stimulates osteoclast activity

• Increases Ca²⁺ reabsorption in kidneys

• Activates vitamin D

Calcitonin

Lowers blood calcium

• Inhibits osteoclasts

Vitamin D

Increases calcium absorption from intestines

Cartilage

Properties

• Flexible connective tissue

• Avascular (slow healing)

• Made of chondrin matrix

Chondrocytes

• Cells that secrete cartilage matrix

Cartilage Types

• Hyaline: most common, joints/trachea

• Fibrocartilage: intervertebral discs

• Elastic: ear

Fibrous Joints

• Immovable

• Example: skull sutures

Cartilaginous Joints

• Slightly movable

• Example: vertebral discs

Synovial Joints

Freely movable

Synovial Fluid Functions

• Lubrication

• Shock absorption

• Nutrient distribution

Common Synovial Joint Types

• Ball-and-socket: shoulder, hip

• Hinge: elbow, knee

• Pivot: atlas-axis, radius-ulna

Muscle Actions

Flexion

• Decreases joint angle

Extension

• Increases joint angle

Abduction

• Away from body midline

Adduction

• Toward body midline

Supination

• Palm up/anterior

Pronation

• Palm down/posterior