Anatomy of Bursae

Bursae

• Bursae are closed sacs of serous membrane, typically collapsed and filled with a thin lubricating fluid.
• Their primary function is to reduce friction, allowing smooth movement between structures.
• Subcutaneous bursae are located between skin and bony prominences (e.g., elbow, knee).
• Subfascial bursae exist beneath deep fascia, while subtendinous bursae facilitate tendon movement over bone.
• Synovial tendon sheaths are elongated bursae that encase tendons in various tunnels.
• Bursae can communicate with synovial cavities in joints.
• Important organs like the heart, lungs, and abdominal viscera are surrounded by collapsed bursal sacs.
• Visceral layers wrap closely around organs, while parietal layers contact body walls.

Skeletal System

• The skeletal system comprises two main parts: the axial skeleton (head, neck, trunk) and appendicular skeleton (limbs, girdles).
• Cartilage and bone form the skeleton, with cartilage being a semirigid connective tissue offering flexibility.
• Perichondrium, a fibrous membrane, covers nearly all cartilage.

Types of Cartilage

• Hyaline cartilage: Found covering articular surfaces; crucial for long bone growth; has poor repair capacity.
• Fibrocartilage: Contains numerous collagen fibers; present in joints and intervertebral discs; repairs slowly.
• Elastic cartilage: Rich in elastic fibers; found in structures like the ear and epiglottis; also repairs with fibrous tissue.

Bone Characteristics

• Bone is a specialized, hard connective tissue essential for body support, protection of organs, movement, and storage of salts.
• The periosteum is a fibrous covering around bones, excluding articular cartilage regions.
• Bone types: compact bone (dense, hard) and spongy (trabecular) bone (contains spaces).

Bone Classification

• Long bones: Tubular shape (e.g., humerus).
• Short bones: Cuboidal shape (e.g., tarsals, carpals).
• Flat bones: Protective function (e.g., cranium, scapula).
• Irregular bones: Various shapes (e.g., vertebrae, facial bones).
• Sesamoid bones: Develop in tendons (e.g., patella).

Bone Markings and Formation

• Bone markings indicate tendon, ligament, and vascular attachments. Includes terms like condyle, crest, epicondyle, and foramen.
• Features can indicate where structures attach or serve as joints.

Bone Development

• Bone growth and maturation take years (e.g., humerus ossification begins at 8 weeks, complete by age 20).
• Derived from mesenchyme through two processes: intramembranous ossification (direct from mesenchyme) and endochondral ossification (from cartilage).

Long Bone Growth

• Growth occurs at cartilaginous epiphyseal plates, where primary and secondary ossification centers form.
• The diaphysis (shaft) grows at each end until the epiphyseal plates are ossified, leading to fusion (synostosis).

Vasculature and Innervation of Bones

• Bones are highly vascularized with nutrient arteries supplying blood, accompanied by veins and sensory nerves.
• Periosteum is sensitive to tension and tearing, contributing to pain sensation during fractures.