Bone Structure and Function Quiz

Human Anatomy and Physiology - BIOL3306

• Course: Human Anatomy and Physiology
• Semester: Fall 2024
• Instructor: Nour Nissan

The Skeletal System

• The skeletal system encompasses bones, joints, and supporting tissues.
• Bones are the main organs of the system. Adults typically have 206 bones.
• Each bone consists of bone (osseous) tissue, dense regular collagenous tissue, dense irregular connective tissue, and bone marrow.

Functions of the Skeletal System

• Bones like the skull, sternum, and ribs protect underlying organs.
• Bones store minerals (calcium, phosphorus, and magnesium salts). These minerals are electrolytes, acids, and bases maintaining electrolyte and acid-base balance in the blood.
• Red bone marrow within bones produces blood cells.
• Yellow bone marrow, found in bones, contains adipocytes (fat-storing cells).
• Bones serve as attachment sites for skeletal muscles, enabling movement around joints.
• The skeleton provides structural support for the body.

Classification of Bones by Shape

• Long bones are longer than wide (e.g., bones in the limbs).
• Short bones are roughly cube-shaped (e.g., wrist and ankle bones).
• Flat bones are thin and broad (e.g., most skull bones and pelvic bones).
• Irregular bones have irregular shapes (e.g., vertebrae).
• Sesamoid bones are small, flat, oval-shaped bones within tendons (e.g., kneecap).

Structure of a Long Bone

• Periosteum: Outer dense irregular connective tissue membrane with blood vessels and nerves.
• Perforating fibers: Collagen that anchors the periosteum.
• Diaphysis: Shaft of the bone, lined by the endosteum (a membrane).
• Epiphyses: Ends of the long bone, filled with red bone marrow and covered with articular cartilage (hyaline cartilage).
• Compact bone: Hard, dense outer bone that resists linear compression and twisting forces.
• Spongy (Cancellous) bone: Inner, honeycombed-like bone. Provides space for bone marrow and resists forces in many directions.
• Epiphyseal lines: Remnants of the epiphyseal plate (growth plate), a line of hyaline cartilage in children and adolescents.

Structure of Short, Flat, Irregular, and Sesamoid Bones

• Share similarities with long bones but may have fewer structures.
• In flat bones, the spongy bone is called diploë.
• Flat and irregular bones sometimes contain air-filled spaces called sinuses.

Blood & Nerve Supply to Bone

• Bones receive blood vessels and sensory fibers.
• Blood supply to long bones comes from the periosteum and one or two nutrient arteries.
• Short, flat, irregular, and sesamoid bones receive blood from vessels penetrating the periosteum.

Red and Yellow Marrow

• Bone marrow consists primarily of blood vessels and adipocytes (yellow bone marrow).
• Yellow bone marrow can convert to red bone marrow in times of emergency.
• Red bone marrow is a network of reticular fibers supporting islands of hematopoietic cells.
• Infants primarily have red bone marrow, but the ratio shifts to yellow marrow as they age.
• Adults have mostly yellow marrow except in flat bones and ends of long bones.

Bone Marrow Transplantation

• Patients with certain blood disorders may benefit.
• A matching donor's marrow is harvested and given to the recipient.
• Recipient's marrow is destroyed before transplantation to allow new cells to take hold.
• New blood cells typically develop in 2-4 weeks.

The Extracellular Matrix of Bone

• Inorganic Matrix: About 65% of bone weight, consisting mainly of calcium salts and phosphorus in a structure called hydroxyapatite. Contributes to bone hardness and resistance to compression/bending.
• Organic Matrix (Osteoid): About 35% of bone weight, composed of protein fibers (mostly collagen), proteoglycans, glycosaminoglycans, glycoproteins, and bone-specific proteins like osteocalcin. Provides flexibility and resistance to twisting/tensile forces.

Bone Cells

• Osteoblasts: Build bone tissue.
• Osteocytes: Maintain bone tissue.
• Osteoclasts: Break down bone tissue.

Osteopetrosis

• Also known as "Marble Bone Disease," it's a genetic disorder involving defective osteoclasts.
• Characterized by increased bone mass, but the bone is weak and brittle.
• Two forms: infantile (more severe) and adult.
• Symptoms vary but may include bone pain, recurrent fractures, nerve trapping, and joint pain.
• Some forms may be fatal.

Histology of Bone

• Compact bone: Hard, dense, outer shell, capable of resisting high stress, organized into osteons (Haversian systems).
• Spongy (Cancellous) bone: Forms a protective framework for bone marrow and resists many directions of force. Organized into trabeculae with concentric lamellae containing osteocytes.

Compact Bone Structure

• Lamellae: Thin layers of bone matrix.
• Osteon (Haversian system): Fundamental unit of compact bone. Contains concentric lamellae, central canal (Haversian canal), and lacunae.

Osteoporosis

• Bone disease caused by inadequate inorganic matrix.
• Results in brittle bones, increased risk of fractures, and slow healing.
• Can be affected by diet, hormones, age, lack of exercise, and other factors.

Bone Growth in Length

• The epiphyseal plate is a hyaline cartilage plate that enables the lengthening of long bones.
• The plate consists of five zones associated with cellular changes, calcification, and ossification.
• Growth essentially ceases once the epiphyseal plate closes (usually during late adolescence).

Bone Growth in Width

• Bone continues to widen through osteoblast activity in the periosteum.
• The deposition of new bone outwards leads to an increase in width.
• Removal of inner bone lamellae through osteoclast activity creates space for the newly formed bone.

Gigantism and Acromegaly

• Gigantism results from excess growth hormone before the epiphyseal plates close leading to excessive longitudinal and appositional growth.
• Acromegaly occurs after the epiphyseal plates close, resulting in enlarged bones in the skull face hands and feet and soft tissues (e.g tongue) sometimes leading to heart/kidney malfunction and diabetes mellitus.

Bone Remodeling

• A continuous process of bone formation and resorption.
• Driven by many factors, including calcium homeostasis, bone repair, replacement of old with new bone, and adapting to stress.
• In healthy adults, bone formation roughly equals bone resorption.
• In children and adolescents, bone formation typically exceeds resorption.
• Factors such as hormones and nutrient intake influence remodeling.

Bone Repair

• Repair of bone fractures involves hematoma formation, then fibro and chondroblast infiltration and forming a soft callus which is eventually replaced by primary and then secondary bone.
• Several classes of fractures exist (simple, compound). Treatment usually involves stabilization and immobilization for several weeks.

Calcium Ion Intake and Fracture Risk

• The National Academy of Sciences recommends high calcium intake, however long term studies have demonstrated no correlation between higher calcium intake and lower fracture rates in the US.
• The ideal intake is around 700mg/day with appropriate vitamin D and K intake.