Chapter 6: Osseous Tissue and Bone Structure

Osseous Tissue and Bone Structure

Introduction

• This lecture covers chapter six, focusing on osseous tissue and bone structure.
• The lecture exam will be on Tuesday.
• A study guide will be posted soon.

Skeletal System

• The skeleton is divided into two main sections:
  • Axial skeleton: 80 bones, including the skull, thorax, and vertebral column, forming the longitudinal axis of the body.
  • Appendicular skeleton: 126 bones, including the limbs and girdles that attach them to the axial skeleton.
• Total of 206 bones in an adult.
• Includes associated cartilage, ligaments, and other connective tissues

Functions of the Skeletal System

• Support: Provides structural support for the body.
• Storage:
  • Minerals: Primarily calcium, but also phosphorus and manganese.
  • Lipids: Stored in yellow bone marrow.
• Production of Red Blood Cells: Occurs in red bone marrow.
• Protection: Protects vital organs such as the heart and lungs via cavities and cages like the rib cage.
• Leverage: Facilitates movement through joints, muscles, and ligaments.

Categories of Bones

• Flat bones: Skull bones like the parietal and frontal bones.
• Sutural bones: Found within the sutures of the skull.
• Long bones: Femur and humerus.
• Irregular bones: Vertebrae.
• Sesamoid bones: Round bones like the patella (kneecap).
• Short bones: Carpals in the wrist.

Bone Surface Markings

• Generally refers to a long bone.
• Head: The round part of the end of the bone.
• Neck: Connects the head to the diaphysis (shaft).
• Diaphysis: The shaft of the bone, the elongated body.
• Process: Any projection or bump on a bone, usually for muscle attachment.
  • Tubercle: A small, rounded projection.
  • Tuberosity: A small, rough projection over a broad area, also for muscle attachment.
  • Trochlea: A smooth, grooved articular process shaped like a pulley.
  • Condyle: A smooth, rounded articular process, forming one half of a joint.
• Foramen: Normal hole in a bone for the exit of nerves and blood vessels.
• Sinuses: Cavities in the frontal and maxillary bones, used as natural amplifiers for voice.
• Meatus: A canal or long tube with openings on both ends (e.g., the ear canal).
• Fissure: An elongated cleft or gap.
• Facet: A joint surface that can be flat or curved. When curved, it is called a condyle.
• Trochanter: A large, rough projection.
• Crest: A prominent ridge.
• Line: A low ridge, more delicate than a crest.
• Spine: A pointed or narrow process used for muscle attachments.
• Ramus: An extension of a bone that makes an angle with the rest of the structure.
• Sulcus: A deep narrow groove.
• Fossa: A shallow depression or recess in a bone surface, often where a muscle lies.

Long Bone Features

• Epiphysis: Expanded area at each end of the bone, largely composed of spongy bone.
• Diaphysis: The shaft of the bone, composed of compact bone.
• Articular Cartilage: Covers portions of the epiphysis that form articulations (joints). It is made of hyaline cartilage and is mostly avascular.
• Metaphysis: Connects the epiphysis to the diaphysis, representing the transition area.
• Medullary Cavity: Located inside the diaphysis, containing yellow bone marrow (adipose tissue).
• Nutrient Artery/Vein: Provides access to the marrow cavity through the nutrient foramen, supplying the osteons of compact bone with blood.
• Epiphyseal Plate: (Growth plate) Area where bone grows in length, especially important during development.
• Periosteum: A thin membrane surrounding almost the entirety of the bone. Contains cell types.

Bone Cells

• Osteocytes:
  • Mature bone cells that cannot divide.
  • Maintain protein and mineral content of surrounding matrix.
  • Found in lacunae (little pockets) separated by layers of matrix (lamellae).
  • Interconnected by canaliculi.
• Osteoblasts:
  • Immature bone cells that perform osteogenesis (creating new bone material).
  • Lay down new bone mineral.
• Osteoclasts:
  • Remove bone material by releasing acids and proteolytic enzymes to dissolve bone matrix.
  • High osteoclast activity can lead to high levels of calcium in the blood.

Compact Bone

• Strong and highly organized.
• Osteon: Functional unit of compact bone, organized in concentric circles.
• Central Canal: Located in the center of each osteon, containing blood vessels.
• Lamellae: Concentric layers or rings around the central canal.
• Lacunae: Small spaces between the lamellae where osteocytes reside.
• Canaliculi: Small channels that connect the lacunae with each other and with the central canal, allowing for nutrient and waste exchange.

Spongy Bone

• Characterized by its architecture, featuring trabeculae (open, hole-like networks).
• Trabeculae create an open network that helps to withstand stress from various angles.
• Has a honeycomb appearance.

Bone Growth

• Appositional Growth: Increases bone diameter of existing bones. Osteogenic cells differentiate into osteoblasts that add bone matrix under the periosteum.
• Endochondral Ossification:
  • Cartilage model enlarges.
  • Blood vessels grow around the edges.
  • Blood vessels penetrate cartilage and enter the central region.
  • Growth continues along with remodeling.
  • Capillaries and osteoblasts migrate into the epiphysis.
  • Epiphysis fills with spongy bone.
• Epiphyseal Closure: At puberty, hormones stimulate increased bone growth and cartilage is replaced. The cartilage narrows until it disappears, leaving the epiphyseal line in adults.
• Intramembranous Ossification:
  • Some bones form without a cartilaginous model.
  • Mesenchymal stem cells differentiate into osteoblasts within embryonic or fibrous connective tissue.
  • Occurs in deeper layers of the dermis.
  • Examples: Bones of the skull, lower jaw, collarbone, and sesamoid bones.

Clinical Disorders

• Pituitary Growth Failure: Inadequate growth hormone production, leading to abnormally short bones.
• Arachondroplasia: Epiphyseal cartilage of long bones grows slowly and is replaced by bone early in life, resulting in short, stocky limbs.
• Marfan's Syndrome: Inherited metabolic condition with excessive cartilage formation at the epiphyseal cartilages, resulting in a very tall person with long, slender limbs.
• Giantism: Overproduction of human growth hormone before the bones fuse, leading to excessive bone growth.
• Agromegaly: Overproduction of human growth hormone in adulthood (after bone fusion), leading to thicker bones.
• Fibrodysplasia: Gene mutation that causes bone to form around skeletal muscle, leading to bones developing in unusual places.

Bone Mineralization

• Bone acts as a mineral reservoir, containing inorganic ions that contribute to osmotic balance and are vital in physiological processes.
• Bone composition:
  • 67% inorganic compounds
  • 33% organic compounds
• Bones contain 99% of the body's calcium.
• Calcium is important for muscle contraction, blood coagulation, and nerve impulse generation.

Calcium Homeostasis

• Maintaining calcium levels is controlled by the intestines, bone cells (osteoclasts and osteoblasts), and kidneys.
• Calcitonin:
  • Hormone synthesized and released by the thyroid gland.
  • Stimulates osteoblast activity.
  • Inhibits osteoclast activity.

Bone Fractures

• A crack or break in a bone due to extreme mechanical stress.
• Repair involves four steps:
  • Fracture hematoma: Formation of a large clot.
  • Internal and external callus formation: Network of spongy bone and cartilage stabilizes the fracture.
  • Spongy bone formation: Replacement of cartilage with spongy bone.
  • Compact bone formation: Spongy bone replaced by compact bone.
• Categories of fractures:
  • Closed or simple: Completely internal, no break in the skin.
  • Open or compound: Projects through the skin.
  • Transverse: Breaks the shaft across the long axis.
  • Spiral: Produced by twisting.
  • Displaced: Produces new and abnormal bone arrangements.
  • Non-displaced: Retains normal alignment.
  • Green stick: One side of the shaft is broken; the other side is bent.
  • Compression: Vertebrae compressed.
  • Comminuted: Shattered affected area with fragments.
  • Epiphyseal: Occurs where the bone matrix is calcifying.
  • Pott's: Affects both medial and lateral malleolus (ankle).
  • Cole's: Break in the distal radius.