Test 2

Bone Structure and Function

  • General Functions of Bone

    • Protection and Support: Provides structural integrity and protects vital organs.
    • Mineral Storage: Primary reservoir for calcium and other minerals.
    • Movement: Serves as levers for muscles to generate movement.
    • Hematopoiesis: Blood cell formation occurs in red bone marrow.
    • Triglyceride Storage: Stores fats in yellow marrow.

  • Basic Anatomy of Long Bone

    • Epiphyses: Ends of long bones.
    • Diaphysis: Shaft of long bone.
    • Epiphyseal Plate: Growth plate in growing bones; turns into an epiphyseal line upon reaching maturity.
    • Articular Cartilage: Hyaline cartilage at bone ends to reduce friction.
    • Medullary Cavity: Contains yellow marrow, site for fat storage.
    • Endosteum: Inner lining of the bone.
    • Periosteum: Outer lining of the bone, containing osteoblasts and osteoclasts.

Types of Bone Tissue

  • Spongy Bone (Cancellous or Trabecular)

    • Characteristics: Lightweight, houses red marrow, appears 'random' in structure.
    • Location: Found in ends of long bones and irregular bones.

  • Compact Bone (Dense Bone)

    • Characteristics: Densely packed and provides support.
    • Anatomy of Compact Bone:
    • Osteon: Functional unit, allows communication through canaliculi.
    • Central Canal: Houses blood vessels and nerves.
    • Concentric Lamella: Rings of bone around the central canal.
    • Interstitial Lamellae: Fill spaces between osteons.
    • Circumferential Lamellae: Rings around the entire bone.

Bone Development and Growth

  • Bone Growth

    • Interstitial Growth: Lengthening occurs at the epiphyseal plates until maturity, forming the epiphyseal line.
    • Appositional Growth: Increases bone width through the addition of new bone layers on existing ones.

  • Bone Formation Types (Ossification)

    • Intramembranous Ossification:

    • Process:

      1. Mesenchyme differentiates into fibroblasts that create a collagen model.
      2. Blood vessels deliver osteoblasts to start ossification.
      3. Spongy bone formed initially, eventually turns into compact bone.

    • Example: Most skull bones develop this way.

    • Endochondral Ossification:

    • Process:

      1. Mesenchyme differentiates into chondroblasts forming a cartilage model.
      2. Nutrient artery invades, initiating primary ossification center.
      3. Spongy bone develops and remodels to establish medullary cavity and compact bone surfaces.
      4. Secondary ossification centers develop in the epiphysis.

    • Example: Most long bones.

Bone Remodeling and Healing

  • Fracture Types

    • Closed (Simple) vs. Open (Compound):
    • Traumatic vs. Pathological Fractures:
    • Examples of Fractures:
    1. Comminuted: Bone shattered into pieces.
    2. Greenstick: One side breaks while the other bends.
    3. Pott’s Fracture: At the distal end of the tibia and fibula.
    4. Colles’ Fracture: At the distal end of the radius.

  • Fracture Repair Stages:

    • Fracture Hematoma: Formation time spans minutes to hours.
    • Soft Callus Formation: Lasts days to weeks, involving fibrocartilage formation.
    • Bony Callus Formation: Takes months to years for bone tissue to fully form.
    • Remodeling: The final adjustments of bone structure occur during this stage.

  • Requirements for Strong Bones:

    • Minerals: Calcium (Ca) and phosphorus (P).
    • Vitamins:
    • Vitamin D: Essential for calcium absorption.
    • Exercise: Promotes the reinforcement of bones through Wolff's Law.
    • Collagen Synthesis: Important for overall bone structure.
    • Hormones:
    • Growth Hormone, Sex Hormones, Parathyroid Hormone (PTH), Calcitonin, Calcitriol.

Bone Disorders

  • Osteopenia vs. Osteoporosis:

    • Osteopenia: Initial stage of bone density loss.
    • Osteoporosis: Severe bone density loss, leading to higher fracture risk.

  • Rickets:

    • Caused by low calcium or vitamin D deficiency, commonly in children.

  • Osteomalacia:

    • Similar to rickets but occurs in older individuals.

  • Osteogenesis Imperfecta:

    • Known as "brittle bone disease," caused by a mutation in collagen.

  • Paget’s Disease:

    • Disorder characterized by abnormal bone remodeling.

Cellular and Tissues Components of Bone

  • Histology of Bone

    • Fiber Composition:

    • Collagen fibers provide toughness and flexibility.

    • Basic Cell Types:

    1. Osteoprogenitor Cells: Stem cells that differentiate into osteoblasts.
    2. Osteoblasts: Cells responsible for bone matrix secretion.
    3. Osteocytes: Mature bone cells; maintain bone tissue.
    4. Osteoclasts: Cells responsible for bone resorption (breakdown).
    • Matrix Components:
    • Inorganic: Calcium salts, make up about 2/3 of the matrix, providing hardness.
    • Organic: Consists of the collagen matrix, comprising approximately 1/3 of bone.

Tissue Types and Repair

  • Primary Tissue Types:

    • Characteristics and classifications of epithelial, connective, muscular, and neural tissues.
    • Importance of understanding functions and locations of each tissue type.

  • Cell Junctions:

    • Tight Junctions: Secure junctions that prevent leakage between cells, e.g., in the brain and gastrointestinal tract.
    • Desmosomes: "Spot welds" that provide strength and support.
    • Gap Junctions: Allow direct communication between cells, important in cardiac and neural tissues.

  • Glandular Epithelium Types:

    • Endocrine Glands: Secrete hormone products directly into the bloodstream impacting target tissues.
    • Exocrine Glands: Secrete their products into ducts leading to external surfaces.

  • Modes of Secretion:

    • Merocrine: Secretion via exocytosis (e.g., salivary glands).
    • Apocrine: Secretion involves the apical portion of the cell breaking away (e.g., mammary glands).

  • Tissue Repair:

    • Variations in healing rates between vascular (well-blood-supplied) and avascular (poor-blood-supplied) tissues.
    • Inflammation Symptoms:
    • Swelling, redness, pain, temperature changes due to histamine release from mast cells.