B3M2C1

BONES

Classification of Bones

  • Based on shape or form:

    • Long bones:

      • Examples: Humerus, Radius, Ulna, etc.

    • Short bones:

      • Examples: Carpal and tarsal bones.

    • Flat bones:

      • Examples: Skull, Sternum, Ribs, etc.

    • Irregular bones:

      • Examples: Vertebrae and hip bones.

  • Based on microscopic appearance:

    • Spongy (Cancellous) Bone:

      • Consists of anastomosing, branching plates or bars.

      • Has inter-communicating spaces filled with bone marrow.

      • Lies internal to compact bone.

    • Compact Bone:

      • Appears as a solid mass with arranged lamellae containing microscopic spaces and canals.

      • Surrounds a large marrow cavity.

Functions of Bones

  • Storage of calcium for blood and tissue fluid management.

  • Provides internal support for the body.

  • Protects vital organs within cranial and thoracic cavities.

  • Serves as muscle and tendon attachment sites.

  • Encloses hemopoietic tissue in marrow for hemopoiesis.

Structure of a Long Bone

Gross or Macroscopic Parts

  • Diaphysis (Shaft):

    • Cylindrical part made of compact bone with marrow cavity.

  • Epiphysis:

    • Broad end with initial hyaline cartilage in early bone development, replaced by spongy bone during growth.

    • Contains epiphyseal cartilage plate for growth.

  • Metaphysis:

    • Spongy bone zone connecting epiphyseal cartilage plate to diaphysis, involved in bone length increase until adulthood.

Bone Matrix

  • Composed of 35% organic matrix and 65% inorganic salts.

  • Organic Matrix:

    • Glycosaminoglycans (e.g., chondroitin sulfate, keratan sulfate, hyaluronic acid) and non-collagen proteins (e.g., osteocalcin, osteopontin).

    • Collagen Type I constitutes 90% of organic matter, providing strength and resilience.

  • Inorganic Component:

    • Mainly calcium and phosphate, contributing to bone hardness.

  • Changes with maturity:

    • Organic content remains constant, while inorganic content increases.

Microscopic Appearance of Diaphysis (Compact Bone)

  • Haversian System (Osteon):

    • Structural unit with components:

      • Haversian Canal: Contains blood vessels, lymphatics, and nerves.

      • Haversian Lamellae: Concentric bony lamellae around the canal, with collagen fiber orientation varying between lamellae.

      • Osteocytes: Found in lacunae between lamellae, communicate via canaliculi for nutrient exchange.

      • Cementing Line: Outer boundary of the Haversian system made of ground substance.

Voltmann's Canal

  • Perpendicular canals connecting Haversian systems to bone surface and marrow cavity, conducting blood vessels and nerves.

  • Periosteum: Dense fibrous tissue covering bone, involved in bone formation.

  • Endosteum: Connective tissue lining marrow cavities, with osteogenic potential.

Calcium Mobilization from Bone

  • Low calcium levels stimulate parathyroid hormone secretion.

  • Osteoblast suppression leads to osteoclast stimulation for bone resorption and calcium release for blood normalcy.

Internal Reorganization of Bone

  • Thickening of trabeculae during ossification leads to primitive Haversian systems.

  • Adult Haversian systems develop through secondary bone formation.

Cartilage

General Characteristics

  • Cells: Chondrocytes in lacunae, varying from spherical to angular.

  • Matrix: Solid yet flexible, made of proteoglycans (chondroitin sulfate, keratan sulfate).

  • Connective Tissue Fibers: Primarily Type II collagen, lesser types present.

Types of Cartilage

  • Hyaline Cartilage: Most common, translucent with masked collagen fibers.

  • Elastic Cartilage: Contains elastic fibers, more opaque and flexible.

  • Fibrocartilage: Dense collagen fiber bundles between hyaline and dense connective tissues.

Cranial Bones

Special Features of the Skull

  • Sutures: Immovable joints between skull bones.

  • Fontanels: Soft spots aiding in skull compression during birth.

  • Sinuses: Air-filled cavities aiding in resonance, not to be confused with mastoid cells.

Cranial Bone Markings

  • Frontal Bone: Forms roof of orbits, with frontal sinuses above the nose.

  • Sphenoid Bone: Keystone of cranial floor, contains sella turcica for pituitary gland.

  • Parietal Bones: Form sides and roof of cranial cavity.

  • Temporal Bones: Located on lower sides of cranium, housing the external auditory meatus.

Neck

Surface Landmarks of the Neck

  • Thyroid Cartilage: Forms laryngeal prominence, attached to hyoid bone.

  • Cricoid Cartilage: Signet ring-shaped, providing muscle attachments in the larynx.

  • External Jugular Vein: Prominent vein on the lateral neck, noticeable in active individuals.

Triangles of the Neck

  • Anterior Triangle: Contains submandibular, submental, carotid, and muscular triangles with various contents including salivary glands and arteries.

  • Posterior Triangle: Divided into occipital and subclavian triangles, containing nerves and vascular structures.

Terms

  • Concussion: Temporary neural dysfunction due to a blow to the head.

  • Contusion: Bruising of brain tissue disrupting functions, leading to potential hematoma formation.

  • Laceration: Means disruption in the continuity of the skin.

Fractures

  • Defined as linear deformation in bone from forces exceeding material strength.

  • Classified by location, fragmentation, and continuity; includes both open and closed types.

Management of Fractures

  • Requires evaluation of neurovascular status and splinting for stabilization.

  • Open Fractures: Require surgical treatment to prevent infection due to increased soft tissue injury.

  • Antibiotic prophylaxis is necessary for open fractures to prevent infection during treatment.

Nonsteroidal Anti-inflammatory Drugs (NSAIDs)

Mechanism of Action

  • Inhibit cyclooxygenase enzymes, reducing pain, inflammation, and fever.

Therapeutic Use and Side Effects

  • Used against low- to moderate-intensity pain, effective as antipyretics, but can cause gastrointestinal issues.

  • Risks include allergic reactions, potential for hypersensitivity, especially for patients with a history of penicillin allergy.

Conclusion

  • The role of bones and related structures in the body is multifaceted, providing support, protection, and functional movement. Understanding their classification, function, and potential pathology aids in comprehensive care.