Big Idea 1 Notes - Skeletal System

Big Idea

Bone as a Living Organ
- Contains all four types of tissues:
  - Connective Tissue: Predominantly bone (osseous) tissue along with cartilage and dense connective tissue covering the bone’s exterior.
  - Nervous Tissue: Present in the nerves associated with bones.
  - Epithelial Tissue: Found in blood vessels that supply nourishment to bones.
  - Muscle Tissue: Skeletal muscle tissue is attached to bones.

Total Count: 206 bones constitute nearly 1/5th of a healthy adult's body weight, including bones, cartilage, ligaments, and joints.
Skeleton Regeneration: Entire skeleton is rebuilt every 7-10 years.
Importance of Skeleton:
- Provides essential support to other body parts.
- Protects delicate organs like the brain.
- Capable of self-repair after injury.

Support: Acts as a framework to support the body's structure.
Protection: Safeguards vital organs; e.g., skull protects the brain, rib cage guards the heart.
Movement: Skeletal muscles are connected to bones via tendons, leveraging bones as levers for movement.

Mineral Storage: Stores minerals such as calcium and phosphate, which can be released into the bloodstream when necessary.
Energy Storage: Stores fat in yellow bone marrow.
Blood Cell Formation (Hematopoiesis): Occurs in red bone marrow of certain bones.
Hormone Production: Vital for maintaining homeostasis.
- Produces osteocalcin, a hormone important for insulin secretion, glucose regulation, and energy usage.
- Helps regulate blood calcium levels.

Criteria: Bones categorized by location (axial vs. appendicular skeletons) and shape, which dictates their function.
Four Main Types:
1. Long Bones:
  - Longer than wide.
  - Mostly in limbs, acting as levers for movement.
  - Examples: Humerus, femur, metacarpals.
2. Short Bones:
  - Cube-shaped, equal width and length.
  - Provide stability with minimal movement.
  - Examples: Carpals, tarsals, patella (sesamoid bone).
3. Flat Bones:
  - Thin and flat, sometimes curved.
  - Large surface area for muscle attachment.
  - Examples: Sternum, scapula, ribs.
4. Irregular Bones:
  - Abnormal shape, highly specialized.
  - Examples: Hip bones, vertebrae.

General Structure:
- Consists of a dense outer layer of compact (cortical) bone and a porous inner layer of spongy bone.
- Basic internal structure is consistent across bones.

Osteons: The structural unit; long cylinders that function as weight-bearing pillars.
- Composed of lamellae: Hollow tubes filled with salts and collagen to resist torsion stress.
- Contains Haversian canals with blood vessels and nerve fibers.

Less organized, lacking osteons.
- Contains trabeculae, tiny struts that resist stress and house bone marrow.
- Types of Bone Marrow:
  - Red Bone Marrow: Responsible for blood cell production.
  - Yellow Bone Marrow: Stores energy in fat.

Often rough with distinct markings due to muscle and ligament activity.
Types of Markings:
- Projections: Where muscles and ligaments attach.
- Surfaces: Form joints.
- Depressions/Openings: Allow blood vessels and nerves to run through.

Osteocytes: Maintain bone structure, housed in lacunae; function like foremen creating a response to stimuli.
Osteoblasts: Responsible for building and constructing bones through calcification.
Osteoclasts: Regenerate bone by absorbing tissue in areas that are not required.

Ossification: Process of forming bone tissue, crucial for embryo formation, growth, and remodeling.
- Types:
  - Intramembranous Ossification: Development from fibrous tissue, e.g., clavicle.
  - Endochondral Ossification: Replacement of cartilage with bone, applicable to most bones.
- Cartilage remains at certain locations, such as articular surfaces and epiphyseal plates for growth.

Continuous process essential to prevent brittleness due to crystallization of calcium.
Process:
- Osteocytes signal osteoclasts to address damage.
- Osteoclasts resorb bone, returning calcium to blood.
- Macrophages facilitate tissue remodeling.
- Osteoblasts build new bone.

Fracture: Break in bone.
Treatment: Needs reduction (realignment) and immobilization for healing.
Repair Steps:
- Hematoma forms at the break site.
- Fibrocartilaginous callus connects broken ends.
- Osteoblasts generate spongy bone to replace the callus.
- Remodeling consolidates bone structure.