Bone

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Bones provide a structural framework for the body and support soft tissues, and constitutes part of the endoskeleton of vertebrates. Vital organs are protected by bones - Skull protects the brain, rib cage protects the heart and lungs, and the vertebrae protect the spinal cord. Bones also act as levers for muscles. When muscles contract, they pull on bones to produce movement.

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Bones store minerals, primarily calcium and phosphate, and release them into the bloodstream as needed. Red bone marrow produces red blood cells, white blood cells, and platelets. Yellow bone marrow stores adipose (fat) tissue, serving as an energy reserve.

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​There are basically 2 types of bone:

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• Compact (Cortical) Bone

  • Dense and forms the outer layer of bones.

  • Strong and heavy.

  • Contains osteons (Haversian systems).

• Spongy (Cancellous or Trabecular) Bone

  • Porous and found at the ends of long bones and inside flat bones.

  • Lighter, houses marrow, and absorbs shock.

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​Calcium is a major component of bones. However, the calcium we absorb by eating food also requires Vitamin D & K, magnesium, potassium and zinc for the calcium to be properly allocated to the required areas.

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For strong bones, collagen is more important than calcium. Without collagen, our bones will just be hard, but brittle. Just imagine dropping a piece of chalk onto the floor. Collagen acts as a binding agent, holding our bones in place, and acting as a form of "shock absorbant".

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Cartilage is a firm but flexible connective tissue found throughout the body. It's not as hard as bone, but it's stiffer than muscle.

Cartilage cushions joints and absorbs shock (e.g., in knees), provides structure in flexible areas (e.g., ears, nose), Forms the fetal skeleton before bone formation, reduces friction between bones in joints (articular cartilage). However, they are slow to heal due to lack of blood vessels (avascular), and relies on diffusion for nutrient supply.

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A tendon is a tough band of dense fibrous connective tissue that connects muscle to bone. It transmits force from muscle contraction to bones, thus causing movement. It also acts like a cable or rope by resisting tension.

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Tendons are composed mostly of collagen (Type I), which gives it high tensile strength. Tendons are arranged in parallel bundles, designed to handle pulling forces.

 

Important tendons include:

• Achilles tendon which connects calf muscles to heel bone.

• Patellar tendon which connects kneecap to shinbone.

 

Like cartilage, tendons are slow to heal due to limited blood supply, and are prone to tendonitis (inflammation of the tendon).(inflammation) or tears.

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A ligament is a tough, fibrous band of connective tissue that connects bone to bone at a joint. They are made mostly of collagen fibers (primarily Type I collagen)

 

The difference between tendon and ligament is that tendons connect muscle to bone, while ligaments connect bone to bone. Ligaments contain nerve endings that help sense joint position and movement, contributing to balance and coordination.

The functions of ligaments are to prevent excessive movement that could cause injury (e.g., hyperextension or dislocation), guide joint motion, and ensure that bones move in coordinated, safe ways. Elastic ligaments (e.g., ligamentum nuchae in the neck of some animals) contain more elastin and stretch more. Most human ligaments prioritize stability over elasticity.

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Examples of ligaments include:

• Anterior Cruciate Ligament (ACL) - Prevents forward movement of tibia relative to femur

• Posterior Cruciate Ligament (PCL) - Prevents backward movement of tibia

• Medial/Lateral Collateral Ligaments (MCL/LCL) - Stabilize sides of the knee

• Ligamentum flavum - Helps maintain upright posture

• Deltoid ligament - Stabilizes medial (inner) side of ankle

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Like cartilage and tendons, ligaments are also slow to heal due to poor blood supply, and the high collagen content resulting in. low cellularity. Some ligaments (like the ACL) don’t heal on their own and may require surgical repair or reconstruction.

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The skeleton is an integrated system that provides structure, enables movement, protects organs, and supports life itself. The skeleton is the framework of bones and cartilage in the body that:

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• Supports the body’s shape

• Protects internal organs

• Enables movement (with muscles)

• Produces blood cells (in bone marrow)

• Stores minerals like calcium and phosphorus

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2 Major Divisions of the Skeleton

1. Axial Skeleton (80 bones) that forms the central axis of the body.

2. Appendicular Skeleton (126 bones) that includes the limbs and girdles that attach to the axial skeleton.

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The skeleton provides protection for our softer internal organs: the skull protects the brain, rib cage protects the heart & lungs, the vertebrae protects the spinal cord, and the pelvis protects the reproductive organs.

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The skeleton uses bones act as levers; joints as pivots, using skeletal muscles pull on bones to produce movement.

The skeleton is also a form of mineral storage, especially calcium and phosphorus, which are released into blood as needed to maintain balance.

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Blood Cell Production (Hematopoiesis) occurs in red marrow of certain bones (e.g., sternum, pelvis) to produce red blood cells, white blood cells, and platelets.

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Yellow marrow in long bones stores fat, which are a form of ebergy storage.

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