Skeletal System

1. 80 Bones
   1. Skull, Vertebral column, rib cage

1. 126 Bones
   1. Limbs, Shoulders, Hips, Clavical

1. Support
2. Protection
3. Movement
4. Mineral Storage/Release
5. Energy Storage

   Annotations:

   • Adipose tissue is found in the yellow marrow
6. Blood Cell Production

   Annotations:

   • Red Marrow produces red blood cells, white blood cells and plasma. Process is called HEMATOPOIESIS (Hemopoiesis).

1. Long Bones

   Annotations:

   • Longer than they are wide. Example: Femus, Tibia, Finger bones.
   1. Long Bone Structure

      Annotations:

      • Consists of a shaft (diaphysis) and two expanded extremities (epiphysis).
      1. Diaphysis

         Annotations:

         • Consists of a think collar of compact bone surrounding a medullary cavity
         1. Medullary Cavity

            Annotations:

            • Contains yellow bone marrow
            1. Yellow Bone Marrow

               Annotations:

               • Fat (energy source)
      2. Epiphysis

         Annotations:

         • Consists of a thin layer of compact bone covering an interior of spongy bone.
         1. Metaphysis

            Annotations:

            • Portion of a long bone between the diaphysis and epiphysis. Contains the epiphyseal plate
            1. Epiphyseal Plate (Growth Plate)

               Annotations:

               • Composed of hyaline cartilage and found in long bones that are still growing in length. Becomes the epiphyseal line (disk) when bone growth stops.
               1. Epiphyseal Line (Disk)

                  Annotations:

                  • Cartilage of the epiphyseal plate is replaced by bone.
      3. Articular Cartilage

         Annotations:

         • A thin layer of hyaline cartilage that covers the ends of the epiphyses.
         • Located in areas where one bone articulates with another bone.
         • Functions: Reduces friction and absorbs shock during movement.
      4. Periosteum

         Annotations:

         • Tough sheath that covers the external surface except for the articular cartilage.
         • Functions: Essential for bone growth in diameter and repair. Point of attachment for ligaments and tendons.
      5. Endosteum

         Annotations:

         • Thin membrane that lines internal surfaces of bone. Essential for bone repair.
2. Short Bones

   Annotations:

   • About as long as they are wide (cube shaped) Example: Carpals, Tarsals
3. Flat Bones

   Annotations:

   • Thin and Flat Example: Scapulae (shoulder blade), sternum, ribs, most bones of the skull. Wormian Bones: Suture bones found between the flat skull bones.
4. Irregular Bones

   Annotations:

   • Have unusual shapes that fit none of the 3 previous classes. Example: Vertebrae and hip bones
5. Sesamoid Bones

   Annotations:

   • Round bones- embedded in tendons. Example: Knee cap

Annotations:

• General term for the soft tissue occupying the medullary cavity of a long bone and the spaces amid the trabeculae of spongy bone.

1. Yellow Bone Marrow

   Annotations:

   • Consists mostly of fat (energy source).
2. Red Bone Marrow

   Annotations:

   • Blood cell forming tissue= hematopoietic tissue.

1. Osteogenic Cells

   Annotations:

   • Stem cells that divide and develop into osteoblasts.
   • Located within the periosteum, endosteum, and the central canal.
   1. Osteoblasts

      Annotations:

      • Bone- building cells.
      • Synthesize and secrete collagen fibers and other organic components of bone matrix.
      • Initiate the process of calcification.
      1. Osteocytes

         Annotations:

         • Mature bone cells.
         • Osteoblasts that have become trapped by the secretion of matrix become osteosytes.
         • No longer secrete matrix.
         • Responsible for maintaining the bone tissue.
         1. Osteoclasts

            Annotations:

            • Large cells derived from the fusion of as many as 50 monocytes (a type of white blood cell).
            • Cells that digest bone matrix- this process is called bone resorption and is part of normal bone growth, development, maintenance, and repair.
            • Concentrated in the periosteum and endosteum.
            • On the side of the cell that faces the bone surface, the plasma membrane is deeply folded into a ruffled border. Here, the osteoclast secretes digestive enzymes to resorb the bone matrix. It also pumps out hydrogen ions to create an acid environment that eats away at the matrix.

Annotations:

• Is the nonliving structural part and consists of:  Water (~25%) Collagen fibers (~25%) Crystalized mineral salts (50%)

1. Collagen Fibers

   Annotations:

   • Provide the bone with flexibility- gives it resilience and the ability to resist stretching and twisting.
   • Frame work for calcification and mineral crystallization.
2. Crystalized Mineral Salts

   Annotations:

   • Mainly hydroxyapatite (interaction of calcium phosphate and calcium carbonate).
   • Trace amounts of magnesium, fluoride, and sulfate.
   • Minerals are deposited among the collagen fibers and crystallize giving bone its characteristic hardness.
3. Mineral Salts

   Annotations:

   • Are like the concrete and collagen fibers are like the metal robs in concrete.
   • Without the collagen fibers, bone would be very brittle.

Annotations:

• All 206 bones are a combination of compact and spongy bone.

1. Compact Bone

   Annotations:

   • The dense, solid, outer layer of the bone.
2. Spongy (Cancellous) Bone

   Annotations:

   • Contains lots of spaces in a honeycomb of needle-like projections called trabeculae.
   • Surrounded by compact bone and contains red marrow.

1. Osteons (Harversian Systems)

   Annotations:

   • Are the fundamental units of compact bone which are multiple cylindrical structural units.
   • Imagine these osteons as weight-bearing pillars that are arranged parallel to one another along the long axis of a compact bone.
   1. Osteon Components

      Annotations:

      • Each osteon consists of a single longitudinal central (Haversian) canal, surrounded by concentric layers of calcified bone matrix called lamellae.
      1. Central Canals

         Annotations:

         • Allow the passage of blood vessels, lymphatic vessels, and nerve fibers.
2. Perforating (Volkmann's) Canals

   Annotations:

   • Connect the blood and nerve supply between the periosteum, central (Haversian) canals and the medullary cavity.
3. Osteocytes and Canaliculi
   1. Osteocytes

      Annotations:

      • Occupy cavities known as lacunae at the junctions of the lamellae. 
   2. Canaliculi

      Annotations:

      • Canals that connect the lacunae to each other and to the central canal.
      • Allow osteocytes to exchange nutrients, wastes, and chemical signals to each other.

1. Spongy (Cancellous) Bone

   Annotations:

   • Does not contain true osteons (no central canals)
   1. Trabeculae

      Annotations:

      • Consists of lamellae arranged in an irregular latticework of thin beams of bone.

Annotations:

• A nuclear scanning test that identifies new areas of bone growth or breakdown.
• Used to evaluate damage (fractures, infection, trauma) to bones and detect cancer.

1. Procedure

   Annotations:

   • A Radioactive (bone-seeking) tracer is injected into a vein and images are collected (gamma camera).
   • Normal bone tissue will appear gray throughout- uniform uptake.
   1. "Cold Spots"

      Annotations:

      • Areas that absorb little or no tracer- decreased metabolism
      • Degenerative bone disease or lack of blood supply to the bone (bone infraction).
      1. "Hot Spots"

         Annotations:

         • Areas that absorb a lot of tracer- rapid bone growth or repair.
         • Fracture that is healing, bone cancer, a bone infection (osteomyelitis), arthritis, or a disease of abnormal bone metabolism (such as Paget's disease).

1. Ossification

   Annotations:

   • Process of bone formation.
2. Calcification

   Annotations:

   • Process of depositing calcium salts within a tissue.

Annotations:

• Before week 7, the human embryotic skeleton is made of stem cells that form fibrous membranes and hyaline cartilage in the shape of the future bones.
• After week 7, bone tissue starts replacing the fibrous membranes and hyaline cartilage by 2 methods.

1. Intramembaneous Ossification

   Annotations:

   • Development of bone from a fibrous membrane.
2. Endochondral Ossification

   Annotations:

   • Development of bone from hyaline cartilage.
3. Bone Growth

   Annotations:

   • Bones grow in length by the addition of bone material by the epiphyseal plate and increase in thickness by appositional growth.