Skeletal Levels of Organization

7:30 PM that same day...

The structural hierarchy of the skeleton is as follows:

- Chemistry/molecular scale: Water, minerals, collagen, and other proteins

- Nanoscale: Mineral crystals are embedded within collagen to form composite fibers

- Submicron scale: Mineralized fibrils are organized into lamellae

- Micron scale: Lamellae from osteons (compact bone) or trabeculae (spongy bone)

- Macroscale: Compact and spongy bone combine to form whole bones

Primary Components of Bone

Inorganic

- Calcium

- Phosphorus (phosphate ions)

- Water

Organic

- Collagen

- Protoglycans, which are negatively charged glycosylated (sugar-modified) proteins

The mineralization of the bone matrix occurs when calcium, phosphat, and water from extracellular fluids combine to form insoluble hydroxyapatite. This substance incorporates into the small pores within collagen fibrils and crystallizes into long, thin, nanosized plates.

Cells in bone (3 types):

1. Osteoclasts, which break down and reabsorb bone (osteolysis)

2. Osteoblasts, which deposit and build new bone

3. Osteocytes, which are mature bone cells that act as sensors for repair--they are embedded in small cavities called lacunae

Bone Forming Processes

Intramembranous ossification- Direct synthesis of bone by specialized stem cells (mesenchymal cells) from fibrous connective tissue

Endochondral ossification- Synthesis of bone from a hyaline cartilage template

Periosteum- A living membrane composed of fibrous connective tissue that forms on the outside of the compact bone

*After formation, bone resorptions and depositions occur continually through bone remodeling to maintain homeostasis of total bone mass and of inorganic components.

Fractures

Simple fracture/closed fracture- In which a bone breaks completely, but the broken ends do not penetrate the skin

Compound fracture/open fracture- In which the ends of the broken bone break through the skin

Comminuted fracture- In which the bone is shattered or broken into several pieces

Greenstick fracture- Occurs in children when one side of a bone breaks and the other side bends due to increased pliability

Impacted fracture- One end of the fractured bone is forced into the interior of the other end

Stress fracture- A set of tiny fractures or fissures in a bone caused by repeated stress on the bone (common in competitive runners)

SKELETAL HOMEOSTASIS

Three hormones control osteoblast and osteoclast activity to help regulate calcium levels in the blood:

1. Parathyroid hormone (PTH): Increases bone resorption by stimulating osteoclasts, leading to increased calcium release from bone

2. Calcitonin: Acts in children to decrease bone resorption, leading to less calcium entering the blood

3. Calcitriol (Vitamin D): Increases absorption of dietary calcium

The osteocytes in cellular extensions are found in canaliculi, a network of bone canals. They allow mechanical information to be rapidly transmitted to other bone cells.

Unit 15) INTEGRATION OF THE SKELETAL SYSTEM explained some homeostatic processes that took place between the skeleton and other systems of the body. For instance, the homeostatic control of blood (plasma) calcium levels requires interaction between the digestive, cardiovascular, and urinary system. Furthermore, the calcium exchange between cells, extracellular fluid, and the bones is partly regulated by the endocrine system.

After wrapping up the skeletal system and trying to come up with puns about the tibia (more on that later), I finally got to research in-depth the system that interests me most: the muscular system! Since this is the system most directly related to exercise and athletics, it makes sense that I would be particularly drawn to it. First, I learned that the muscular system is composed mainly of skeletal muscle, however, cardiac muscle is responsible for heart contraction and smooth muscle is found in many organs and blood vessels.

MUSCLE STRUCTURES AND FUNCTIONS

Muscle tone- Low levels of muscle contraction to maintain strength

Treppe- A stepwise increase in contraction tension that occurs with muscle fibers suddenly stimulated from a state of rest

Two types of muscle contractions:

1. Isotonic contractions move a load as the length of the muscle changes

i) Concentric contractions involve the muscle shortening to move a load

ii) Eccentric contractions occur as the muscle lengthens

2. Isometric contractions occur as the muscle produces tension without changing length to maintain posture and joint stability

Four layers of connective tissue enclose and provide structure to muscles:

1. Epimysium- Wraps around the outer layer of each muscle fiber

- Allows muscle to contract and move powerfully while maintaining structural integrity

- Separates muscle from other tissues and organs

- Composed of a thick layer of collagen fibers

2. Fascia- Surrounds the epimysium

- Connectibe tissue found around body organs

- May contain adipose tissue to insulate and protect the muscle

3. Perimysium- A middle layer of connective tissue which binds fascicles (groups of muscle fibers/cells)

4. Endomysium- Encases each individual muscle fiber

- Located around the plasma membrane (sarcolemma) of skeletal muscle fiber

Pennate muscles- Are feather shaped and form different fascicle arrangements at an angle to the tendon

Fusiform muscles- Have fascicles that are spindle shaped to give the muscle a large central body

End: 9:30 PM

#physiology #skeletalsystem #anatomy #homeostasis #capacitybuilding #seniorproject #muscularsystem