To express the functions of the musculoskeletal system.
To understand bone formation.
To explain muscle physiology.
To emphasize essential aspects of nursing care in osteoarthritis and osteoporosis.
MUSCULOSKELETAL SYSTEM
The musculoskeletal system, also known as the locomotor system, consists of bones, muscles, cartilage, tendons, and ligaments.
In an adult human, there are 206 bones of various shapes and sizes.
Babies are born with approximately 300 bones, which fuse together as they grow, reducing the total count.
Joints, such as the elbow and knee joints, facilitate movement; without joints, the skeletal structure would be rigid.
MUSCULOSKELETAL SYSTEM (CONT'D)
Cartilage: A cushioning tissue that protects joints subjected to forces during movement.
Ligaments: Provide strength to joints and can be attached to or independent of the joint capsule.
Movement in joints occurs through the contraction of opposing muscles.
FUNCTIONS OF THE MUSCULOSKELETAL SYSTEM
Protection: Safeguards internal organs and offers support to soft tissues.
Support: Helps maintain an erect posture.
Blood Production: Occurs in the red bone marrow.
Storage: Stores fat and minerals in yellow bone marrow.
Mineral Balance: Regulates mineral storage and release to meet bodily needs, particularly calcium.
Lifting Power: Works with muscles and bones in the upper and lower limbs for movement.
BONES
Bones are highly vascularized and innervated organs comprising bone tissue, bone marrow, and periosteum, a connective tissue covering.
They serve multiple functions including protection, support, facilitation of movement, and as sites for blood formation through bone marrow.
BONE TISSUE
Calcium Storage: Bones store almost all (99%) calcium in the body, crucial for various physiological functions including muscle contraction, blood clotting, cellular membrane permeability, and nerve impulse transmission.
Hierarchical Structure: Bone tissue has a hierarchical arrangement from macro to nano levels, composed of organic extracellular matrix and mineralized carbonated apatite.
BONE ORGANIZATION
Inorganic Components: Majorly consist of calcium and phosphate in the form of hydroxyapatite crystals, with additional traces of citrate and magnesium.
Bone is classified as a mineralized tissue, with an organic matrix strengthened by calcium phosphate deposition influenced by genetic, metabolic, and mechanical factors.
BONE MICROSTRUCTURE
Contains non-mineralized organic structures like the extracellular matrix (ECM) consisting of type I collagen and various matrix proteins (proteoglycans, glycoproteins, sialoproteins).
The ECM plays a vital role in bone structure and health.
BONE CELLS
Osteoprogenitor Cells
Definition: Mesenchymal cells predisposed to become bone tissue, resembling fibroblasts in morphology.
Function: Serve as precursor cells differentiating into osteoblasts through mitosis.
Osteoblasts
Definition: Cubic-shaped cells composing 4-6% of total bone cells, located on bone surfaces.
Function: Known for bone formation; synthesize and secrete type I collagen fibers and matrix proteins, forming uncalcified osteoid tissue.
Components: Contain endoplasmic reticulum, Golgi apparatus, and secretory vesicles to facilitate their functions.
Osteocytes
Definition: Make up 90-95% of bone cells with an average lifespan of 25 years.
Function: Derived from osteoblasts, they remain in calcified matrix and have reduced activity.
Structure: Lacunae form around them and they represent the final stage of osteoblast activity, unable to regenerate spontaneously.
Osteoclasts
Definition: Multinucleated cells formed by the fusion of blood-derived monocytes, responsible for bone tissue resorption and destruction.
Function: Active in bone formation, degrading old, worn-out bone while osteoblasts build new tissue.
Characteristics: Large cells (100 μm), rich in mitochondria and vacuoles.
PERIOSTEUM
Structure: A thick external layer surrounding bones, consisting of an outer fibrous layer (collagen fibers and fibroblasts) and a rich inner layer containing osteoprogenitor cells.
Function: Houses blood vessels, lymphatic vessels, and nerve fibers; plays a crucial role in the nourishment, growth, and repair of bone tissue.
ENDOSTEUM
Description: A thinner layer than the periosteum, covers all inner cavities of bones, including Havers’ canals and marrow cavities.
Importance: Essential for the maintenance and repair of bone structure and function.
TYPES OF BONE TISSUE
PRIMARY BONE TISSUE
Forms during fetal development and acts in bone repair. Transient and transforms into secondary bone in adults.
Typically found at the joints of flat skull bones, alveoli of teeth, and tendon insertions.
SECONDARY BONE TISSUE
Commonly seen in adults, includes long, short, and irregular bones with lamellar structure.
Morphologically split into cortical (20% of skeleton, dense and firm) and cancellous (80% of skeleton, spongy).
SPONGIOUS BONE
Characterized by a 50-90% porosity, commonly within the epiphysis and metaphysis of long and short bones as well as flat bones.
Nourished through cytoplasmic extensions via canaliculi from bone marrow vessels.
COMPACT BONE
Forms the diaphyseal part of long bones, with minimal spongy bone facing the medullary cavity.
Comprised of cylindrical units known as osteons or Havers systems; contains Havers canals (20-100 μm) central to bone vascularization.
BONE FORMATION (OSSIFICATION)
Definition: The process by which bone is shaped by osteoblasts, involving the deposition of minerals like calcium and phosphorus in osteoid tissue.
Calcification: Defined as the deposition of calcium salts in tissues; occurs in two primary forms of ossification.
INTRAMEMBRANOUS OSSIFICATION
Process: Bone grows through fibrous membranes. Mesenchymal cells cluster to form ossification centers which differentiate into osteoblasts, secreting extracellular components to form a hardened matrix.
Outcome: Formation of bone-like osteoid tissue which eventually calcifies, leading to periosteum formation and subsequent bone layers.
ENDOCONDRAL OSSIFICATION
Process: Involves development from hyaline cartilage; primarily responsible for forming skeletal bones except for flat bones and those of the skull.
Undergoes a sequence where mesenchymal cells differentiate into chondroblasts, producing cartilage matrix, and subsequently into osteoblasts.
Primary Ossification Center: Develops in the diaphysis (middle region), while secondary ossification centers appear at the epiphyses (ends of long bones).
Osteoclasts degrade some cancellous bone to create the medullary cavity, allowing blood vessels and tissue to permeate, completing the maturation of the bone structure.
CYCLE OF BONE REMODELING
Phases of Remodeling:
1. Quiescent Period: Activation process begins with precursor cells differentiating into osteoclasts.
2. Resorption Period: Increased osteoclastic activity due to local cytokines and hormones.
3. Reversal: Activated osteoblasts gather to switch from resorption to bone formation.
4. Building Period: Osteoblasts synthesize osteoid to form new bone tissue; this process lasts approximately 4-6 months.
5. Termination: Completing all controlled processes for the formation of a normal bone structure.
MUSCLE TISSUE
Comprises approximately half of the body's mass, categorized into three types:
1. Skeletal Muscle
2. Smooth Muscle
3. Cardiac Muscle
SKELETAL MUSCLE
Characteristics: Most abundant muscle type without intercalated discs; muscle fibers can extend along the entire length of muscles and contain multiple nuclei.
Is organized by connective tissue:
- Epimysium: Outer connective tissue covering the whole muscle.
- Perimysium: Connective tissue around each fascicle (bundle of muscle cells).
- **Myofibr