Functions and Structure of Bones

Functions of Bones

• Support: Serves as the body's framework
• Protection: Safeguards internal organs, such as the brain within the skull
• Movement: Provides leverage for muscles to facilitate motion
• Mineral Storage: Stores calcium and phosphorus, essential for various body functions
• Blood Cell Formation: Red bone marrow is the site of hematopoiesis (blood cell formation)

Bone Structure

• Compact Bone: The dense, hard outer layer of bone
• Spongy Bone: The porous inner layer containing trabeculae (thin plates of bone)
• Periosteum: A tough membrane covering the outer surface of bone
• Endosteum: A membrane lining the medullary cavity (hollow space within bone)

Bone Cells

• Osteoblasts: Responsible for building new bone tissue
• Osteocytes: Maintain the bone matrix, the supporting structure of bone
• Osteoclasts: Break down bone tissue, contributing to bone remodeling

Bone Growth and Development

• Intramembranous Ossification: Formation of flat bones, like those in the skull, directly from mesenchymal tissue
• Endochondral Ossification: Development of long bones, like the femur, involving cartilage as a precursor

Bone Remodeling and Repair

• Constant Renewal: Bones continuously undergo remodeling, a process of breakdown and rebuilding
• Healing Stages:
  • Hematoma Formation: Blood clot formation at the fracture site
  • Fibrocartilaginous Callus Formation: A soft callus forms, bridging the fracture gap
  • Bony Callus Formation: The callus is replaced by hard bone
  • Bone Remodeling: The callus is remodeled into a normal bone structure

Axial Skeleton

• Skull: Protects the brain, composed of cranial and facial bones
• Vertebral Column: Supports the body and protects the spinal cord
• Thoracic Cage: Protects the heart and lungs, comprising ribs and sternum

Appendicular Skeleton

• Pectoral Girdle: Clavicles and scapulae, connecting the arms to the body
• Upper Limbs: Humerus, radius, ulna, carpals, metacarpals, and phalanges
• Pelvic Girdle: Hip bones, linking the legs to the body
• Lower Limbs: Femur, tibia, fibula, tarsals, metatarsals, and phalanges

Joints

• Fibrous Joints: Immovable joints, such as the sutures in the skull
• Cartilaginous Joints: Slightly movable joints, like the intervertebral discs
• Synovial Joints: Freely movable joints, including the shoulder and knee

Common Disorders

• Osteoporosis: Weakening of bones due to low calcium levels
• Fractures: Breaks in bones, categorized as simple, compound, or stress fractures

Functions of Muscle Tissue

• Producing Movement: Muscle contractions generate motion
• Maintaining Posture: Muscles help keep the body in an upright position
• Stabilizing Joints: Muscles provide support and stability to joints
• Generating Heat (Thermogenesis): Muscle activity produces heat, contributing to body temperature regulation

Types of Muscle Tissue

• Skeletal Muscle: Voluntary, striated muscles attached to bones, enabling voluntary movements
• Cardiac Muscle: Involuntary, striated muscles found in the heart, responsible for heart contractions
• Smooth Muscle: Involuntary, non-striated muscles in the walls of hollow organs (e.g., stomach, blood vessels), controlling organ function

Muscle Contraction

• Sarcomere: The functional unit of muscle contraction, containing the protein filaments responsible for contraction
• Sliding Filament Theory: Actin and myosin filaments slide past each other, shortening the muscle
• Neuromuscular Junction: Where a nerve signal triggers muscle contraction through the release of acetylcholine (ACh)
• ATP: The energy source for muscle contractions

Muscle Fiber Types

• Slow-Twitch (Type I): Fatigue-resistant fibers suited for endurance activities
• Fast-Twitch (Type II): Fibers that fatigue quickly, used for power and speed

Muscle Disorders

• Muscular Dystrophy: A genetic disorder causing progressive muscle degeneration and weakness
• Myasthenia Gravis: An autoimmune disorder affecting the neuromuscular junction, leading to muscle weakness and fatigue

Functions of Bones

• Bones provide structural support for the body.
• They protect vital organs, such as the brain within the skull.
• Bones act as levers for muscle movement.
• They serve as a reservoir for minerals like calcium and phosphorus.
• Red bone marrow within bones is responsible for blood cell formation, a process called hematopoiesis.

Bone Structures

• Compact bone is the dense outer layer of bone, providing strength.
• Spongy bone, found internally, has a porous structure with trabeculae, which helps distribute stress.
• The periosteum is a membrane covering the outer surface of bone.
• The endosteum lines the medullary cavity, the central hollow space within bone.

Bone Cells

• Osteoblasts are responsible for building new bone tissue.
• Osteocytes maintain bone tissue and are mature bone cells.
• Osteoclasts break down bone tissue, contributing to bone remodeling and calcium release.

Bone Growth and Development

• Intramembranous ossification is the process of forming flat bones like those in the skull.
• Endochondral ossification is the process of forming long bones, such as the femur.

Bone Remodeling and Repair

• Bone is constantly renewed through a process called remodeling.
• Healing after fractures involves several stages:
  • Hematoma formation: Blood clot forms at the fracture site.
  • Fibrocartilaginous callus formation: A soft callus made of cartilage forms.
  • Bony callus formation: The soft callus is replaced by hard bone.
  • Bone remodeling: The bony callus is remodeled into normal bone.

Axial Skeleton

• The skull protects the brain and consists of cranial bones for the braincase and facial bones for the face.
• The vertebral column supports the body and protects the spinal cord.
• The thoracic cage, composed of ribs and the sternum, encloses and protects the heart and lungs.

Appendicular Skeleton

• The pectoral girdle, including the clavicles and scapulae, connects the upper limbs to the body.
• Upper limbs consist of the humerus, radius, ulna, carpals, metacarpals, and phalanges.
• The pelvic girdle, formed by the hip bones, connects the lower limbs to the body.
• Lower limbs are composed of the femur, tibia, fibula, tarsals, metatarsals, and phalanges.

Joints

• Fibrous joints are immovable joints, such as the sutures in the skull.
• Cartilaginous joints are slightly movable joints, like the intervertebral discs.
• Synovial joints allow free movement, such as the shoulder and knee joints.

Common Disorders

• Osteoporosis is characterized by weak bones due to low calcium levels.
• Fractures are breaks in bones, classified as simple (closed), compound (open), and stress fractures.

Functions of Muscle Tissue

• Muscle tissue is responsible for movement, maintaining posture, stabilizing joints, and generating heat (thermogenesis).

Types of Muscle Tissue

• Skeletal muscle is voluntary and striated, attached to bones for movement.
• Cardiac muscle is involuntary and striated, found only in the heart.
• Smooth muscle is involuntary and non-striated, found in hollow organs like the stomach and blood vessels.

Muscle Contraction

• The sarcomere is the functional unit of muscle contraction, composed of actin and myosin filaments.
• The sliding filament theory explains how muscle contraction occurs: actin and myosin slide past each other, shortening the muscle.
• The neuromuscular junction is where a nerve signal triggers muscle contraction by releasing acetylcholine (ACh).
• ATP is the energy source for muscle contractions.

Muscle Fiber Types

• Slow-twitch (Type I) fibers are fatigue-resistant and used for endurance activities.
• Fast-twitch (Type II) fibers fatigue quickly and are used for power and speed.

Muscle Disorders

• Muscular dystrophy is a genetic disorder causing muscle degeneration.
• Myasthenia gravis is an autoimmune disorder affecting neuromuscular transmission.