Integumentary System

Functions and Protection

The integumentary system serves as the body's first line of defense, providing protection against environmental hazards, pathogens, and physical injury.

• Physical Barrier: The skin prevents entry of pathogens and minimizes water loss.

• Chemical Protection: Secretions such as sweat and sebum create an acidic environment that inhibits microbial growth.

• Biological Protection: Immune cells in the skin (e.g., Langerhans cells) detect and respond to pathogens.

• UV Protection: Melanin produced by melanocytes absorbs and disperses ultraviolet radiation.

Integration with Other Systems in Thermoregulation

The integumentary system works with the muscular, cardiovascular, and nervous systems to regulate body temperature.

• Muscular System: Shivering generates heat through muscle contractions.

• Cardiovascular System: Blood vessels in the dermis dilate (vasodilation) or constrict (vasoconstriction) to release or conserve heat.

• Nervous System: Sensory receptors detect temperature changes and signal the hypothalamus to initiate thermoregulatory responses.

Cell Types and Accessory Organs

The epidermis contains several specialized cell types, each with distinct functions.

• Keratinocytes: Produce keratin, providing strength and waterproofing.

• Melanocytes: Synthesize melanin for UV protection.

• Langerhans Cells: Immune surveillance.

• Merkel Cells: Sensory receptors for touch.

Accessory organs include hair, nails, sweat glands, and sebaceous glands, each contributing to protection, sensation, and homeostasis.

Structure and Function of Sensory Corpuscles

• Lamellated (Pacinian) Corpuscle: Detects deep pressure and vibration; located deeper in the dermis.

• Meissner’s Corpuscle: Sensitive to light touch; found in dermal papillae.

Disorders of the Integumentary System

• Psoriasis: Chronic inflammatory skin condition.

• Acne: Inflammation of sebaceous glands.

• Skin Cancer: Uncontrolled growth of skin cells (e.g., melanoma, basal cell carcinoma).

Skeletal System

Functions of the Skeletal System

The skeletal system provides structural support, protection, movement, mineral storage, and blood cell production.

• Support: Framework for the body.

• Protection: Shields vital organs (e.g., skull protects brain).

• Movement: Acts as levers for muscles.

• Mineral Balance: Stores calcium and phosphate; releases them as needed.

• Hematopoiesis: Blood cell formation in red marrow.

Bone Tissue Structure

• Compact Bone: Dense, organized into osteons; provides strength.

• Spongy Bone: Porous, contains trabeculae; supports marrow and reduces weight.

Structure of a Typical Long Bone

• Diaphysis: Shaft, composed of compact bone.

• Epiphyses: Ends, mostly spongy bone.

• Metaphysis: Region between diaphysis and epiphysis; contains growth plate.

• Medullary Cavity: Central cavity containing marrow.

• Periosteum: Outer fibrous covering.

Bone Growth and Ossification

• Endochondral Ossification: Bone develops from hyaline cartilage; forms most bones (e.g., long bones).

• Intramembranous Ossification: Bone develops directly from mesenchymal tissue; forms flat bones (e.g., skull).

Comparison Table: Endochondral vs. Intramembranous Ossification

Bone Disorders, Fractures, and Healing

• Osteoporosis: Reduced bone density, increased fracture risk.

• Fracture Healing: Involves hematoma formation, fibrocartilaginous callus, bony callus, and bone remodeling.

Homeostasis of Blood Calcium

Blood calcium levels are tightly regulated by hormonal control.

• Low Ca2+ (<8.6 mg/dL): Parathyroid hormone (PTH) is released, stimulating osteoclasts to release Ca2+ from bone, increasing renal reabsorption, and activating vitamin D for intestinal absorption.

• High Ca2+ (>10.6 mg/dL): Calcitonin is released from the thyroid, inhibiting osteoclasts and promoting Ca2+ deposition in bone.

Equation:

Joints: Types and Structure

• Functional Classification: Synarthroses (immovable), Amphiarthroses (slightly movable), Diarthroses (freely movable).

• Structural Classification: Fibrous, cartilaginous, synovial joints.

• Synovial Joints: Have a joint cavity, articular cartilage, synovial membrane, and accessory structures (ligaments, bursae, menisci).

Movements at Joints

• Flexion/Extension: Decreasing/increasing angle between bones.

• Abduction/Adduction: Moving away/toward midline.

• Rotation, Circumduction: Rotating around axis, circular movement.

Muscular System

Functions and Characteristics

The muscular system enables movement, maintains posture, and produces heat.

• Movement: Muscles contract to move bones.

• Posture: Continuous muscle activity maintains body position.

• Heat Production: Muscle contractions generate heat.

Types of Muscle Tissue

• Skeletal Muscle: Voluntary, striated, attached to bones.

• Cardiac Muscle: Involuntary, striated, found in heart.

• Smooth Muscle: Involuntary, non-striated, found in walls of organs.

Structure of Muscle

• Gross Structure: Muscle belly, tendons, origin, insertion.

• Microscopic Structure: Muscle fibers, myofibrils, sarcomeres.

• Origin vs. Insertion: Origin is the fixed attachment; insertion moves with contraction.

Excitation-Contraction Coupling

This process links the arrival of an action potential at the neuromuscular junction to muscle contraction.

• Action potential arrives at axon terminal, releasing acetylcholine (ACh).

• ACh binds to receptors on the muscle fiber, triggering depolarization.

• Depolarization spreads along sarcolemma and T-tubules.

• Calcium ions are released from the sarcoplasmic reticulum.

• Calcium binds to troponin, moving tropomyosin and exposing binding sites on actin.

• Myosin heads bind to actin, initiating contraction.

Sliding Filament Theory

Describes how muscle fibers contract by the sliding of actin and myosin filaments.

• Myosin heads attach to actin, forming cross-bridges.

• Power stroke: Myosin pulls actin filaments toward the center of the sarcomere.

• ATP binds to myosin, causing detachment from actin.

• Cycle repeats as long as calcium and ATP are present.

• Relaxation occurs when calcium is reabsorbed and tropomyosin blocks binding sites.

Muscle Twitch Phases

• Latent Period: Time between stimulus and contraction onset.

• Contraction Period: Muscle fibers shorten.

• Relaxation Period: Muscle returns to resting length.

Increasing Muscle Contraction Strength

• Recruitment of more motor units.

• Increasing frequency of stimulation (temporal summation).

• Optimal muscle length (length-tension relationship).

Leverage Systems in the Body

• First-Class Lever: Fulcrum between effort and load (e.g., neck extension).

• Second-Class Lever: Load between fulcrum and effort (e.g., standing on tiptoe).

• Third-Class Lever: Effort between fulcrum and load (e.g., biceps curl).

Comparison Table: Leverage Systems

Muscle Actions and Terminology

• Agonist: Primary mover in an action.

• Antagonist: Opposes the agonist.

• Synergist: Assists the agonist.

• Fixator: Stabilizes origin.

Muscular System Disorders

• Muscular Dystrophy: Genetic disorder causing muscle weakness.

• Myasthenia Gravis: Autoimmune disorder affecting neuromuscular junction.

• Fibromyalgia: Chronic pain and fatigue.

Additional info: These notes expand on the review guide by providing definitions, examples, and academic context for each topic, suitable for exam preparation in Anatomy & Physiology.