Integumentary System

Structure and Function of the Skin

The skin, also known as the cutaneous membrane, is the largest organ of the human body and serves as a protective barrier against environmental hazards.

• Cutaneous membrane: Another term for the skin, distinguishing it from other body membranes such as serous or synovial membranes.

• Main functions: Protection, sensation, thermoregulation, excretion, and synthesis of vitamin D.

Cell Types in the Epidermis

The epidermis is the outermost layer of the skin, composed primarily of specialized cells.

• Keratinoctyes: About 90% of epidermal cells; produce keratin, a protein that provides strength and waterproofing.

• Melanocytes: Produce melanin pigment, found mainly in the stratum basale.

• Merkel cells: Sensory cells associated with touch.

• Langerhans cells: Immune cells involved in defense.

Layers of the Epidermis

The epidermis consists of several layers, each with distinct functions and cell types.

• Stratum basale: Deepest layer; contains stem cells that divide to produce new keratinocytes.

• Stratum spinosum: Provides strength and flexibility.

• Stratum granulosum: Cells begin to die and accumulate keratin.

• Stratum lucidum: Present only in thick skin (palms, soles); provides extra protection.

• Stratum corneum: Outermost layer; consists of dead, keratinized cells.

Pigment-Producing Cells

Melanocytes, which produce melanin pigment, are located in the stratum basale.

• Melanin: Protects against UV radiation and determines skin color.

Functions of Epidermal Cells

• Keratinoctyes: Provide structure, produce secretions, and contribute to immune response.

• Stem cells: Located in the stratum basale, responsible for continual cell division.

Specialized Skin Layers

• Stratum lucidum: Found only in areas of high mechanical stress (palms, soles, fingertips).

Histology of Skin Tissue

Microscopic images of skin typically show epithelial tissue in the epidermis and connective tissue in the dermis.

Dermis Structure and Function

The dermis is a layer of dense, irregular connective tissue beneath the epidermis.

• Collagen and elastin fibers: Provide strength and elasticity.

• Blood supply: Nourishes the epidermis and supports sensory receptors.

• Layers: Papillary (superficial, smaller) and reticular (deeper, thicker).

Skin Glands and Thermoregulation

• Eccrine glands: Involved in thermoregulation (sweating for cooling).

• Apocrine glands: Play a role in emotional sweating.

Sensory Receptors in Skin

• Free nerve endings: Detect pain, temperature, and light touch (e.g., insect walking on skin).

• Meissner corpuscles: Detect fine touch.

• Lamellated corpuscles: Detect pressure and vibration.

Skeletal System

Bone Structure and Classification

Bones are classified by shape and function, and are composed of various tissues and minerals.

• Long bones: e.g., humerus, femur; have a shaft and two ends.

• Short, irregular, sesamoid, and sutural bones: Other classifications based on shape.

• Epiphysis: End region of long bones; site of epiphyseal (growth) plate.

• Diaphysis: Shaft of long bone.

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

• Periosteum: Outer membrane covering bone.

• Endosteum: Membrane lining the marrow cavity.

Bone Tissue Composition

• Compact bone: Composed of osteons (Haversian systems).

• Spongy bone: Composed of trabeculae.

• Major minerals: Calcium and phosphorus are stored in bone tissue.

Microscopic Structure of Bone

Bones contain canals and lamellae for nutrient and waste exchange.

• Volkmann's canals: Transverse canals for blood vessels.

• Haversian canals: Central canals in osteons.

• Lacunae: Small spaces housing osteocytes.

• Concentric lamellae: Rings of bone matrix around Haversian canals.

Bone Growth and Remodeling

• Epiphyseal plate: Site of bone growth in length during development.

• Bone deposition and resorption: Influenced by stress and exercise; lack of weight-bearing activity increases risk of bone loss.

Axial vs. Appendicular Skeleton

• Axial skeleton: Skull, vertebrae, ribs, sternum.

• Appendicular skeleton: Limbs (humerus, femur), girdles.

Muscular System

Muscle Tissue Types and Features

Muscle tissue is specialized for contraction and movement.

• Skeletal muscle: Striated, voluntary, elongated cells, multiple nuclei, parallel fibers.

• Cardiac muscle: Striated, involuntary, intercalated discs, single nuclei.

• Smooth muscle: Non-striated, involuntary, single nuclei.

Muscle Movements and Actions

• Flexion: Decreasing the angle between two bones (e.g., bending the arm).

• Extension: Increasing the angle between two bones.

• Abduction: Moving a limb away from the midline.

• Adduction: Moving a limb toward the midline.

• Plantar flexion: Pointing toes downward (e.g., standing on tiptoe).

• Dorsiflexion: Raising the foot upward.

• Supination: Rotating the forearm so the palm faces up.

• Pronation: Rotating the forearm so the palm faces down.

Functions of Skeletal Muscle Tissue

• Movement: Voluntary control of body parts.

• Posture: Maintaining body position.

• Heat production: Shivering to generate heat.

• Joint stabilization: Supporting and stabilizing joints.

Joints and Movement

Types of Joints

• Synovial joints: Freely movable (diarthroses).

• Cartilaginous joints: Slightly movable (amphiarthroses).

• Fibrous joints: Immovable (synarthroses).

Body Cavities

Major Body Cavities

• Thoracic cavity: Contains heart and lungs.

• Abdominal cavity: Contains digestive organs.

• Diaphragm: Separates thoracic and abdominal cavities.

Tables

Comparison of Epidermal Layers

Major Bone Regions

Key Equations

• Bone mineral storage:

Additional info:

• Some content inferred from standard Anatomy & Physiology curriculum, such as the functions of skin layers and bone regions.

• Tables and explanations expanded for clarity and completeness.