Integumentary System

Structure and Function of the Skin

The integumentary system consists primarily of the skin, which serves as the body's largest organ and provides protection, sensation, and regulation of body temperature.

• Epidermis: The outermost layer of the skin, composed of stratified squamous epithelium. It is avascular and relies on diffusion from the underlying dermis for nutrients.

• Dermis: The deeper layer beneath the epidermis, containing connective tissue, blood vessels, nerves, and accessory structures.

Layers of the Dermis

• Papillary Layer: The superficial layer, composed of loose connective tissue. Contains dermal papillae that interlock with the epidermis, increasing surface area for exchange.

• Reticular Layer: The deeper, thicker layer, composed of dense irregular connective tissue. Provides strength and elasticity to the skin.

Skin Markings and Clinical Relevance

• Lines of Cleavage (Langer's Lines): Natural orientation of collagen fibers in the dermis. Incisions made parallel to these lines heal better and with less scarring.

• Flexure Lines: Dermal folds at or near joints, where the dermis is tightly secured to deeper structures.

• Stretch Marks (Striae): Tears in the dermis due to rapid stretching, such as during pregnancy or weight gain.

Skin Color and Clinical Conditions

• Melanin: Pigment produced by melanocytes; responsible for skin color and protection against UV radiation.

• Carotene: Yellow-orange pigment from diet, accumulates in the stratum corneum and fat.

• Hemoglobin: Oxygen-carrying pigment in red blood cells; gives skin a pinkish hue in light-skinned individuals.

• Clinical Conditions:

  • Pallor: Paleness due to reduced blood flow or anemia.

  • Jaundice: Yellowing of the skin due to bilirubin accumulation, often from liver dysfunction.

  • Bronzing: Bronze coloration, may indicate Addison's disease (adrenal insufficiency).

Hair and Nails

• Hair: Composed of keratinized cells; growth is affected by nutrition, hormones, and genetics. Hair growth occurs in cycles (anagen, catagen, telogen).

• Nails: Plates of hard keratin protecting the dorsal surface of fingers and toes.

Glands of the Skin

• Sudoriferous (Sweat) Glands:

  • Eccrine Glands: Widely distributed, secrete watery sweat for thermoregulation.

  • Apocrine Glands: Located in axillary and genital areas; secrete a thicker sweat, often associated with body odor.

• Sebaceous (Oil) Glands: Secrete sebum into hair follicles; lubricates skin and hair.

Skin Cancer and Burns

• Skin Cancer: Uncontrolled growth of skin cells. Types include basal cell carcinoma, squamous cell carcinoma, and melanoma.

• Burns: Classified by depth (first, second, third degree). Severity assessed by the "rule of nines," which estimates the percentage of body surface area affected.

Skeletal System

Types of Cartilage and Bone

The skeletal system provides support, protection, and movement. It is composed of bones and cartilage, which differ in structure and function.

• Types of Cartilage:

  • Hyaline Cartilage: Most abundant; found in articular surfaces, costal cartilages, nose, trachea, and larynx.

  • Elastic Cartilage: Contains elastic fibers; found in the ear and epiglottis.

  • Fibrocartilage: Contains thick collagen fibers; found in intervertebral discs, pubic symphysis, and menisci.

• Bone Types:

  • Long Bones: Longer than they are wide (e.g., femur, humerus).

  • Short Bones: Cube-shaped (e.g., carpals, tarsals).

  • Flat Bones: Thin, flattened, and usually curved (e.g., sternum, skull bones).

  • Irregular Bones: Complicated shapes (e.g., vertebrae, hip bones).

Bone Structure and Growth

• Gross Anatomy:

  • Diaphysis: Shaft of a long bone; contains medullary cavity filled with yellow marrow.

  • Epiphyses: Ends of long bones; contain spongy bone and red marrow.

  • Periosteum: Dense connective tissue covering the outer surface of bone.

  • Endosteum: Lines the medullary cavity and spaces within spongy bone.

• Microscopic Structure:

  • Osteon (Haversian System): Structural unit of compact bone, consisting of concentric lamellae around a central canal.

  • Lamellae: Layers of bone matrix.

  • Lacunae: Small spaces housing osteocytes.

  • Canaliculi: Tiny channels connecting lacunae for nutrient exchange.

• Bone Growth:

  • Intramembranous Ossification: Bone develops from fibrous membranes (e.g., flat bones of the skull).

  • Endochondral Ossification: Bone forms by replacing hyaline cartilage (e.g., long bones).

Bone Remodeling and Homeostasis

• Bone Remodeling: Ongoing replacement of old bone tissue by new bone tissue, involving osteoblasts (bone-forming cells) and osteoclasts (bone-resorbing cells).

• Hormonal Regulation:

  • Parathyroid Hormone (PTH): Increases blood calcium by stimulating osteoclast activity.

  • Calcitonin: Lowers blood calcium by inhibiting osteoclasts.

• Factors Affecting Bone Growth: Nutrition (calcium, vitamin D), hormones (growth hormone, sex hormones), and mechanical stress.

Bone Repair and Disorders

• Bone Repair: Involves hematoma formation, fibrocartilaginous callus formation, bony callus formation, and bone remodeling.

• Bone Disorders:

  • Osteomalacia: Softening of bones due to vitamin D deficiency in adults.

  • Osteoporosis: Decreased bone mass and increased fracture risk, common in elderly.

  • Paget's Disease: Disorganized bone remodeling, leading to enlarged and misshapen bones.

Axial and Appendicular Skeleton

Axial Skeleton

The axial skeleton forms the central axis of the body and includes the skull, vertebral column, and thoracic cage.

• Skull: Protects the brain and forms the structure of the face.

• Vertebral Column: Supports the body and protects the spinal cord. Consists of cervical, thoracic, lumbar, sacral, and coccygeal regions.

• Thoracic Cage: Composed of ribs and sternum; protects the heart and lungs.

Vertebral Column Details

• Intervertebral Discs: Pads of fibrocartilage between vertebrae, providing cushioning and flexibility.

• Ligaments:

  • Longitudinal Ligaments: Run along the length of the vertebral column, providing stability.

  • Ligamentum Flavum: Connects adjacent vertebrae, contains elastic fibers.

• Special Vertebrae:

  • Atlas (C1): Supports the skull, allows nodding motion.

  • Axis (C2): Has the dens (odontoid process), allows rotation of the head.

Appendicular Skeleton

The appendicular skeleton includes the bones of the limbs and girdles that attach them to the axial skeleton.

• Pectoral Girdle: Clavicle and scapula; attaches upper limbs to the trunk.

• Upper Limb: Humerus, radius, ulna, carpals, metacarpals, phalanges.

• Pelvic Girdle: Hip bones (ilium, ischium, pubis); attaches lower limbs to the trunk.

• Lower Limb: Femur, tibia, fibula, tarsals, metatarsals, phalanges.

Functional Differences in Limbs

• Upper Limb: Adapted for mobility and manipulation; joints allow a wide range of motion.

• Lower Limb: Adapted for weight-bearing and locomotion; joints are more stable but less mobile.

• Weight-Bearing Bones: Femur, tibia, and talus bear most of the body's weight.

Table: Comparison of Upper and Lower Limbs

Key Terms and Definitions

• Osteon: The structural unit of compact bone.

• Osteoblast: Bone-forming cell.

• Osteoclast: Bone-resorbing cell.

• Epiphyseal Plate: Growth plate in long bones where lengthening occurs during development.

• Periosteum: Membrane covering the outer surface of bones.

• Endosteum: Membrane lining the internal bone surfaces.

Formulas and Equations

• Rule of Nines (for burn assessment):

• Calcium Homeostasis:

Additional info: Some explanations and definitions were expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.