Chapter - 6: The Integumentary System

Overview of the Integumentary System

The integumentary system consists of the skin and its accessory structures. It serves as the body's first line of defense and plays a vital role in protection, sensation, and homeostasis.

• Functions: Protection, temperature regulation, sensation, metabolic functions, blood reservoir, excretion.

• Main components: Epidermis, dermis, hypodermis, hair, nails, glands.

Structure of the Epidermis

The epidermis is the outermost layer of the skin, composed primarily of keratinized stratified squamous epithelium.

• Layers of the Epidermis (from deep to superficial):

  1. Stratum basale (germinativum): Single row of stem cells; site of mitosis.

  2. Stratum spinosum: Several layers of keratinocytes; contains dendritic cells.

  3. Stratum granulosum: 3-5 layers; keratinization begins here.

  4. Stratum lucidum: Present only in thick skin (palms, soles); thin, clear layer.

  5. Stratum corneum: 20-30 layers of dead, keratinized cells; provides protection.

• Cell types: Keratinocytes (produce keratin), melanocytes (produce melanin), dendritic (Langerhans) cells (immune defense), Merkel cells (touch receptors).

Structure of the Dermis

The dermis is a connective tissue layer beneath the epidermis, providing strength and elasticity to the skin.

• Layers:

  • Papillary layer: Areolar connective tissue; contains dermal papillae, capillaries, and sensory receptors.

  • Reticular layer: Dense irregular connective tissue; contains collagen and elastic fibers, glands, and hair follicles.

• Structures found in the dermal layer: Blood vessels, nerves, sweat glands, sebaceous glands, hair follicles, arrector pili muscles.

Skin Color and Pigmentation

Skin color is determined by the amount and type of melanin, carotene, and hemoglobin present in the skin.

• Melanin: Produced by melanocytes; protects against UV radiation.

• Carotene: Yellow-orange pigment from diet; accumulates in stratum corneum.

• Hemoglobin: Oxygenated pigment in red blood cells; gives pinkish hue.

Accessory Structures of the Skin

Accessory structures include hair, nails, and glands, each with specialized functions.

• Hair: Provides protection, sensation, and thermoregulation.

• Nails: Protect distal phalanges, aid in grasping.

• Glands:

  • Sebaceous glands: Secrete sebum for lubrication.

  • Sudoriferous (sweat) glands: Eccrine (thermoregulation), apocrine (odor, puberty).

Functions of the Integumentary System

• Protection: Physical, chemical, and biological barriers.

• Body temperature regulation: Sweat glands and blood flow adjustments.

• Cutaneous sensation: Sensory receptors for touch, pain, temperature.

• Metabolic functions: Synthesis of vitamin D.

• Blood reservoir: Skin holds up to 5% of body’s blood volume.

• Excretion: Nitrogenous wastes and salt in sweat.

Skin Cancer

Skin cancer is the uncontrolled growth of abnormal skin cells. The three major types are:

• Basal cell carcinoma: Most common, least malignant; arises from stratum basale.

• Squamous cell carcinoma: Arises from keratinocytes of stratum spinosum; can metastasize.

• Melanoma: Cancer of melanocytes; most dangerous due to rapid metastasis.

AB CDE Rule for Melanoma: Asymmetry, Border irregularity, Color variation, Diameter >6mm, Evolving shape /size.

Burns

Burns are c lassified by depth and severity:

• First-degree: Epidermis only; redness, pain.

• Se"cond-degree: Epidermis and part of dermis; blisters.

• Third-degree: Full thickness; destroys entire skin layer, may appear white or charred.

Rule of Nines: Used to estimate the percentage of body surface area affected by burns.

Chapter 6: The Skeletal System

Types and Functions of Cartilage

Cartilage is a resilient, semi-rigid connective tissue found in various parts of the body.

• Types: Hyaline (most abundant, articular surfaces), elastic (ear, epiglottis), fibrocartilage (intervertebral discs, pubic symphysis).

• Functions: Support, flexibility, shock absorption, smooth surfaces for joint movement.

Bone Structure and Classification

Bones are classified by shape and structure, and each bone has distinct anatomical features.

• Shapes: Long, short, flat, irregular, sesamoid.

• Gross anatomy: Diaphysis (shaft), epiphyses (ends), metaphysis, articular cartilage, periosteum, endosteum, medullary cavity.

• Microscopic anatomy: Osteons (Haversian systems), lamellae, lacunae, canaliculi, central canal.

Cells of Bone Tissue

• Osteogenic cells: Stem cells that differentiate into osteoblasts.

• Osteoblasts: Bone-forming cells; synthesize bone matrix.

• Osteocytes: Mature bone cells; maintain bone tissue.

• Osteoclasts: Bone-resorbing cells; break down bone matrix.

Bone Formation and Growth

• Bone develops through two main processes:

• Intramembranous ossification: Forms flat bones (e.g., skull, clavicle) from mesenchymal tissue.

• Endochondral ossification: Forms most bones of the body from hyaline cartilage templates.

Epiphyseal plate: Site of longitudinal bone growth in children; replaced by epiphyseal line in adults.

Bone Remodeling and Homeostasis

Bone is continuously remodeled through the coordinated actions of osteoblasts and osteoclasts.

• Remodeling: Replaces old bone with new bone; adapts to stress.

• Hormonal regulation: Parathyroid hormone (PTH) increases blood calcium by stimulating osteoclasts; calcitonin lowers blood calcium.

• Calcium homeostasis equation:

Bone Fractures and Repair

• Types of fractures: Simple, compound, comminuted, greenstick, spiral, impacted, etc.

• Repair process: Hematoma formation → fibrocartilaginous callus → bony callus → bone remodeling.

Disorders of Bone

• Osteomalacia/Rickets: Softening of bones due to vitamin D deficiency.

• Osteoporosis: Decreased bone mass and increased fracture risk.

• Paget’s disease: Disorganized bone remodeling.

Chapter 7: The Axial and Appendicular Skeleton

Overview of the Skeleton

The human skeleton is divided into the axial and appendicular skeletons.

• Axial skeleton: Skull, vertebral column, thoracic cage.

• Appendicular skeleton: Limbs and girdles (pectoral and pelvic).

Vertebral Column

• Regions: Cervical (7), thoracic (12), lumbar (5), sacrum, coccyx.

• Curvatures: Cervical and lumbar (concave), thoracic and sacral (convex).

• Intervertebral discs: Fibrocartilage pads that absorb shock.

• Functions: Protect spinal cord, support head, provide attachment for ribs and muscles.

Thoracic Cage

• Components: Sternum, ribs (12 pairs), thoracic vertebrae.

• Functions: Protects heart and lungs, supports shoulder girdles and upper limbs.

Appendicular Skeleton

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

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

• Upper limb bones: Humerus, radius, ulna, carpals, metacarpals, phalanges.

• Lower limb bones: Femur, tibia, fibula, tarsals, metatarsals, phalanges.

Joints

• Types: Fibrous, cartilaginous, synovial.

• Synovial joints: Most movable; features include joint cavity, articular cartilage, synovial fluid, ligaments.

• Examples: Hinge (elbow), ball-and-socket (shoulder, hip), pivot (atlas/axis), saddle (thumb).

Table: Comparison of Bone Cells

Additional info:

• Some content was inferred and expanded for academic completeness, such as detailed bone cell functions and the calcium homeostasis equation.