Integumentary System

Function of the Integumentary System

The integumentary system is the body's first line of defense and includes the skin, hair, nails, and associated glands. It serves multiple protective, regulatory, and sensory functions.

• Protection: Acts as a barrier against pathogens, chemicals, and physical injuries.

• Regulation: Helps control body temperature and water loss.

• Sensation: Contains sensory receptors for touch, pain, and temperature.

• Excretion: Removes waste products through sweat.

• Synthesis: Produces vitamin D when exposed to sunlight.

Layers of Skin: Order and Characteristics

The skin consists of three main layers, each with distinct structures and functions.

• Epidermis: Outermost layer; composed of stratified squamous epithelium. Contains keratinocytes, melanocytes, and other cells. Responsible for protection and water resistance.

• Dermis: Middle layer; contains connective tissue, blood vessels, nerves, and glands. Provides strength, elasticity, and nourishment to the epidermis.

• Hypodermis (Subcutaneous Layer): Deepest layer; consists mainly of adipose tissue for insulation and energy storage.

Epidermis: Fibers, Cells, and Layers

The epidermis is made up of several layers, each with specific cell types and functions.

• Keratinocytes: Main cell type; produce keratin for waterproofing and protection.

• Melanocytes: Produce melanin, which gives skin its color and protects against UV radiation.

• Langerhans Cells: Immune cells that help defend against pathogens.

• Strata (Layers):

  • Stratum basale (germinativum): Deepest layer; site of cell division.

  • Stratum spinosum: Provides strength and flexibility.

  • Stratum granulosum: Contains granules for waterproofing.

  • Stratum lucidum: Present only in thick skin (palms, soles).

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

Apoptosis

Apoptosis is programmed cell death, a process essential for removing damaged or unnecessary cells in the skin and maintaining tissue health.

Dermis: Layers, Characteristics, Cells, Vascularity

The dermis is a connective tissue layer beneath the epidermis, providing structural support and housing various components.

• Layers:

  • Papillary layer: Superficial; contains dermal papillae and capillaries.

  • Reticular layer: Deep; dense irregular connective tissue with collagen and elastin fibers.

• Cells: Fibroblasts, macrophages, mast cells.

• Vascularity: Rich blood supply for nutrient delivery and thermoregulation.

Stratum Basale and Dermal Papillae

The stratum basale is the deepest epidermal layer, responsible for cell division. Dermal papillae are projections of the dermis that interlock with the epidermis, forming fingerprints and increasing surface area for nutrient exchange.

Incision Directions and Cleavage Lines

Cleavage lines (Langer's lines) are patterns of collagen fibers in the dermis. Surgeons use these lines to guide incisions for better healing and less scarring.

Additional info: Flexure lines are skin folds near joints; knowledge of their location is not required for this course.

Blisters

Blisters are fluid-filled sacs caused by friction, burns, or other damage separating the epidermis from the dermis.

Skin Color: Pigments

Skin color is determined by three main pigments:

• Melanin: Brown-black pigment produced by melanocytes.

• Carotene: Yellow-orange pigment from diet, stored in the skin.

• Hemoglobin: Red pigment in blood, visible in fair skin.

Hair: Structure, Function, and Types

Hair serves protective, sensory, and thermoregulatory functions. It consists of several parts:

• Shaft: Visible part above the skin.

• Root: Embedded in the skin.

• Bulb: Enlarged base where hair growth occurs.

• Arrector pili muscle: Smooth muscle causing hair to stand (goosebumps).

• Types: Vellus (fine, unpigmented), terminal (coarse, pigmented).

• Color: Determined by melanin type and amount.

Nails: Structure and Function

Nails are protective coverings on the fingers and toes, aiding in grasping and manipulation.

• Parts: Nail plate, nail bed, matrix (growth area), lunula (white crescent).

• Function: Protection, support, and sensory enhancement.

Glands of the Skin

The skin contains several types of glands with distinct functions.

• Sudoriferous (Sweat) Glands:

  • Eccrine: Widely distributed; produce watery sweat for cooling.

  • Apocrine: Located in axillary/genital areas; produce thicker secretion, active after puberty.

• Sebaceous Glands: Secrete sebum (oil) for lubrication and waterproofing; found near hair follicles.

• Ceruminous Glands: Produce earwax in the ear canal.

Functions and Descriptions of Skin Functions

• Protection

• Temperature regulation

• Sensation

• Excretion

• Vitamin D synthesis

Homeostatic Imbalances

Disorders of the skin can disrupt homeostasis, leading to various conditions such as infections, allergies, and cancers.

Types of Skin Cancer

Skin cancer is classified by cell type and malignancy. The ABCD rule helps detect melanoma.

Burns: Classification and Treatment

Burns are classified by depth and severity. The "rule of nines" estimates body surface area affected.

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

• Second-degree: Epidermis and part of dermis; blisters.

• Third-degree: Full thickness; may require grafts.

Rule of Nines: Divides body into regions, each representing 9% (or multiples) of total surface area.

Skeletal System

Cartilages: Types and Locations

Cartilage is a flexible connective tissue found in various locations.

• Hyaline cartilage: Most common; found in nose, trachea, ends of long bones.

• Elastic cartilage: Flexible; found in ear and epiglottis.

• Fibrocartilage: Tough; found in intervertebral discs, pubic symphysis.

Cartilage Growth

Cartilage grows by two mechanisms:

• Appositional growth: Cells in the perichondrium add new layers to the surface.

• Interstitial growth: Chondrocytes divide and expand within the tissue.

Functions of Bones

• Support: Framework for the body.

• Protection: Shields vital organs.

• Movement: Acts as levers for muscles.

• Mineral storage: Stores calcium and phosphorus.

• Blood cell formation: Occurs in bone marrow (hematopoiesis).

Types of Bones and Locations

Parts of a Long Bone

• Diaphysis: Shaft

• Epiphysis: Ends

• Metaphysis: Region between diaphysis and epiphysis

• Medullary cavity: Central cavity containing marrow

• Periosteum: Outer covering

Bone Marrow

Bone marrow is the soft tissue inside bones responsible for blood cell production.

• Red marrow: Produces red and white blood cells.

• Yellow marrow: Stores fat.

Joints

Classification and Examples

Joints are classified by structure and function.

• Fibrous joints: Immovable (e.g., sutures in skull).

• Cartilaginous joints: Slightly movable (e.g., intervertebral discs).

• Synovial joints: Freely movable (e.g., knee, shoulder).

Synovial Joint Structure

• Articular cartilage: Covers bone ends.

• Joint cavity: Contains synovial fluid.

• Synovial membrane: Produces fluid.

• Ligaments: Stabilize joint.

• Bursa: Fluid-filled sac reducing friction.

Bones: Stimulation and Growth

Bones grow and remodel in response to mechanical stress and hormonal signals.

• Osteogenic cells: Stem cells that differentiate into bone-forming cells.

• Osteoblasts: Build new bone matrix.

• Osteocytes: Mature bone cells maintaining bone tissue.

• Osteoclasts: Break down bone matrix.

Chemical Composition of Bone

• Organic: Collagen fibers for flexibility.

• Inorganic: Hydroxyapatite (calcium phosphate) for hardness.

Bone Growth and Hormonal Regulation

Bones grow by endochondral (from cartilage) and intramembranous (from membrane) ossification. Parathyroid hormone regulates calcium levels by stimulating osteoclasts.

Fractures: Types and Repair

• Types: Simple, compound, comminuted, greenstick, spiral, etc.

• Repair Steps:

  1. Hematoma formation

  2. Fibrocartilaginous callus formation

  3. Bony callus formation

  4. Bone remodeling

Stress on Bones

Bones adapt to stress by remodeling; excessive stress can lead to fractures.

Summary Table: Key Cells in Bone Tissue

Key Equations

• Calcium homeostasis:

Additional Info

Developmental aspects of the integumentary and skeletal systems are not required for this course.