Tissues, Membranes, and the Integumentary System: Study Guide

Tissues, Membranes, & the Integumentary System

Epithelium and Its Characteristics

The epithelium is a fundamental tissue type that lines body surfaces and cavities, providing protection, absorption, filtration, and secretion.

• Cellularity: Composed almost entirely of tightly packed cells.

• Polarity: Has an apical (top) and basal (bottom) surface.

• Avascularity: Lacks blood vessels; nutrients diffuse from underlying tissues.

• Regeneration: High capacity for renewal due to frequent cell division.

Simple vs. Stratified Epithelium

Epithelium is classified by the number of cell layers present.

• Simple Epithelium: Single layer of cells; specialized for absorption, secretion, and filtration.

• Stratified Epithelium: Multiple layers; provides protection against abrasion.

Cell Shapes - Squamous, Cuboidal, Columnar

Cell shape is a key feature in epithelial classification.

• Squamous: Flat, scale-like cells; found where diffusion or filtration occurs.

• Cuboidal: Cube-shaped cells; often involved in secretion and absorption.

• Columnar: Tall, column-like cells; specialized for absorption and secretion.

Types of Simple Epithelium and Locations

Simple epithelium types are adapted for specific functions and locations.

• Simple Squamous: Air sacs of lungs, lining of heart, blood vessels.

• Simple Cuboidal: Kidney tubules, ducts of small glands.

• Simple Columnar: Digestive tract lining, gallbladder.

• Pseudostratified Columnar: Trachea, upper respiratory tract (appears layered but is not).

Types of Stratified Epithelium and Locations

Stratified epithelium provides protection in areas subject to wear and tear.

• Stratified Squamous: Skin (epidermis), mouth, esophagus.

• Stratified Cuboidal: Sweat glands, mammary glands.

• Stratified Columnar: Rare; found in male urethra.

• Transitional Epithelium: Urinary bladder (stretches as organ fills).

Glandular Epithelium - Endocrine vs. Exocrine Glands

Glandular epithelium forms glands that secrete substances.

• Endocrine Glands: Ductless; secrete hormones directly into blood (e.g., thyroid, pituitary).

• Exocrine Glands: Have ducts; secrete onto body surfaces or into cavities (e.g., sweat, salivary glands).

Connective Tissue Characteristics

Connective tissue supports, binds, and protects other tissues and organs.

• Extracellular Matrix: Abundant; consists of fibers (collagen, elastic, reticular) and ground substance.

• Vascularity: Varies from avascular (cartilage) to highly vascular (bone).

• Cells: Includes fibroblasts, chondrocytes, osteocytes, and others.

Major Connective Tissue Classes

Connective tissues are classified based on structure and function.

• Loose Connective Tissue: Areolar, adipose, reticular.

• Dense Connective Tissue: Dense regular, dense irregular, elastic.

• Cartilage: Hyaline, elastic, fibrocartilage.

• Bone: Compact and spongy bone.

• Blood: Fluid connective tissue.

Muscle Tissue - Skeletal, Cardiac, Smooth

Muscle tissue is specialized for contraction and movement.

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

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

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

Nervous Tissue

Nervous tissue is responsible for transmitting electrical impulses throughout the body.

• Neurons: Specialized cells for communication.

• Neuroglia: Support, protect, and nourish neurons.

Body Membranes - Epithelial vs. Connective Tissue

Body membranes cover surfaces, line cavities, and form protective sheets.

• Cutaneous Membrane: Skin; dry, protective.

• Mucous Membrane: Lines body cavities open to exterior; moist (e.g., digestive, respiratory tracts).

• Serous Membrane: Lines closed cavities; secretes serous fluid (e.g., pleura, pericardium).

• Synovial Membrane: Connective tissue; lines joint cavities.

Functions of the Skin

The skin is the largest organ and serves multiple vital functions.

• Protection: Against mechanical, chemical, and biological damage.

• Regulation: Body temperature and water loss.

• Sensation: Detects touch, pain, temperature.

• Metabolic: Synthesis of vitamin D.

• Excretion: Removal of wastes via sweat.

Structure of Skin (Epidermis, Dermis, Subcutaneous Layer, & Appendages)

The skin consists of three main layers and various appendages.

• Epidermis: Outermost layer; stratified squamous epithelium.

• Dermis: Middle layer; connective tissue, contains blood vessels, nerves, glands.

• Subcutaneous Layer (Hypodermis): Deepest; adipose tissue, anchors skin to underlying structures.

• Appendages: Hair, nails, sweat and sebaceous glands.

Importance of Melanin

Melanin is a pigment produced by melanocytes in the epidermis.

• Function: Protects against UV radiation; determines skin color.

• Clinical Relevance: Deficiency or excess can lead to disorders (e.g., albinism, hyperpigmentation).

Clinical Examples

Various clinical conditions are associated with skin and tissues.

• Infections: Bacterial, viral, fungal (e.g., impetigo, herpes).

• Allergies: Contact dermatitis, eczema.

• Burns: Classified by depth and severity.

• Skin Cancer: Basal cell carcinoma, squamous cell carcinoma, melanoma.

Homeostatic Imbalances - Infections & Allergies, Burns, Skin Cancer

Disruptions in skin homeostasis can lead to disease.

• Infections: Pathogen invasion.

• Allergies: Immune response to harmless substances.

• Burns: Damage from heat, chemicals, electricity.

• Skin Cancer: Uncontrolled cell growth.

ABCD Rule

The ABCD rule helps identify malignant melanoma.

• Asymmetry: Two sides of the mole do not match.

• Border: Edges are irregular or blurred.

• Color: Multiple colors or uneven distribution.

• Diameter: Greater than 6 mm.

Rule of Nines

The Rule of Nines estimates the percentage of body surface area affected by burns.

• Body is divided into regions, each representing 9% (or multiples) of total surface area.

• Used to guide fluid resuscitation and treatment.

Body Region	% of Total Surface Area
Head & Neck	9%
Each Arm	9%
Each Leg	18%
Anterior Trunk	18%
Posterior Trunk	18%
Perineum	1%

Vernix Caseosa, Alopecia, and Gray Hair

These terms relate to skin and hair conditions.

• Vernix Caseosa: Waxy, protective coating on newborn skin.

• Alopecia: Hair loss; can be genetic or due to disease.

• Gray Hair: Loss of pigment production in hair follicles.

Skin Colors - Redness, Blanching, Jaundice, Bruises

Skin color changes can indicate underlying health conditions.

• Redness (Erythema): Increased blood flow; may indicate inflammation or fever.

• Blanching (Pallor): Reduced blood flow; may indicate anemia or shock.

• Jaundice: Yellowing due to bilirubin accumulation; often indicates liver dysfunction.

• Bruises (Ecchymoses): Blood leakage under skin due to trauma.