STUDYGUIDE-CH4_5-AP1 (copy)

Tissue: The Living Fabric

Epithelial Tissue

• Description: Covers body surfaces, lines cavities, and forms glands.

• Functions: Protection, absorption, filtration, excretion, secretion, and sensory reception.

Features of Epithelial Tissue

1. Classification: Can be covering/lining or glandular epithelium.

2. Polarity: Has an upper apical surface and a lower basal surface.

3. Cell Arrangement: Continuous sheets with minimal space; adjacent cells bound by desmosomes and tight junctions.

4. Support: Underlined by a basement membrane derived from connective tissue.

5. Vascularity: Innervated but avascular, with high regeneration capacity.

Classification of Epithelia

• Naming: First part indicates layer number (simple or stratified), second describes cell shape (squamous, cuboidal, columnar).

• Simple Epithelium: Single layer, functions mainly in absorption, secretion, filtration.

• Stratified Epithelium: Multiple layers, primarily provides protection.

Glandular Epithelia

1. Endocrine Glands: Ductless, secrete hormones into blood/lymph.

2. Exocrine Glands: Have ducts, secrete onto surfaces or body cavities.

   • Types:

     • Unicellular: Secrete mucus (e.g., intestinal or respiratory linings).

     • Multicellular: Composed of a duct and secretory cells, classified by duct structure/mechanism of secretion.

       • Simple (unbranched) vs. Compound (branched).

       • Secretion types: Merocrine (via exocytosis) or Holocrine (cell rupture).

Connective Tissue

Common Characteristics

• Arises from mesenchyme; varies from avascular to highly vascularized.

• Composed mostly of nonliving extracellular matrix that separates cells.

Structural Elements

1. Ground Substance: Interstitial fluid, cell adhesion proteins, proteoglycans, protein fibers.

2. Fibers:

   • Collagen: Provides high tensile strength.

   • Elastic: Stretches and recoils.

   • Reticular: Forms networks at tissue interfaces.

3. Major Classes: Each type has specific immature/mature cell forms.

Types of Connective Tissue

1. Proper Connective Tissue:

   • Loose Connective Tissue: Includes areolar, adipose, reticular.

   • Functions: Support, bind, defend, store nutrients (e.g., Areolar tissue).

2. Cartilage: Avascular, lack nerve fibers; types include:

   • Hyaline: Most abundant, firm yet pliable.

   • Elastic: Found in flexible areas like the ear.

   • Fibrocartilage: Strong support (e.g., intervertebral discs).

Membranes

Cutaneous Membrane

• Description: Dry membrane with keratinized stratified squamous epithelium, thicker dense irregular connective tissue.

Mucous Membranes

• Description: Wet membranes lining cavities open to the exterior; contain stratified squamous/simple columnar over connective tissue.

Serous Membranes

• Description: Moist membranes in closed cavities, featuring simple squamous epithelium over loose connective tissue.

The Integumentary System

Skin Structure

• Layers: Epidermis (epithelial tissue) and Dermis (connective tissue).

• Hypodermis: Subcutaneous tissue; anchors skin to muscle, shock absorber, insulator.

Epidermis

• Keratinocytes: Produce keratin for protection.

• Melanocytes: Produce melanin, the pigment for skin color.

• Dendritic Cells: Macrophages activating immune response.

• Merkel Cells: Associated with sensory nerve endings.

Layers of the Epidermis

1. Stratum Basale: Site of mitosis.

2. Stratum Spinosum: Several layers, contains keratinocytes and dendritic cells.

3. Stratum Granulosum: Keratinocytes undergoing physical changes.

4. Stratum Lucidum: Only in thick skin, composed of dead keratinocytes.

5. Stratum Corneum: Outermost layer, protects with dead keratinocytes.

Dermis

• Structure: Strong, flexible connective tissue, rich in vessels and nerves.

• Layers:

  • Papillary Layer: Forms fingerprints.

  • Reticular Layer: Forms cleavage and flexure lines.

Skin Color Determinants

• Melanin: Two forms; protects from UV damage.

• Carotene: Yellow-orange pigment from foods, accumulates in skin.

• Hemoglobin: Pink hue visible through skin transparency.

Glands Associated with Skin

1. Sweat Glands:

   • Eccrine: Found on palms, soles, forehead; prevent overheating.

   • Apocrine: In axillary and anogenital areas; produce fat- and protein-rich sweat.

   • Ceruminous: In ear canal, secrete earwax.

   • Mammary: Secrete milk.

2. Sebaceous Glands:

   • Function: Secrete sebum; lubricates skin/hair, slows water loss.

Skin Functions

• Protection: Chemical (skin secretions), physical (continuity and keratinized cells), biological (immune cells).

• Temperature Regulation: Sweat production and blood flow adjustments.

• Sensation: Cutaneous sensory receptors in skin layers.

• Metabolic Functions: Synthesizes vitamin D.

• Reservoir: Holds blood supply.

• Excretion: Limited waste removal.

Skin Cancer and Burns

1. Skin Cancer Types:

   • Basal Cell Carcinoma: Least malignant, from stratum basale.

   • Squamous Cell Carcinoma: Derived from stratum spinosum; can metastasize.

   • Melanoma: Highly metastatic, from melanocytes. Evaluated by ABCDE rule.

2. Burns:

   • Cause: Heat, electricity, radiation, chemicals.

   • Risks: Dehydration, infection.

   • Types: First-degree (epidermis), Second-degree (epidermis+dermis), Third-degree (full thickness).