Tissue Introduction & Epithelial Tissue

Tissue Introduction & Epithelial Tissue

• Human bodies develop from single to multicellular cells, specializing.
• The human body is an interdependent system; failure of one cell group can be catastrophic.
• Cells specialize into tissues, then organs.
• Tissues are groups of similar cells, structured and functioning in a similar manner.

Types of Tissues

• Epithelial: Coverings and linings of surfaces
• Connective: Support (e.g., bone, ligaments, fat)
• Muscle: Movement
• Nervous: Control (e.g., brain, nerves, spinal cord)

Function of Epithelial Tissue

• Protection: Skin protects against sunlight, bacteria, and physical damage.
• Absorption: Lining of the small intestine absorbs nutrients into the blood.
• Filtration: Lining of kidney tubules filters wastes from blood plasma.
• Secretion: Different glands produce perspiration, oils, digestive enzymes, and mucus.

Characteristics of Epithelial Tissue

• Continuous sheets: Arranged like tiles
• Apical surface: Top surface bordering an open space (lumen)
• Basement membrane: Underside, anchoring to connective tissue
• Avascular: Lacks blood vessels; nourished by connective tissue.
• Regenerate quickly: Can repair quickly.

Classification of Epithelial Tissue

• Cell Shape: Squamous (flattened, like fish scales), Cuboidal (cube-shaped), Columnar (column-shaped)
• Cell Layers: Simple (single layer), Stratified (many layers)
• Classification is based on the cell type at the apical surface.

Simple Squamous Epithelium

• Structure: Single layer of flattened cells
• Function: Absorption, filtration
• Not effective protection: Single layer, only absorbs
• Location: Walls of capillaries, air sacs in lungs, forming serous membranes in body cavities.

Simple Cuboidal Epithelium

• Structure: Single layer of cube-shaped cells
• Function: Secretion and transport in glands, filtration in kidneys
• Location: Glands and ducts (e.g., pancreas, salivary), kidney tubules, covers ovaries

Simple Columnar Epithelium

• Structure: Elongated cells with nuclei at same level
• Function: Absorption, protection, secretion
• Special features: Microvilli, goblet cells, producing mucus
• Location: Linings of the entire digestive tract

Pseudostratified Epithelium

• Structure: Irregularly shaped cells with nuclei at different levels, appearing stratified but all reach the basement membrane
• Function: Absorption and secretion and Cilia
• Location: Respiratory and reproductive tracts

Stratified Squamous Epithelium

• Structure: Many layers, usually cuboidal/columnar at the base, squamous at the top
• Function: Protection
• Keratin: Protein accumulating in older cells making the skin waterproof and tough
• Location: Skin (keratinized), mouth, and throat (non-keratinized)

Transitional Epithelium

• Structure: Many layers, base cells are cuboidal/columnar, surface cells vary, changing between simple and stratified form when stretching
• Function: Allows stretching and changing size
• Location: Urinary bladder, ureters, and urethra

Glands

• Single or multiple cells secreting products
• Secretion: Protein in aqueous solution (hormones, acids, oils)
• Endocrine glands: No ducts, release secretion into blood vessels (e.g., thyroid, adrenal, pituitary).
• Exocrine glands: Contain ducts, release secretion onto epithelial surface (e.g., sweat, oil, salivary, mammary).

Shapes of Exocrine Glands

• Branching: Simple (single, unbranched duct) or compound (branched)
• Shape: Tubular (tube-shaped), alveolar (flask- or sac-shaped), tubuloalveolar (both tubes and sacs).

Modes of Secretion

• Merocrine: Released by exocytosis, no change to the gland (e.g., sweat, salivary glands)
• Holocrine: Gland ruptures, releasing secretion and dead cells (e.g., sebaceous glands).

Explore the fundamental concepts of human tissues, focusing on the types of tissues and the specific functions of epithelial tissue. Understand how cells specialize into tissues, their roles in the body, and the characteristics that define epithelial tissue. This quiz will test your knowledge of these essential biological structures.