Introduction to Tissues and Epithelial Tissue

Tissue Introduction & Epithelial Tissue

• Tissues are groups of cells with similar structure and function
• Human bodies develop from single to multicellular cells. Cells specialize.
• The body is an interdependent system. Malfunction of one cell group can be catastrophic

Cells to Tissues

• Specialized cells form tissues.
• Tissues then combine to form organs.

Types of Tissues

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

Function of Epithelial Tissue

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

Characteristics of Epithelial Tissue

• Continuous sheets (like tiles)
• Apical surface: Top surface of cells, borders an open space (lumen).
• Basement membrane: Underside of epithelial cells, anchors to connective tissue.
• Avascular: Lacks blood vessels.
• Nourished by connective tissue.
• Regenerate and repair quickly.

Classification of Epithelial Tissue

• Cell Shape:
  • Squamous: Flattened, like fish scales
  • Cuboidal: Cube-shaped
  • Columnar: Column-shaped
• Cell Layers:
  • Simple: One layer of cells
  • Stratified: Many layers of cells
• Named for the cell type at the apical surface

Simple Squamous Epithelium

• Structure: Single layer of flattened cells
• Function: Absorption and filtration
• Not effective protection due to single layer.
• Location: Walls of capillaries, air sacs in lungs, serous membranes in body cavities

Simple Cuboidal Epithelium

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

Simple Columnar Epithelium

• Structure: Elongated layer of cells with nuclei at the same level.
• Function: Absorption, protection, secretion. When open to body cavities called mucous membranes.
• Special features: Microvilli (increase surface area and absorption), goblet cells (protective mucus)
• Location: Linings of the entire digestive tract

Pseudostratified Epithelium

• Structure: Irregularly shaped cells with nuclei at different levels, appear stratified, but all cells reach basement membrane
• Function: Absorption and secretion, goblet cells (produce mucus), Cilia (sweep mucus)
• Location: Respiratory linings and reproductive tract

Stratified Squamous Epithelium

• Structure: Many layers, usually cuboidal/columnar at the bottom and squamous at the top
• Function: Protection, keratin (protein) waterproofs and toughens the skin
• Location: Skin (keratinized), mouth, and throat

Transitional Epithelium

• Structure: Many layers, cells at the base are cuboidal or columnar, cells at the surface vary, Change between stratified and simple as tissue is stretched out.
• Function: Allows stretching (changes size).
• Location: Urinary bladder, ureters, and urethra

Glands

• One or more cells that make and secrete a product
• Secretion: Protein in an aqueous solution (hormones, acids, oils)
• Endocrine glands: No duct, release secretion into blood vessels (often hormones), e.g., thyroid, adrenal, pituitary
• Exocrine glands: Contain ducts, empty onto epithelial surfaces; e.g., sweat, oil, salivary, mammary glands

Shapes of Exocrine Glands

• Branching: Simple (single, unbranched duct) or Compound (branched)
• Shape: Tubular (shaped like a tube) or Alveolar (shaped like flasks or sacs). Tubuloalveolar (has both tubes and sacs)

Modes of Secretion

• Merocrine: Released by exocytosis without altering the gland (e.g., sweat and salivary glands).
• Holocrine: Gland ruptures and releases secretion and dead cells (sebaceous glands).

Explore the fundamental aspects of tissues and the vital role of epithelial tissue in the human body. This quiz covers the types of tissues, their functions, and the specific characteristics of epithelial tissue. Understand how specialized cells work together to form organs and systems in a multicellular organism.