Epithelial_tissue

Epithelial Tissue Overview

• Epithelial tissue: A type of tissue that covers body surfaces and lines cavities.

Levels of Body Organization

• Chemical Level: Atoms and molecules forming cells.

• Cellular Level: Smooth muscle cell forms tissue.

• Tissue Level: Smooth muscle tissue forms muscle layers.

• Organ Level: Various organs such as stomach, liver, intestines.

• System Level: Digestive system encompasses all related organs.

• Organismal Level: Total of all organ systems in a body.

Basic Tissues of the Body

• Definition of Tissue: A group of similarly specialized cells that perform a common function.

• Four Main Tissue Types in Humans:

  • Epithelial: Covers body surfaces and lines cavities.

  • Connective: Binds and supports body parts.

  • Muscular: Moves body parts.

  • Nervous: Receives, interprets, and sends signals.

Components of Epithelial Tissue

• Types of Tissues Involved:

  • Skin: External protective layer.

  • Epithelium: Covers surfaces.

  • Connective Tissue: Supports epithelial cells.

  • Muscle Tissue: Allows movement.

  • Nervous Tissue: Conducts signals.

Characteristics of Epithelia

• Etymology: "Epithelial" comes from Greek: theleo (to grow) + epi (upon).

• Functionality:

  • Form membranes covering body or organ surfaces.

  • Form secretory elements such as glands.

Functions of Epithelial Tissue

• Protection: Acts as a barrier against physical damage.

• Secretion: Produces substances (e.g., mucus, enzymes).

• Absorption: Major function in intestines and kidneys.

• Selective Permeability: Regulates entry and exit of substances.

• Sensation: Contains sensory cells for perception.

• Repairs: High turnover and regeneration capacity.

• Moisture Control: Maintains hydration of body surfaces.

Classification of Epithelia

• Based on Cell Shape:

  • Squamous: Wider than taller.

  • Cuboidal: Equal width and height.

  • Columnar: Taller than wider.

• Based on Number of Layers:

  • Simple: One layer of cells.

  • Stratified: Multiple layers of cells.

  • Pseudostratified: Appears layered due to differing cell heights but is a single layer.

Types of Simple Epithelia

• Simple Squamous Epithelium:

  • Thin, flat cells providing minimal barrier for diffusion; found in linings of blood vessels.

• Simple Cuboidal Epithelium:

  • Cube-shaped; involved in secretion and absorption; found in gland ducts and kidney tubules.

• Simple Columnar Epithelium:

  • Taller cells; involved in secretion and absorption; nuclei aligned towards base; found in digestive tract.

Types of Stratified Epithelia

• Stratified Squamous Epithelium:

  • Multiple layers; basal cells are cuboidal, while surface cells are flattened; provides protection against abrasion (e.g., skin).

• Stratified Columnar Epithelium:

  • Basal cells cuboidal; apical cells columnar; provides protection and secretion; found in male urethra and some gland ducts.

Transitional Epithelium

• Functionality: Stretches to allow distension, found in urinary organs.

• States:

  • Relaxed: Cells appear 'pillow'-like.

  • Distended: Cells become more flat as they stretch.

Glands Overview

• Definition: Specialized epithelial cells or groups of cells that secrete substances.

• Types of Glands:

  • Exocrine Glands: Secrete onto a surface via ducts (e.g., sweat glands).

  • Endocrine Glands: Secrete hormones directly into the bloodstream; lack ducts.

Exocrine Glands and Their Mechanisms

• Types of Secretion Mechanisms:

  • Holocrine: Entire cell disintegrates to release secretory products.

  • Merocrine: Secretion occurs via exocytosis; cell remains intact.

  • Apocrine: Portions of the cell pinch off to release secretion.

Classifications of Exocrine Glands

• By Number of Cells:

  • Unicellular Glands: Single-cell glands such as goblet cells.

  • Multicellular Glands: Composed of multiple cells.

• By Organization:

  • Simple Glands: No branching ducts.

  • Compound Glands: Branching ducts.