Epithelial Tissue Overview

Tissues

• Tissues are groups of cells working together for a specific function.
• Histology studies the structure and composition of tissues and organs at the microscopic level.
• There are four main types of tissues:
  • Epithelial: covers the body surface and lines hollow organs.
  • Connective: supports other tissues and binds them together.
  • Muscle: allows the body to move.
  • Nervous: made up of nerve cells that carry messages throughout the body.

Epithelial Tissue

• Functions: support, secretion, protection, and sensory reception.
• Shapes: squamous (flat), cuboidal (cube-like), columnar (column-like)
• Layers:
  • Simple: single layer of cells.
  • Stratified: multiple layers of cells stacked on top of each other.
• Types:
  • Keratinized stratified squamous epithelium: protects the body from stress and forms the skin's epidermis.
  • Non-keratinized stratified squamous epithelium: lacks keratin.
  • Simple squamous epithelium (endothelium): lines blood vessels and the heart.
  • Stratified squamous epithelium: found on the surface of the skin, tongue, and esophagus.
  • Simple cuboidal epithelium: lines ducts and secretory glands of organs in the body.
  • Stratified cuboidal epithelium: lining of some ducts, occurs in the excretory ducts of sweat glands and salivary glands.
  • Simple columnar epithelium: lining of the stomach and intestine, specialized for absorption, has cilia and microvilli.
  • Stratified columnar epithelium: small areas of the pharynx and mammary glands, provides protection and facilitates milk movement through ducts.
  • Pseudostratified ciliated columnar epithelium: lines the nasal cavity, trachea, bronchi, and other parts of the respiratory tract.
• Transitional epithelium: stratified epithelium that can withstand stretching and recoiling.
  • Appearance: changes based on stretching, can look plump and cuboidal when flat, found in the urinary bladder and ureter.

Glands

• Endocrine glands: release hormones into the bloodstream.
• Exocrine glands: secrete substances onto the body surface through ducts.

Connective Tissue

• Functions: support, protect, and give structure to other tissues and organs.
• Types:
  • Fibrous: dense connective tissue (e.g., tendons, ligaments) and loose connective tissue (e.g., areolar, adipose, reticular).
  • Fluid: blood and lymph.
  • Supporting: cartilage and bone.
• Cell types and functions:
  • Fibroblasts: secrete collagen proteins, maintain the structural framework of tissues.
  • Macrophages: ingest and degrade dead cells, debris, tumor cells, and foreign materials.
  • Adipocytes: provide energy storage, insulation, and cushioning around soft organs.
  • Mesenchymal cells: support and maintain other cells.
  • Melanocytes: produce and distribute melanin.
  • Mast cells: protect the body from foreign invaders and toxins.
  • Lymphocytes: part of the immune system, fight foreign invaders.
  • Plasma cells: produce antibodies, play a critical role in the immune response.
• Adipose tissue: loose connective tissue composed of adipocytes, stores energy, insulates the body, and cushions internal organs.
• Loose connective tissue:
  • Areolar tissue: supports organs and tissues, holds fluid.
  • Adipose tissue: storage, insulation, cushioning.
  • Reticular tissue: provides a supporting framework, located in the spleen, liver, and lymph nodes.
• Dense connective tissue: mostly made up of tough protein fibers (collagen).