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Animal Tissues

• Tissue is a group of similar cells, tightly bound together by intercellular material, performing a specific function.
• Tissues are broadly categorized into four main groups:
  • Epithelial Tissues
  • Connective Tissues
  • Muscular Tissues
  • Nervous Tissues

Epithelial Tissues

• Functions:

  • Covering Epithelial: Covers the outer surfaces of the body, like the skin.
  • Lining Epithelial: Lines most organs, including blood vessels.
  • Also forms glands that produce secretions.

• General Characteristics:

  • Cells arranged in one or more layers.
  • Minimal intercellular substance.
  • Lack blood vessels.
  • Richly innervated.
  • Usually rests on a basement membrane.
  • High capacity for regeneration due to wear and tear during bodily functions.

Types of Epithelial Tissues

• Classification by arrangement of cells in layers:

  • Simple Epithelium: Cells arranged in a single layer.
    • Simple Squamous
    • Simple Cuboidal
    • Simple Columnar
  • Stratified Epithelium: Cells arranged in multiple layers.
    • Stratified Squamous
    • Stratified Columnar
    • Stratified Cuboidal
  • Pseudostratified Columnar Epithelium appears layered but is actually a single layer with different heights; nuclei appear at different levels.

• Classification by cell shape:

  • Squamous: Thin, flat cells resembling scales. Nuclei are centrally located and oval-shaped.
  • Cuboidal: Cube-shaped cells. Nuclei are spherical and centrally located. Found in glands and ducts.
  • Columnar: Tall, elongated cells. Nuclei are oval and are located near the base of the cell. Functions include secretion (stomach producing mucus) and absorption (intestine). Also found lining glands, bile ducts, and pancreatic ducts. Further categorized into Ciliated or non-ciliated types depending on presence of cilia.

Basement Membrane

• A specialized layer separating the epithelium from the underlying connective tissue.

Nervous Tissues

• Composed of neurons (nerve cells) and neuroglia (supporting cells).

• Neurons transmit electrical signals throughout the body. Components include:

  • Dendrites receive signals from other cells.
  • Axon transmits signals away from the cell body.
  • Myelin sheath insulation created by Schwann cells enhancing signal speed.
  • Nodes of Ranvier gaps between myelin sheath on the axon.
  • Cell body contains the nucleus.

• Neuroglia support and protect neurons; one type is Schwann cells.

• Synapse: The region where neurons communicate with other neurons, glands, or muscle cells. The transmission of information across the synapse involves electrochemical processes.