Biology Chapter 2: Tissue Organization

Chapter 2: The Tissue Level of Organization

• The human body contains over 200 types of cells.
• These cells are categorized into four main tissue types.

Types of Tissues

• Epithelial tissue: Lines internal and external body surfaces, and forms glands.
• Connective tissue: Supports, connects, and separates different tissues and organs.
• Muscle tissue: Enables movement.
• Nervous tissue: Coordinates and controls bodily functions.

Tissue Membranes

• Thin layers of cells that cover the exterior body surfaces, organs, internal cavities, and movable joints.
• Two main types exist:
  • Connective membrane: Includes cutaneous (skin), synovial (joints), and serous membranes (internal cavities).
  • Epithelial membrane: Includes mucous membranes that line body cavities open to the exterior (digestive, respiratory, urinary, reproductive tracts).

Embryonic Origin of Tissues

• Tissues originate from three embryonic germ layers (ectoderm, mesoderm, endoderm).
• Ectoderm develops into epidermis, nervous system components, and certain glands.
• Mesoderm gives rise to connective tissues, muscle tissues, and components of body systems.
• Endoderm forms the lining of many internal organs and parts of the digestive system.

Epithelial Tissues

• Composed mostly of cells with little extracellular material.
• Consist of three basic types of connections between cells:
  • Tight junctions
  • Anchoring junctions
  • Gap junctions

Classification of Epithelial Tissues

• Classified based on the shape of the cells and the number of cell layers.
  • Squamous: flattened cells
  • Cuboidal: cube-shaped cells
  • Columnar: elongated cells
  • Simple: single layer of cells
  • Stratified: multiple layers of cells

Glandular Epithelium

• Specialized epithelial tissue that synthesizes and secretes substances.
• Two types:
  • Endocrine glands: Ductless; secretions released directly into the bloodstream or surrounding tissues.
  • Exocrine glands: Possess ducts; secretions released onto the surface of a body cavity or external environment.

Connective Tissues

• Diverse tissue type that connects, supports, and separates other tissues.
• Classified into:
  • Connective tissue proper: Loose (areolar, adipose, reticular) and dense (regular, irregular, elastic) connective tissues.
  • Supportive connective tissues: Cartilage and bone.
  • Fluid connective tissue: Blood and lymph.

Muscle Tissues and Motion

• Specialized tissue that enables movement.
• Three types:
  • Skeletal muscle: Attached to bones; responsible for voluntary movement.
  • Cardiac muscle: Forms the heart walls; responsible for pumping blood (involuntary).
  • Smooth muscle: Found in the walls of internal organs; responsible for involuntary movements.

Nervous Tissue

• Excitable tissue responsible for communication and control.
• Two main cell types:
  • Neurons: Responsible for transmitting electrical signals
  • Neuroglia: Support and nourish neurons (various types).