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Chapter 5: Tissues Lecture Notes

5.1 Cells Are Organized into Tissues

  • Organizational Structure: Complex organisms' cells are organized into tissues.
  • Definition of Tissue: A tissue is defined as a group of similar cells that share a common function.
  • Histology: The study of tissues.
  • Four Major Types of Tissues:
    • Epithelial Tissue: Provides protection, secretion, absorption, and excretion.
    • Connective Tissue: Binds, supports, protects, fills spaces, stores fat, and produces blood cells.
    • Muscle Tissue: Responsible for movement.
    • Nervous Tissue: Conducts impulses for coordination, regulation, integration, and sensory reception.

5.2 Tissue Types and Characteristics

Table 5.1 Four Major Tissue Types

  • Epithelial Tissue:

    • Function: Protection, secretion, absorption, excretion.
    • Location: Covers body surface, lines internal organs, composes glands.
    • Characteristics: Avascular (lack blood vessels), cells tightly packed, readily divide.

  • Connective Tissue:

    • Function: Binds, supports, protects, fills spaces, stores fat, produces blood cells.
    • Location: Widely distributed throughout body.
    • Characteristics: Mostly have good blood supply, cells are spaced further apart with an extracellular matrix in between.

  • Muscle Tissue:

    • Function: Movement.
    • Location: Attached to bones, within walls of hollow internal organs, and the heart.
    • Characteristics: Capable of contraction in response to stimuli.

  • Nervous Tissue:

    • Function: Conducts impulses for coordination, regulation, integration, and sensory reception.
    • Location: Brain, spinal cord, nerves.
    • Characteristics: Cells communicate with each other and with other parts of the body.

5.3 Intercellular Junctions

Table 5.2 Types of Intercellular Junctions

  • Tight Junctions:

    • Characteristics: Close spaces between cells by fusing cell membranes.
    • Example: Cells lining the small intestine.

  • Desmosomes:

    • Characteristics: Bind cells by forming "spot welds" between membranes.
    • Example: Outer skin layer cells.

  • Gap Junction:

    • Characteristics: Form tubular channels between cells that permit exchanges of substances.
    • Example: Cardiac muscle cells and muscle cells in the digestive tract.

5.4 Epithelial Tissues

General Characteristics
  • Cover organs and body surfaces.
  • Line cavities and hollow organs.
  • Constitute glands.
  • Exhibit a free surface externally and a basement membrane internally.
  • Avascular; nutrients diffuse from underlying connective tissues.
  • Readily dividing cells for quick healing.
  • Cells are densely packed.
  • Classification based on cell shape and number of layers.
Shapes
  • Squamous: Flat cells.
  • Cuboidal: Cube-shaped cells.
  • Columnar: Tall cells.
Layers
  • Simple: One layer of cells.
  • Stratified: Multiple layers of cells.
  • Pseudostratified: Appears layered but is a single layer.

5.5 Types of Epithelial Tissues

Simple Squamous Epithelium
  • Single layer of thin, flat cells.
  • Substances pass easily through air sacs (alveoli) and capillaries.
  • Sites of diffusion and filtration.
  • Found in walls of air sacs, capillaries, and blood vessels.
Simple Cuboidal Epithelium
  • Single layer of cube-shaped cells.
  • Function: Secretion and absorption.
  • Locations: Kidney tubules, thyroid follicles, ducts of some glands, covering ovaries.
Simple Columnar Epithelium
  • Single layer of elongated cells with nuclei near the basement membrane.
  • May contain microvilli, cilia, and goblet cells (which secrete mucus).
  • Functions: Secretion and absorption.
  • Locations: Lines the uterus, stomach, and intestines.
Pseudostratified Columnar Epithelium
  • Single layer of cells appearing layered due to varying nucleus levels.
  • Often has cilia and goblet cells.
  • Functions: Protection from infection.
  • Locations: Lines respiratory passageways.
Stratified Squamous Epithelium
  • Many layers with outermost being squamous and deeper cuboidal.
  • Functions: Protection.
  • Locations: Outer layer of skin (epidermis), oral cavity, vagina, anal canal.
Stratified Cuboidal Epithelium
  • 2 to 3 layers of cube-shaped cells.
  • Function: More protection than a single layer.
  • Locations: Lines ducts of mammary, sweat, and salivary glands, and pancreas.
Stratified Columnar Epithelium
  • Several layers with the top layer being elongated.
  • Functions: Protection and secretion.
  • Locations: Part of male urethra and lining of larger ducts of excretory glands.
Transitional Epithelium
  • Composition: Many layers of cuboidal and elongated cells that can stretch.
  • Functions: Stretchability and protection.
  • Locations: Lines urinary bladder, ureters, and part of urethra.

5.6 Glandular Epithelium

Definition
  • Composed of cells that produce and secrete substances into ducts or body fluids.
  • TYPES of Glands:
    • Endocrine Glands: Secrete into tissue fluid or blood.
    • Exocrine Glands: Secrete into ducts that open onto surfaces.
Structural Types of Exocrine Glands
  • Unicellular: One cell (e.g., goblet cells).
  • Multicellular: Many cells, simple or compound; examples include sweat and salivary glands.
Features of Exocrine Glands
  • Simple Glands: Non-branching ducts.
  • Compound Glands: Branching ducts.
  • Tubular Glands: Form epithelial-lined tubes.
  • Alveolar Glands: Sac-like dilations.
Types of Glandular Secretion
  • Merocrine Glands: Secretions by exocytosis; e.g., salivary and sweat glands.
  • Apocrine Glands: Small parts of the cell are lost during secretion; e.g., mammary glands.
  • Holocrine Glands: Entire cells filled with product are released; e.g., sebaceous glands.

5.7 Connective Tissues

General Characteristics
  • Most abundant tissue type by