Anatomy and Physiology Chapter 3

Tissue Types Overview

• Tissues are categorized into groups of similar cells that perform specific functions.
• The four primary tissue types are epithelial, connective, nervous, and muscle tissue.

Epithelial Tissue

• Acts as the lining, covering, and glandular tissue throughout the body.
• Covers both external and internal surfaces.
• Functions include:
  • Protection: Serves as the first line of defense in immunity.
  • Absorption: Facilitates nutrient uptake in the stomach and small intestine.
  • Filtration: Involved in kidney filtration processes.
  • Secretion: Glandular epithelia secrete substances like sweat, oil, enzymes, and mucus.

Hallmarks of Epithelial Tissue

• Special Contacts: Epithelial cells form continuous sheets, except in glandular epithelium.
• Polarity: Each epithelial membrane has an apical (free) surface exposed to outside or internal cavities, which may have microvilli or cilia.
• Support: Epithelial cells rest on a basement membrane anchored by connective tissue.
• Avascular but Innervated: Epithelia lack direct blood supply, yet they contain nerve endings.
• Regeneration: Epithelial tissues regenerate quickly when nourished.

Classification of Epithelial Tissue

• By Cell Arrangement:
  • Simple Epithelium: One cell layer.
  • Stratified Epithelium: Multiple cell layers.
• Glandular Epithelium: Comprises cells that produce and secrete substances, derived from blood materials.

Types of Glands

• Endocrine Glands: Ductless; hormones diffuse directly into blood (e.g., thyroid, pituitary).
• Exocrine Glands: Contain ducts; secrete substances to the epithelial surface (e.g., sweat glands, pancreas).

Connective Tissue

• Most abundant and diverse tissue type in the body.
• Primarily connects, supports, and binds other tissues.
• Hallmarks include:
  • Common Origin: All connective tissues originate from mesenchyme.
  • Blood Supply Variation: Generally well-vascularized, with exceptions like tendons (poor supply) and cartilage (avascular).
  • Extracellular Matrix: Composed of living cells and non-living substances that provide support.

Types of Connective Tissue

• Dense Connective Tissue: Includes dense irregular connective tissue found in fasciae, dermis, and joint capsules; arranged to withstand multi-directional tension.
• Loose Connective Tissue: Softer with more cells and fewer fibers. Types include:
  • Areolar Tissue: Most widely distributed, cushions organs and retains tissue fluid.
  • Adipose Tissue: Specialized for fat storage, insulation, and protection.
  • Reticular Tissue: Forms internal frameworks of organs and supports blood cell formation.

Blood

• Classified as a connective tissue due to its composition of blood cells in a fluid matrix (plasma).
• Functions in transportation throughout the body, handling nutrients, waste, and gases.

Muscle Tissue

• Specialized for contraction to generate movement.
• Types include:
  • Skeletal Muscle: Voluntary control, striated, multinucleated.
  • Cardiac Muscle: Involuntary control, striated, with intercalated discs, unique to the heart.
  • Smooth Muscle: Involuntary, non-striated, found in hollow organs; facilitates peristalsis for food movement.

Nervous Tissue

• Composed of neurons and neuroglia.
• Neurons: Responsible for transmitting electrochemical impulses; have long processes to transmit signals over distance.
• Neuroglia: Support cells that protect and insulate neurons within the nervous system.