Histology: Cell Types and Modifications

Cell Development and Differentiation

• Cells in multicellular organisms grow, mature, and differentiate into specialized types.
• Over 200 differentiated cell types exist in the human body, forming tissues.
• Tissues consist of groups of similar cells serving a common function.
• Histology is the study of animal and plant tissues, involving thin section preparation and microscopic examination.

Types of Cells in the Human Body

Stem Cells

• Capable of division and differentiation into various cell types (e.g., bone, epithelial).

Bone Cells

• Essential for bone production and repair.
• Types include:
  • Osteoclasts: dissolve bone tissue.
  • Osteoblasts: create new bone.
  • Osteocytes: communicate with other bone cells.

Blood Cells

• Red Blood Cells (RBC): transport oxygen.
• White Blood Cells (WBC): divided into:
  • Granulocytes
  • Monocytes
  • Lymphocytes (subtypes include neutrophils, phagocytic, and basophils, involved in pathogen defense).
• Platelets: aid in blood clotting.

Muscle Cells

• Also called Myocytes; long, tubular cells supporting organ function and peristalsis.

Sex Cells

• Responsible for reproduction through:
  • Oogenesis: formation of egg cells.
  • Spermatogenesis: formation of sperm cells.

Fat Cells

• Produce and store fats in a clustered arrangement, known as adipose tissues.

Nerve Cells

• Neurons: transmit and relay signals throughout the body, facilitating communication.

Epithelial Cells

• Line surfaces and cavities, playing pivotal roles in communication and protection.
• Types include:
  • Epithelium
  • Endothelium
  • Mesothelium

Cartilage Cells

• Chondrocytes are the primary cells responsible for forming cartilage, residing within lacunae.

Types of Tissues

• Four primary types in animals:
  • Epithelial
  • Connective
  • Muscular
  • Nervous
• Organs consist of multiple tissue types, working together for specific functions, like the stomach which contains:
  • Columnar epithelial cells for absorption.
  • Smooth muscle tissues for peristalsis.
  • Nervous tissues for signaling.
  • Blood as connective tissue for nutrient transport.

Epithelial Tissues

• Composed of specialized cells organized in one or more layers.
• Categories include:
  • Simple Epithelium: single layer.
  • Stratified Epithelium: multiple layers.
• Shapes of epithelial cells:
  • Squamous: flattened (found in alveoli and capillaries for gas exchange).
  • Cuboidal: cube-shaped with larger cytoplasm, facilitating absorption and secretion.
  • Pseudostratified: appears stratified but consists of varying cell heights, often found in respiratory pathways.

Connective Tissues

• Characterized by dispersed cells and extensive extracellular matrix (ECM).
• ECM components include:
  • Protein fibers (collagen, elastic, reticular).
  • Ground substances, predominantly secreted by connective tissue cells.
• Types of ECM:
  • Solid (bone)
  • Soft (connective tissues)
  • Liquid (blood)
• Functions include:
  • Protection
  • Cushioning
  • Fat storage
  • Nutrient and waste transport
  • Maintenance of structure.