Introduction to Histology Quiz

Introduction to Histology

• Histology is the study of tissues, focusing on how cells organize into functional tissues.
• It is vital for diagnostics (histopathology) and research into human diseases, drug treatments, and biomarkers.
• Tissue samples need to be fixed (chemically or physically), embedded in resin or wax, and sliced thinly using a microtome for light microscopy.
• Staining is crucial for visualizing specific structures. Eosin (red) stains cytoplasm, and haematoxylin (purple) stains the nucleus. H&E staining combines both. Other stains like immunohistochemistry use antibodies to reveal specific proteins.
• Electron microscopy (transmission and scanning) allows for higher resolution imaging.

Four Main Tissue Classifications

• Muscle tissue
• Epithelial tissue
• Connective tissue (e.g., cartilage, blood) - blood fulfills the definition of connective tissue by containing cells suspended in a medium.
• Nervous tissue

Epithelial Tissue

• Epithelial tissue forms coverings or glands.

• Covering epithelium: lines cavities and covers surfaces

• Glandular epithelium: includes secretory epithelial cells with an acinus region for product formation.

• Epithelial cells adhere to a basement membrane (basal end) via hemidesmosomes and neighbouring cells via desmosomes. This structure helps maintain tissues' integrity and function.

• Epithelial tissue is classified based on the number of cell layers and cell shape.

• Number of layers: simple (one layer) / stratified (multiple layers). Simple epithelium lines surfaces where minimal friction exists (e.g., alveoli, pericardium). Stratified epithelium is found in areas experiencing high friction (e.g., mouth, esophagus), offering protection.

• Cell shape: cuboidal (cube-shaped), squamous (flat), columnar (taller than wide).

• Specializations:

  • Ciliated: have microtubule-based cilia for moving substances (e.g., mucus in the respiratory tract).
  • Keratinized: surfaces with protective layers of keratin, derived from dead cells (e.g., skin, hair, nails).

• Exceptions:

  • Pseudostratified: appears stratified but is a single layer with cells positioned at different levels.
  • Transitional/urothelium: stratified epithelium with variable cell shape adapting to stretch; umbrella cells in the top layer prevent urine leakage.

Cell Polarity

• Cell polarity refers to the asymmetrical distribution of functions/specializations within a cell, maintaining structure and function.
• The apical (luminal) side faces the exterior/lumen where specializations (microvilli, cilia) reside, while the basal side anchors to the basement membrane. The lateral/intercellular side connects adjacent epithelial cells via cell junctions.

Cell Junctions

• Tight junctions (TJ), adherens junctions (ZA), gap junctions (CJ), desmosomes (D), and hemidesmosomes (HD). These help maintain cell and tissue structure and function.

Cilia vs. Microvilli

• Cilia are motile structures (with microtubules) and are longer, while microvilli (with actin filaments) are smaller and non-motile.
• Microvilli are often highly developed in absorptive tissues, while cilia are found in specific places like respiratory and reproductive tracts.

Keratinization

• A special characteristic of certain squamous epithelial cells.
• Keratin (a protein) is produced and accumulates in cells, which eventually die. This creates a protective layer.

Secretory Epithelial Cells

• Individual secretory cells (like goblet cells) and gland structures (e.g., multicellular glands) are forms of secretory epithelial cells.