Histology Overview

Histology is the study of tissues and their microstructure, organization, and functions within organs. It helps understand tissue types, their development from embryonic layers, and their roles in health and disease. Key branches include general histology (tissue microstructure) and splanchnology (organ microstructure). Tissues are composed of cells with common origin, connected via extracellular matrix, and classified as epithelial, connective, muscular, nervous, supportive, blood, and germinative tissues.

Core Concepts & Key Elements

• Histology: science of tissues, including microstructure, ultramicrostructure, and functions.
• Cytology: study of cells' function and structure.
• Branches:
  • General histology: tissue microstructure.
  • Splanchnology: organ microstructure.
• Tissues: built from cells with shared origin, structure, physiology, functions; connected by extracellular matrix.
• Main tissue types: epithelial, connective, muscular, nervous, supportive, blood, germinative.
• Epithelium:
  • Origin: from ectoderm, mesoderm, endoderm.
  • Structure: cells tightly packed, minimal extracellular matrix.
  • Basement membrane: basal layer cells lie on it.
  • No blood, lymph vessels, or nerves within tissue.
  • Functions: protective, secretory, sensory.
• Superficial epithelium:
  • Covers outside body, inner lining of hollow organs, serous surfaces.
  • Types:
    • Simple epithelium (single layer): squamous, cuboidal, columnar, pseudostratified.
    • Stratified epithelium (multi-layered).
  • Special forms: non-keratinized (esophagus, tongue), keratinized (stratum corneum).
• Types of simple epithelium:
  • Squamous:
    • Endothelium: blood/lymph vessels, heart.
    • Mesothelium: serous membranes (pleura, peritoneum).
    • Pneumocyte: alveolar cells in lungs.
  • Cuboidal and columnar: shape depending on organ function.
  • Microvilli: increase absorption (e.g., intestinal epithelium).
  • Pseudostratified: found in trachea, bronchi.
• Glandular epithelium:
  • Secretory cells form glands.
  • Exocrine: secretion via ducts.
  • Endocrine: secretion directly into bloodstream.
  • Secretion modes:
    • Apocrine: part of cell detaches.
    • Merocrine: exocytosis, no cell damage.
    • Holocrine: entire cell destroyed.
  • Gland types (based on terminal shape): acinus, tubulus, alveolae.
  • Gland classification (based on terminal units): simple, branched, compound.
  • Alveolae: small, spherical/mucous secreting units.
• Muscle and pigmented epithelium:
  • Myoepithelium: smooth muscle cells around glands.
  • Pigmented epithelium (retina): protects against light; more pigment = less protection.

High-Yield Facts

• Tissue definition: built from cells with a common origin, structure, and functions, connected by extracellular matrix.
• Basement membrane: all basal layer cells lie on it.
• Epithelium functions: protection, secretion, sensory.
• Simple epithelium shapes: squamous (flat), cuboidal (square), columnar (tall).
• Endothelium: lines blood and lymph vessels.
• Mesothelium: lines serous cavities.
• Microvilli: increase surface absorption area.
• Gland types:
  • Exocrine: ducted secretion.
  • Endocrine: bloodstream secretion.
• Secretion modes:
  • Apocrine, merocrine, holocrine.
• Alveolae units: mucous or serous in glands.
• Pigmented epithelium: more pigment means less light protection, visible vessels.

Summary Table

Mini-Schema (ASCII)

Histology
 ├─ Tissues
 │   └─ Built by cells + ECM
 ├─ Epithelium
 │   ├─ Origin: ectoderm, mesoderm, endoderm
 │   ├─ Single-layer (simple) or multilayered (stratified)
 │   ├─ Shapes: squamous, cuboidal, columnar, pseudostratified
 │   └─ Functions: protection, secretion, sensory
 ├─ Glandular Epithelium
 │   ├─ Exocrine (ducts)
 │   └─ Endocrine (blood)
 ├─ Secretion mechanisms
 │   ├─ Apocrine
 │   ├─ Merocrine
 │   └─ Holocrine
 └─ Special structures
     ├─ Microvilli
     └─ Alveolae units

Rapid-Review Bullets

• Histology is the study of tissues' microstructure and functions.
• Tissues originate from embryonic ectoderm, mesoderm, endoderm.
• Epithelial cells form close, polarized layers; basement membrane supports them.
• No blood or lymph vessels are within epithelial tissues.
• Types of simple epithelium: squamous, cuboidal, columnar, pseudostratified.
• Endothelium lines vessels; mesothelium lines serous membranes.
• Microvilli increase absorption surface in intestines.
• Glandular epithelium secretes via exocrine or endocrine routes.
• Secretion modes include apocrine, merocrine, holocrine.
• Alveolae are small secretory units with mucous cells.
• Pigmented epithelium in retina protects against light; more pigment = less protection.
• Glands can be simple, branched, or compound.
• Endothelium and mesothelium are specialized simple epithelial tissues.
• Epithelium provides protection, secretion, sensory input.
• The epithelium in the ear detects vibrations.
• The stratum corneum is keratinized, non-nuclear epithelium.
• The respiratory alveolar epithelium facilitates gas exchange.
• The retina's pigmented epithelium contributes to visual protection.
• Glandular epithelium's secretory units determine gland structure.
• "Extracellular matrix" links tissue cells.
• The basement membrane underpins epithelial cell attachment.
• Glands' terminal units: acini, tubules, alveolae.
• The number of terminal units determines if a gland is simple, branched, or compound.
• Myoepithelial cells assist in gland secretion.