Histology Essentials: Tissue Structure and Cell Function

Posted on Jan 31, 2026 in Biology

Histology Fundamentals and Cell Structures

Histology Definition

Histology: Microscopic examination of biological structures that are both structurally and functionally related.

Cytoplasmic Membrane Functions

Cytoplasmic Membrane: Regulates interactions between cells, acts as a mechanical barrier, and provides transport for specific molecules.

Epithelial Tissue and Glands

Epithelial Tissue Characteristics

Epithelial Tissue: Closely linked cells that form continuous sheets and resist external forces. Forms include Epithelium and Glands.

Epithelial Functions

  • Protection
  • Transcellular transport
  • Secretion
  • Absorption
  • Selective semipermeable movement control

Epithelial Characteristics

  • Cell complexes are linked by junctions.
  • Little extracellular matrix.
  • Avascular (lacks blood vessels).
  • Nourished through the basal lamina.

Intercellular Junctions

Types of Junctions

  • Occluding Junctions (Tight Junctions): Unions between cells that present an impenetrable barrier, preventing the passage of substances.
  • Anchoring Junctions: Provide strong adhesion between cells and also to the basal lamina.
  • Gap Junctions: Allow the passage of ions or small molecules between cells.

Apical Surface Modifications

  • Microvilli: Finger-like cytoplasmic projections that arise from the free surface of the cell toward the lumen. Function: Primarily absorption.
  • Cilia: Long, motile, hair-like structures that arise from the apical cell surface. Their core is composed of an axoneme. Function: Transport of substances.

Histological Staining Techniques

  • Hematoxylin: Stains nuclei purple (basic dye reacting with acidic components).
  • Eosin: Stains cytoplasm pink (acidic dye reacting with basic components).

Glandular Epithelium

Gland: Formed from epithelial cells that leave the surface on which they developed, penetrate the connective tissue, and develop a basal lamina around them.

Gland Types by Secretion Release

  • Endocrine Gland: Releases its product directly into blood vessels or lymphatic vessels.
  • Exocrine Gland: Releases its product onto an external or internal epithelial surface. Has three forms of secretion:
    • Holocrine Secretion: The entire cell disintegrates to release its contents as the secretory product.
    • Merocrine Secretion: The cell remains intact during secretion.
    • Apocrine Secretion: The cell releases only small portions of its apical cytoplasm as the secretory product.

Connective Tissue Classification and Roles

Connective Tissue Functions

Functions: Provides structural support, serves as a medium for exchange, supports defense and protection, and acts as a depot for body fat.

Connective Tissue Classification

Connective tissue is divided into General Connective Tissue (Loose, Dense, Reticular, Adipose) and Specialized Connective Tissue (Cartilage, Bone, Blood).

General Connective Tissue Types

  • Loose Connective Tissue (Areolar)

    Acts as the first barrier against pathogens. Location: Found beneath epithelial tissue (e.g., respiratory and digestive tracts).

  • Dense Connective Tissue

    Tissue containing more fibers compared to cells. Function: Provides resistance to traction and stretching.

  • Reticular Connective Tissue

    Consists of Type III Collagen (reticular fibers). Serves as a structural skeleton and supports parenchyma formation.

  • Adipose Connective Tissue

    Provides insulation and stores triglycerides for energy.

    • Lipogenesis: Triglyceride formation.
    • Lipolysis: Triglyceride degradation or usage.
    White Adipose Tissue (Unilocular)

    Predominant in developed humans. Function: Stores nutrients and provides secondary energy sources.

    Brown Adipose Tissue (Multilocular)

    Found primarily in newborns (e.g., neck area). Highly vascularized and linked to heat production (thermogenesis).

Extracellular Matrix (ECM)

Extracellular Matrix (ECM): Composed of ground substance and fibers. Resists compression and stretching forces.

Ground Substance Composition

Ground Substance: An amorphous, gel-like material comprising: Glycosaminoglycans, Proteoglycans, and Glycoproteins.

Connective Tissue Cells: Macrophages

Macrophages: Belong to the Mononuclear Phagocytic System. They phagocytose foreign substances and old or damaged cells, contributing to the initiation of the immune response.

Nervous Tissue Components

Nervous System Cell Categories

Cells of the nervous system are classified into two categories: Neurons and Glia.

Glial Cell Functions

Glial Cells (Neuroglia): Provide physical and metabolic support to neurons.

Specific Glial Cell Types

  • Oligodendrocytes: Myelinate axons in the Central Nervous System (CNS).
  • Microglia: Perform phagocytic action (immune defense).
  • Astrocytes: Provide structural and metabolic support to neurons.

Layers of the Cerebellar Cortex

Function is to refine motor actions. The layers are:

  1. Molecular Layer
  2. Purkinje Cell Layer (containing Purkinje cells)
  3. Granule Layer

The Meninges: Connective Tissue Coverings

The three connective tissue coverings of the brain and spinal cord:

  • Dura Mater: Dense outer layer of the meninges.
  • Arachnoid Mater: Middle layer of the meninges. Contains the subarachnoid space below it (where Cerebrospinal Fluid (CSF) circulates).
  • Pia Mater: Innermost, thin, highly vascular layer.