Introduction to Cell Histology – Key Vocabulary

Histology

The study of cells and tissues, including their structure and function.

H&E Stain

The combination of hematoxylin and eosin dyes used to provide contrast in most routine tissue sections.

Hematoxylin

A basic, blue dye that binds negatively charged (basophilic) molecules such as nucleic acids.

Eosin

An acidic, pink-red dye that binds positively charged (acidophilic) molecules such as cytoplasmic proteins.

Basophilic

Describes structures that stain with basic dyes (e.g., DNA, RNA, rER, nucleolus).

Acidophilic (Eosinophilic)

Describes structures that stain with acidic dyes (e.g., cytoplasm, collagen, membranes).

Fixation

Initial tissue-prep step that inactivates degradative enzymes and preserves structure by preventing autolysis.

Dehydration

Removal of water from a specimen through graded alcohols during tissue processing.

Clearing

Replacement of alcohol with organic solvent to prepare tissue for infiltration with paraffin or plastic.

Infiltration

Penetration of tissue with melted paraffin or resin to provide rigidity for sectioning.

Embedding

Allowing infiltrated tissue to harden in a block so it can be trimmed and sectioned.

Microtome

Instrument that slices thin tissue sections (≈1–10 µm) for microscopic examination.

Artifact

Structural distortion introduced during tissue processing (e.g., folds, tears, “eyelash” defects).

Epithelium

Tissue category forming protective/secretory linings and glands; avascular, highly cellular, rests on basement membrane.

Basement Membrane

Specialized ECM composed of basal lamina plus reticular lamina anchoring epithelium to connective tissue.

Apical Surface

Free, adluminal surface of an epithelial cell facing a lumen or external environment.

Basal Surface

Side of an epithelial cell adjacent to basement membrane; abluminal.

Lateral Surface

Side of an epithelial cell in contact with neighboring cells.

Mesothelium

Simple squamous epithelium lining closed body cavities (pleura, peritoneum, serous pericardium).

Endothelium

Simple squamous epithelium lining blood and lymphatic vessels.

Connective Tissue

Tissue category characterized by sparse cells, abundant ECM (fibers + ground substance), and usually rich vascularity.

Loose Connective Tissue

Connective tissue with loosely arranged collagen, abundant ground substance, and scattered cells.

Dense Irregular Connective Tissue

Connective tissue with thick collagen bundles arranged haphazardly; resists stress in multiple directions.

Dense Regular Connective Tissue

Connective tissue with parallel collagen bundles and fibroblasts, providing tensile strength (e.g., tendons, ligaments).

Collagen

Major structural protein of ECM; eosinophilic in H&E, bright blue in trichrome.

Elastic Fiber

Stretchable fiber stained black/dark blue by Weigert’s elastic stain.

Mucosa

Epithelium plus underlying loose CT (lamina propria) and often muscularis mucosae lining body cavities that open to exterior.

Submucosa

Supportive dense CT layer beneath mucosa containing vessels and nerves.

Serosa

Outer simple squamous epithelium (mesothelium) with thin CT covering organs in body cavities.

Muscle Tissue

Contractile tissue composed of skeletal, cardiac, or smooth muscle cells rich in eosinophilic proteins.

Skeletal Muscle

Voluntary, striated, multinucleated muscle with peripheral nuclei and parallel fibers.

Cardiac Muscle

Involuntary, striated, branched muscle with single central nucleus and intercalated discs.

Smooth Muscle

Involuntary, non-striated, spindle-shaped muscle with single central nucleus.

Nervous Tissue

Tissue specialized to receive, transmit, and integrate information; contains neurons and glial cells.

Neuron

Excitable cell with a cell body, axon, and dendrites that conducts electrical signals.

Glial Cell

Supportive cell of nervous system; surrounds neuronal elements and maintains homeostasis.

Axon

Long neuronal process conducting impulses away from the cell body; appears wavy or round in sections.

Parenchyma

Functional, epithelial or specialized cell component of an organ.

Stroma

Supportive connective-tissue framework of an organ.

Capsule

Dense connective tissue layer that encloses an organ.

Cortex

Outer region of an organ, often functionally distinct.