Tissue Processing (Blocks & Slides), in Visit Clinic

A tissue slide is a thinly cut section of biological tissue mounted on a glass microscope slide, usually fixed, embedded, sectioned and stained to reveal cellular and structural detail. Pathologists examine tissue slides under a microscope to diagnose disease, assess margins, or study morphology in research and teaching. Common staining methods include hematoxylin and eosin and special or immunohistochemical stains.

Tissue processing prepares specimens for microscopic examination. Steps include fixation to preserve structure; grossing; dehydration through graded alcohols; clearing with xylene or alternatives; paraffin infiltration and embedding; microtome sectioning; mounting on slides; staining (commonly hematoxylin and eosin); coverslipping; and labeling. Processed slides enable pathologists to examine cellular detail and produce diagnostic reports.

Blocking in histopathology is a preparatory step that prevents nonspecific staining by occupying tissue sites or inhibiting endogenous activities before antibody application. Common blockers include normal serum, bovine serum albumin, casein, Fc‑receptor blockers, and agents that quench endogenous peroxidase or biotin. Effective blocking improves signal-to-noise ratio and specificity in immunohistochemistry and other antibody‑based tissue assays.

Fix tissue promptly in 10% neutral buffered formalin, then dehydrate through graded ethanols, clear with xylene, and embed in paraffin. Cut 3–5 µm sections on a microtome, float on warm water, pick up on glass slides and dry/heat. Deparaffinize, rehydrate, stain (e.g., H&E), rinse, dehydrate, clear, and mount with coverslip for microscopy.

A slide is a single thin tissue section mounted on glass, stained and examined under a microscope. A block is the paraffin-embedded tissue specimen (FFPE) from which multiple slides can be cut. The block contains the original tissue and serves as an archival source for recuts or additional testing, whereas a slide is one fixed view of a section from that block.

The four tissue types are: epithelial — sheets of tightly packed cells on surfaces and cavities for protection, absorption, secretion, and forming glands; connective — varied cells (fibroblasts, adipocytes) in an extracellular matrix that support, bind, defend, and transport; muscle — contractile fibers (skeletal, cardiac, smooth) producing movement and force; nervous — neurons and glia that transmit signals and integrate information.