Histology Overview & Cytology

Vocabulary flashcards covering histology definitions, slide preparation, staining techniques, and cellular components based on medical lecture notes.

Histology

The study of the normal microscopic structure of cells and tissues, also known as "microanatomy."

Fixation

The first step of slide preparation used to preserve tissue morphology and maintain cellular architecture; it must occur immediately to prevent autolysis.

Formalin

A buffered isotonic solution of $37\%$ formaldehyde used as a common fixative in tissue preparation.

Glutaraldehyde

A fixative used for electron microscopy that reacts with amine groups to prevent degradation by proteases.

Dehydration

The gradual removal of water from a tissue specimen using increasing concentrations of alcohol to avoid shrinkage and distortion.

Clearing

The removal of alcohol from a specimen using a lipid solution like xylene or benzene, making the tissue transparent.

Infiltration

The process of placing tissue in melted paraffin until it becomes completely permeated to impart a firm consistency.

Embedding

The formation of the specimen into a solid structure using paraffin or epoxy resins to permit very thin sectioning.

Microtome

An instrument used to slice a specimen into very thin sections during slide preparation.

Hematoxylin

A basic dye (basophilic) that reacts with acidic cellular components like the nucleus and Rough ER, staining them blue.

Eosin

An acidic dye (acidophilic) that reacts with basic cellular components like proteins and collagen, staining them pink.

Wright and Giemsa Stain

Staining technique particularly used for studying bone marrow and peripheral blood; labels neutrophils with pink granules.

Sudan black

A lipid-soluble dye useful for diagnosing metabolic diseases involving intracellular accumulations of cholesterol or phospholipids.

Periodic Acid Schiff (PAS)

A staining procedure that makes intracellular glycogen and carbohydrates appear magenta.

Feulgen reaction

A modification of the PAS procedure used to specifically stain the DNA of cell nuclei.

Orcein

A stain used to visualize elastic fibers, making them appear dark or black.

Silver staining

A metal impregnation technique using silver salts to visualize reticular fibers and elements of nervous tissue.

Bright-field Microscope

A microscope that uses ordinary light passing through a stained specimen; structures smaller than $0.2\,\mu m$ cannot be clearly distinguished.

Fluorescence Microscope

A microscope that uses UV or excitation light to make fluorescent substances appear bright against a dark background.

Phase Contrast Microscope

A microscope that detects differences in refractive index to visualize living, unstained cells in culture.

Confocal Microscope

A microscope using a focused laser beam and pinhole aperture to produce high-resolution 3D reconstructions from optical sections.

Birefringence

The ability of highly organized molecules, such as collagen or microtubules, to rotate polarized light and appear bright against a dark background.

Scanning Electron Microscope (SEM)

An electron microscope where beams pass over the surface of cells to create 3D-like topographical images.

Transmission Electron Microscope (TEM)

An electron microscope where beams pass through the cell to show greater internal details like organelles.

Nucleus

The largest organelle, containing DNA, RNA, nucleoplasm, and chromatin; it is the site where instructions for protein synthesis are encoded.

Euchromatin

Active chromatin that is stretched or uncoiled so that the genetic information of DNA can be transcribed.

Heterochromatin

Inactive chromatin that is condensed or coiled and typically associated with the nuclear envelope.

Nucleosome

A unit of chromatin consisting of DNA wrapped around histone proteins to help compact the DNA molecule.

Nuclear Pore

An avenue of communication between the nucleoplasm and cytoplasm, closed by a thin diaphragm and irregularly distributed.

Nucleolus

A basophilic region inside the nucleus consisting of RNA and protein; the site of ribosomal RNA synthesis.

Cytosol

The gel-like fluid of the cytoplasm that remains after excluding organelles and inclusion bodies.

Organelles

Metabolically active internal cellular structures that carry out essential functions and are generally membrane-bounded.

Inclusions

Metabolically inert accumulations of cellular products, such as lipid droplets or pigments, that are generally not membrane-bound.

Plasmalemma

Also known as the cell membrane; a trilaminar structure composed of phospholipids and proteins that controls permeability.

Amphipathic

A property of phospholipids describing the presence of both a hydrophilic (water-loving) head and a hydrophobic (water-hating) tail.

Glycocalyx

A delicate cell-surface coating formed by oligosaccharide chains extending outward from the cell membrane.

Rough Endoplasmic Reticulum (RER)

A system of membrane-bounded cisternae with attached ribosomes; involved in synthesizing proteins for export or the cell membrane.

Smooth Endoplasmic Reticulum (SER)

An organelle lacking ribosomes involved in phospholipid/steroid synthesis, drug detoxification, and $Ca^{2+}$ sequestration.

Ribosomes

Complexes of RNA and proteins consisting of large and small subunits; they translate mRNA messages into proteins.

Golgi Apparatus

An organelle involved in packaging, sorting, and modifying proteins; it does not stain with H&E and appears as a pale/clear area.

Mitochondria

The "powerhouse" of the cell that generates energy ($ATP$) through oxidative phosphorylation.

Cristae mitochondrialis

Folds of the inner mitochondrial membrane that contain enzymes for oxidative phosphorylation and the electron transport system.

Peroxisomes

Small spherical bodies containing catalase and oxidative enzymes; involved in lipid metabolism and detoxification of alcohol.

Lysosomes

Membrane-bounded digestive organelles containing approximately $40$ different hydrolytic enzymes.

Autophagy

The lysosomal process of digesting unneeded or nonfunctional organelles.

Lipofuscin

A pale brown "wear-and-tear" pigment composed of undigested material following lysosomal activity, especially in long-lived cells.

Proteasomes

Membrane-free cytoplasmic and nuclear protein complexes that degrade denatured or nonfunctional polypeptides.

Centrosome

A granular area in the cytoplasm adjacent to the nucleus that contains a pair of centrioles and organizes microtubule growth.

Centriole

A structure consisting of nine triplets of microtubules; provides basal bodies for the formation of cilia and flagella.

Hemosiderin

A dense brown pigment made of denatured ferritin proteins with bound iron, resulting from the phagocytosis of Red Blood Cells.

Microfilaments

The smallest cytoskeletal component, $5-7\,nm$ in diameter, composed of actin subunits.

Intermediate Filaments

Cytoskeletal components $8-10\,nm$ in diameter, such as keratin and neurofilaments, providing strong mechanical stability.

Microtubules

The largest cytoskeletal component, $25\,nm$ in diameter, composed of tubulin heterodimers; serves as tracks for organelle movement.