Introduction to Histology and Cell Biology

Vocabulary practice flashcards covering fundamental histology concepts, tissue preparation, microscopy techniques, and cellular ultrastructure based on lecture materials.

Histology

The branch of science focused on the microscopic study of cells and tissues.

Epithelial Tissue

A primary tissue consisting of aggregated polyhedral cells with a small amount of extracellular matrix, functioning in the lining of surfaces or body cavities and glandular secretion.

Connective Tissue

A primary tissue containing several types of fixed and wandering cells embedded in an abundant extracellular matrix, primarily functioning in the support and protection of tissues and organs.

Muscle Tissue

A primary tissue composed of elongated contractile cells accompanied by a moderate amount of extracellular matrix, specialized for generating strong contractions and body movements.

Nervous Tissue

A primary tissue made of elongated cells with extremely fine processes and very small amounts of extracellular matrix, dedicated to the transmission of electrical nerve impulses.

Formalin

A $37\%$ aqueous solution of formaldehyde used during fixation to preserve tissue by preventing enzymatic degradation, terminating cellular metabolism, killing pathogens, and hardening the specimen.

Embedding

The tissue preparation process of infiltrating and surrounding dehydrated tissue with a hardened supporting medium (typically paraffin) to enable thin sectioning and mounting onto glass slides.

Hematoxylin

A basic dye acting as a positive stain that binds to anionic components of cells and tissues—such as phosphate groups of nucleic acids, sulfate groups of glycosaminoglycans, and carboxyl groups of proteins—imparting a dark blue or violet color.

Eosin

An acidic dye acting as a negative stain that binds to cationic cellular components, particularly the ionized amino groups of proteins, imparting a red or pink color.

Periodic Acid–Schiff (PAS) Reaction

A histological staining method specifically used for the detection and visualization of carbohydrates and carbohydrate-rich molecules.

Feulgen Reaction

A specialized histochemical staining method specifically utilized to identify and selectively stain cellular DNA.

Fluorescence In Situ Hybridization (FISH)

A hybridization technique that utilizes fluorescently labeled complementary DNA or RNA probes to localize and detect specific genetic sequences directly on intact chromosomes or tissue sections.

Autoradiography

A method used to localize newly synthesized macromolecules by incubating cells with a radioactive precursor (such as $^3\text{H-T}$), coating the specimen with a photographic silver bromide ($\text{AgBr}$) emulsion, and developing the reduced silver grains.

Transmission Electron Microscope (TEM)

A microscope that passes an accelerated electron beam through ultrathin tissue sections to form high-resolution two-dimensional images projected onto a fluorescent screen or CCD detector.

Scanning Electron Microscope (SEM)

An electron microscope that scans a focused electron beam across the metallic-coated surface of a specimen, collecting secondary/backscattered electrons to create a three-dimensional surface representation on a monitor.

Atomic Force Microscope (AFM)

A high-resolution scanning probe microscope that maps topography at the molecular or atomic level using a sharp probe tip on an oscillating cantilever, tracked by a laser reflected onto a photodiode detector.

Body Fluid Compartments

The fluid distribution of total body water ($\text{TBW} = 0.6 \times \text{body weight}$), divided into intracellular fluid ($66\%$ of TBW) and extracellular fluid ($33\%$ of TBW), with extracellular fluid further subdivided into interstitial fluid ($80\%$) and plasma ($20\%$).

Prokaryotic Cell

A simple single-celled organism (such as bacteria and blue-green algae) measuring approximately $1\,\mu\text{m}$ in diameter ($\frac{1}{10}$ the size and $\frac{1}{1000}$ the volume of an average human cell) that lacks a membrane-bound nucleus and membranous organelles, concentrating its genetic material within a nucleoid.

Fluid Mosaic Model

The structural representation of the cell membrane describing it as a dynamic, amphipathic phospholipid bilayer embedded with cholesterol, integral transmembrane proteins, and peripheral proteins.

Phospholipid

An amphipathic membrane lipid consisting of a hydrophilic, polar phosphate head group and two hydrophobic, non-polar fatty acid hydrocarbon tails.

Cholesterol (Membrane)

An amphipathic steroid molecule intercalated among phospholipid tails that provides mechanical stability, strength, and rigidity to the cell membrane.

Integral Membrane Proteins

Proteins embedded directly within the hydrophobic core of the lipid bilayer, often spanning the entire membrane as transmembrane channels, pumps, carriers, receptors, linkers, or enzymes.

Peripheral Membrane Proteins

Membrane-associated proteins that do not penetrate the hydrophobic core of the bilayer and are instead loosely bound to integral proteins or membrane lipids on either surface.

Glycocalyx (Cell Coat)

A carbohydrate-rich exterior cell coat consisting of oligosaccharide chains attached to membrane proteins (glycoproteins) and lipids (glycolipids), functioning in cell recognition, signaling, and intercellular adhesion.

Heterochromatin

The highly condensed, tightly coiled, transcriptionally inactive state of chromatin that displays intense dark staining in histological sections.

Euchromatin

The loosely packed, transcriptionally active form of chromatin that carries active gene-coding DNA sequences and stains lightly in microscope preparations.

Nuclear Envelope

A double membrane consisting of an inner and outer nuclear membrane separated by a perinuclear (cisternal) space, perforated by nuclear pore complexes and reinforced internally by the nuclear lamina.

Nucleolus

A dense, non-membranous intranuclear structure surrounding transcriptionally active DNA that codes for ribosomal RNA (rRNA), serving as the primary factory for ribosome synthesis and assembly.

Microtubules

Rigid, non-branching hollow cylindrical cytoskeletal structures ($25\,\text{nm}$ diameter) formed from $\alpha$- and $\beta$-tubulin heterodimers that polymerize in the presence of GTP and $\text{Mg}^{2+}$, functioning as railway tracks for organelle movement.

Kinesin and Dynein

Microtubule-dependent motor proteins utilizing ATP hydrolysis, where kinesin transports cargo anterograde toward the plus ($+$, peripheral) end, and dynein transports cargo retrograde toward the minus ($-$) end.

Actin Filaments (Microfilaments)

Thin, flexible cytoskeletal filaments ($7\,\text{nm}$ diameter) formed by the polymerization of globular G-actin monomers into double-helical filamentous F-actin in a process requiring ATP, $\text{K}^+$, and $\text{Mg}^{2+}$.

Intermediate Filaments

Tough, rope-like cytoskeletal fibers ($8\text{--}12\,\text{nm}$ diameter) built of coiled-coil dimers assembled into staggered tetramers, forming a stable, non-assembling/disassembling framework that resists mechanical tension.

Vimentin

A Class III intermediate filament protein ($54\,\text{kDa}$) found in fibroblasts, cells of mesenchymal origin, and the lens of the eye that provides mechanical support to maintain cell shape.

Desmin

A Class III intermediate filament protein ($53\text{--}54\,\text{kDa}$) found predominantly in muscle cells (especially smooth muscle) that provides structural anchoring for the contractile machinery.

Nuclear Lamins

Class V intermediate filament proteins (lamins A, B, and C) present in all cell types that polymerize into a meshwork scaffold supporting the inner nuclear membrane and organizing chromatin.

Centrosome

The principal microtubule-organizing center (MTOC) in animal cells, consisting of a pair of orthogonally oriented centrioles surrounded by dense pericentriolar material (PCM).

Ribosome

A non-membranous ribonucleoprotein complex consisting of a large $60\text{S}$ subunit and a small $40\text{S}$ subunit (forming an $80\text{S}$ complex in eukaryotes) that translates mRNA into polypeptide chains.

Svedberg Unit (S)

A unit of sedimentation velocity equal to $10^{-13}\,\text{s}$, measuring the rate at which macromolecular particles settle during high-speed centrifugation.

Rough Endoplasmic Reticulum (rER)

A membrane-bound network of flattened cisternae studded with ribosomes on its cytosolic surface, functioning in the synthesis, initial folding, and vesicular packaging of secretory and membrane proteins.

Smooth Endoplasmic Reticulum (sER)

A ribosome-free membranous tubular network responsible for synthesizing lipids, phospholipids, and steroid hormones, sequestering intracellular $\text{Ca}^{2+}$, and detoxifying organic toxins and drugs.

Golgi Apparatus

A series of flattened, membrane-enclosed cisternae divided into a cis Golgi network (facing the rER) and a trans Golgi network (facing the plasma membrane), specialized for post-translational modification and protein sorting.

COP-II and COP-I Coats

Vesicle coat protein complexes mediating intracellular trafficking, where COP-II drives anterograde transport from the rER to the cis Golgi, and COP-I facilitates retrograde retrieval from the Golgi back to the rER.

Clathrin

A triskelion-structured protein coat that forms a lattice around transport vesicles budding from the trans Golgi network destined for regulated secretion or targeting to lysosomes.

Mannose-6-Phosphate Receptor

A transmembrane receptor located in the trans Golgi network that identifies phosphorylated mannose residues on acid hydrolases to package them into clathrin-coated vesicles destined for lysosomes.

Lysosome

A membrane-bound organelle containing acid hydrolases maintained at an acidic pH ($4.5\text{--}5.0$) by proton pumps, specialized for degrading phagocytosed material, digesting obsolete organelles (autophagy), and executing apoptosis.

Peroxisome

A single-membrane organelle containing oxidases and catalase that performs $\alpha$- and $\beta$-oxidation of very long-chain fatty acids (VLCFA), synthesizes plasmalogens and bile acids, and converts reactive oxygen species and $\text{H}_2\text{O}_2$ to water and oxygen.

Mitochondrion

A double-membraned organelle of endosymbiotic prokaryotic origin containing an outer membrane, cristae-folded inner membrane, and matrix, responsible for synthesizing cellular ATP via aerobic respiration.