General Histology and Cell Biology

Comprehensive vocabulary review flashcards covering Cell Biology and Histology lectures: cell membrane, cytoplasmic organelles, cytoskeleton, cell inclusions, the nucleus, and epithelial tissue classifications.

Cell Membrane (Plasmalemma)

The outer limiting membrane surrounding the cell, measuring $7.5\text{--}10\,\text{nm}$ in thickness, visible only by electron microscopy, and displaying a trilaminar appearance consisting of two electron-dense dark lines separated by an electron-lucent central line.

Phospholipid Bilayer

The lipid foundation of the cell membrane, arranged as a double layer where hydrophilic (water-attracting) heads face outward toward water and hydrophobic (water-repelling) tails face inward away from water.

Transmembrane Proteins

A major class of large integral membrane proteins that completely span the lipid bilayer and function as membrane channels.

Peripheral Proteins

Membrane proteins that are loosely attached to either the inner or outer surface of the lipid bilayer and can be easily extracted.

Glycocalyx (Cell Coat)

A carbohydrate-rich outer coat composed of glycolipids and glycoproteins projecting from the cell surface; functions in cell-to-cell adhesion, immunity, and formation of the basement membrane.

Phagocytosis

A form of endocytosis known as 'cell eating' used to engulf solid particles via pseudopodia (e.g., macrophages engulfing bacteria).

Pinocytosis

A form of endocytosis known as 'cell drinking' whereby the cell membrane invaginates to ingest extracellular fluid droplets into vesicles.

Exocytosis

The cellular process opposite to phagocytosis by which membrane-bound vesicles fuse with the plasma membrane to expel waste products or secrete substances outside the cell.

Mitochondria

Double-membraned organelles known as the powerhouse of the cell that produce energy ($\text{ATP}$) via specialized enzymes, contain their own DNA, and can divide to meet the cell's energetic demands.

Mitochondrial Cristae

Complex folds formed by the inner mitochondrial membrane that project into the matrix space to increase the surface area for energy production.

Basophilia

The blue staining property of acidic cellular components (such as nuclear $\text{DNA}$ and ribosomal/$\text{RER}$ $\text{RNA}$) when reacting with the basic dye Hematoxylin (e.g., seen in plasma cells).

Acidophilia

The red/pink staining property of basic cellular components (such as cytoplasm rich in mitochondria) when reacting with the acidic dye Eosin (e.g., seen in renal tubules).

Ribosomes

Non-membranous protein factories measuring $20\text{--}30\,\text{nm}$ in diameter, composed of small and large subunits formed of $\text{rRNA}$ and approximately $80$ different protein molecules.

Free Polyribosomes (Polysomes)

Clusters of ribosomes bound to a single $\text{mRNA}$ strand in the cytoplasm that synthesize proteins for internal cellular use, the cytosol, and the cytoskeleton.

Rough Endoplasmic Reticulum (RER)

A membranous organelle formed of long, flattened parallel cisternae studded with ribosomes; continuous with the outer nuclear membrane and prominent in cells specialized for protein secretion like fibroblasts and plasma cells.

Smooth Endoplasmic Reticulum (SER)

A membranous network of communicating short, narrow tubules lacking ribosomes; functions in lipid biosynthesis (steroid hormones), drug detoxification, glycogen metabolism, and calcium ion release/reuptake in muscles.

Golgi Apparatus

A membranous organelle discovered by Camillo Golgi in $1898$, composed of stacks of $4\text{--}10$ saccules and transport/secretory vesicles, responsible for concentrating, storing, packaging, and secreting proteins synthesized in the $\text{RER}$.

Negative Golgi Image

A pale, unstained cytoplasmic region observed adjacent to the nucleus in cells stained with H&E, caused by the non-staining lipids of the Golgi apparatus surrounded by deeply basophilic cytoplasm.

Cis Face (Immature Face)

The convex outer receiving face of the Golgi apparatus saccules that accepts transfer vesicles carrying newly synthesized proteins from the $\text{RER}$.

Trans Face (Mature Face)

The concave exit face of the Golgi apparatus saccules that packages and releases large secretory vesicles and primary lysosomes.

Primary Lysosomes

Freshly synthesized, small, spherical membranous organelles with a homogeneous core containing hydrolytic enzymes (acid hydrolases).

Heterolysosome

A secondary lysosome formed by the fusion of a primary lysosome with a phagocytosed solid external particle for intracytoplasmic digestion.

Multivesicular Body

A secondary lysosome formed by the fusion of a primary lysosome with pinocytosed fluid particles.

Autophagic Vacuole

A secondary lysosome formed when primary lysosomes fuse with dead, damaged, or non-functional cellular organelles.

Residual Body

The remaining undigested portion left inside a lysosome following enzymatic digestion, which is ultimately expelled outside the cell by exocytosis.

Cytoskeleton

A non-membranous structural framework composed of microfilaments, intermediate filaments, and microtubules that maintains cell shape, permits whole cell movement, and facilitates organelle transport.

Microfilaments (Actin Filaments)

Thin contractile protein strands measuring $5\text{--}9\,\text{nm}$ in diameter formed of actin; found in skeletal muscle, the cell cortex under the plasma membrane, the core of microvilli, and contractile rings during cell division.

Myosin Filaments

Thick contractile filaments measuring $12\text{--}16\,\text{nm}$ in diameter found in muscle cells that interact with sliding actin filaments to produce muscle contraction.

Intermediate Filaments

Non-contractile structural cytoskeletal filaments measuring $10\,\text{nm}$ in diameter (intermediate between microfilaments and microtubules) that provide tensile support to the cell shape.

Keratin (Cytokeratin) Filaments

Intermediate filaments found in epithelial cells (such as the epidermis of the skin) that support cellular architecture, protect against injury, and reduce dehydration.

Vimentin Filaments

Intermediate filaments located specifically within connective tissue cells, such as fibroblasts.

Neurofilaments

Intermediate filaments located within neurons that maintain cellular integrity and support nerve cell shape.

Microtubules

Hollow non-membranous tubules measuring $25\,\text{nm}$ in diameter, formed of tubulin protein molecules; essential for supporting cell shape, mitotic spindle formation, and constructing centrioles, cilia, and flagella.

Centrioles

A pair of mutually perpendicular, non-membranous structures whose cylindrical walls contain $27$ microtubules arranged into $9$ triplet bundles ($9 \times 3$); critical for cell division and forming basal bodies of cilia.

Cilia

Motile hair-like epithelial cell projections measuring $10\text{--}15\,\mu\text{m}$ in length and $0.2\,\mu\text{m}$ in diameter that beat rapidly in one direction to propel secretions (found in the trachea, uterus, and fallopian tube).

Ciliary Axoneme (Shaft)

The structural internal core of a cilium composed of $20$ microtubules arranged as $9$ peripheral doublets surrounding $2$ central singlets.

Alpha Glycogen Particles

Clusters of glycogen particles aggregated into rosettes found in liver cells, visible under electron microscopy.

Beta Glycogen Particles

Single small glycogen particles found dispersed individually in muscle fibres, visible under electron microscopy.

Best's Carmine

A special histological stain used in light microscopy that specifically stains stored intracellular glycogen granules red.

Sudan Black and Osmic Acid

Special stains used on frozen histological sections that reveal intracellular lipid droplets by staining them black.

Cell Inclusions

Non-living cytoplasmic accumulations of stored metabolites or inert substances, categorized into glycogen granules, lipid droplets, and endogenous/exogenous pigments.

Vesicular (Open-Face) Nucleus

A lightly stained, basophilic nucleus with clearly visible chromatin details and nucleoli, characteristic of metabolically active cells like liver cells.

Condensed Nucleus

A deeply basophilic, densely compacted nucleus showing no visible internal chromatin architecture, characteristic of inactive cells such as circulating lymphocytes.

Epithelial Tissue

An avascular primary body tissue composed of tightly cohesive cells resting on a basement membrane with minimal intercellular matrix, nourished by diffusion from underlying connective tissue.

Simple Squamous Epithelium

A single layer of thin, flattened epithelial cells with bulging nuclei; lines blood vessels (e.g., aorta) and lung alveoli.

Simple Cuboidal Epithelium

A single layer of cube-shaped cells with central, rounded nuclei; forms the lining of thyroid follicles and renal tubules.

Simple Columnar Epithelium

A single layer of tall column-shaped cells with oval basal nuclei; categorized into secretory (stomach lining), absorptive (small intestine), or ciliated (fallopian tube).

Pseudostratified Columnar Epithelium

An overcrowded epithelial layer where all cells rest on the basement membrane but their nuclei sit at varying heights, giving a false stratified appearance; can be ciliated (trachea, bronchi) or non-ciliated (large gland ducts).

Stratified Squamous Epithelium

A multilayered protective epithelium with columnar/cuboidal basal cells, polyhedral middle cells, and flat superficial squamous cells; exists in non-keratinized form (oral cavity, esophagus) and keratinized form (epidermis of skin).

Transitional Epithelium (Urothelium)

A specialized stratified urinary tract epithelium (bladder, ureter) capable of stretching; consists of $4\text{--}6$ cell layers with large dome-shaped umbrella cells when empty, flattening to $2\text{--}3$ layers when distended.

Glandular Epithelium (Acinus and Duct)

Epithelial tissue specialized for secretion, fundamentally organized into a secretory unit (acinus) and a conducting pathway (duct).

Serous Glands

Exocrine glands that produce a thin, watery secretion rich in digestive enzymes (e.g., the parotid salivary gland).

Mucous Glands

Exocrine glands that produce a thick, viscid mucous secretion that is poor in enzymes (e.g., unicellular goblet cells).

Neuroepithelium

A specialized sensory epithelium adapted to receive external stimuli, composed of tall sensory cells with hairlets, supporting cells, and basal precursor cells (found in taste buds, the retina, organ of Corti, and olfactory epithelium).