Cell Biology, Cytology, and Tissue Organization

Comprehensive vocabulary flashcards covering cell structure, membrane transport, organelles, the cell cycle, histology, tissue classification, glandular secretion, and embryonic development.

Amphipathic Molecules

Molecules that possess both hydrophilic (water-loving) and hydrophobic (water-fearing) regions, such as phospholipids with polar heads facing outward and nonpolar tails facing inward.

Plasma Membrane

The selectively permeable outer boundary and gatekeeper of the cell, composed of a phospholipid bilayer with embedded cholesterol and proteins.

Cytology

The scientific study of cells.

Fluid-Mosaic Model

A model describing the plasma membrane in which the fluid component represents the pliable phospholipid bilayer affected by cholesterol, and the mosaic component represents the embedded membrane proteins.

Aquaporins

Membrane channel proteins that allow water molecules to cross the plasma membrane more quickly than expected.

Erythrocytes

Red blood cells (RBCs), which are the most abundant cells in the body, specialize in oxygen transportation, and have a $120\,\text{day}$ life cycle.

Cystic Fibrosis

An inherited genetic condition caused by abnormal or faulty chloride ($Cl^-$) channel proteins, leading to thick mucus in the bronchial tubes and pancreatic ducts as well as salty sweat.

Golgi Apparatus

An organelle termed the "mailman of the cell" that creates vesicles to package and deliver proteins synthesized on the rough endoplasmic reticulum.

Mitochondria

The powerhouse organelles of the cell that serve as the major sites for the cellular production of ATP.

Lysosomes

Organelles that act as the garbage disposal of the cell, fusing with endocytic vesicles to digest internalized substances and breakdown cellular waste.

Diffusion

The passive movement of molecules down a concentration gradient from an area of higher concentration to lower concentration without requiring cellular energy (ATP).

Osmosis

The diffusion of water across a differentially (selectively) permeable membrane until the concentrations of a substance are equalized.

Osmotic Pressure

The pressure that develops in a system due to osmosis, responsible for water being absorbed by the kidneys and taken up by tissue capillaries.

Hypotonic Solution

A solution with a lower solute concentration than the intracellular fluid, causing water to enter the cell and leading to cytolysis (cell bursting) in animal cells or turgor pressure in plant cells.

Hypertonic Solution

A solution with a higher solute concentration than the intracellular fluid, causing water to exit the cell and resulting in cellular shriveling (crenation).

Facilitated Transport

Passive transport of a specific solute (such as glucose or amino acids) down its concentration gradient through the assistance of a membrane carrier protein.

Active Transport

The transport of a specific solute across the plasma membrane up or against its concentration gradient (from low to high) through the use of carrier proteins (pumps) and cellular energy (ATP).

Phagocytosis

A form of bulk endocytosis where amoeboid-type cells engulf large solid particles (such as bacteria or food) by forming an endocytic vesicle.

Pinocytosis

A form of bulk endocytosis that occurs when vesicles form around liquid or very small particles, visible only with electron microscopy.

Exocytosis

A form of bulk active transport where a vesicle formed by the Golgi body fuses with the plasma membrane to secrete substances (e.g., insulin) or expel waste products outside the cell.

Desmosomes

Adhesion junctions consisting of internal cytoplasmic plaques attached to the cytoskeleton and joined by integral membrane proteins, holding cells together in tissues that stretch (e.g., heart, stomach, bladder).

Tight Junctions

Intercellular junctions where plasma membrane proteins attach in zipper-like fastenings to form impermeable tissue barriers (e.g., epithelial lining of stomach, kidney tubules, blood-brain barrier).

Gap Junctions

Intercellular junctions formed by joined identical plasma membrane channels that allow direct communication and the flow of ions and small molecules between adjacent cells for synchronized contractions.

Nucleolus

A non-membrane-bound, dark-staining structure located inside the nucleus comprised of protein and RNA that produces ribosomes.

Transcription

The first step of protein synthesis, in which ribonucleotides and RNA polymerase copy a DNA template strand to produce a complementary RNA molecule.

Translation

The second step of protein synthesis, in which ribosomal RNA, transfer RNA, and mature messenger RNA convert codon sequences into a newly synthesized protein.

Codon

A three-nucleotide base unit in mRNA that directs amino acid assembly, beginning with the start codon AUG and terminating with a stop codon (UAA, UAG, or UGA).

Centrosome

A cellular structure located near the nucleus containing a pair of cylindrical centrioles that organizes microtubules during cell division.

Interphase

The portion of the cell cycle where a cell spends the majority of its time maintaining normal metabolic functions and preparing for division through $G_1$, S, and $G_2$ phases.

Apoptosis

Programmed cell death or cell suicide, which is a normal, beneficial process that promotes proper bodily development.

Histology

The scientific study of tissues.

Epithelial Tissue

A primary tissue type covering body surfaces, lining cavities, and forming glands, characterized by cellularity, apical-basal polarity, basement membrane attachment, and avascularity.

Endothelium

The simple squamous epithelium that lines the lumen of blood vessels.

Pseudostratified Columnar Epithelium

An epithelium where cells falsely appear not to all attach to the basement membrane, whose ciliated form contains goblet cells that secrete mucin to form mucus.

Transitional Epithelium

A stratified epithelium found in the urinary bladder, ureters, and part of the urethra, composed of cells capable of changing shape to permit organ distention without leakage.

Endocrine Glands

Ductless glands derived from epithelial tissue that release their secretions, called hormones, directly into interstitial fluid and the bloodstream.

Exocrine Glands

Glands derived from epithelial tissue that secrete their physiological products through a duct onto an internal or external surface.

Merocrine Glands

Exocrine glands, such as salivary glands, that package their secretions into vesicles and release them across the cell membrane by exocytosis.

Apocrine Glands

Exocrine glands, such as mammary glands, that accumulate secretions in the apical portion of the cell, which then pinches off to release the product.

Holocrine Glands

Exocrine glands, such as oil-producing glands, that accumulate secretions throughout the entire cell until the cell completely disintegrates to discharge the secretions.

Mast Cells

Wandering cells located in connective tissue proper that contribute to inflammation by producing and secreting histamine (a vasodilator) and heparin (an anticoagulant).

Mesenchyme

The first embryonic connective tissue to arise in the body, consisting of star- and spindle-shaped cells in a gel-like ground substance with immature protein fibers, giving rise to all adult connective tissues.

Mucus Connective Tissue

An embryonic connective tissue, also known as Wharton's jelly, displaying a mucoid appearance and found exclusively in the umbilical cord.

Hyaline Cartilage

The most abundant cartilage in the body, characterized by a glassy appearance and found in the nose, trachea, larynx, costal cartilages, articular ends of long bones, and the fetal skeleton.

Fibrocartilage

A weight-bearing, shock-absorbing cartilage rich in collagen fibers with sparse ground substance, located in the intervertebral discs, pubic symphysis, and menisci of the knee joint.

Elastic Cartilage

A flexible cartilage containing abundant elastic fibers that provides resilience and flexibility to structures such as the external ear and epiglottis.

Osseous Connective Tissue

A solid supporting connective tissue forming the majority of the mass of bones, providing structural framework, delicate organ protection, and storage for calcium and phosphorus.

Glial Cells

Non-excitable supporting cells of nervous tissue that protect, nourish, and support neurons.

Mucous Membrane

A body membrane (mucosa) composed of epithelium and connective tissue that lines compartments and passageways opening to the outside of the body (digestive, respiratory, urinary, and reproductive tracts).

Serous Membrane

A membrane lining closed internal body cavities composed of a simple squamous mesothelium that secretes watery serous fluid to reduce friction between visceral and parietal layers.

Synovial Membrane

A joint-lining membrane made of areolar connective tissue and superficial squamous epithelial cells lacking a basement membrane, which secretes synovial fluid to reduce friction and nourish articular cartilage.

Ectoderm

The outermost primary germ layer of the embryo, responsible for forming the epidermis of the skin, hair, nails, exocrine skin glands, and nervous tissue.

Mesoderm

The middle primary germ layer of the embryo that differentiates into all muscle tissue, serous membranes, blood vessels, and mesenchyme (which forms all connective tissues).

Endoderm

The innermost primary germ layer of the embryo, giving rise to the epithelial lining of the middle ear, auditory tube, and the digestive, respiratory, reproductive, and urinary tracts.