Human Anatomy - Chapter 02: The Cellular Level of Organization

Vocabulary flashcards covering cellular organization, plasma membrane structure, membrane transport, organelles, cytoskeleton, cellular junctions, cell cycle, and mitosis based on Chapter 2 of Saladin and York's Human Anatomy.

Cytology

The scientific study of cell structure and function.

Cell Theory

The fundamental biological principles stating that all living organisms are composed of cells, cells are the basic structural and functional units of life, all cells arise from preexisting cells, all cells share a similar basic chemical composition, and body functions derive from cellular activity.

Metabolism

The sum of all internal chemical changes in an organism, involving taking in molecules, chemically altering them to construct structures or supply energy, controlling physiology, and excreting waste products.

Homeostasis

The ability of an organism to maintain a stable internal environment, such as regulating body temperature, blood glucose levels, and fluid balance.

Responsiveness

The ability of cells—especially nerve and muscle cells—to sense and react to environmental stimuli.

Light Microscope (LM)

An optical instrument that uses visible light passing through thin tissue sections to produce magnified images of cellular structures.

Transmission Electron Microscope (TEM)

An advanced microscope that directs an electron beam through ultrathin slices of a specimen to produce high-resolution images of intracellular structures.

Scanning Electron Microscope (SEM)

An electron microscope that uses an electron beam to scan the surface of a specimen, yielding detailed three-dimensional images of surface features.

Cell Shapes

The diverse morphological forms assumed by human cells to suit specific functions, including squamous, cuboidal, columnar, polygonal, stellate, spheroidal, discoidal, fusiform, and fibrous shapes.

Squamous Cells

Thin, flat, and scaly cells that line structures such as the esophagus, alveoli, and the outer layer of skin (epidermis).

Cuboidal Cells

Cells that are approximately equal in height and width, shaped like cubes, such as liver cells.

Columnar Cells

Cells that are distinctly taller than they are wide, forming the inner lining of organs like the stomach and intestines.

Stellate Cells

Cells featuring multiple pointed, starlike processes extending from the main cell body, characteristic of nerve cell bodies.

Fusiform Cells

Elongated cells with a thick middle section and tapered ends, characteristic of smooth muscle cells.

Fibrous Cells

Long, slender, threadlike cells found in skeletal muscle tissues and nerve axons.

Apical Surface

The upper surface of an epithelial cell that faces an internal lumen or exterior cavity, often specialized for absorption or secretion.

Basal Surface

The lower surface of an epithelial cell that anchors the cell to deeper tissues via a basement membrane.

Intracellular Fluid (ICF)

The clear fluid environment contained within a cell, also known as the cytosol.

Extracellular Fluid (ECF)

All body fluids located outside of cells, including tissue (interstitial) fluid, blood plasma, lymph, and cerebrospinal fluid.

Phospholipids

The most abundant membrane lipids (75\t\t\%), possessing a hydrophilic phosphate head and two hydrophobic fatty acid tails, forming a bilayer.

Glycocalyx

A fuzzy surface coat on the extracellular face of the plasma membrane, composed of glycolipids and glycoproteins, that functions in cushion protection, cell identity, and cell adhesion.

Transmembrane Proteins

Proteins that pass completely through the phospholipid bilayer of the plasma membrane, featuring hydrophilic regions facing outer/inner fluid and hydrophobic regions embedded in the lipid core.

Peripheral Proteins

Membrane proteins that do not penetrate the lipid bilayer but adhere strictly to either the intracellular or extracellular face of the plasma membrane.

Filtration

A passive transport process in which physical pressure forces fluid and small solutes through a selectively permeable membrane, such as capillary blood pressure forcing fluid through capillary walls.

Simple Diffusion

The net movement of particles down a concentration gradient from an area of higher concentration to lower concentration without energy expenditure.

Osmosis

The net diffusion of water molecules across a selectively permeable membrane toward a side with a higher concentration of nonpermeating solutes.

Aquaporins

Transmembrane channel proteins specialized to allow rapid flow of water molecules through the plasma membrane during osmosis.

Facilitated Diffusion

The carrier-mediated transport of a solute across a membrane down its concentration gradient without expenditure of cellular energy.

Active Transport

The carrier-mediated transport of a solute across a membrane up its concentration gradient, requiring energy expenditure in the form of ATP.

Sodium-Potassium ($\text{Na}^+-\text{K}^+$) Pump

An active transport carrier protein that ejects $3\,\text{Na}^+$ ions out of the cell and pumps $2\,\text{K}^+$ ions into the cell per cycle using ATP, essential for maintaining resting membrane potential and cell volume.

Pinocytosis

A form of endocytosis ('cell drinking') in which the plasma membrane dimples and pinches off vesicles containing droplets of extracellular fluid.

Receptor-Mediated Endocytosis

A selective form of endocytosis in which specific extracellular solute molecules bind to surface receptors, causing the membrane to sink in and form an internal vesicle.

Phagocytosis

A type of endocytosis ('cell eating') in which cells like white blood cells use pseudopods to surround and engulf foreign particles or microbes into internal vesicles.

Exocytosis

A process of releasing material from a cell when a secretory vesicle fuses with the plasma membrane and discharges its contents into the extracellular fluid.

Microvilli

Short plasma membrane extensions that serve primarily to increase surface area on specialized absorptive cells, forming a brush border.

Motile Cilia

Hairlike cell surface processes containing an axoneme core of microtubules that beat rhythmically to move mucus and fluids across epithelial surfaces.

Flagellum

A long, whiplike cell surface projection containing an axoneme, present in humans exclusively as the tail of a sperm cell to provide motility.

Pseudopods

Dynamic, cytoplasm-filled extensions of the plasma membrane that continuously change shape, utilized in amoeboid locomotion and phagocytosis.

Kartagener Syndrome

A hereditary disease characterized by a lack of dynein arms in cilia and flagella, resulting in male sterility due to immotile sperm and severe pulmonary congestion due to impaired mucus clearance.

Cellular Junctions

Specialized protein structures that link adjacent cells together or attach them to extracellular material, including tight junctions, desmosomes, gap junctions, and hemidesmosomes.

Tight Junctions

Intercellular junctions where cell-adhesion proteins interlock like a zipper around the apical perimeter of cells, sealing off the intercellular space and preventing gastric acid or bacteria from passing between cells.

Desmosomes

Patch-like protein junctions (plaques) anchored to intermediate filaments that hold adjacent cells tightly together at specific points, preventing tissue tears under physical stress.

Pemphigus Vulgaris

An autoimmune disease in which misguided autoantibodies attack desmosome proteins in the skin, leading to widespread blistering and loss of tissue fluid.

Hemidesmosomes

Half-desmosome structures that anchor epithelial cells to the underlying basement membrane.

Gap Junctions

Communicating junctions composed of ring-like transmembrane protein complexes (connexons) surrounding a water-filled channel, allowing direct passage of ions, glucose, and amino acids between cells.

Cytoskeleton

An intracellular network of protein filaments—including microfilaments, intermediate filaments, and microtubules—that supports cell shape, organizes contents, and directs internal movement.

Microfilaments

Thin cytoskeletal filaments ($6\,\text{nm}$ thick) made of actin protein that form the membrane-supporting terminal web and participate in muscle contraction.

Intermediate Filaments

Stiff cytoskeletal elements ($8\text{--}10\,\text{nm}$ in diameter) that give the cell structural shape, resist mechanical stress, and form keratin in epidermal cells.

Microtubules

Hollow cylindrical structures ($25\,\text{nm}$ in diameter) composed of tubulin protofilaments that radiate from the centrosome, hold organelles in place, and form cilia, flagella, and mitotic spindle fibers.

Nucleus

The largest organelle in eukaryotic cells, enclosed by a double-membraned nuclear envelope with nuclear pores, containing genetic material in the form of chromatin.

Rough Endoplasmic Reticulum

An extensive system of interconnected parallel membrane cisterns studded with ribosomes, continuous with the nuclear envelope, responsible for synthesizing membrane lipids and proteins destined for secretion or lysosomes.

Smooth Endoplasmic Reticulum

A tubular network of membrane cisterns lacking ribosomes that synthesizes steroids and lipids, detoxifies drugs and alcohol, and manufactures cellular membranes.

Sarcoplasmic Reticulum

A specialized form of smooth ER in skeletal and cardiac muscle cells that stores calcium ions and releases them to trigger muscle contraction.

Ribosomes

Small granular complexes of protein and RNA, found free in cytosol or attached to the rough ER and nuclear envelope, that translate genetic code and assemble amino acids into proteins.

Golgi Complex

An organelle consisting of $4\text{--}6$ stacked, flattened membrane cisterns that receives crude proteins from the rough ER, chemically edits and packages them, and dispatches them in Golgi vesicles.

Proteasomes

Hollow cylindrical protein complexes in the cytoplasm that degrade unwanted or damaged proteins that have been tagged for destruction, breaking them down into short peptides.

Lysosomes

Membrane-bound organelles containing acidic digestive enzymes that digest unwanted material, carry out autophagy of extra or aged organelles, and execute programmed cell death (apoptosis).

Peroxisomes

Organelles containing oxidative enzymes that break down fatty acids, neutralize free radicals, detoxify alcohol and blood-borne toxins, and use catalase to convert excess hydrogen peroxide into water and oxygen.

Mitochondria

Double-membraned organelles specialized for aerobic respiration to synthesize ATP, featuring inner membrane folds called cristae, an internal matrix, and circular mitochondrial DNA (mtDNA).

Endosymbiosis Theory

The evolutionary theory proposed by Dr. Lynn Margulis stating that mitochondria evolved from primitive aerobic bacteria that invaded and lived symbiotically within early eukaryotic cells.

Kearns-Sayre Syndrome (KSS)

A mitochondrial disease caused by spontaneous mtDNA mutations in the early embryo, characterized by eye movement muscle weakness, retinal degeneration, hearing/vision loss, and cardiac conduction flaws.

Centrioles

A pair of perpendicular cylindrical microtubule assemblies located in the centrosome that play a role in organizing mitotic spindle fibers and form the basal bodies of cilia.

Inclusions

Non-essential, non-membrane-bound structures in the cytoplasm, comprising stored cell products (glycogen granules, fat droplets, pigments) or internalized foreign matter (dust, viruses).

Cell Cycle

The sequence of events extending from one cell division to the next, divided into interphase ($G_1$, S, and $G_2$ phases) and the mitotic (M) phase.

Interphase

The non-dividing portion of the cell cycle consisting of $G_1$ (growth and normal metabolism), S (DNA synthesis), and $G_2$ (growth and preparation for mitosis) phases.

Mitosis

The process of nuclear division in somatic cells that serves growth, tissue repair, and cell replacement, consisting of four phases: prophase, metaphase, anaphase, and telophase.

Prophase

The first phase of mitosis in which chromatin condenses into visible chromosomes (each consisting of two sister chromatids joined at a centromere), the nuclear envelope breaks down, and centrioles sprout spindle fibers.

Metaphase

The second phase of mitosis during which chromosomes align along the cell equator (midline) and spindle fibers attach to their kinetochores.

Anaphase

The third phase of mitosis in which centromeres divide and spindle fibers pull sister chromatids to opposite poles of the cell.

Telophase

The final stage of mitosis during which chromosomes gather at each pole, decondense back into chromatin, nuclear envelopes re-form, nucleoli reappear, and the mitotic spindle vanishes.

Cytokinesis

The division of the cytoplasm into two distinct daughter cells via a cleavage furrow, overlapping with late anaphase and telophase.

Stem Cells

Immature, unspecialized cells that possess developmental plasticity, enabling them to self-renew and develop into one or more mature cell types.

Pluripotent Stem Cells

Embryonic stem cells derived from pre-embryos of up to 150 cells that have the capability to develop into any mature cell type in the human body.