Cellular Organization, Membrane Transport, and Tissues

Vocabulary flashcards reviewing cellular organization, cell organelles, membrane transport mechanisms, cell junctions, and primary tissue types from Chapters 3 and 4 of Fundamentals of Anatomy & Physiology.

Selectively Permeable Membrane

A biological membrane that permits the free passage of certain substances while restricting others, maintaining cellular homeostasis by restricting polar molecules unless specific channels or transport proteins are present.

Fick's Law of Diffusion

A formula stating that the rate of net solute diffusion across a membrane is directly proportional to the diffusion coefficient ($D$), membrane surface area ($A$), and concentration difference ($\Delta C$), and inversely proportional to membrane thickness ($d$): $\text{Rate} = \frac{D \cdot A \cdot \Delta C}{d}$.

Integral Membrane Protein Functions

Transmembrane proteins categorized by function into transporters, enzymes, cell surface receptors, cell surface identity markers, cell adhesion molecules, and cytoskeletal linkers.

Simple Diffusion

Passive transport in which unassisted nonpolar or lipid-soluble molecules (such as $\text{O}_2$, $\text{CO}_2$, fatty acids, and steroids) pass directly through the phospholipid bilayer down their concentration gradient without requiring ATP or transport proteins.

Facilitated Diffusion

Passive, protein-mediated transport of hydrophilic molecules or ions across the plasma membrane down their concentration gradient without the expenditure of cellular ATP.

Carrier Proteins

Transmembrane transport proteins that contain specific binding sites for a target solute and undergo conformational shape changes to move the solute across the plasma membrane.

Channel Gating

The mechanism by which ion channels transition between open and closed states, classified into passive (constitutively open), ligand-gated, voltage-gated, phosphorylation-gated, and mechanically-gated types.

Membrane Potential

The electrical voltage gradient across a cell membrane produced by the active concentration and passive leakage of ions (such as $\text{K}^+$ leakage out through passive channels), resulting in net negative charge accumulation along the inner membrane surface.

Primary Active Transport

The direct expenditure of energy derived from ATP hydrolysis by membrane pumps to move solutes across a membrane against their electrochemical gradient.

$\text{Na}^+/\text{K}^+$ Pump

A primary active transport protein ($\text{Na}^+/\text{K}^+\text{-ATPase}$) that hydrolyzes one ATP molecule to export $3\,\text{Na}^+$ ions out of the cell and import $2\,\text{K}^+$ ions into the cytosol against their respective concentration gradients.

Secondary Active Transport

Coupled transport mechanism in which the downhill movement of one solute down its established electrochemical gradient (such as $\text{Na}^+$) provides the energy to drive another solute uphill against its gradient.

Exocytosis

An active bulk transport process in which intracellular membrane-bound vesicles fuse with the plasma membrane in a $\text{Ca}^{2+}$-dependent manner to discharge their contents into the extracellular space.

Endocytosis Modes

Mechanisms for internalizing bulk materials or fluid into the cell via plasma membrane invagination, categorized into phagocytosis, pinocytosis, and receptor-mediated endocytosis.

Phagocytosis

A specialized form of endocytosis ('cell eating') in which pseudopodia surround and engulf large solid particles or bacteria, forming a phagosome that fuses with a lysosome for degradation.

Pinocytosis

A form of endocytosis ('cell drinking') where the plasma membrane unselectively invaginates to internalize small droplets of extracellular fluid and dissolved solutes into tiny vesicles.

Receptor-Mediated Endocytosis

Selective endocytosis initiated by the binding of specific extracellular ligands to target membrane surface receptors, concentrating the ligands inside coated pits and vesicles.

Transcytosis

The endocytic internalization of a substance on one side of a cell layer, its vesicular transport through the cytoplasm, and its exocytic release on the opposite side.

Motor Proteins

Cytoskeletal ATP-driven motor molecules, specifically kinesins and dyneins, that walk along microtubule tracks to transport membrane-bound vesicles and organelles throughout the cell.

Germline Cells

Reproductive sex cells and their developmental precursors, comprising spermatozoa in males and ova in females.

Somatic Cells

All non-germline, body cells that constitute the tissues and organs of an organism.

Organelle

A specialized, discrete internal cell structure that performs a specific metabolic or structural task required for cellular function.

Cytoplasm

The entire cellular content situated between the plasma membrane and the nuclear envelope, comprising the cytosol and suspended organelles.

Cytosol

The concentrated, gel-like fluid portion of the cytoplasm (intracellular fluid or ICF) in which cellular solutes and organelles reside.

Chromatin

The nuclear complex formed by double-stranded DNA coiled around packaging proteins, forming the structural material of chromosomes.

Genome

The complete set of genetic instructions encoded within nuclear DNA, consisting of over 3 billion base pairs and approximately 25,000 genes in humans.

Gene

A specific nucleotide sequence within a segment of DNA that encodes the necessary instructions to synthesize a functional protein.

Transcription

The nuclear process of synthesizing a complementary messenger RNA (mRNA) molecule using a specific DNA gene sequence as a template.

Translation

The cytoplasmic process in which ribosomes decode the codon sequence of an mRNA molecule to assemble amino acids into a polypeptide chain.

Sickle-Cell Anemia Mutation

A single base-pair genetic mutation in the $\beta$-globin gene that substitutes glutamate (Glu) with valine (Val) at amino acid position 6, altering hemoglobin protein structure and cell morphology.

Rough Endoplasmic Reticulum (RER)

A continuous network of folded membrane sacs studded with fixed ribosomes, serving as the site of protein synthesis for membrane, lysosomal, or secretory proteins.

Smooth Endoplasmic Reticulum (SER)

Tubular endoplasmic reticulum lacking ribosomes, responsible for lipid and steroid synthesis, glycogen metabolism, intracellular $\text{Ca}^{2+}$ storage, and drug detoxification.

Golgi Apparatus

An organelle composed of flattened membranous cisternae that receives newly synthesized proteins at its cis face, modifies and glycosylates them, and sorts them into vesicles dispatched from its trans face.

Lysosomes

Membrane-bound digestive organelles generated by the Golgi apparatus filled with acid hydrolase enzymes that break down worn-out organelles, cellular debris, and engulfed extracellular material.

Autolysis

The self-destruction of an injured or oxygen-deprived cell caused by lysosomal membrane breakdown and the uninhibited release of digestive enzymes into the cytosol.

Peroxisomes

Membrane-bound organelles that metabolize fatty acids and amino acids, producing toxic hydrogen peroxide ($\text{H}_2\text{O}_2$) which resident catalase enzymes neutralize.

Proteasome

A barrel-shaped cylindrical protein complex that degrades unneeded, damaged, or misfolded intracellular proteins into short peptides via proteolysis.

Ubiquitin

A small regulatory polypeptide attached to unwanted or damaged proteins, marking them for recognition and destruction by the proteasome.

Cytoskeleton

An organized intracellular network composed of three protein filament types—microtubules, actin microfilaments, and intermediate filaments—that provides cell structure, mechanical strength, and motility.

Microvilli

Small, non-motile fingerlike projections of the apical plasma membrane that expand surface area to enhance absorption efficiency in epithelial cells.

Cilia

Motile, hair-like cellular projections containing microtubules that beat in coordinated, rhythmic waves to move fluids or mucus across epithelial surfaces.

Flagella

Long, solitary microtubule-based motile projections, such as the tail of a spermatozoon, that propel an entire cell forward.

Histology

The microscopic study of tissues and their structural organization within organs.

Epithelial Tissue

A primary tissue type consisting of closely packed, highly cellular sheets covering body surfaces, lining internal cavities and lumens, and forming glands; characterized as avascular, innervated, and highly regenerative.

Cell Junctions

Specialized multiprotein structures that mediate cell-to-cell or cell-to-matrix adhesion and communication, divided into communicating, occluding, and adhesion junctions.

Tight Junctions

Occluding cell-cell junctions that form continuous, impermeable seals encircling apical borders to block paracellular solute movement between adjacent epithelial cells.

Adherens Junctions

Adhesion cell-cell junctions linked internally to a circumferential actin microfilament belt, preventing tissue separation during physical contraction.

Desmosomes

Button-like 'spot weld' cell-cell junctions anchored internally to intermediate filaments, distributing mechanical stress across epithelial sheets to prevent tearing.

Hemidesmosomes

Cell-matrix anchoring junctions that attach the basal cell membrane of epithelial cells to the underlying basement membrane via intermediate filaments.

Gap Junctions

Communicating cell-cell junctions composed of transmembrane connexon channels that allow direct intercellular movement of ions and small polar molecules.

Connexon

A tubular protein channel composed of six connexin subunits that aligns with a matching channel on an adjacent cell to create a functional gap junction pore.

Apical Surface

The free, unattached surface of an epithelial cell oriented toward the exterior environment, a body cavity, or an organ lumen, often featuring cilia or microvilli.

Basal Surface

The bottom border of an epithelial cell attached to the underlying basal lamina and connective tissue via hemidesmosomes.

Endothelium

The simple squamous epithelium that lines the inner lumen of blood vessels, heart chambers, and lymphatic vessels.

Mesothelium

The simple squamous epithelial layer covering closed serous body cavities (peritoneum, pleura, and pericardium).

Mucous Membranes (Mucosa)

Epithelial membranes lining body cavities that open to the exterior, backed by an areolar connective tissue layer known as the lamina propria.

Serous Membranes (Serosa)

Epithelial membranes lining closed internal body cavities, consisting of mesothelium over loose connective tissue that secretes lubricating serous fluid.

Synovial Membranes

Non-epithelial connective tissue membranes that line the joint cavities of synovial joints and secrete lubricating synovial fluid.

Endocrine Glands

Ductless glands that secrete chemical messengers called hormones directly into the surrounding interstitial fluid to diffuse into the bloodstream.

Exocrine Glands

Glands containing ducts through which secretions are discharged onto epithelial surfaces or into organ lumens.

Hormone

A chemical messenger secreted by endocrine glands or isolated endocrine cells into the blood that travels to distant target tissues containing specific binding receptors.

Goblet Cell

A specialized unicellular exocrine gland embedded within mucous membranes that synthesizes and secretes protective mucus.

Merocrine Secretion

A mode of exocrine secretion in which products are released from membrane-bound vesicles via exocytosis without damaging the secretory cell.

Apocrine Secretion

A mode of exocrine secretion in which the secretory product accumulates in the apical cytoplasm, which then pinches off from the cell.

Holocrine Secretion

A mode of exocrine secretion in which an entire mature cell ruptures and dies, releasing its accumulated contents as the secretory product (e.g., sebaceous glands).

Cytogenic Glands

Specialized glands that secrete whole living cells rather than molecular products, such as testes releasing sperm or ovaries releasing ova.

Connective Tissue Classification

The structural classification dividing connective tissues into connective tissue proper (loose and dense), fluid connective tissue (blood), and supporting connective tissue (cartilage and bone).

Mesenchyme

Embryonic connective tissue consisting of star-shaped pluripotent stem cells set in a gel-like extracellular matrix, serving as the origin of all adult connective tissues.

Pluripotent

The developmental capacity of an unspecialized embryonic stem cell to differentiate into any cell type found in the human body.

Multipotent

The capability of a progenitor stem cell to differentiate into a limited number of specialized cell types within a specific tissue lineage.

Differentiation

The biological process by which a generalized, unspecialized stem cell matures into a structurally and functionally specialized cell type.

Fibroblasts

Active, primary cells of connective tissue proper that synthesize and secrete extracellular fibers (collagen, elastic, reticular) and ground substance.

Chondrocytes

Mature cartilage cells that maintain the surrounding cartilage matrix while residing within small matrix cavities called lacunae.

Glycosaminoglycans (GAGs)

Highly negatively charged polysaccharide chains (such as chondroitin sulfate, keratan sulfate, and hyaluronic acid) that attract cations and water to form a hydrated extracellular gel.

Collagen Fibers

Thick, unbranched extracellular protein fibers possessing high tensile strength that resist pulling forces and stretching.

Elastic Fibers

Long, thin branching extracellular fibers composed of elastin that allow tissues to stretch and recoil back to their original resting shape.

Reticular Fibers

Fine, highly branched collagenous fibers that form delicate, sponge-like structural frameworks (stroma) supporting cells in soft organs.

Areolar Connective Tissue

A widely distributed loose connective tissue proper featuring a loose framework of all three fiber types, abundant gel-like ground substance, and diverse cell types (fibroblasts, macrophages, fat cells, mast cells).

Adipose Tissue

Loose connective tissue proper dominated by closely packed adipocytes (fat cells) that store triglycerides for energy storage, thermal insulation, and organ cushioning.

Reticular Connective Tissue

Loose connective tissue composed of a delicate network of reticular fibers and reticular cells that forms the supporting framework (stroma) of lymphoid organs, liver, and bone marrow.

Stroma vs Parenchyma

Stroma refers to the structural, supporting connective tissue framework of an organ, whereas parenchyma refers to the functional tissue cells performing the organ's primary duties.

Dense Regular Connective Tissue

Connective tissue proper characterized by densely packed, parallel collagen fibers with high tensile strength in one direction, forming tendons and ligaments.

Dense Irregular Connective Tissue

Connective tissue proper featuring randomly interwoven collagen fibers that withstand tension exerted in multiple directions, forming the dermis and organ capsules.

Hyaline Cartilage

Cartilage featuring a glossy, firm matrix with fine collagen fibers surrounded by perichondrium; provides flexible support and reduces friction at joint surfaces (articular, costal, respiratory, nasal cartilages).

Elastic Cartilage

Flexible cartilage rich in elastic fibers surrounded by perichondrium, maintaining structural shape and elasticity in the epiglottis and external ear (pinna).

Fibrocartilage

Tough, compressible cartilage packed with thick collagen fibers and lacking a perichondrium; absorbs shock and resists tension in intervertebral discs and knee menisci.

Interstitial Growth

Cartilage growth mechanism occurring within immature cartilage in which internal chondroblasts divide, synthesize new matrix, and expand the tissue from within.

Appositional Growth

Cartilage growth mechanism in which stem cells in the deep perichondrium differentiate into chondroblasts on the outer surface, adding successive matrix layers to the cartilage exterior.