Cell Structure and Cell Transport

Vocabulary flashcards covering cellular structures, organelle functions, membrane composition, junction types, fluid compartments, and membrane transport processes based on Veterinary Physiology lecture notes.

Cytosol

The liquid component of the cytoplasm that surrounds intracellular organelles.

Cytoplasm

All contents of a cell except the nucleus, including all organelles as well as the cytosol.

Adipocytes

Specialized cells for lipid storage in which $95\%$ of the cell mass is triglycerides, acting as the main storehouse of energy-giving nutrients in the body.

Chromatin

Loosely packed DNA spread throughout the nucleus that represents the active working DNA.

Chromosomes

Densely packed DNA structures organized specifically for cell division.

Nucleolus

A nuclear structure where large amounts of ribosomal RNA and proteins accumulate to synthesize ribosome subunits.

Polysome

A cellular structure formed during protein synthesis when multiple ribosomes attach to the same mRNA strand.

Rough Endoplasmic Reticulum (RER)

A netlike labyrinth of branching tubules and flattened sacs with attached ribosomes, responsible for synthesizing membrane proteins, secretory proteins, and lysosomal proteins.

Smooth Endoplasmic Reticulum (SER)

A network of tubules and vesicles lacking attached ribosomes, primarily involved in lipid synthesis and serving as an intracellular calcium store.

Golgi Apparatus

A collection of flattened membrane-enclosed compartments called cisternae that modifies, sorts, and packages proteins and lipids into vesicles for transport.

Lysosome

A vesicular organelle containing around 60 digestive hydrolases that breaks down damaged cellular structures, ingested food particles, and bacteria.

Peroxisome

A vesicular organelle containing oxidases that combine oxygen with hydrogen ions to form $H_2O_2$, and catalase to decompose $H_2O_2$; involved in fatty acid $\beta$-oxidation and lipid biosynthesis.

Mitochondrion

A self-replicating organelle known as the powerhouse of the cell that generates ATP from food molecules via oxidative phosphorylation.

Cytoskeleton

A network of fibrillar proteins organized into microfilaments, microtubules, and intermediate filaments that provides structural shape, mechanical strength, intracellular movement tracks, and aids in cell division.

Integral Proteins

Permanently attached, intrinsic membrane proteins that typically span the bilayer as transmembrane proteins and act as channels, transporters, or receptors.

Peripheral Proteins

Membrane proteins attached only to one surface of the lipid bilayer without penetrating through it, which easily detach and function as enzymes or channel controllers.

Simple Diffusion

Passive transport directly through the lipid bilayer without requiring transport proteins, where the rate is directly proportional to concentration gradient and lipid solubility.

Facilitated Diffusion

Passive transport across a membrane mediated by specific carrier proteins or channels down a concentration gradient without requiring cellular energy.

Phagocytosis

A type of endocytosis involving the cellular ingestion of large solid particles.

Pinocytosis

A type of endocytosis involving the cellular ingestion of small particles or fluids.

Tight Junctions

Intercellular junctions that form a seal between adjacent cells to prevent the passage of molecules through the intercellular space.

Gap Junctions

Intercellular junctions composed of connexin transmembrane proteins that create channels allowing ions and small molecules to pass directly between cells.

Adherens Junctions

Anchoring intercellular junctions that connect the actin filaments of neighboring cells to provide mechanical stability.

Desmosomes

Anchoring intercellular junctions containing cadherin family proteins (desmoglein and desmocollin) that anchor intermediate filaments to provide strong cell-to-cell adhesion.

Intracellular Fluid (ICF)

The fluid inside cells, filling the intracellular space and constituting approximately $40\%$ of body weight.

Extracellular Fluid (ECF)

The fluid outside cells, constituting approximately $20\%$ of body weight, divided into plasma, interstitial fluid, and transcellular water.

Hydrophilic Substances

Polar or ionic 'water-loving' molecules that readily dissolve in water but cannot directly cross the hydrophobic lipid bilayer without channels or carriers.

Hydrophobic Substances

Nonpolar 'water-fearing' molecules that do not dissolve in water but cross the lipid membrane directly.

Osmolarity

The concentration of solute particles expressed per liter of solution, which varies with temperature and pressure.

Osmolality

The concentration of solute particles expressed per kilogram of solvent, unaffected by temperature and pressure, with normal plasma osmolality being approximately $275\text{--}295\,mOsm/kg$.

Tonicity

The effective osmotic pressure generated by non-permeant solutes that determines the direction of passive water movement across a semipermeable membrane.

Effective Osmoles

Solutes (such as ions, albumin, and mannitol) that cannot penetrate the membrane between compartments and thus generate lasting osmotic gradients.

Ineffective Osmoles

Solutes (such as ethanol and urea) that freely cross cellular membranes and do not create lasting osmotic gradients or water shifts.

Ligand-Gated Ion Channels

Protein channels that open when a specific chemical ligand binds to them, facilitating fast, direct signal transduction.

Voltage-Gated Ion Channels

Protein channels in excitable cells that open at a threshold membrane voltage and operate in deactivated, activated, and inactivated states.

Primary Active Transport

Active transport directly powered by the breakdown of ATP or similar energy molecules to move substances against a concentration gradient.

Secondary Active Transport

Active transport driven by the energy stored in an ion concentration gradient (typically $Na^+$ or $H^+$), coupling downhill movement of the driving ion to uphill movement of another substance.

Transcytosis

A transport mechanism in which macromolecules enter a cell by endocytosis on one side, move through the cytoplasm in vesicles, and exit by exocytosis on the opposite side.