General Physiology - Homeostasis, Membrane Transport & Chemical Messengers

Comprehensive vocabulary flashcards generated from lecture notes on foundation physiology, homeostasis, epithelial transport, cell membrane diffusion, ion distribution, active transport, tonicity, chemical messengers, and signal transduction.

Physiology

The study of function, specifically how cells, tissues, organs, and organ systems work and integrate biology, chemistry, and physics.

Anatomy

The study of biological structure.

Homeostasis

The maintenance of a relatively stable internal environment within dynamic, narrow physiological limits despite continuous internal or external changes.

Steady State

A condition in which a physiological variable remains relatively constant over time because energy is continuously expended to maintain it.

Equilibrium

A state in which a variable is not changing and no energy input is required to maintain it due to the absence of a net driving force.

Negative Feedback

The primary homeostatic mechanism in which a change in a regulated variable triggers responses that oppose the initial change, returning the variable back toward its set point.

Positive Feedback

A regulatory control mechanism where a change in a variable triggers responses that amplify the original change in the same direction until a stopping event intervenes.

Feedforward Regulation

An anticipatory homeostatic response that begins before a regulated variable actually deviates, reducing the potential magnitude of the deviation.

Afferent Pathway

The path within a reflex arc that carries sensory input signal from the receptor toward the integrating center.

Efferent Pathway

The path within a reflex arc that carries response output signals away from the integrating center to an effector.

Intracellular Fluid (ICF)

The fluid inside cells, comprising the largest body-water compartment ($67\%$ of total body fluid).

Extracellular Fluid (ECF)

The body fluid outside cells, composed of plasma ($7\%$ of total body fluid) and interstitial fluid ($26\%$ of total body fluid).

Typical Cellular Ion Distribution

$\text{Na}^+$ and $\text{Ca}^{2+}$ concentrations are high outside the cell, whereas $\text{K}^+$ and protein concentrations are high inside the cell.

Apical Membrane

The surface of an epithelial plasma membrane that faces the lumen, body cavity, or external environment.

Basolateral Membrane

The surface of an epithelial plasma membrane anchored to the basement membrane, facing the interstitial fluid and nearby blood vessels.

Paracellular Transport

The passive diffusion of water and small solutes between adjacent epithelial cells through tight junction spaces.

Transcellular Transport

The controlled movement of substances directly through an epithelial cell, requiring entry across one membrane and exit across the opposite membrane.

Net Flux

The numerical difference between two individual one-way fluxes moving solute particles across a membrane or boundary in opposite directions.

Electrochemical Gradient

The combined force of the chemical concentration gradient and the electrical potential gradient across a membrane that drives ion movement.

Ligand-Gated Ion Channel

A membrane protein channel that opens or closes in response to the specific binding of a chemical messenger (ligand).

Voltage-Gated Ion Channel

An ion channel whose opening or closing is triggered by changes in the electrical membrane potential across the cell membrane.

Mechanically Gated Ion Channel

An ion channel that opens or closes in response to physical deformation, stretch, or mechanical pressure on the plasma membrane.

Leak Channels

Ion channels that maintain continuous baseline open behavior, allowing continuous passive resting movement of ions across the membrane.

Facilitated Diffusion

Passive mediated transport using a transmembrane protein carrier to move a solute down its concentration gradient without direct ATP energy expenditure.

Primary Active Transport

Active transport mechanism that directly hydrolyzes ATP to move a solute uphill against its concentration or electrochemical gradient.

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

A primary active transporter that directly hydrolyzes ATP to pump $3\,\text{Na}^+$ out of the cell and $2\,\text{K}^+$ into the cell per cycle.

Secondary Active Transport

Transport driven by the potential energy stored in an existing ion gradient (commonly $\text{Na}^+$) to move another substance against its gradient without direct ATP hydrolysis at the transporter.

Cotransport (Symport)

A secondary active transport pathway in which both the driving ion and the coupled solute move across the membrane in the same direction.

Countertransport (Antiport)

A secondary active transport pathway in which the driving ion and the coupled solute move across the membrane in opposite directions.

Osmosis

The net diffusion of water across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration.

Osmolarity

The total concentration of all dissolved solute particles in a solution, measured in osmole per liter (Osm/L or mOsm/L).

Aquaporins

Specialized transmembrane protein channels that facilitate rapid passive transport of water molecules across cell membranes.

Isotonic Solution

A solution containing $300\,\text{mOsm/L}$ of non-permeating solutes, causing no net movement of water and no change in cell volume.

Hypotonic Solution

A solution containing less than $300\,\text{mOsm/L}$ of non-permeating solutes relative to the cell interior, causing net water entry into the cell and leading to cell swelling.

Hypertonic Solution

A solution containing greater than $300\,\text{mOsm/L}$ of non-permeating solutes relative to the cell interior, causing net water loss from the cell and leading to cell shrinkage.

Agonist

A chemical ligand or drug that binds to a receptor and mimics or triggers the natural cellular physiological response.

Antagonist

A ligand or drug that binds competitively to a receptor without activating it, thereby blocking the binding and physiological action of the natural ligand.

Down-Regulation

A decrease in the total number of target-cell receptors for a specific messenger, usually occurring in response to long-term elevated messenger levels, decreasing cellular responsiveness.

Up-Regulation

An increase in the total number of target-cell receptors for a specific messenger, usually occurring in response to chronically low messenger concentrations, increasing sensitivity.

G-Protein-Coupled Receptor (GPCR)

A major family of plasma membrane receptors coupled to heterotrimeric G proteins ($\alpha$, $\beta$, $\gamma$ subunits) that exchange GDP for GTP to activate downstream enzymes or ion channels.

cAMP Second-Messenger Pathway Sequence

The sequential signaling pathway: First messenger $\rightarrow$ GPCR $\rightarrow$ Gs protein $\rightarrow$ adenylyl cyclase $\rightarrow$ ATP converted to cAMP $\rightarrow$ PKA activation $\rightarrow$ target protein phosphorylation $\rightarrow$ cellular response.

Signal Amplification

A property of second-messenger cascades where one activated cell-surface receptor triggers the enzymatic synthesis or activation of exponentially larger numbers of downstream cellular signaling molecules.

Acclimatization

A reversible physiological adjustment made by an individual organism in response to repeated or prolonged exposure to an environmental change.

Paracrine Substance

A chemical messenger secreted into the extracellular fluid that acts locally on nearby target cells.

Autocrine Substance

A chemical messenger secreted into the extracellular fluid that acts locally on the exact same cell that produced it.