PA-CAT key terms

The standard reference stance in anatomy: standing upright, face and eyes forward, arms at the sides with palms forward, and feet flat and parallel.

A thin double-layered membrane that lines closed body cavities; the parietal layer attaches to the cavity wall, while the visceral layer covers organs, and lubricating fluid between them reduces friction.

Describing structures located behind the parietal peritoneum, such as the kidneys and pancreas, which are not suspended within the peritoneal cavity and therefore move less with body position.

A rapid, self-propagating change in a neuron or muscle cell membrane voltage caused by ion channel opening, used to transmit electrical signals over long distances.

The concentration of dissolved particles per kilogram of solvent; it determines water movement across membranes and is regulated to maintain cell volume and blood pressure.

The volume of blood ejected from one ventricle during a single heartbeat; it equals end-diastolic volume minus end-systolic volume and influences cardiac output.

A control mechanism in which a change in a physiological variable triggers responses that oppose the initial change, helping keep internal conditions near a stable set point.

The volume of plasma filtered by the kidneys' glomeruli per unit time; it estimates kidney function and depends on filtration pressure, surface area, and permeability.

A protein or RNA molecule that speeds a biochemical reaction by lowering its activation energy without being consumed, typically acting on specific substrates at an active site.

The substrate concentration at which an enzyme works at half its maximum velocity; a lower Km indicates stronger substrate binding and higher apparent affinity.

The ATP-producing process in which electrons move through mitochondrial membrane protein complexes, creating a proton gradient that drives ATP synthase.

The cytoplasmic pathway that splits one glucose molecule into two pyruvate molecules, producing a small net gain of ATP and NADH without requiring oxygen.

Control of enzyme activity by a molecule binding at a site distinct from the active site, changing the enzyme's shape and either enhancing or reducing its catalytic function.

A type of cell division that produces two genetically identical daughter cells with the same chromosome number as the parent, used for growth and tissue repair.

The passive net movement of particles from an area of higher concentration to one of lower concentration, driven by random molecular motion until equilibrium is approached.

A two-layer sheet of phospholipids forming the core of cell membranes, with water-loving heads facing outward and water-fearing tails facing inward, creating a selective barrier.

Programmed cell death in which a cell dismantles itself in an orderly way, avoiding inflammation and helping remove damaged or unnecessary cells during development and tissue maintenance.

A laboratory staining method that divides bacteria into Gram-positive and Gram-negative groups based on differences in cell wall peptidoglycan thickness and outer membrane presence.

The ability of bacteria to survive and multiply in the presence of an antibiotic that would normally inhibit or kill them, often through genetic changes or acquired resistance genes.

A form of asexual reproduction in prokaryotes in which one cell replicates its DNA and divides into two genetically similar daughter cells, allowing rapid population growth.

A heat-stable lipopolysaccharide found in the outer membrane of Gram-negative bacteria; it can trigger fever, inflammation, and shock when released into the bloodstream.

One of two or more alternative DNA sequences at a given gene locus; different alleles may produce different traits or no observable effect.

A genetic relationship in which both alleles at a locus are fully expressed in the phenotype, so neither masks the other, as in AB blood type.

The proportion of individuals carrying a particular genotype who actually show the associated phenotype; incomplete penetrance means some carriers appear unaffected.

A heritable change in the DNA sequence of a gene or chromosome; it can alter protein structure or expression and may be harmful, neutral, or beneficial.

A concentration unit equal to the number of moles of solute dissolved in one liter of solution, commonly used to express laboratory solution strengths.

A logarithmic scale expressing the acidity or alkalinity of a solution as the negative logarithm of hydrogen ion activity; lower values indicate more acidic conditions.

When a system at equilibrium is disturbed by a change in concentration, pressure, or temperature, the system shifts in the direction that partially offsets the disturbance.

A chemical bond formed when two atoms share one or more pairs of electrons, creating a stable connection that can be nonpolar or polar depending on electronegativity.

A solution containing a weak acid and its conjugate base, or a weak base and its conjugate acid, that resists large pH changes when small amounts of acid or base are added.

A specific group of atoms within an organic molecule that gives the molecule characteristic chemical properties and reactivity, such as hydroxyl, carbonyl, or amino groups.

A property of molecules that are not superimposable on their mirror images; chiral molecules often have a carbon bonded to four different groups and can rotate polarized light differently.

An electron-rich chemical species that donates a pair of electrons to an electron-poor atom, forming a new bond during reactions such as substitution or addition.

One of two or more molecules with the same molecular formula but different arrangements of atoms or different spatial orientations, leading to distinct chemical or physical properties.

A learning process in which a neutral stimulus becomes associated with a meaningful stimulus and, after repeated pairing, elicits a response similar to the meaningful stimulus.

A learning process in which the likelihood of a behavior changes because of its consequences, such as rewards increasing behavior and punishments decreasing it.

A framework predicting health behaviors from beliefs about susceptibility, severity, benefits, barriers, and cues to action, often used to design health interventions.

A composite measure of a person's social position based on income, education, and occupation; it strongly influences access to resources and health outcomes.

The psychological discomfort felt when a person holds two or more conflicting beliefs or acts in ways inconsistent with beliefs; people are motivated to reduce this tension.