Introduction to Physiology and Homeostasis; Cell Physiology; The Plasma Membrane; Neural and Hormonal Communication

Vocabulary flashcards covering key terms from physiology notes (Chapters 1–4).

Homeostasis

Dynamic, relatively stable internal environment maintained by body systems to sustain cell survival.

Internal environment

Fluid surrounding body cells; includes extracellular fluid (ECF).

Extracellular fluid (ECF)

Fluid outside cells but inside the body, made up of plasma and interstitial fluid.

Intracellular fluid (ICF)

Fluid within the cells.

Interstitial fluid

Fluid between cells that bathes them and exchanges substances with plasma.

Plasma

Liquid component of blood; part of the extracellular fluid.

Dynamic steady state

Constant regulation in which controlled variables continuously change but remain within narrow limits.

Negative feedback

Counteracts a deviation from the set point to restore normal conditions.

Positive feedback

Amplifies a change; activity proceeds in the same direction until a stopping mechanism occurs (e.g., birth).

Feedforward

Anticipatory responses that prepare the system for a change before it occurs.

Set point

Desired value of a controlled variable within the body’s regulatory system.

Sensor (receptor)

Component that detects deviations from the set point and reports them to the control center.

Integrator (control center)

Compares input with the set point and determines the corrective action.

Effector

Body part that carries out the corrective response to restore homeostasis.

Intrinsic control

Local regulatory mechanism built into an organ.

Extrinsic control

Regulation initiated outside an organ (by nervous or endocrine systems) to alter organ activity.

Levels of organization

From chemical level to cells, tissues, organs, body systems, and the whole organism.

Tissues (four primary types)

Muscle, nervous, epithelial, and connective tissues.

Organ

Two or more tissue types organized to perform a specific function (e.g., stomach).

Body system

A group of related organs that perform common functions (e.g., circulatory system).

11 body systems

Circulatory, digestive, respiratory, urinary, skeletal, muscular, integumentary, immune, nervous, endocrine, reproductive.

Nutrients

Substances cells obtain from the environment for growth and energy.

O2 and CO2 levels

Oxygen and carbon dioxide concentrations must be regulated in the internal environment.

pH

Acidity/alkalinity of the internal environment; must be tightly regulated.

Water, salts, electrolytes

Concentrations must be controlled to maintain cell volume and function.

Temperature

Body temperature must be kept within a narrow range for enzyme function.

Volume and pressure

Plasma volume and blood pressure must be maintained for proper distribution.

Homeostatic control system

Network of components that maintains a factor at a nearly constant level.

Levels of organization (PL)

Chemical level; cellular level; tissue level; organ level; body system level; organism level.

Cell theory

All living things arise from preexisting cells; cells are the basic units of life.

DNA

Genetic material; directs protein synthesis and cell replication.

RNA (mRNA, tRNA, rRNA)

Mediates transcription and translation of genetic information into proteins.

miRNA/siRNA

Regulatory RNAs that can silence gene expression via RNA interference (RNAi).

Genome/Proteome/Epigenetics

Genome: complete DNA; Proteome: complete set of proteins; Epigenetics: heritable changes in gene activity without DNA sequence changes.

Mitochondria

Powerhouses of the cell; generate most ATP via glycolysis, citric acid cycle, and oxidative phosphorylation.

ATP

Adenosine triphosphate; the cell’s primary energy currency.

Ribosome

Site of protein synthesis; free ribosomes in cytosol and ribosomes on rough ER.

Endoplasmic reticulum (ER)

Rough ER has ribosomes and synthesizes proteins; smooth ER lacks ribosomes and handles lipid synthesis and packaging.

Golgi complex

Packages, modifies, and sorts proteins for secretion or delivery to membranes or organelles.

Lysosome

Digestive organelle with hydrolytic enzymes; intracellular digestion.

Proteasome

Protein degradation machine that recycles damaged or misfolded proteins.

Peroxisome

Detoxifies reactive molecules; contains catalase to break down H2O2.

Nucleus/DNA/RNA

Nucleus houses DNA; site of transcription; controls cell activities via gene expression.

Cytosol

Fluid component of cytoplasm; site of many enzymatic reactions.

Cytoskeleton (microtubules, microfilaments, intermediate filaments)

Protein scaffolding that gives structure, organizes organelles, and enables movement.

Cell membrane (plasma membrane)

Phospholipid bilayer with embedded proteins; separates intracellular from extracellular space.

Phospholipid bilayer

Two-layer arrangement of phospholipids; hydrophilic heads face water, hydrophobic tails inward.

Cholesterol (membrane)

Stabilizes membrane fluidity and structure.

Lipid rafts

Organized membrane microdomains rich in cholesterol and sphingolipids, hosting specific receptors.

Glycocalyx

Carbohydrate coating on cell surface; involved in recognition and protection.

Integral vs peripheral proteins

Integral span the membrane; peripheral coat the exterior or interior surface.

Schwann cells/Oligodendrocytes

Cells that form myelin in PNS/CNS, respectively, speeding nerve conduction.

Myelin/Nodes of Ranvier

Myelin insulates axons; Nodes are gaps where action potentials are regenerated.

Action potential

Rapid, all-or-none depolarization-repolarization event that travels along the membrane.

Graded potential

Local, variable-amplitude changes that can summate but decay with distance.

Refractory period

Absolute: no new AP can be generated; Relative: stronger stimulus required after an AP.

Synapse

Junction between neurons or neuron and effector where signaling occurs.

Neurotransmitter/Neuromodulator/Neurohormone

Neurotransmitters: fast signaling across synapse; Neuromodulators: modulate synaptic responses; Neurohormones: hormones released into blood by neurons.

Excitatory/inhibitory postsynaptic potentials (EPSP/IPSP)

EPSP: depolarizes postsynaptic cell; IPSP: hyperpolarizes it.

Second messenger pathways

Intracellular signaling cascades (e.g., cAMP, IP3/Ca2+, DAG) triggered by receptor activation.

GPCR (G-protein-coupled receptor)

Receptors that activate G proteins to trigger second messenger cascades.

Tyrosine kinase/JAK-STAT

Receptor pathways; Tyrosine kinase: receptor itself is enzyme; JAK-STAT: receptor-associated JAKs activate STAT transcription factors.

cAMP/PKA pathway

First messenger binds receptor → G protein activates adenylyl cyclase → cAMP → PKA → phosphorylation of target proteins.

Ca2+/IP3/DAG pathway

PLC cleaves PIP2 into IP3 and DAG; IP3 releases Ca2+; Ca2+ activates CaM kinase; DAG activates PKC.

Eicosanoids (prostaglandins, thromboxanes, leukotrienes)

Local lipid mediators derived from arachidonic acid; regulate inflammation, pain, respiration, etc.

NSAIDs/COX/LOX

Drugs that inhibit cyclooxygenase (COX) or lipoxygenase (LOX) to reduce prostaglandin or leukotriene formation and inflammation.

Hydrophilic vs lipophilic hormones

Hydrophilic: water-soluble; act on surface receptors. Lipophilic: fat-soluble; act on intracellular receptors.

Hormone response element (HRE)

DNA sequence that hormone–receptor complex binds to regulate gene transcription.

Receptor regulation

Receptor number and affinity can be up- or down-regulated by hormones or disease.

Paracrine/autocrine signaling

Local chemical messengers acting on nearby or the same cell that secreted them.

Endocrine vs nervous system specificity

Nervous: specificity via anatomy; Endocrine: specificity via receptor distribution and affinity.

Signal transduction termination

Mechanisms to stop signaling include enzyme degradation, receptor internalization, and phosphatases.