Physiology: Intercellular Communication and Signal Transduction

Vocabulary practice flashcards covering cellular communication methods, messenger chemical and functional classes, receptor dynamics, and signal transduction pathways based on the provided lecture transcript.

Direct Communication

Cellular communication that occurs directly between adjacent cells via gap junctions, allowing small ions and molecules to flow bidirectionally.

Gap Junctions

Membrane junctions made of connexins that allow direct, bidirectional communication between adjacent cells in tissues such as cardiac muscle, smooth muscle, glands, neurons, and the retina.

Connexins

Membrane proteins that construct gap junction channels, allowing small ions and molecules to pass directly between cell cytoplasms.

Indirect Communication

Cellular communication where a cell releases a chemical messenger into the interstitial fluid to bind to a receptor on a target cell.

Signal Transduction

The multi-step sequence of events inside a cell that is triggered by the binding of a chemical messenger to its target cell receptor.

Paracrine

A functional class of chemical messenger that is released into interstitial fluid and acts locally on nearby target cells.

Autocrine

A specialized type of chemical messenger that is secreted by a cell and binds to receptors on the exact same cell.

Growth Factors

Protein messengers acting as paracrines that stimulate cell proliferation and differentiation.

Clotting Factors

Protein paracrines that stimulate the formation of blood clots.

Cytokines

Peptide messengers secreted by immune cells that help coordinate defenses against infections.

Neurotransmitters

Chemical messengers released by neurons from axon terminals across a synaptic cleft to bind receptors on target neurons, muscles, or glands.

Hormones

Chemical messengers secreted by endocrine glands into the bloodstream to travel to distant target cells.

Neurohormones

Messengers released by neurosecretory cells directly into the bloodstream to act at distant target sites.

Lipophilic Messengers

Fat-loving, hydrophobic chemical messengers that are lipid soluble, cross plasma membranes freely, and bind to intracellular receptors.

Lipophobic Messengers

Water-soluble, hydrophilic chemical messengers that cannot cross plasma membranes independently and must bind to membrane-bound receptors.

Amino Acid Messengers

Lipophobic chemical messengers synthesized in neurons within the brain and spinal cord that function exclusively as neurotransmitters.

Amine Messengers

Chemical messengers derived from amino acids that are typically lipophobic and can act as paracrines, neurotransmitters, or hormones.

Peptide/Protein Messengers

Chemical messengers formed by polypeptide chains of $3$ to $100+$ amino acids that are lipophobic and function as paracrines, neurotransmitters, or hormones.

Steroid Messengers

Lipophilic chemical messengers synthesized on demand that cross the plasma membrane freely and function as hormones.

Eicosanoid Messengers

Lipophilic chemical messengers synthesized on demand by almost all cells that act as paracrines and contribute to pain induction and inflammatory responses.

Carrier Proteins

Plasma proteins that bind hydrophobic/lipophilic messengers in the bloodstream to facilitate their transport.

Free Hormone

The unbound portion of hydrophobic hormone in blood, usually comprising less than $1\%$ of total hormone, which leaves plasma first to bind target receptors.

Specificity

The selective nature of a receptor that allows it to bind to only one messenger or a specific class of messengers.

Affinity

The strength with which a specific receptor binds to a chemical messenger.

Saturation

The state when $100\%$ of available target receptors are bound by chemical messengers, causing target cell response magnitude to plateau.

Upregulation

An increase in the total number of target cell receptors above normal levels, typically occurring in response to prolonged exposure to low messenger concentrations.

Ligand

Any molecule that specifically binds to another molecule, such as a receptor.

Receptor Agonist

A ligand that binds to a receptor and induces a biological response in the target cell.

Receptor Antagonist

A ligand that binds to a receptor without producing a response, thereby competing with agonists and blocking their action.

Fast Ligand-Gated Channels

Ion channels in which the receptor binding site and the channel gate are part of the exact same membrane protein structure.

Slow Ligand-Gated Channels

Ion channels in which the receptor and channel are separate membrane proteins coupled together via an intermediate G protein.

Enzyme-Linked Receptors

Transmembrane receptors where the messenger-binding site faces extracellular fluid and the active enzyme site faces the cytosol on the same protein structure.

G Protein-Linked Receptors

Receptors that activate intracellular membrane-bound G proteins to link receptor binding with separate effector channels or enzymes.

Second Messenger

An intracellular chemical generated during signal transduction that serves to greatly amplify the biological response inside the cell.

Cyclic AMP (cAMP)

A key intracellular second messenger produced when an activated G protein stimulates its target enzyme to amplify cellular responses.