Human Physiology Chapter 6: Communication, Integration, and Homeostasis

Flashcards covering the vocabulary of cell-to-cell communication, signal transduction pathways, molecule types, and reflex control systems based on Chapter 6.

Electrical signals

Changes in the membrane potential of a cell that serve as physiological signals.

Chemical signals

Molecules secreted by cells into the extracellular fluid (ECF) that act as ligands to communicate with target cells.

Gap junctions

A form of local communication that creates cytoplasmic bridges between adjacent cells.

Contact-dependent signals

Local signals that require cell-to-cell contact through cell adhesion molecules (CAMs).

Paracrine signal

A chemical signal secreted by a cell that diffuses through the extracellular fluid to act on nearby cells.

Autocrine signal

A chemical signal that acts on the same cell that secreted it.

Hormones

Chemical signals secreted into the blood by the endocrine system for long-distance communication throughout the body.

Neurocrine molecules

Chemical signals secreted by neurons, which include neurotransmitters, neuromodulators, and neurohormones.

Neurotransmitters

Neurocrine molecules that diffuse across a narrow extracellular space to a target cell to produce a rapid effect.

Neuromodulators

Neurocrine molecules that act as paracrine or autocrine signals and typically have slower effects than neurotransmitters.

Neurohormones

Neurocrine molecules released by neurons into the blood for distribution to distant targets.

Cytokines

Peptides synthesized and secreted by all nucleated cells in response to stimuli; they can act as both local and long-distance signals.

Lipophilic signal molecules

Signal molecules that diffuse through the cell membrane and bind to cytosolic or nuclear receptors.

Lipophobic signal molecules

Signal molecules that cannot cross the cell membrane and must bind to receptors on the cell surface.

Signal transduction

The process where a transducer converts an extracellular signal (first messenger) into an intracellular signal (second messenger) to trigger a response.

Signal amplification

A mechanism where an amplifier enzyme turns one ligand-receptor complex into many intracellular second messenger molecules.

Receptor-channels

Chemically gated (ligand-gated) ion channels that open or close in response to ligand binding, altering membrane permeability.

G protein-coupled receptors (GPCR)

Membrane receptors with a cytoplasmic tail linked to a three-part transducer molecule known as a G protein.

Receptor-enzymes

Catalytic receptors where ligand binding activates an intracellular enzyme, such as tyrosine kinase or guanylyl cyclase.

Tyrosine kinase (TK)

An enzyme that transfers a phosphate group from ATP to a tyrosine amino acid of a protein.

Integrin receptors

Membrane-spanning proteins that bind extracellular matrix proteins or ligands and attach to the cytoskeleton via anchor proteins.

Calmodulin

An intracellular regulatory protein that binds to $Ca^{2+}$ to alter the activity of other proteins.

Nitric oxide (NO)

A short-acting gaseous paracrine or autocrine molecule that causes vasodilation and activates guanylyl cyclase to produce cGMP.

Eicosanoids

Lipid signaling molecules derived from arachidonic acid, including leukotrienes and prostanoids.

Prostanoids

A subgroup of eicosanoids, consisting of prostaglandins and thromboxanes, involved in sleep, inflammation, pain, and fever.

Agonist

A molecule that mimics the primary ligand to activate a receptor and elicit a response.

Antagonist

A molecule that blocks receptor activity by binding to it without activating it, preventing a response.

Down-regulation

The reduction in receptor number or binding affinity to decrease a cell's responsiveness to a signal.

Up-regulation

The increase in receptor number to enhance a cell’s sensitivity to a signal, often in response to low ligand concentrations.

Tonic control

A control pattern where a single signal regulates a parameter by varying its frequency or intensity.

Antagonistic control

A control pattern where two different signals have opposing effects on a target, such as insulin and glucagon.

Threshold

The minimum stimulus required to initiate a reflex response.

Afferent pathway

The input signal path that connects a sensor or receptor to an integrating center.

Integrating center

A region, such as the CNS or an endocrine cell, that evaluates input signals against a setpoint and initiates an output signal.

Efferent pathway

The output signal path that carries information from an integrating center to a target or effector.