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Physiology Ch. 5 exam review

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  • What are the 5 basic steps of cell communication?

    1) Signal 2) Reception 3) Transduction 4) Response 5) Termination

  • What determines if a signaling molecule is produced 'on demand' or stored in vesicles?

    Whether the signaling molecule can pass through membranes on its own (small/hydrophobic = on demand) or cannot (large/hydrophilic = stored in vesicles).

  • Name the 5 major chemical classes of messengers in the human body.

    Amino acid messengers, amine messengers, peptide/protein messengers, steroid messengers, eicosanoid messengers.

  • What are amino acid messengers and where are they synthesized?

    Hydrophilic neurotransmitters like glutamine, aspartate, glycine, and GABA, synthesized in the cytoplasm of neurons and stored in vesicles.

  • Which amine messengers are catecholamines and what is their origin?

    Dopamine, norepinephrine, and epinephrine; all derived from the amino acid tyrosine.

  • How are peptide/protein messengers synthesized and processed before secretion?

    Translated as prepropeptides in rough ER, cleaved to propeptides, further processed in Golgi, then packaged in secretory vesicles for release.

  • What is the key characteristic of steroid messengers regarding membrane passage and storage?

    Steroids are hydrophobic, diffuse through membranes easily, cannot be stored, and are synthesized on demand from cholesterol in smooth ER.

  • From what are eicosanoid messengers primarily synthesized?

    From membrane phospholipids or second messengers into arachidonic acid, then via COX or lipoxygenase pathways into prostaglandins, thromboxanes, leukotrienes.

  • What are the two types of direct cell communication?

    Gap junctions (connexin protein channels allowing ion/metabolite passage) and juxtacrine signaling (direct cell surface protein contact).

  • Define paracrine signaling and give examples.

    Chemical messengers secreted and diffusing short distances to neighboring cells; examples include growth factors, clotting factors, cytokines.

  • What is autocrine signaling?

    A form of paracrine signaling where the source cell is also the target cell, often seen in development and cancer cells.

  • What distinguishes hormonal (endocrine) signaling from other types?

    Hormones travel through the blood from source to distant target cells, often secreted by endocrine glands.

  • Where can receptors be located on a target cell?

    On the cell surface membrane or intracellularly in the cytoplasm or nucleus.

  • What is the function of intracellular receptors in cell signaling?

    Hydrophobic signals bind cytoplasmic or nuclear receptors forming hormone-receptor complexes that regulate gene transcription via hormone response elements.

  • What are the three domains of cell-surface receptors?

    1) External docking site for ligand, 2) Transmembrane domain, 3) Cytoplasmic tail region.

  • Name the three types of cell-surface receptors.

    Ion channel-linked receptors, G protein-linked receptors, enzyme-linked receptors.

  • How do ion channel-linked receptors function?

    Ligand binding changes receptor shape to open or close ion channels, converting chemical signals into electrical signals.

  • What role do G protein-linked receptors play in signaling?

    Ligand binding activates G-proteins that trigger intracellular signaling cascades; targeted by ~60% of prescription drugs.

  • What is the function of enzyme-linked receptors?

    They act as enzymes or associate with enzymes inside the cell, often phosphorylating proteins to trigger responses.

  • What factors influence the magnitude of a target cell's response to a signal?

    Signal concentration, number of receptors, and receptor affinity for the ligand.

  • What is receptor down-regulation and up-regulation?

    Down-regulation: decrease in receptor number due to high signal levels; Up-regulation: increase in receptor number due to low signal levels.

  • What are agonists and antagonists in receptor signaling?

    Agonists bind receptors and cause a response; antagonists bind but do not cause a response, competing for receptor sites.

  • What are second messengers in signal transduction?

    Small intracellular molecules triggered by receptor activation that amplify and relay the signal inside the cell.

  • Give examples of second messengers and their pathways.

    cAMP (activates protein kinase A), cGMP (activates protein kinase G), IP3 (releases Ca2+ from ER), DAG (activates protein kinase C), Ca2+ ions.

  • How does Ca2+ function as a second messenger?

    Regulates processes like muscle contraction, synapses, blood clotting; binds calmodulin to activate enzymes; maintained at low cytosolic levels.

  • What are the three general categories of cellular responses to signaling?

    Change membrane potential, change metabolic rate, change gene expression.

  • How is the signal cascade terminated in target cells?

    Via negative feedback loops or enzymatic degradation of the signal, stopping receptor activation and ending the response.