Human Physiology Chapter 5 Chemical Messengers

Direct and Indirect communication.

What are the two modes of intercellular communication?

Communication that occurs through gap junctions, involving connexins and connexons.

What is direct intercellular communication?

Direct and Indirect communication.

What are the two modes of intercellular communication?

Communication that occurs through gap junctions, involving connexins and connexons.

What is direct intercellular communication?

Ions and small molecules.

What type of information is communicated through gap junctions?

In heart muscle and smooth muscle that controls intestines and blood vessels.

Provide an example of where direct intercellular communication occurs.

The concentration of the messenger, the number of receptors, the sensitivity of the receptors, and the identity of the responding receptor.

What factors influence the strength of target cell response in indirect communication?

Paracrine, Autocrine, Neurotransmitters, and Hormones.

What are the functional classes of chemical messengers?

A molecule that diffuses through extracellular fluid to reach a nearby target cell.

What is a paracrine chemical messenger?

A molecule secreted by a cell that acts upon itself.

What is an autocrine chemical messenger?

Growth factors, clotting factors, and cytokines.

What are examples of paracrine messengers?

By neurons at the axon terminal, and they diffuse across the synapse.

How are neurotransmitters released?

Acetylcholine, which impacts skeletal muscle.

Give an example of a neurotransmitter and its function.

Synthesized and released into interstitial fluid, then transported through the blood to target cells.

How are hormones transported in the body?

Insulin produced by b-cells in the pancreas.

What is an example of a hormone?

Hormones secreted by specialized neurons.

What are neurohormones?

Vasopressin, secreted by neurosecretory cells in the posterior pituitary.

Give an example of a neurohormone.

Lipid soluble and hydrophobic; they can cross cell membranes.

What are the major characteristics of lipophilic chemical messengers?

Water soluble and hydrophilic; they require assistance to cross cell membranes.

What are lipophobic chemical messengers?

Lipophobic/hydrophilic.

What are amino acid messengers characterized as?

Glutamate, aspartate, glycine, and gamma-aminobutyric acid (GABA).

What are some examples of amino acid neurotransmitters?

They are derived from amino acids.

How are amine messengers derived?

Epinephrine.

Give an example of a catecholamine.

Derived from cholesterol.

What is the origin of steroid messengers?

Lipophilic/hydrophobic, derived from phospholipid/arachidonic acid.

What is a characteristic of eicosanoid messengers?

Freely soluble in interstitial fluid/blood.

What is the typical solubility of hydrophilic messengers in the bloodstream?

Often bound to carrier proteins.

How do hydrophobic messengers typically travel in the blood?

In the plasma membrane, cytosol, or nucleus.

Where are receptors for chemical messengers located in the target cell?

Concentration of the messenger, number of receptors, and the affinity of the receptor.

What influences the target cell response to chemical messengers?

Ligands that bind to receptors and induce a response.

What are receptor agonists?

Ligands that bind to receptors and block a response.

What are receptor antagonists?

They enter the cytosol, bind to receptors, and activate transcription.

How do lipophilic messengers typically effect gene activation?

It promotes the opening of an ion channel, leading to an influx of ions.

What happens when a lipophobic chemical messenger binds to a channel-linked receptor?

It induces a change in conformation, activating its kinase activity.

What does the binding of a chemical messenger to an enzyme-linked receptor cause?

Activating an associated G-protein which then activates effector molecules.

What is the role of G-protein linked receptors in signal transduction?

Steroid messengers and eicosanoid messengers.

Which types of chemical messengers cannot be stored in the cell?

On the rough endoplasmic reticulum, then they are cleaved and transported to the Golgi.

How are peptide/protein messengers synthesized?

Channel-linked receptors.

What receptor type facilitates a fast target cell response?

It is specific, transient, and reversible.

What is one property of the binding of chemical messengers to their receptors?

An increase in receptors increases the chances of messenger binding.

How does the presence of receptors affect response to chemical messengers?

Acetylcholine binding to nicotinic receptors causes rapid sodium ion influx.

What is an example of a fast response induced by a chemical messenger?

Activates the receptor's kinase activity for intracellular signaling.

In chemical messenger interactions, what does autophosphorylation do?

Only cells with receptors for the hormone can respond to it.

What is the specificity of hormone actions based on?

It reverts the G-protein back into its inactive state.

How does GTP hydrolysis affect G-protein activity?

They control cell growth and differentiation.

What role do growth factors play as chemical messengers?

They are produced only when needed and not stored.

What does 'synthesized on demand' imply for certain chemical messengers?

Lipophilic messengers exert slower, long-lasting effects, while lipophobic messengers have rapid responses.

What accounts for the variation in response speed between lipophilic and lipophobic messengers?

Small molecules, peptides, proteins, and steroids.

What types of substances can act as chemical messengers?

In the interstitial fluid and bloodstream.

In what bodily fluids do hydrophilic messengers typically operate?

From phospholipids in cell membranes.

How are eicosanoids synthesized?

The compatibility and affinity between the messenger and the receptor.

What determines whether a messenger binds to its receptor?

Higher concentrations increase likelihood of receptor binding.

How does the concentration of a messenger impact target cell response?

To transmit signals between cells to regulate biological processes.

What is the primary function of chemical messengers?

As hormones, neurotransmitters, autocrines, or paracrines.

How are messengers classified based on their function?

Their lipid solubility and hydrophobic nature.

What properties allow lipophilic messengers to penetrate cell membranes?

They enhance or mimic the effects of the natural messenger.

What is the effect of agonists on receptor activity?

They transport hydrophobic messengers and prevent them from being metabolized quickly.

What role do carrier proteins play for hydrophobic messengers in the bloodstream?

It is typically rapid and often causes immediate cellular responses.

What is a key characteristic of neurotransmitter action at postsynaptic receptors?

One messenger can activate multiple signaling proteins, leading to a larger response.

What is the process of signal amplification in cellular signaling?

It prevents overreaction to high levels of messenger over time.

Why is receptor downregulation an important cellular mechanism?

They usually bind to surface receptors due to their lipophobic nature.

What type of receptor action occurs with peptide hormones?

They relay signals received by receptors to target molecules inside the cell.

How do second messengers function in signal transduction?

A greater likelihood of messenger binding at lower concentrations.

What is an effect of increased receptor affinity?

The neurotransmitter is taken back into the presynaptic neuron after signaling.

What is the process of neurotransmitter reuptake?

They relay signals from the receptor to elicit a cellular response.

What role do intracellular signal transduction pathways play?

A single messenger can activate multiple second messengers, leading to a wide-ranging effect.

How does second messenger signaling amplify cellular responses?

To bind lipophilic messengers and mediate gene expression changes.

What is the function of intracellular receptors?

Endocrine signaling involves the release of hormones into the bloodstream for widespread effect.

What distinguishes endocrine signaling from other forms of signaling?

Signal reception, signal transduction, and cellular response.

What are the three main components of signal transduction?

Autocrine signals act on the same cell that secretes them, while paracrine signals act on nearby cells.

How do autocrine signals differ from paracrine signals?

It prevents overstimulation of the cell by reducing receptor sensitivity after prolonged exposure to a signal.

What is the significance of receptor desensitization?

Long-lasting effects due to changes in gene expression.

What type of effects do steroid hormones generally have?

Proteins that act as chemical messengers in the immune response.

What are cytokines?