Chemical Messengers

What are the two organ systems used for homeostatic regulation in the body?

The nervous system (N.S.) and the endocrine system (E.S.)

How does the anatomical design of the nervous system differ from the endocrine system?

The N.S. has direct connections via synapses and is in close proximity to target cells, while the E.S. uses hormones that travel through the bloodstream to distant target cells.

What type of signals are used by the nervous system?

Electrical impulses and neurotransmitters.

What type of signals are used by the endocrine system?

Chemical signals known as hormones.

How fast is the signal conduction in the nervous system compared to the endocrine system?

The N.S. is very fast (milliseconds), while the E.S. is slower (seconds to minutes, sometimes longer).

What is the duration of signal effects in the nervous system?

Short-lived; effects end quickly when the stimulus stops.

What is the duration of signal effects in the endocrine system?

Long-lasting; effects may persist even after hormone release stops.

How is the nervous system integrated into central regulatory systems?

It is centralized in the CNS (brain and spinal cord) with highly specific integration.

How is the endocrine system linked to the central nervous system?

It is linked via the hypothalamus and has broad regulatory influence over many body systems.

What are neurohormones?

Signaling molecules produced by nerve cells that are released into the bloodstream to act like hormones.

What are paracrines?

Chemical messengers that exert effects on cells near their secretion sites.

What are autocrines?

Chemical messengers secreted into extracellular fluid that act upon the cell that secreted them.

What are pheromones?

Chemicals secreted by an organism into the environment to elicit a specific behavioral or developmental response in another member of the same species.

What are eicosanoids?

Modified fatty acids that are products of arachidonic acid metabolism, functioning as paracrine or autocrine substances.

What determines a signal's specific message?

The original chemical signal (first messenger), the specific chemical receptor for the signal, the mechanism of signal transduction, and the enzymes/chemicals in the target cell that respond.

What is signal transduction?

The carrying of an extracellular signal across a membrane into a cell, which may require creating a new chemical (second messenger) within the target cell.

What is one example of a signal transduction mechanism?

Open/close membrane ion channels coupled to receptors, which may alter cell polarity.

What role does adenylate cyclase play in signal transduction?

It produces cyclic nucleotides (cAMP, cGMP) that act as second messengers.

What is the function of phosphodiesterase enzymes in relation to cAMP and cGMP?

They recycle cAMP and cGMP after use.

How can nitric oxide (NO) function in signal transduction?

It can act as a gaseous chemical signal, often linked to cGMP.

What is a unique feature of gene expression alteration in cells during signal transduction?

It can occur usually without requiring a second messenger.