Flashcards in Physiology chapter 2-Intercellular communication and signal transduction Deck (19):
What are the different means in which intercellular communication takes place?
Through gap junctions, transiently through the presence of identifying markers and through extracellular chemical messengers.
How does communication through gap junctions occur?
Through the specialized gap junctions, small ions and molecules are directly exchanged between interacting cells without ever entering the ECF.
How does communication occur through transient link-up?
The presence of identifying markers on the surface membrane of some cells permits them to directly link up transiently and interact with certain other cells in a specialized way.
What are the four different types of extracellular chemical messengers?
Paracrines, neurotransmitters, hormones, neurohormones.
What do extracellular chemical messengers do, generally?
In each case, a specific chemical messenger is synthesized by specialized cells to serve a designated purpose.
On being released into the ECF by proper stimulation, these signalling agents act on other particular cells, the messenger's target cells, in a prescribed manner.
The chemical messenger must bind to a target receptor to exert its effect.
What are paracrines?
Local chemical messengers whose effect is exerted only on neighbouring cells in the immediate environment of their site of secretion.
How do paracrines work?
They are distributed by simple diffusion so their action is restricted to short distances, they do not gain entry to the blood due to enzymes that inactivate them.
What's an example of a paracrine?
Histamine, released from specific connective tissue to dilate blood vessels for increase blood flow during inflammation.
Neurons communicate directly with the cells they innervate by releasing neurotransmitters. These are very short-range chemical messengers that are released in response to action potentials.
Like paracrines, they diffuse from their site of release across a narrow extracellular space to act locally on only an adjoining target cell.
What are hormones?
Long-range chemical messengers that are specifically secreted into the blood by endocrine glands in response to an appropriate signal.
How do hormones communicate?
The blood carries them to other sites of the body where, they exert the effects on their target cells some distance away from the site off release.
Only the target cells of a particular hormone have membrane receptors for binding with this hormone. non-target cells are not affected.
Wnerhat are neurohormones?
Hormones released into the blood by neurosecretory neurons.
How do neurosecretory hormones operate?
Instead of directly innervating their target, they release a neurohormone into the blood on appropriate stimulation.
The neurohormone is then distributed through the blood to distant target cells.
What is signal transduction?
The process by which incoming signals are conveyed to the target cell's interior for execution.
How do lipid-soluble extracellular chemical messengers assert their effects?
They can gain entry into the cell by dissolving in and passing through the lipid bi-layer of the plasma membrane and bind to receptors inside the target cell to initiate the desired response.
What are the major water-soluble extracellular chemical messengers?
Protein hormones and neurotransmitters.
How do primary messengers exert their effects?
Bind to their matching receptor and brings the desired response by either:
1-opening or closing channels
2-activating second-messenger systems
What is the second messenger pathway?
Binding of the first messenger to a membrane receptor serves as a signal for activating the intracellular second messenger. The second messenger ultimately relays the orders through a series of biochemical intermediates to particular intracellular proteins that carry out the dictated response.