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mediators that accomplish indirect communication between cells
molecules that reversibly bind to protein receptors at an area called the binding site |
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| process by which a chemical messenger is released from a cell into the extracellular fluid |
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cell to which the chemical messenger goes and binds to a receptor, thereby eliciting a response
whether or not a target cell responds to a chemical messenger is ultimately dependent on that cell having an appropriate receptor for that chemical messenger |
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| functional classification of chemical messengers |
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Definition
autocrine
paracrine
neurotransmitter
hormones
neurohormones
cytokines |
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Definition
| messengers secreted by a cell into the interstitial fluid that then binds to a receptor located on the same cell that secreted it |
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| messenger secreted into the interstitial fluid where it diffuses and subsequently binds to receptors on nearby target cells (a single messenger may have autocrine and paracrine activity) |
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| messenger secreted by a neuron into the interstitial fluid where it diffuses and subsequently binds with a receptor on nearby target cells. The target cell may be another nerve, a gland, or a muscle. |
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| the junction between a neuron and its target cell |
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| messengers secreted by secretory cells (in this case called endocrine cells) into the interstitial fluid that subsequently make their way into the plasma. Hormones are in turn distributed to target cells (ones with appropriate receptors) throughout the body via the bloodstream. |
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| messengers secreted by neurons (neurosecretory cells) into the interstitial fluid, which then make their way into the plasma. These neurohormones are distributed to target cells throughout the body via the bloodstream. These are just like hormones, with the only difference being a neuron is the secretory cell. |
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Definition
messengers which may act like a paracrine agent, autocrine agent, or hormone
ex: interleukins and interferons (substances secreted by WBCs playing a role in immune function) |
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Term
| transport of chemical messengers |
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Definition
autocrine, paracrine, neurotransmitters, and many cytokines diffuse through the interstitial fluid to their target tissue. These substances quickly degrade, minimizing the spread of their effect.
hormones, neurohormones, and some cytokines are transported in the blood. Two forms of transport are utilized. The type of transport is determined whether the messenger is hydrophilic or lipophilic |
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| hydrophilic messenger transport |
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Definition
| hydrophilic messengers dissolve easily in plasma (which is primarily water) and therefore do not require any type of carrier molecule. |
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| lipophilic messenger transport |
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Definition
lipophilic messengers do not readily dissolve into the plasma, and are therefore transported in the plasma primarily bound to a carrier molecule. Messengers that are transported by carriers are in dynamic equilibrium with small amount of unbound (also referred to as free) messenger in plasma.
only free messenger is active!
as free messenger binds to its receptor, this shifts the equilibrium between bound and free messenger, thus releasing additional messenger from the carrier molecules. This is referred to as dynamic equilibrium.
free hormone may last for minutes; hormone bound to a carrier may last for hours. |
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