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Author Topic: what is teh mechanism of vomiting?  (Read 1788 times)

Offline annie123

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what is teh mechanism of vomiting?
« on: 15/12/2013 20:37:27 »
After experiencing a nasty bug through food contamination I wondered what actually is happening when the stomach throws up what's in it and lots more besides. I know 'reflex' is one answer but what does that actually mean? Do stomach muscles contract? If so, what makes them? And why in response to some things and not others? How does it recognize a harmful organism?And why have such organisms not evolved to create a defence from the stomach's reaction so that they can stay in there and do their job? ANd what do anti vomiting medications do to calm things down?


 

Offline cheryl j

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Re: what is teh mechanism of vomiting?
« Reply #1 on: 15/12/2013 22:02:12 »
Vomiting can be caused by food poisoning, or ingestion of noxious substances when chemoreceptors in the stomach respond to irritants or toxins produced by unfriendly bacteria.  Distension of the stomach (bloating) can also cause trigger it. Emotional upset, unpleasant sights or smells, fear, pain, motion sickness, morning sickness, and increased pressure in the brain can also cause vomiting.

Different nerve path ways may be involved, depending on the cause.
The vagus nerve or the tenth cranial nerve, is involved when the gag reflex is triggered in the throat. The 8th cranial nerve from the inner ear can trigger it in motion sickness. The brain itself can trigger it as a protective response to poisons and anesthetics or high alcohol intake.
 
In the vomitting process, parasympathetic nerves cause reverse contractions, or  retro-peristalsis, in the middle of small intestine, which pushes digestive tract contents into the stomach and through the relaxed pyloric sphincter at the top of the stomach. The abdominal muscles also help. Then sympathetic nerves are  stimulated, and they are responsible accompanied by pallor, sweating, and increased heart rate that often occurs towards the end.

The vomiting reflex is a problem with general anesthetics, which is why they insist patients not eat anything, even if the surgery does not involve the digestive tract. With anesthetics (and alcohol) the gag reflex becomes suppressed, but the vomiting reflex becomes overly sensitive for a period of time as the patient becomes unconscious and again as they regain consciousness. This means there is a dangerous period of time where the patient may vomit, but not cough and expel the contents, as a normal, conscious person would, and anything in the stomach or small intestine might be aspirated into the lungs. In emergency surgery, they cannot be sure what the patient has recently eaten.

Wikipeida says most of the anti-vomiting and anti nausea drugs work by blocking nerve receptors. Some remedies may simply act by coating the irritated digestive tract. The common, over the counter drug, Gravol inhibits the stimulation of certain nerves in the brain and inner ear to suppress nausea, vomiting, dizziness, and vertigo. It is not effective with all types of nausea and vomiting.
« Last Edit: 15/12/2013 22:11:18 by cheryl j »
 

Offline annie123

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Re: what is teh mechanism of vomiting?
« Reply #2 on: 18/12/2013 01:42:21 »
Thanks for the full reply. I do wonder how the reflex reactions to different substances are conditioned, especially as they are not the same always from one person to another. Why does the smell or taste of one substance trigger a vomit response in one person and not another etc. And what is the benefit for the body when vomiting is induced in response to pain, fear, pregnancy etc which do not severely threaten it physically?
 

Offline RD

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Re: what is teh mechanism of vomiting?
« Reply #3 on: 18/12/2013 03:06:23 »
... And what is the benefit for the body when vomiting is induced in response to pain, fear ...

The release of adrenaline, e.g. triggered by fear,  can cause nausea ... http://en.wikipedia.org/wiki/Adrenaline#Mechanism_of_action

Voiding the digestive system could help survival : making more blood-flow available for muscles in a flight-or-flight situation.
 

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Re: what is teh mechanism of vomiting?
« Reply #3 on: 18/12/2013 03:06:23 »

 

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