~untuk memahami dengan lebih detail tentang bagaimana seseorang itu muntah/vomitting..
-dari wikipedia
Receptors on the floor of the fourth ventricle of the brain represent a chemoreceptor trigger zone, known as the area postrema, stimulation of which can lead to vomiting. The area postrema is a circumventricular organ and as such lies outside the blood-brain barrier; it can therefore be stimulated by blood-borne drugs that can stimulate vomiting or inhibit it.
There are various sources of input to the vomiting center:
- The chemoreceptor trigger zone at the base of the fourth ventricle has numerous dopamine D2 receptors, serotonin 5-HT3 receptors, opioid receptors, acetylcholine receptors, and receptors for substance P. Stimulation of different receptors are involved in different pathways leading to emesis, in the final common pathway substance P appears to be involved.[1]
- The vestibular system which sends information to the brain via cranial nerve VIII (vestibulocochlear nerve). It plays a major role in motion sickness and is rich in muscarinic receptors and histamine H1 receptors.
- Cranial nerve X (vagus nerve), which is activated when the pharynx is irritated, leading to a gag reflex.
- Vagal and enteric nervous system inputs that transmit information regarding the state of the gastrointestinal system. Irritation of the GI mucosa by chemotherapy, radiation, distention, or acute infectious gastroenteritis activates the 5-HT3 receptors of these inputs.
- The CNS mediates vomiting arising from psychiatric disorders and stress from higher brain centers.[2]
The vomiting act encompasses three types of outputs initiated by the chemoreceptor trigger zone: Motor, parasympathetic nervous system (PNS), and sympathetic nervous system (SNS). They are as follows:
- Increased salivation to protect the enamel of teeth from stomach acids (excessive vomiting leads to dental erosion). This is part of the PNS output.
- A deep breath is taken to avoid aspiration of vomit.
- Retroperistalsis, starting from the middle of the small intestine, sweeping up the contents of the digestive tract into the stomach, through the relaxed pyloric sphincter.
- A lowering of intrathoracic pressure (by inspiration against a closed glottis), coupled with an increase in abdominal pressure as the abdominal muscles contract, propels stomach contents into the esophagus as the lower esophageal sphincter relaxes. The stomach itself does not contract in the process of vomiting except for at the angular notch, nor is there any retroperistalsis in the esophagus.
- Vomiting is ordinarily preceded by retching.
- Vomiting also initiates an SNS response causing both sweating and increased heart rate.
2 comments:
wow... nnt sy kna baca smula scara lbih tekun utk memahami.. but thanks for sharing this ye nur :)
yep.. copy pun takpe wawa..
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