Chemoreceptor trigger zone
The chemoreceptor trigger zone (CTZ) is an area of the
Evolutionary significance
The CTZ is in the medulla oblongata, which is
Chemoreception
Since the CTZ is located in the area postrema, a sensory circumventricular organ, it does not have a
The CTZ has many different types of receptors, which are specific to different types of toxins or drugs that might be present in the bloodstream and thus that can affect the CTZ. Types of CTZ receptors include
The receptors on the surface of the neuron are chemoreceptors that are activated from direct contact of emetic substances in the blood, whereas the receptors that are deeper down on the dendrites are receptors that are activated in response to the activated chemoreceptors on the surface.[5]
Communication
The vomiting center of the brain refers to the groups of loosely organized neurons in the medulla that include the CTZ within the area postrema and the
The CTZ communicates with the other parts of the vomiting center through neurons that contain
Phosphodiesterases
Recent studies have found that
H-channels
Most of the neurons located in the CTZ express hyperpolarization-activated cation channels (H-channels).
The vomiting center of the brain
This integrates the emetic response. This is the area in which "a final decision is made" about whether to evoke an emetic response. This decision is based heavily on the information which the CTZ relays to the rest of the vomiting center, but also the chemoreceptors in the
Damage to the CTZ
Damage to the CTZ can come via stroke, physical injury, or over-excitation resulting in neuron death. Once the damage has occurred, the effects can cause the emetic response to disappear, or cause the emetic response to heighten, in some cases causing intractable vomiting that leave patients in severe distress. In cases such as these, if the damage is severe enough, little can be done to inhibit an intractable vomiting response because the chemoreceptors in the CTZ are physically damaged or hindered in some way. Recently, it has been discovered that physical changes in the area postrema and CTZ do cause or inhibit emesis.[12] Specifically, compression of blood vessels which are physically located near in or around the CTZ, and that result in physical compression of the area postrema as a whole, have been found to be the cause of chronic medically intractable emesis and weight loss.[12] Surgical microvascular decompression resulted in postoperative and long-term resolution of emesis.[12]
Antiemetic medications
Antiemetic medications often target the CTZ to completely inhibit or greatly reduce vomiting. Most of these work by not allowing certain blood-borne drugs (usually pain killers or
Antiemetic drugs coupled with pain relieving medications
Oftentimes, doctors will "pre-treat" patients who might exhibit emetic responses due to drugs they prescribe them. Usually pain relieving drugs such as opioids are co-prescribed with anti-emetic drugs to stop the emetic response due to the pain reliever before it can even mediate its effects on the CTZ. This way, the patient does not have to worry about the doctors prescription to treat their pain causing them to be in severe discomfort via vomiting.
Chemotherapy
Chemotherapy is a major cause of emesis, and often can cause severe and frequent emetic responses. This is because chemotherapy agents circulating in the blood activate the CTZ in such a way as to cause emesis.[13] Patients receiving chemotherapy are often prescribed antiemetic medications.
See also
References
- ISBN 978-0387095615. Retrieved 16 August 2014.)
{{cite book}}
:|last1=
has generic name (help)CS1 maint: multiple names: authors list (link - ^ .
- ^ S2CID 28944289.
- S2CID 4815723.
- ^ a b c Hori, N. et al. (2000). Brainstem slice studies of receptor activation in the mouse area postrema. Society for Neuroscience Abstracts. 26(1-2) Abstract No.-716.13.
- ^ PMID 19302436.
- ^ PMID 11749934.
- ^ PMID 4387255.
- ^ S2CID 43192630.
- ^ S2CID 23070726.
- ^ Encarnacion, H. J. et al. (2009). Vomiting. Compendium-Continuing Education for Veterinarians. 31(3): 122-+.
- ^ PMID 21121735.
- PMID 3062170.