Pharmacology - Antiemetics

Summary

This video provides an in-depth look at the physiology and pharmacology of vomiting, also known as emesis. It explores the brain structures involved in the vomiting reflex, such as the vomiting center and chemoreceptor trigger zone, and how sensory input, including motion sickness and emotional stimuli, can trigger nausea. The video also discusses various medications used to treat nausea and vomiting, including histamine 1 receptor antagonists, serotonin 5-HT3 receptor antagonists, dopamine 2 receptor antagonists, and muscarinic receptor antagonists, highlighting their mechanisms of action, uses, and potential side effects.

Takeaways

• 😀 Vomiting, or emesis, is the involuntary expulsion of stomach contents through the mouth, triggered by a reflex known as the emetic reflex.
• 😀 The vomiting reflex is primarily controlled by the vomiting center in the brainstem, specifically in the medulla oblongata, which contains muscarinic receptors.
• 😀 The chemoreceptor trigger zone (CTZ), located near the vomiting center, is influenced by chemical signals like dopamine and serotonin, leading to vomiting.
• 😀 The chemoreceptor trigger zone is outside the blood-brain barrier, making it more sensitive to circulating substances like chemotherapy agents.
• 😀 Motion sickness, caused by disturbances in the inner ear's labyrinth, can also trigger the vomiting reflex via the vestibular nuclei in the brainstem.
• 😀 Emotional responses, pain, repulsive smells, and visuals can stimulate higher brain centers, which send signals to the vomiting center, inducing vomiting.
• 😀 The stomach contains enteric chromatin cells that release serotonin, stimulating sensory nerve fibers and the vagus nerve, leading to vomiting.
• 😀 The vomiting reflex involves various bodily responses, such as relaxing the lower esophageal sphincter, contracting the diaphragm and abdominal muscles, and increasing heart rate and salivation.
• 😀 Antiemetic medications are used to prevent and manage nausea and vomiting, including histamine 1 receptor antagonists, serotonin receptor antagonists, dopamine receptor antagonists, and muscarinic receptor antagonists.
• 😀 Side effects of antiemetic drugs vary by class, including drowsiness (histamine blockers), headaches (serotonin blockers), and extrapyramidal symptoms (dopamine blockers).

Q & A

What is vomiting, and what is the medical term for it?

Vomiting, also known as emesis or throwing up, is an involuntary and forceful expulsion of the stomach's contents through the mouth.

What role does the medulla oblongata play in vomiting?

The medulla oblongata houses the vomiting center, which, when stimulated, triggers the vomiting reflex. This area contains muscarinic receptors that are involved in initiating vomiting.

How does the chemoreceptor trigger zone (CTZ) contribute to vomiting?

The CTZ is located near the vomiting center in the medulla oblongata and is stimulated by circulating chemicals. It contains dopamine-2 and serotonin (5-HT3) receptors, which, when activated, trigger the vomiting reflex.

Why is the chemoreceptor trigger zone outside the blood-brain barrier?

The CTZ is located outside the blood-brain barrier to make it more accessible to circulating substances like chemotherapy agents, which can trigger vomiting when detected by the CTZ.

What causes motion sickness and how does it relate to vomiting?

Motion sickness occurs when the vestibular system in the inner ear sends conflicting signals to the brain. These signals stimulate the vestibular nuclei in the brainstem, which then activate the CTZ and vomiting center, leading to vomiting.

What role does the brain's higher centers play in vomiting?

Higher centers of the brain, such as those responsible for processing emotional and sensory stimuli, can trigger vomiting when individuals experience overwhelming emotions, pain, or unpleasant sights or smells.

What types of cells in the stomach are involved in vomiting, and how do they contribute?

Enterochromaffin cells in the stomach release serotonin in response to cytotoxic agents, which activate sensory nerve fibers like the vagal nerve. These signals are sent to the vomiting center to initiate the vomiting reflex.

What happens during the vomiting reflex, and how is food expelled from the body?

During vomiting, the lower esophageal sphincter relaxes, abdominal and diaphragm muscles contract to increase intra-abdominal pressure, and the epiglottis closes to prevent food from entering the lungs. This coordinated effort expels food from the stomach through the mouth.

What are antiemetics, and how do they work to prevent vomiting?

Antiemetics are medications used to prevent or treat nausea and vomiting. They work by blocking specific receptors (like histamine-1, serotonin-5-HT3, or dopamine-2) involved in the vomiting reflex, thus preventing its activation.

What are some side effects of histamine-1 receptor antagonists used as antiemetics?

Histamine-1 receptor antagonists, such as promethazine, are commonly used for motion sickness and morning sickness. They can cause side effects like drowsiness and sedation.