**Question:** Epornithic is:

A. A neurotransmitter
B. A vasoconstrictor
C. A vasodilator
D. A bronchodilator

**Correct Answer:** C. A vasodilator

**Core Concept:** Epornithic is a chemical compound found in the venom of certain snakes, particularly those belonging to the family Elapidae (cobras, kobras, and taipans). It is a potent vasodilator, which means it causes an increase in blood vessel diameter.

**Why the Correct Answer is Right:** Epornithic works by blocking the action of endothelin, a potent vasoconstrictor (narrower blood vessel) produced by the endothelium (inner lining) of blood vessels. By blocking endothelin, epornithic triggers a compensatory mechanism, where the body releases more nitric oxide (NO), a vasodilator (widens blood vessels). This leads to increased blood flow and dilation of blood vessels, which is why epornithic is a vasodilator.

**Why Each Wrong Option is Incorrect:**

A. Epornithic is not a neurotransmitter. A neurotransmitter is a chemical messenger that transmits signals between neurons or from the neuron to the target cell. Epornithic, being a vasodilator, does not fit the definition of a neurotransmitter.

B. Epornithic does not function as a vasoconstrictor. As explained earlier, it works as a vasodilator by blocking endothelin and causing increased nitric oxide release.

D. Epornithic is not a bronchodilator. A bronchodilator is a medication that relaxes the smooth muscle in the airways, widening them and improving airflow in the lungs. Since epornithic functions as a vasodilator, it does not have bronchodilator properties.

**Clinical Pearl:** Epornithin, the biologically active form of epornithic, is present in the venom of certain elapid snakes. It plays a role in the snake's defense mechanism by causing vasodilation and increasing blood flow, making it harder for prey to be consumed and assisting the snake in venom delivery and subsequent tissue damage.