Question

Eicosanoids are NOT effective as hormones because?

1) they are hydrophobic and cannot dissolve easily in the blood.
2) they have a very short half-life and would degrade before reaching the target cell.
3) the signaling cell cannot regulate when they diffuse through the membrane.
4) all of the above

Answer 1

Eicosanoids, including prostaglandins derived from unsaturated fatty acids, are local signaling molecules that are not transported in blood like typical hormones such as estrogen or thyroid hormone. They regulate local functions like inflammation, making them ineffective as hormones for long-range signaling in the body.

Step-by-step explanation:

Eicosanoids are not typically classified as hormones because of certain distinguishing characteristics. Hormones are generally understood to be secreted into the bloodstream, traveling throughout the body to exert effects on various tissues. Eicosanoids, however, are local signaling molecules with a short half-life and are not transported in the blood to the same extent as traditional hormones. They are synthesized from omega-3 and omega-6 fatty acids and partake in vital bodily functions such as inflammation regulation, circulation, and muscle movement. Their inherent properties make them crucial in local bodily functions rather than acting as hormones that convey messages over longer distances within the body.

Typical hormones such as estrogen, testosterone, prolactin, and thyroid hormone are secreted by endocrine glands and can travel through the bloodstream to reach various organs and tissues. In contrast, eicosanoids, like prostaglandins derived from unsaturated fatty acids, operate locally near their site of synthesis. Furthermore, due to their lipid-based nature, eicosanoids cannot move easily in the water-based blood plasma, which is another reason why they are not effective as hormones.