Myocardium normally utilizes:
**Core Concept**
Myocardium, the muscular layer of the heart, requires a continuous supply of energy to maintain its contractile and electrical functions. This energy is primarily derived from the breakdown of fatty acids and glucose, but with a preference for fatty acids.
**Why the Correct Answer is Right**
The myocardium predominantly utilizes fatty acids as its primary source of energy. This is due to the presence of high levels of mitochondria in cardiac myocytes, which are specialized for fatty acid oxidation. The enzyme carnitine palmitoyltransferase I (CPT I) plays a crucial role in the transport of long-chain fatty acids into the mitochondria, where they are broken down to produce acetyl-CoA and ultimately ATP.
**Why Each Wrong Option is Incorrect**
**Option A:** While glucose is an essential energy source for the myocardium, especially during periods of high energy demand or ischemia, it is not the primary source of energy.
**Option B:** Lactate is not a typical energy source for the myocardium, as it is primarily produced in skeletal muscle during anaerobic metabolism.
**Option C:** Ketones, produced during fasting or ketogenic diets, can be used by the myocardium as an energy source, but are not the primary source of energy.
**Clinical Pearl / High-Yield Fact**
In the setting of ischemia or hypoxia, the myocardium shifts towards glucose utilization as its primary energy source, a phenomenon known as the "glucose paradox."
**Correct Answer: C. Fatty acids.**