During starvation, which of the following shows the most marked increase in plasma concentration:
**Core Concept**
In starvation, the body undergoes a series of physiological adaptations to maintain energy homeostasis. The liver plays a crucial role in this process by breaking down stored glycogen and releasing glucose into the bloodstream. However, as starvation progresses, the liver's glycogen stores are depleted, and it begins to rely on alternative energy sources. One of these sources is the breakdown of ketone bodies, which are produced by the liver from fatty acids.
**Why the Correct Answer is Right**
During prolonged starvation, the body's primary energy source shifts from glucose to ketone bodies. Ketone bodies are produced by the liver through the breakdown of fatty acids, which are released from adipose tissue. As the liver increases its production of ketone bodies, their plasma concentration also rises. This increase in ketone bodies is a hallmark of starvation and is used by the body as an alternative energy source. The liver produces three types of ketone bodies: acetoacetate, beta-hydroxybutyrate, and acetone.
**Why Each Wrong Option is Incorrect**
**Option A:** Glucose levels would actually decrease during starvation as the body's glycogen stores are depleted and glucose production from the liver decreases.
**Option B:** Insulin levels would decrease during starvation as the body no longer requires insulin to facilitate glucose uptake by cells.
**Option C:** Urea levels may increase during starvation as the body breaks down muscle protein to use as an energy source, but this is not the most marked increase in plasma concentration during starvation.
**Clinical Pearl / High-Yield Fact**
In diabetic ketoacidosis (DKA), the body produces high levels of ketone bodies due to a lack of insulin. This can lead to a severe metabolic acidosis, which can be life-threatening if not treated promptly. It is essential to monitor ketone body levels in patients with DKA to guide treatment.
**Correct Answer:** C.