**Core Concept**
Hydroxyethyl starch (HES) is a type of colloid solution used for fluid resuscitation in critically ill patients. It is a synthetic, non-human-derived plasma volume expander that works by increasing the intravascular volume through osmotic effects.

**Why the Correct Answer is Right**
HES solutions contain hydroxyethylated amylopectin molecules, which are highly branched and have a high molecular weight. These molecules are able to remain in the intravascular space for an extended period, thereby increasing the oncotic pressure and preventing fluid shift from the intravascular space to the interstitial space. This is particularly useful in patients with hypovolemia or shock.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because HES is not a human-derived plasma volume expander, unlike albumin.
**Option B:** This option is incorrect because HES does not primarily work through the Ringer's lactate mechanism, but rather through osmotic effects.
**Option C:** This option is incorrect because HES is not a synthetic form of dextran.

**Clinical Pearl / High-Yield Fact**
It is essential to note that HES solutions have been associated with increased risk of acute kidney injury and mortality in critically ill patients. Therefore, their use should be carefully weighed against the benefits, and alternative fluid resuscitation strategies should be considered whenever possible.

**Correct Answer: D. Synthetic, non-human-derived plasma volume expander.**