**Core Concept**
Incretins are a group of gastrointestinal hormones that play a crucial role in glucose homeostasis by stimulating insulin secretion in response to meal intake. They are released from the intestinal mucosa in response to nutrient ingestion and help to regulate blood glucose levels.

**Why the Correct Answer is Right**
The incretin effect is a physiological response that enhances insulin secretion in the presence of elevated blood glucose levels. This is primarily mediated by the hormones GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide). GLP-1 and GIP act on the pancreatic beta cells to increase insulin secretion, which in turn lowers blood glucose levels. This response is glucose-dependent, meaning that insulin secretion is only stimulated when blood glucose levels are elevated.

**Why Each Wrong Option is Incorrect**
**Option A:** Increased heart rate is not a function of incretin. This is a function of the autonomic nervous system, specifically the sympathetic nervous system.
**Option C:** Increased respiratory rate is also not a function of incretin. This is typically a response to hypoxia or other respiratory stimuli.
**Option D:** Stimulate erythropoiesis is not a function of incretin. Erythropoiesis is the process of red blood cell production, and it is regulated by erythropoietin, a hormone produced by the kidneys.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that incretin hormones like GLP-1 and GIP are glucose-dependent, meaning they only stimulate insulin secretion when blood glucose levels are elevated. This is in contrast to sulfonylureas, which stimulate insulin secretion regardless of glucose levels.

**✓ Correct Answer: B. Increased insulin secretion**