**Core Concept:** Stress-induced analgesia is a phenomenon where psychological stress reduces pain perception. This occurs through the release of various stress hormones and neurotransmitters, which modulate pain pathways.

**Why the Correct Answer is Right:** Cortisol, a glucocorticoid hormone, is released during stress in response to the hypothalamic-pituitary-adrenal (HPA) axis activation. Cortisol has anti-inflammatory and immunosuppressive effects, which can lead to reduced pain perception.

**Why Each Wrong Option is Incorrect:**

A. Endorphins are endogenous opioids that reduce pain, not increase it. Endorphins are not involved in stress-induced analgesia.

B. Norepinephrine is a neurotransmitter involved in the stress response, but it does not directly cause stress-induced analgesia.

C. Serotonin is primarily involved in mood regulation and appetite control, not pain modulation. Its release during stress does not result in stress-induced analgesia.

**Clinical Pearl:** Stress-induced analgesia can be exploited in clinical scenarios where increased pain sensitivity is desired, such as during dental procedures or minor surgeries. However, excessive stress can lead to impaired wound healing and immune response.

**Correct Answer:** D. Cortisol is the correct hormone involved in stress-induced analgesia.