On exposure to cold, all are seen EXCEPT:March 2013
**Core Concept**
Cold exposure triggers a cascade of physiological responses aimed at maintaining core body temperature. This involves the activation of the hypothalamic-pituitary-adrenal (HPA) axis, the release of catecholamines, and the vasoconstriction of peripheral blood vessels.
**Why the Correct Answer is Right**
When exposed to cold, the body's initial response is to conserve heat by reducing blood flow to the skin and extremities through vasoconstriction. This is mediated by the release of catecholamines (e.g., norepinephrine) from the adrenal glands, which stimulates alpha-adrenergic receptors on the smooth muscle of blood vessels, leading to their constriction. Additionally, the HPA axis is activated, resulting in the release of cortisol, which helps to mobilize energy stores and maintain core body temperature.
**Why Each Wrong Option is Incorrect**
* **Option A:** Cold-induced vasodilation is not a typical response to cold exposure. While some individuals may exhibit this response, it is not a universal or expected physiological reaction.
* **Option B:** Cold-induced diaphoresis (sweating) is not a typical response to cold exposure. Sweating is usually associated with heat loss, not heat conservation.
* **Option C:** Cold-induced bradycardia (slowed heart rate) is not a typical response to cold exposure. The body's initial response to cold is often to increase heart rate and blood pressure to maintain core body temperature.
**Clinical Pearl / High-Yield Fact**
The "diving reflex" or "diving response" is a physiological response to cold water immersion, characterized by bradycardia, peripheral vasoconstriction, and apnea (cessation of breathing). This reflex is mediated by the stimulation of the trigeminal nerve and the release of catecholamines.
**Correct Answer:** B. Cold-induced diaphoresis is not a typical response to cold exposure.