At 20-degree centigrade atmospheric temperature, body reacts by
**Core Concept**
The body's response to cold stress involves the activation of the hypothalamic-pituitary-adrenal (HPA) axis, leading to the release of hormones that help to maintain body temperature. This process is mediated by the hypothalamus, which acts as the primary temperature regulatory center in the body.
**Why the Correct Answer is Right**
When the body detects a drop in temperature, the hypothalamus triggers the release of thyrotropin-releasing hormone (TRH), which stimulates the release of thyroid-stimulating hormone (TSH) from the pituitary gland. TSH then stimulates the thyroid gland to release thyroid hormones, including triiodothyronine (T3) and thyroxine (T4), which help to increase metabolic rate and generate heat. This is known as non-shivering thermogenesis.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the body's response to cold stress. While the hypothalamus is involved in temperature regulation, the response to cold is not solely mediated by the sympathetic nervous system.
**Option B:** This option is incorrect because it is not specific to the body's response to cold stress. The HPA axis is involved in a wide range of physiological processes, including stress response and regulation of the immune system.
**Option C:** This option is incorrect because it is not accurate. The thyroid gland is responsible for releasing thyroid hormones, but it is not directly involved in the body's response to cold stress.
**Clinical Pearl / High-Yield Fact**
In addition to the release of thyroid hormones, the body's response to cold stress also involves the activation of brown adipose tissue, which is a type of fat that is highly metabolically active and helps to generate heat.
**Correct Answer: B.**