Ans. a. Shivering (Ref: Ghai 7/e pe p115)Neonates lack shivering mechanism. (A1IMS November 2006 Repeat)"On exposure to cold and wet environment, the neonate tries to generate heat by increased activity (crying with agitated movement) and a sympathetic surge that causes vasoconstriction and non-shivering thermogenesis in the brown fat. Babies attempt to conserve heat by peripheral vasoconstriction. ""Brown fat is a well-vascularized, sympathetically innervated lipid collection located in the axillae, groin, nape of the neck, interscapular area and perineal area. Cold stress causes the release of norepinephrine that uncouples beta-oxidation in fat with resultant heat generation. Preterm and small-for-gestational age inf ants have immature thermogenic response because of scanty brown fat stores."Role of Brown Fat in Thermogenesis* A newborn baby is more prone to develop hypothermia because of large surface area per unit of body weight.* In infants, brown fat is an important site of thermogenesis. It results in the so-called non-shivering thermogenesis.* Brown fat is located around the adrenal glands, kidney, nape of neck, interscapular and axillary region.* Metabolism of brown fat leads to heat production.* Blood floiving through the brown fat becomes warm and through circulation, transfers heat to other parts of the body. This mechanism oh heat production is know n as non-shivering thermogenesisy.