Which of the following statements about cutaneous shunt vessels is true (AIIMS 2011 MAY)
|A||Perform nutritive function|
|B||Have role in thermoregulation|
|C||Not under the control of autonomic nervous system|
|D||These vessels are evenly distributed throughout the skin|
I. In the fingers, palms, and ear lobes, short channels connect arterioles to venules, bypassing the capillaries. These arteriovenous (A-V) anastomoses, or shunts, have thick, muscular walls and are abundantly innervated, presumably by vasoconstrictor nerve fibers.
II. The amount of heat lost from the body is regulated to a large extent by varying the amount of blood flowing through the skin.
III. Blood flow in response to thermoregulatory stimuli can vary from 1 to as much as 150 mL/100 g of skin/min, and it has been postulated that these variations are possible because blood can be shunted through the anastomoses.
IV. Therefore they play an important role in regulation of body temperature and one of the earliest changes in Hot climate is cutaneous vasodilation due to opening of shunt vessels and the reverse occurs in cold weather.