Passage
Skin grafting is a procedure in which healthy skin from a different region of the body is transplanted onto an area of absent or damaged skin. Skin grafts are used for partial-thickness burns, which damage the epidermis and dermis, and for full-thickness burns, which damage the epidermis, dermis, and hypodermis. Superficial burns injure only epidermal tissue and heal without skin grafts. Skin grafting has greatly improved the long-term survival of burn victims. However, because grafted skin cannot effectively dissipate heat, burn survivors are at an increased risk of hyperthermia (abnormally high body temperature) , a condition that can lead to heat-related medical emergencies such as heat stroke. The greater the grafted body surface area (BSA) , the greater the risk for complications related to thermoregulation.Heat acclimation (HA) is the process by which the body increases heat tolerance through adaptive changes in the sympathetic control of skin heat dissipation. It can be induced in healthy individuals by repeated exercise at elevated ambient temperature and humidity. A group of researchers tested whether skin graft recipients could also undergo HA. Skin graft recipients who were otherwise healthy and had at least 15% grafted BSA were recruited for the study, as were controls with no history of receiving grafts. The skin graft recipients were split into two groups, those with 15%-40% grafted BSA and those with >40% grafted BSA. For a period of seven days, subjects participated daily in 90 min of exercise at 50% maximal oxygen consumption in a room where the temperature was maintained at 40°C. Exercise modality, fluid intake, and frequency and duration of rest were strictly monitored.On the days immediately preceding and following the HA regimen, the heat tolerance of participants was tested with a 90-min exercise regimen at a fixed heat production rate (Figure 1) . Tolerance testing was halted before 90 min for subjects whose internal body temperature exceeded 40°C. The change in internal temperature of participants was calculated by subtracting their internal temperature before exercise from their internal temperature at exercise cessation (either once temperature reached 40°C or at the 90-min endpoint) .
Figure 1 HA in controls and in skin graft recipients
Adapted from Schlader ZJ, Ganio MS, Pearson J, et al. J Appl Physiol. 2015;119(1) :69-76.
-What physiological change occurs in the skin of control subjects during HA exercise?

Question

Passage
Skin grafting is a procedure in which healthy skin from a different region of the body is transplanted onto an area of absent or damaged skin. Skin grafts are used for partial-thickness burns, which damage the epidermis and dermis, and for full-thickness burns, which damage the epidermis, dermis, and hypodermis. Superficial burns injure only epidermal tissue and heal without skin grafts. Skin grafting has greatly improved the long-term survival of burn victims. However, because grafted skin cannot effectively dissipate heat, burn survivors are at an increased risk of hyperthermia (abnormally high body temperature) , a condition that can lead to heat-related medical emergencies such as heat stroke. The greater the grafted body surface area (BSA) , the greater the risk for complications related to thermoregulation.Heat acclimation (HA) is the process by which the body increases heat tolerance through adaptive changes in the sympathetic control of skin heat dissipation. It can be induced in healthy individuals by repeated exercise at elevated ambient temperature and humidity. A group of researchers tested whether skin graft recipients could also undergo HA. Skin graft recipients who were otherwise healthy and had at least 15% grafted BSA were recruited for the study, as were controls with no history of receiving grafts. The skin graft recipients were split into two groups, those with 15%-40% grafted BSA and those with >40% grafted BSA. For a period of seven days, subjects participated daily in 90 min of exercise at 50% maximal oxygen consumption in a room where the temperature was maintained at 40°C. Exercise modality, fluid intake, and frequency and duration of rest were strictly monitored.On the days immediately preceding and following the HA regimen, the heat tolerance of participants was tested with a 90-min exercise regimen at a fixed heat production rate (Figure 1) . Tolerance testing was halted before 90 min for subjects whose internal body temperature exceeded 40°C. The change in internal temperature of participants was calculated by subtracting their internal temperature before exercise from their internal temperature at exercise cessation (either once temperature reached 40°C or at the 90-min endpoint) .

Figure 1 HA in controls and in skin graft recipients
Adapted from Schlader ZJ, Ganio MS, Pearson J, et al. J Appl Physiol. 2015;119(1) :69-76.
-What physiological change occurs in the skin of control subjects during HA exercise?

Quizplus · Accepted Answer

11ecba2d_0fad_dd8d_a3bf_9549d091a768_MD0008_00 Thermoregulation, the maintenance of body temperature within the normal physiological range, is a major homeostatic function of skin. Thermoregulatory centers in the hypothalamus monitor body temperature by processing information from internal and surface (skin) thermoreceptors. When there is a significant change in body temperature, the hypothalamic center coordinates the physiological responses necessary to reset the temperature back within the normal range. When body temperature is above normal (as would occur during HA exercise), the following processes cool the body (ie, decrease body temperature): Vasodilation (widening) of skin arterioles increases blood flow to skin capillaries and maximizes heat loss through the skin. This occurs because blood, which is warmed in the body core, transfers heat to the environment when it passes through skin capillaries. Vasodilation occurs when the smooth muscle surrounding the blood vessels relaxes (Choice B). Sweat, a hypotonic solution, is secreted onto the skin surface by sweat (sudoriferous) glands. Heat loss and subsequent cooling occur due to the evaporation of the water in the sweat, an endothermic process that absorbs heat from the body. When body temperature is below normal, the following processes warm the body (ie, increase body temperature): Vasoconstriction (narrowing) of skin arterioles minimizes heat loss by diverting warm blood away from skin capillaries and toward blood vessels in the interior of the body. Vasoconstriction occurs when the smooth muscle surrounding the blood vessels contracts (Choice A). Shivering generates heat through rhythmic involuntary contractions of skeletal muscle. (Choices C and D) In this scenario, the controls are exercising in a hot environment, so the arrector pili muscles (attached to hair follicles in the skin) would not contract. However, in cold environments, sympathetic signaling causes contraction of the arrector pili muscles, which causes piloerection (hairs standing upright). Piloerection, which impedes heat loss by trapping heat near the skin surface, is not an efficient means of heat retention in humans due to insufficient body hair. Educational objective: One major function of the skin is thermoregulation. Body temperature can be increased by vasoconstriction of skin arterioles, shivering, and (in hairier animals) piloerection. Body temperature can be decreased by vasodilation of skin arterioles and sweating.