acutephysiologicalresponsestoheatstress

acutephysiologicalresponsestoheatstress内容摘要：

ry (.,tidal) volume. Effector Mechanisms of Acute Heat Exposure • Vasodilation of Cutaneous Vasculature (Increased Skin Blood Flow) • Increased Sweat Rate Vasodilation of Cutaneous Vasculature (Increased Skin Blood Flow) • There is threshold above which skin blood flow will increase. Skin blood flow carries heat by convection from the deep body tissues to the skin, which may lead to sensible and/or insensible heat loss. Vasodilation of Cutaneous Vasculature (Increased Skin Blood Flow) • Skin blood flow is dependent on both core temperature and skin temperature as: Increased skin blood flow is proportional to core temperature at any given skin temperature. Increased skin temperature will decrease the core temperature threshold. Heat Transfer by Skin Blood Flow • Dependent on the rate of blood flow and on the differences in temperature between arterial blood leaving the core on its way to the skin and venous blood returning to the core from the skin. Increases in the rate of blood flow, conduction of tissues, and the difference between core and skin temperatures will increase the heat transfer. • As ambient temperature increases, there is an increased dependence on insensible (evaporative) heat loss mechanisms and a decreased dependence on sensible (convection and radiation) heat loss mechanisms to minimize exerciseinduced increases in core temperature. • Evaporative heat loss is dependent on skin blood flow (provides latent heat for the evaporation of sweat) and on secretion of perspiration from the sweat glands. Types of Sweat Glands 1. Apocrine glands nervous or emotional sweat due to neurochemical stimuli。 secretion is a watery substance that contains lipids, trace of color, and odor。 most monly found on the palms of the hands, soles of the feet, arm pits, groin area, face, and upper lip. Types of Sweat Glands 2. Eccrine glands respond to thermal stress by secreting a watery substance which contains electrolytes and is generally colorless and odorless。 there are to 4 million eccrine glands and are most numerous on the sole of the feet and least numerous on the back, although the back eccrine glands are the first to respond to increases in core temperature. Sweat Rate • People who sweat more (1) have larger sweat glands, (2) have a greater amount of sweating per gland, (3) have a higher sweating rate per unit of tubular length or unit volume of secretory coil, (4) have a reduced hidromeiotic effect, and (5) the sweat glands have a greater cholinergic (AcH) sensitivity. • Hidromeiotic Effect increased skin wettedness decreases sweating. Sweat Rate • Sweat rate is dependent on both core temperature and skin temperature as: Increased sweat rate is proportional to core temperature at any given skin temperature. Increased skin temperature will decrease the core temperature threshold. • Generally, the heat dissipating responses are sufficient to。