VITAL SIGNS

VITAL SIGNS Temperature 1. Temperature is the degree of hotness of coldness of a body or environment or a measure of warmth or coldness of an object or substance with reference to some standard value. 2. Skin is warm in pyrexial conditions e.g. hyperthyroidism and cold in peripheral circulatory failure and myxedema. 3. Sites - mouth, axilla, groin and the rectum with the temperature of the mouth and rectum being ½ºC higher than that of the groin and axilla. 4. A central core is maintained at 37ºC but the temperature of the periphery varies according to environmental temperature. 5. Normal temperature range is 36.6 - 37.2 ºc in the morning and 37.2 ºc (overall). 6. In children: 36.5 - 37.5 ºc TEMPERATURE REGULATION  Body temperature (BT) consists of the core temperature and skin temperature.  Core temperature is the temperature of the deep tissues which is almost constant within a + 0.6ºC daily variation except in cases of febrile illness.  The normal core temperature range is 36.6 – 37.2ºC.  Skin temperature rises and falls with variation in the temperature of the surroundings.  BT increases during exercise and varies with extremes of temperature of surroundings.  Individuals tolerate wide ranges of environmental temperatures because the inner temperature of our bodies is maintained close to 37ºC by a number of temperature regulating mechanisms such as behavioural and reflex responses.  If the mechanisms are inadequate for the circumstances we encounter or are disordered the body temperature cannot be maintained and hyperthermia or hypothermia results. Temperature HOMEOSTASIS 1. TEMPERATURE Set point 2. Set at 37ºC under influence of the thermoregulatory centre in the hypothalamus. 3. Preset temperature is regulated by neuropetides acting on this site. 4. Thermoregulatory centre measures the temperature of blood which flows through it and it any change is detected appropriate action is taken. 2. Homeostasis  Core temperature represents the balance between the gains and heat losses by the body (controlled by balancing heat production and heat loss).  The range of temperature over which neither heat production nor increased evaporative loss is used to maintain temperature is called the thermoneutral zone.  When heat production is greater than heat loss, the heat builds up in the body rising the body temperature and when heat loss is greater than production, body heat and temperature decrease.  Gains and losses are regulated by neural and hormonal control mechanisms.  Homeostasis of body temperature is important because healthy survival depends on biochemical reactions driven by enzymes (temperature dependent)  Regulated through nervous feedback mechanism  Key players in temperature homeostasis include i. Skin and its blood vessels ii. Sweat glands iii. Hypothalamus – contains the regulatory centres  Links several parts of the nervous system including the autonomic nervous system (ANS), pituitary gland, limbic system and brain stem (parts controlling muscle contraction)  Connections enable the hypothalamus to coordinate all autonomic, hormonal and behavioural responses. iv. Thermoreceptors  Situated in hypothalamus, skin, respiratory and gastro-intestinal tracts  Central receptors (in hypothalamus) monitor core temperature ·  Peripheral receptors monitor surface temperature and give advance warning of any threat to body temperature from the environment  A change in core temperature activates sweating or shivering whereas alterations in skin temperature provoke changes in cutenous blood flow. v. Nerves vi. Hormones – TRH, TSH 3. Regulation  Temperature receptors in the hypothalamus detect changes in the body’s internal temperature with the help of temperature receptors (cold and warm) in the skin and deep body tissues such as spinal cord, abdominal viscera and around great veins in the upper abdomen and thorax.  Receptors detect cold rather than warmth as they are destined to prevent hypothermia.  Signals from the periphery and deep organs reach the anterior hypothalamus (central temperature signals) where they are detected and then transmitted to the posterior hypothalamus to combine with signals from other areas of the body (peripheral temperature signals).  Combined signal then controls the heat-producing and conserving reactions of the body.  Hypothalamus coordinates effector mechanisms that maintain core temperature close to 37ºC by adjusting heat gains and losses in response to signals from sensory receptors monitoring the core and surface temperature. Effector Mechanisms  Hot Environment - can cause hyperthermia heat balance is maintained by reducing heat gain through minimising activity and shading the body (choice of clothes and shelter) and simultaneously increasing heat loss by cutenous vasodilatation, sweating and choosing situation that lead to surface cooling e.g. cold shower, fan.  Cold Environment - can cause hypothermia is heat balance is attained by increasing production of heat and minimising losses. Heat production can be increased by shivering, stimulating metabolism (non-shivering thermogenesis), increasing appetite and physical activity. Simultaneously heat losses are reduced by cutenous vasoconstriction (increases insulation of the core), putting on clothes (increased insulation of the body) and choosing warmer places to be. 1. Temperature-decreasing Mechanisms 2. Vasodilatation is caused by inhibition of the sympathetic centres in the posterior hypothalamus which usually cause vasoconstriction. 3. Sweating - an additional 1ºC increase in body temperature causes enough sweating to remove 10 times the basal rate of body heat production.