Body Heat and Temperature Regulation PDF

Body Heat and Temperature Regulation ANSC 101 Learning Objectives To familiarize students with how the body regulate its temperature, and relate it to animal production To give students a background on how the body responds to heat and cold To know the normal values and r...

Body Heat and Temperature Regulation ANSC 101 Learning Objectives To familiarize students with how the body regulate its temperature, and relate it to animal production To give students a background on how the body responds to heat and cold To know the normal values and relate it to abnormal conditions like hypothermia and hyperthermia Chapter Outline Body Temperature Hibernation Gradients of Temperature Awakening from Hibernation Diurnal Temperature Brown Fat vs. White Fat Physiologic Response to Heat Hypothermia and Hyperthermia Circulatory Adjustments Hypothermia Evaporative Heat Loss Fever Responses to Extreme Heat Heat Stroke and Impaired Evaporation Physiologic Response to Cold Reduction of Heat Loss Increase of Heat Production Body Temperature Chemical reactions of the body and therefore the bodily functions rely on body temperature Elevated temperature = accelerated reactions Lowered temperature = depressed reactions Mammals and birds maintain a constant level of body temperature regardless of the ambient temperature. Therefore classified as, Homeotherms (Greek, “Homo” – same, “therm” – heat) or warm blooded animals. Retrieved: ©Cold- blooded Vs Warm- blooded animals - Definition, Examples list and Differences (laboratoryinfo.com) Body Temperature Poikilotherm (Greek, poikilos – various, therm – heat) animals have a body temperature that varies with the temperature of the environment. Example of this animals include: some snakes, frogs, turtles, lizards, iguana, crocodile, grasshopper, lobster, butterflies, etc. Retrieved: ©Cold- blooded Vs Warm- blooded animals - Definition, Examples list and Differences (laboratoryinfo.com)  Body Temperature The temperature were obtained by rectal insertion of a thermometer in resting animals. Source: Andersson, B.E. and Jonasson, H. (1993) Temperature regulation and environmental physiology. In: Dukes’ Physiology of Domestic Animals, 11th edn (eds M.J. Swenson and W.O. Reece). Cornell University Press, Ithaca, NY.  Body Temperature Gradients of Temperature Different parts of the body can differ in temperature because of differences in metabolic rate, blood flow, or distance from the surface. The liver and brain for example has a higher temperature than blood, and are therefore cooled by blood circulation. The core temperature is higher than the temperature in the limbs or even higher than the rectal temperature. Rectal temperature represents a true steady state of temperature.  Body Temperature Diurnal Temperature Variations in temperature related to the time of day Animals that are active during the day and sleep at night have body temperature that are lower in the morning than in the afternoon. Opposite is true for nocturnal (night active) animals. Heat Is produced constantly in the body as a result of metabolism. If there were no provisions for losing heat, temperature of the body may become intolerable Two principal means of losing heat are: Radiation Conduction Convection Evaporation of water from the skin and respiratory passageways Mechanisms of Heat Loss Retreived: Identifying and Managing Accidental Hypothermia - JEMS: EMS, Emergency Medical Services - Training, Paramedic, EMT News Mechanisms of Heat Loss Retrieved: 3. Heat Transfer from the Human Body - Mypdh.engineer  Physiologic Response to Heat Circulatory adjustments In as much as circulatory blood is a distributor of body heat, heat can be lost from the blood if blood is brought to the skin surface and exposed to a gradient for loss to the environment. Retrieved: Local or Subdermal Plexus Flaps | Veterian Key  Physiologic Response to Heat Circulatory adjustments The amount of blood circulating to the skin is controlled by sympathetic vasoconstrictor fibers to the blood vessels. Constriction of Thermosensitive blood vessels and An increase in tone Conserve heat cells in the rostral diversion of blood hypothalamus from the surface respond to warming by Lets more activating A decrease in physiologic and blood go to Heat loss tone behavioral heat the surface loss mechanism The temperature of the blood circulated to the brain acts as the stimulus in decreasing tone to improve heat loss  Physiologic Response to Heat Evaporative heat loss Evaporation of water results in cooling Loss of water by evaporation is referred to as insensible water loss; this includes water lost from the skin surfaces and water lost in the heated exhaled air. 25% of the heat produced by an animal at rest is lost through insensible means. Evaporative heat loss is increased by sweating (varies in animals) and panting  Sweat glands There are two types: 1. apocrine and 2. eccrine Eccrine sweat glands are those typically found in humans but are sparse among domesticated animals. They open directly onto the skin’s surface. Apocrine sweat glands open into the hair follicle, leading to the surface of the skin. Horses, cattle, sheep, dogs and cats have apocrine sweat glands disseminated over the body surface.  Sweat glands Apocrine sweat is a proteinaceous, white, odorless, milky fluid that is formed slowly and continuously. On the skin surface, it mixes with sebum from the sebaceous glands to form a protective emulsion. Retreived:(1) (PDF) SKIN COVER SYSTEM AND HISTOLOGICAL STUDIES CONDUCTED ON TURKISH LOCAL SHEEP BREEDS (researchgate.net)  Panting Dissipate heat load because of greater amounts of air are made to go over moist surfaces. Most effective in the Canidae family, but it is also observed in other domestic animals Panting is an increase in dead space ventilation without change in the respiratory alveolar ventilation. A decreased tidal volume is also associated with this, to prevent hyperventilation.  Panting In cattle, panting is accompanied by an increase in salivation, and the salivary secretion promotes cooling by evaporation. Salivary secretion by evaporation can results in metabolic acidosis because of the loss of bicarbonate and phosphate buffers. Increase in sweating and panting are brought about by increased in blood temperature, subsequent adjustments by the hypothalamus, and reflexes produced by local heating of the skin.  Physiologic Response to Heat Responses to Extreme Heat Different animal species differ in their ability to withstand heat. As humidity increases, evaporation from insensible losses is reduced and less cooling occurs. Of all domestic animals, cattle and sheep are the most tolerant, they can withstand temperatures as high as 43 C with humidity above 65% Physiologic Response to Heat Cold Activates body heating mechanisms, just as excess heat activates body cooling mechanisms. With excess cooling, heat is either conserved by reducing heat loss or is generated to compensate for that which is lost. The physiologic responses to cold are activated by blood temperature and local reflexes, as are the responses to heat.  Physiologic Response to Cold Reduction of Heat Loss e.g. Animals curling down when they lie down (Behavioral Response) This is done to reduce the surface area exposed to the cold. Piloerection (goosesbumps) occurs to increase the insulation value of their hair and fur. With sustained exposure to cold, the hair coat thickens and the amount of subcutaneous fat increases. Opposite of vasodilation, peripheral vessels are constricted by an increase in vasoconstrictor tone. Physiologic Response to Cold Reduction of Heat Loss Retrieved: Piloerection - Definition of Piloerection (healthbenefit stimes.com)  Physiologic Response to Cold Reduction of Heat Loss Blood returning in the veins from the colder legs is close to the warmer blood in the arteries going to the legs. Because of temperature differences, heat is transferred from the arteries to the veins. This decreases the gradient for heat loss from the arterial blood to the environment. This is called the countercurrent system. Physiologic Response to Cold Reduction of Heat Loss  Physiologic Response to Cold Increase of Heat Production When the ability to reduce heat loss is not adequate to maintain normal body temperature, heat must be produced. Critical temperature – the temperature to which body temperature decreases before heat generation Shivering – is one means by which heat is generated for withstanding cold. It is a generalized rhythmic contraction of muscles. 30 – 50% of the energy of the muscles is converted to heat.  Physiologic Response to Cold Increase of Heat Production Other methods include: Epinephrine and Norepinephrine are both released in increased amounts in the cold. Brown fat vs White fat Brown fat is found in newborn mammals and hibernating animals Thyroid hormone potentiates the effect of Epinephrine and Norepinephrine.  Hypothermia and Hyperthermia Hypothermia Reduction of the deep body temperature below normal in non-hibernating homeotherms. Normally occurs as a result of prolonged exposure to cold, coupled with an inability of the heat-conserving and heat- generating mechanisms Tolerance to lowered body temperature varies among species. e.g. in dogs death can occur at 25 degrees Celsius  Hypothermia and Hyperthermia Hypothermia Hypothermia can readily occur during central nervous system anesthesia because the hypothalamic response to cold blood is depressed. Anesthesia can also suppress adrenocortical secretion During procedures, external heat sources are often fitted to surgical tables for the maintenance of the body temperature.  Hypothermia and Hyperthermia Hyperthermia Is an elevation of deep body temperature that is brought on by microorganism-caused disease. Hyperthermia is usually beneficial because immunologic mechanisms are accelerated and the high temperature induced is detrimental to the microorganisms, but it can be damaging if allowed to go too high. Usually around 41 C During fever, the set point of the hypothalamus is elevated. Shivering and a feeling of coolness are characteristics of beginning fever.  Hypothermia and Hyperthermia Heat Stroke and Impaired Evaporation Hyperthermia or fever can be associated with heat stroke. Heat production exceeds the evaporative capacity of the environment and occurs when humidity is high. This can also occur when evaporative mechanism is impaired as a result of loss of body fluid or reduced blood volume. Review Questions 1. What part of the brain has a temperature regulating center? A. Medulla B. Thalamus C. Hypothalamus D. Cerebral Cortex 2. Variations in temperature related to the time of day are known as: A. Diurnal Temperatures B. Core Temperatures C. Poikilotherms D. Ambient Temperatures Review Questions 1. Nocturnal animals have body temperatures that are lower in the morning than in the afternoon A. True B. False 2. Which sweat gland type predominates among the domestic animals? A. Eccrine B. Apocrine Review Questions 1. Which one of the ff. animals has the greatest heat loss from sweating? A. Sheep B. Cats C. Dogs D. Horses E. Pigs 2. Increased blood flow to the skin would increase heat loss? A. True B. False The End Thanks for listening Suggested Readings: Andersson BE, Johansson H. Temperature regulation and environmental physiology. In: Swenson MJ, Reece WO, eds. Dukes’ Physiology of Domestic Animals. 11th Ed. Ithaca, NY: Cornell University Press, 1993. Folk GE, Jr, Larson A, Folk MA. Physiology of hibernating bears. Proceedings of the third international conference on bear research and management, June 1974. In: Pelton MR, Lentfer JW, Folk, GE, eds. Bears----Their Biology and Management. Morges, Switzerland: International Union for Conservation of Nature and Natural Resources, 1976:373-380.