LECTURE 8 Body Heat and Temperature Regulation Homeotherm- warm blooded (mammals and birds) Poikilotherm- cold blooded (reptiles and amphibians) I. Body Temperature (Reece Table 11.1 p 335) A. Gradients of Temperature 1. different temperatures in different body tissues B. Diurnal Temperature 1. time of day a. animals that are active during the day tend to have lower temps in the morning than in the afternoon b. nocurnal animals have higher temps in afternoon than in the morning 2. heat storage-camel (Figure 1 Reece p 335) a. water conservation technique heat increases during day and is dissipated at night II. Physiologic Responses to Heat and Cold A. Responses to Heat 1. Circulatory Adjustments a. blood vessels dilate b. increased surface area increases heat loss http://www.ttuhsc.edu/som/obgyn/faculty/prien/lecture%20notes/asft2401/bodytemp.htm (1 of 6) [6/19/2008 3:25:59 PM]
c. controlled by the brain (hypothalamus) temperature 2. Evaporative Heat Loss a. evaporation = cooling b. defined as insensible water loss 1. includes water lost from: c. sweating and panting a. skin surface (sweat) b. through exhaled air 1. heat loss due to sweating varies wide between species d. eccrine sweat glands a. most effect in humans 1. most common in humans 2. in dogs and cats found on the footpad for lubrication e. apocrine sweat gland 1. found in most domestic species 2. proteinaceous in nature in the dog 3. usefulness in heat regulation (thermoregulatory function) a. horse - most b. cattle c. sheep http://www.ttuhsc.edu/som/obgyn/faculty/prien/lecture%20notes/asft2401/bodytemp.htm (2 of 6) [6/19/2008 3:25:59 PM]
d. dog e. cat f. swine - least B. Responses to Cold 1. Reduction of Heat Loss a. Is activated by blood temperature b. reduced exposed surface area c. piloerection of hair d. blood supply 1. vasoconstriction of peripheral vessels 2. countercurrent blood supply of legs 2. Increase of Heat Production a. critical temperature temperature which triggers heat generation b. shivering 75% of muscle movement "lost" as heat c. epinephrine and norepinephrine- brown fat metabolism d. thyroid hormone- BMR C. Responses to Extreme Environmental Temperatures 1.combination of heat and humidity 2. critical environments a. pig - 95 F / 65% RH http://www.ttuhsc.edu/som/obgyn/faculty/prien/lecture%20notes/asft2401/bodytemp.htm (3 of 6) [6/19/2008 3:25:59 PM]
b. birds - 100 F/ 75% RH, 113 rectal c. cat- 104 F/ 65% RH d. dog- 106 F rectal temp e. cattle and sheep - 109 F/ 65% RH f. human- varies with physical condition III. Hibernation the act of resting in a dormant state in a protected burrow A. Characteristics of Hibernation 1. only in warm blooded animals 2. autonomous- controlled solely by the animal itself 3. radical- involving overt changes in physiology as well as cellular and subcellular changes 4. physiologic function continue at a reduced rate 5. body temperature is lowered to survival level B. Awakening from Hibernation 1. required periodic urination 2. self protective mechanism to prevent freezing C. Brown Fat verses White Fat 1. cells have faster metabolic rate a. contains more mitochondria b. high oxygen consumption rate c. high oxygen consumption and MR lead to heat to warm body http://www.ttuhsc.edu/som/obgyn/faculty/prien/lecture%20notes/asft2401/bodytemp.htm (4 of 6) [6/19/2008 3:25:59 PM]
2. brown fat also found in new born IV. Hypothermia and Hyperthermia A. Hypothermia- pathologic reduction in core body temperature (70-80 F) 1. prolonged exposure to cold air temperature a. temperature is specie dependent 2. exposure to low water temperature a. faster than air exposure due heat conductivity of water b. occurs at higher water temperatures 3. during anesthesia a. loss of control of hypothalamus B. Hyperthermia- pathologic elevation in core body temperature 1. Fever a.elevation of body temperature in response to a bacterial or viral infection b. high temperature improves immune response c. higher temperatures is also directly detrimental to infecting organism d. due to the set point of the hypothalamus being altered 1. body sense the temperature of the blood is too low. 2. generally self limiting (106 F) 2. Heat Stroke and Impaired Evaporation a. heat load exceeds cooling effects of evaporation http://www.ttuhsc.edu/som/obgyn/faculty/prien/lecture%20notes/asft2401/bodytemp.htm (5 of 6) [6/19/2008 3:25:59 PM]
3. Hyperthermia is also associated with times of extreme fluid loss. Back to S.D. Prien Last Modified: 01/14/99 9:36PM 1999, Sam Prien & Department of Animal Science & Food Technology Texas Tech University Questions or comments about this page? Send to Dr. Sam Prien: obgsdp@ttuhsc.edu http://www.ttuhsc.edu/som/obgyn/faculty/prien/lecture%20notes/asft2401/bodytemp.htm (6 of 6) [6/19/2008 3:25:59 PM]