Temperature Regulation

Convection : Convection is the process of a fluid (water or air) flowing by the skin and carrying away body heat. When the body is immersed in water and the body is moving (treading water), nearly all heat is lost by convection. Heat is transferred by conduction between objects

. A man is sailing in the Caribbean and falls from his yacht. The boat continues to sail forward and he cannot get back onboard. Water temperature is 26.7°C (80°F). He keeps swimming and treading water trying to keep up with the boat, and after 6 hours in the water, he begins to show signs of hypothermia. transfer of heat to the environment by a moving fluid (air or water). Convective heat loss is proportional to the temperature gradient & velocity of the liquid What is this individual's primary mode of heat loss? A. Conduction B. Convection C. Radiation D. Respiration E. Evaporation

Moderate Hypothermia

28-32C A-Mild Hypothermia B-Malignant hypothermia C-Moderate hypothermia D-Severe Hypothermia

Mild Hypothermia

32-35C A-Mild Hypothermia B-Malignant hypothermia C-Moderate hypothermia D-Severe Hypothermia

Severe Hypothermia

<28 A-Mild Hypothermia B-Malignant hypothermia C-Moderate hypothermia D-Severe Hypothermia

Mild hypothermia This patient has mild hypothermia characterized by body temperature in the 32-35°C range, shivering, tachycardia, peripheral vasoconstriction, increased blood pressure and agitated state. Immersion in cold water is the most common cause of accidental hypothermia. The convective heat transfer coefficient in water is 100 times that of air - this means that the body can lose heat to water at a rate 100x that to air such that body temperature when immersed in water can fall very quickly. For this reason, if immersed in cold water it is best to stay as still as possible in order to reduce convective heat loss. Moderate hypothermia is characterized by body temperature 28-32°C, bradycardia, decreased respiration rate, eventually leading to unconsciousness while maintaining pupillary reflexes. Severe hypothermia is characterized by body temperature <28°C, coma, lack of pupillary reflexes and asystole. Frostbite, cold injury at the extremities, can occur with prolonged cold exposure. Artificial hypothermia is induced in controlled situations (e.g. prior to surgery).

A 15-year old girl falls through the ice while skating on an outdoor pond. She is removed from the water within 1 minute, but dry clothing is not available. The emergency medical team arrive after 20 minutes. At this point, the girl is shivering uncontrollably and she is very agitated. Her skin is pale and cold to touch. Her heart rate is 80 bpm, blood pressure is 130/100 mmHg and ear (tympanic) temperature is 34°C. Given this presentation, what is the most likely diagnosis? A. Mild hypothermia B. Moderate hypothermia C. Severe hypothermia D. Frostbite E. Artificial hypothermia F. Patient presentation is within normal limits

Radiation : Every object emits energy in the form of electromagnetic radiation. The rate increases with temperature. Radiation is the principal way a resting human body loses heat in still air that is cooler than the skin temperature. The mean skin temperature of a healthy individual (calculated as a weighted average of different skin areas) is around 33°C (91.4°F), so this individual loses heat to the environment. Radiation is the primary mechanism of heat loss at rest. The transfer of energy between two objects in direct contact is called conduction, such as heat loss from sitting on a cold chair (or bench). There is some conduction from this individual's skin t the air, but more heat is lost by convection. Convection is the process of a fluid (water or air) carrying away the heat that is conducted to the surface of a body. There is always some convection in air because warm air rises above cooler air, but if there is no wind, as in this case, less heat is lost by convection than radiation. The body can lose small amounts of heat through respiration. Evaporation occurs during sweating as water evaporates from the skin. This becomes a major mechanism of heat loss during exercise and at high temperatures, but not at rest in moderate/low ambient temperatures.

A 25-year-old male sits on a park bench studying for his college exams. He is wearing only shorts. It is 21°C (70°F) with no breeze. While sitting in the shade, the majority of body heat will be lost from this individual via which of the following mechanisms that is Heat transfer by electromagnetic waves between solid objects. ? A. Conduction B. Convection C. Radiation D. Respiration E. Evaporation

Sleeping in cold weather

A 28-year-old medical student wakes up each day at 6am and goes to bed each night at 11pm. She has a normal circadian rhythm, typically does not drink alcohol and eats a balanced diet. She does not exercise but meditates daily using the Headspace app and she loves to sleep with the fan on. Which of the following changes to her routine would produce the greatest decrease in ambient temperature (Ta)? A. Drinking an alcoholic beverage B. Sleeping in cold weather C. Eating a carbohydrate-rich meal D. Fasting for 12 hours E. Jogging for 30 minutes

Jogging for 30 minutes : Exercise increases the metabolic rate up to 15 times the basal rate, which directly increases body temperature more than any other option. Alcohol can make one feel warmer because blood vessels dilate and move warm blood to the surface f the body, but over time this actually lowers the core body temperature as heat is dissipated. Drinking a hot beverage can increase body temperature minimally for a short period of time, but it will not exceed the heat produced by exercise. The process of digesting, absorbing and processing nutrients generates heat by increasing metabolic rate by 10-20%. This food induced thermogenesis is greatest after eating a high-protein meal and less after eating carbohydrates and lipids. Fasting reduces metabolism, which reduces heat production, and lowers body temperature.

A 28-year-old medical student wakes up each day at 6am and goes to bed each night at 11pm. She has a normal circadian rhythm, typically does not drink alcohol and eats a balanced diet. She does not exercise but meditates daily using the Headspace app. Which of the following changes to her routine would produce the greatest increase in peak body temperature? A. Drinking an alcoholic beverage B. Drinking hot coffee C. Eating a carbohydrate-rich meal D. Fasting for 12 hours E. Jogging for 30 minutes

5 pm Body temperature normally fluctuates over the day, as controlled by a person's circadian rhythm and activity, with the lowest levels around 4-6am and the highest levels around 4-6pm (for a person who sleeps at night and stays awake during the day).

A 30-year old patient with obsessive-compulsive disorder and no other health problems wakes each day at 7am and goes to bed each night at 11pm. He has a normal circadian rhythm, sleeps soundly and does not exercise. Assuming his normal routine, at which of the following times of day is his body temperture most likely highest? A. 5 am B. 7 am C. Noon D. 5 pm E. 11 pm

In the anus Rectal temperature (in the anus) is the most accurate, but is not used as often as the others due to inconvenience. Tympanic temperature (in the ear) is frequently used in clinical settings. Oral temperature (in the mouth) is on average 0.5°C lower than rectal temperature. Axillary temperature (under the arm) is typically lower than oral and can be variable. Temperature of the forehead will give an indication as to skin temperature, which is not a good estimate of core body temperature

A 4-year old girl is having a wellness visit before starting kindergarten. The nurse starts the appointment by measuring the temperature. Which of the following locations would provide the most accurate measurement of core body temperature? A. In the anus B. In the ear C. In the mouth D. Under the arm E. On the forehead

Beta-adrenergic Newborn babies and infants experience a greater degree of heat loss than adults because they cannot shiver to maintain body temperature. They rely on non-shivering thermogenesis, which is facilitated by a greater amount of brown adipose tissue. When cold-stressed, norepinephrine binds to - adrenergic receptors in brown fat stimulating heat production.

A 6-month old baby girl has tossed her blanket off while sleeping. The room temperature is 20°C (68°F). When checked by her mother, the baby's skin is cool to the touch. Which of the following target tissue receptors are currently activated in the baby to directly increase heat production due to brown adipose tissue? A. Alpha-adrenergic B. Beta-adrenergic C. Muscarinic acetylcholine D. Nicotinic acetylcholine

Conduction Conduction is the transfer of heat between objects which are in direct contact. In this example, the skin is in direct contact with the non-moving water. Since the water is at a lower temperature than the skin surface, there will be net conductive heat loss / transfer from skin to the water. Convection is the transfer of heat resulting from the movement of a liquid or a gas - since the water is not moving in this example, convective heat loss from the skin will be minimal. Radiation is heat transfer in the form of electromagnetic waves between solid objects not in direct contact. Evaporation of fluid from the surface if the skin requires a water vapor pressure gradient, with evaporation rate becoming negligible at ambient humidity > 75%. Since water is effectively 100% humid, evaporative heat loss will be negligible in this example.

An individual is sitting still in a bath tub filled with water. His body (with exception of his head and neck) is under the water. The water temperature is lower than his body surface temperature. Assuming there is absolutely no movement of the water surrounding his body, by which mechanism will the heat most likely be transferred from his skin to the water which is Transfer of heat between objects which are in direct contact (Ex. Chair). Requires a temperature gradient ? A. Conduction B. Convection C. Radiation D. Evaporation

core body temperature

An naked individual at rest in a room exposed to ambient temperature of 23C to 35C in dry air can maintain almost _____________ despite wide changes in Ta & Ts A- Increase in temp B-Lowest and highest temp C-Constant core body temperature D- Decrease in temp

An increase in cutaneous blood flow Remember that the body is always producing heat and therefore must continuously dissipate heat. It achieves this by increasing blood flow to the skin (increased cutaneous blood flow), from where heat can be transferred to the environment. All of the other options in this answer will effectively increase heat storage and increase Tb.

At an ambient temperature (Ta) of 32°C (89.6°F), core body temperature (Tb) is most likely maintained by which of the following mechanisms? A. A decrease in heat conduction from core to skin B. A decrease in sweating C. An increase in cutaneous blood flow D. An increase in non-shivering thermogenesis E. An increase in skeletal muscle heat production

Age: declines with age, Sex: 5-10% increase in men, Hormones: thyroid and catecholamines increase cellular MR, Digestive States

Basal Metabolic Rate (BMR) is the minimum level of energy required to exist accounts for 50-70% of daily energy expenditure, 70 kcal/hr = 1 C/hr. what is BMR is influenced by? A-Age: declines with age, Sex: 5-10% increase in women , Hormones: thyroid and catecholamines increase cellular BMR, Digestive States B-Age: increase with age, Sex: 5-10% increase in men, Hormones: thyroid and catecholamines increase cellular MR, Digestive States C-Age: increase with age, Sex: 50% increase in men, Hormones: thyroid and catecholamines increase cellular MR, Digestive States D-Age: declines with age, Sex: 5-10% increase in men, Hormones: thyroid and catecholamines increase cellular MR, Digestive States

hypothalamic control located in the anterior hypothalamus. It determines the temperature set point

Body heat is produced by muscular exercise, digestion of food and all of the vital processes that contribute to basal metabolic rate. Body is lost by radiation, conduction, convection and evaporation of water Thermoregulation is primarily under : A-hypothalamic control located in the Posterior hypothalamus. It determines the temperature set point B-hypothalamic control located in the anterior hypothalamus. It determines the temperature set point C-hyperthalamic control located in the anterior hypothalamus. It determines the temperature set point D-hypothalamic control located in the posterior rami of spinal cord. It determines the temperature set point

Heat loss

Body temperature is constant when heat gain = heat loss. If gain > loss heat storage goes up (Tb increases) and If gain is < loss heat storage goes down (Tb decreases) . what is due to Evaporation, Radiation, Conduction, Convection? A- Heat loss B- Heat gain

Heat gain

Body temperature is constant when heat gain = heat loss. If gain > loss heat storage goes up (Tb increases) and If gain is < loss heat storage goes down (Tb decreases) . what is due to Metabolism Muscular activity, Food intake, Brown adipose tissue and Environment? A- Heat loss B- Heat gain

convection & conduction

Heat produced in the body enters the blood & is conveyed to the body surface from where heat is dissipated/lost. Heat transfer occurs from area of higher temperature to area of lower temperature In the heat transfer between the core & environment, for heat loss, surface temp must be lower than at the core In Heat transfer from core to the skin, Heat is transferred to the skin by : A-Conduction B-convection & conduction C- Radiation D-Evaporation

Conduction

Heat produced in the body enters the blood & is conveyed to the body surface from where heat is dissipated/lost. Heat transfer occurs from area of higher temperature to area of lower temperature In the heat transfer between the core & environment, for heat loss, surface temp must be lower than at the core In Heat transfer from core to the skin, Rate of heat transfer by _______________ across the subcutaneous fat is relatively constant A-Conduction B-convection & conduction C- Radiation D-Evaporation E-Convection

Convection

Heat produced in the body enters the blood & is conveyed to the body surface from where heat is dissipated/lost. Heat transfer occurs from area of higher temperature to area of lower temperature In the heat transfer between the core & environment, for heat loss, surface temp must be lower than at the core Rate of heat transfer by ________ depends on cutaneous blood flow A-Conduction B-convection & conduction C- Radiation D-Evaporation E-Convection

Catabolism

Heat storage is the Energy required to change the temperature of 1 kg of a substance by 1C and is the rate which the body temperature rises or falls as its heat content increases or decreases. 1Kcal of heat energy is required to increase temperature of 1 Kg by 1C. What liberates energy from organic molecules and the energy is liberates is used to do work OR released as heat A- Anabolism B- Catabolism

Heat collapse (hyperthermia)

Hyperthermia is Elevation of Tb > normal Tset range due to overwhelming of thermoregulatory mechanisms. Hyperthermia Environmental conditions are prolonged exposure to heat (high Ta), high ambient humidity, physical exertion. -Inability to maintain CO leads to transient collapse. -Lie down and take a moment A-Heat stroke (hyperthermia) B-Mild hyperthermia C-Malignant hyperthermia D-Heat collapse (hyperthermia)

Heat stroke (hyperthermia)

Hyperthermia is Elevation of Tb > normal Tset range due to overwhelming of thermoregulatory mechanisms. Hyperthermia Environmental conditions are prolonged exposure to heat (high Ta), high ambient humidity, physical exertion. This occurs above 40C from regular body temp which can lead to Thermoregulatory failure (Sweat ceases), CND dysfunction (headache, confusion, coma, seizure, come) and Death A-Heat stroke (hyperthermia) B-Mild hyperthermia C-Malignant hyperthermia D-Heat collapse (hyperthermia)

Increase in core body temp

In women, an additional monthly cycle of temperature variation is characterized by a ____________ in the immediate post ovulation period. _ that is caused by increase 0.5C in the post-ovulatory period owing to the action of the hormone progesterone which is secreted from the ovarian corpus luteum A- Increase in core body temp B-Lowest and highest temp C-Constant core body temperature D- Decrease in temp

Shivering Pyrogenic pathogens stimulate release interleukin-1 and other cytokines from immune cells which act to increase production of prostaglandins, ultimately raising the hypothalamic temperature set-point. The hypothalamus now "thinks" that the body temperature is too low (because the core body temperature is lower than the new set-point temperature) and initiates mechanisms for generating heat - shivering, vasoconstriction, and shunting blood away from the venous plexus near the skin surface.

Pyrogenic (fever-inducing) pathogens cause which of the following effects that is asynchronous involuntary skeletal muscle contraction such that. - This increases muscle tone and tremors - increases rate of heat production 5x BMR ? A. Decreased production of interleukin-1 (IL-1) B. Decreased hypothalamic temperature set point (Tset) C. Shivering D. Vasodilation of blood vessels in the skin

Rectal > Ear > oral > axillary

Rectal temp (Core body temp) is 0.5C higher compared to oral what are the Temperature of body parts in order? A-axillary > Ear > oral > Rectal B-oral > Ear > oral > Rectal C-Ear > Ear > oral > Rectal D-Rectal > Ear > oral > axillary

Heat dissipation at high Ta (hot)

Regulation of skin temperature is controlled by the ANS. What results in decreases sympathetic nervous activity such that Vasodilation ---> Heat loss? A-Heat dissipation at low Ta (cold) B-Heat dissipation at high Ta (hot) C-Heat dissipation at low Ta (hot) D-Heat dissipation at high Ta (cold)

Heat dissipation at low Ta (cold)

Regulation of skin temperature is controlled by the ANS. What results in increases sympathetic nervous activity NE via A1 adrenoreceptors so: Vasoconstriction -- Heat storage (aka increase in body temp) A-Heat dissipation at low Ta (cold) B-Heat dissipation at high Ta (hot) C-Heat dissipation at low Ta (hot) D-Heat dissipation at high Ta (cold)

Lowest and highest temp

The normal core body temperature in adults undergoes regular circadian fluctuation where core body temperature is ________ 6 AM and ______ 6PM A- Increase in core body temp B-Lowest and highest temp C-Constant core body temperature D- Decrease in temp

the thermoreceptors in the spinal cord & anterior hypothalamus itself.

The thermoregulatory center receives info about ambient temperature from cold & warmth thermoreceptors in the skin & about core Tb from A-the thermoreceptors in the spinal cord & posterior hypothalamus itself. B-the thermoreceptors in the spinal cord & anterior hypothalamus itself. C-the thermoreceptors outside the spinal cord & anterior hypothalamus itself. D-the thermoreceptors outside the spinal cord & posterior hypothalamus itself.

37C (98.6F) Range: 36-37.5C (97-99.5ZF)

Thermoregulation is primarily under hypothalamic control located in the anterior hypothalamus. It determines the temperature set point which is Homeostatically regulated. Skin temperature varies and depends on ambient temperature and Cutaneous blood flow. Body temperature (Tb) varies with activity so Increases with exercise and ambient temperature (Ta) Decreases with cold weather what is Normal core body temperature A-37C (98.6F) Range: 36-37.5C (97-99.5ZF) B-38C (98.6F) Range: 36-37.5C (97-99.5ZF) C-39C (1--F) Range: 36-37.5C (97-99.5ZF) D-40C (98.6F) Range: 36-37.5C (97-103.3)

. Sweat secretion/Sweat glands Sympathetic cholinergic fibers innervate sweat glands and stimulation of these glands (with ACh) leads to an increase in sweat production mediated via muscarinic M3 receptors. Brown fat thermogenesis (non-shivering thermogenesis) is mediated by sympathetic (norepinephrine) stimulation of beta-3 adrenoceptors on BAT. Constriction of cutaneous blood vessels is mediated via sympathetic (norepinephrine) stimulation of alpha-1 adrenoceptors on vascular smooth muscle cells. Shivering is stimulated by somatic nervous system cholinergic innervation of skeletal muscle. Here ACh release at the neuromuscular junction sets in motion a chain of events leading to skeletal muscle contraction. Control of thermoregulatory behavior (putting on extra clothes and moving around more when cold, switching on a fan and moving away from direct heat source when hot) involve higher brain centers.

Which human thermoregulatory response is most likely controlled by cholinergic sympathetic fibers & can deliver up to 6L fluid/hr to skin? Controlling the rate of its production can regulate Loss of heat by evaporation of water from the skin surface . A. Brown fat thermogenesis B. Constriction of cutaneous blood vessels C. Shivering thermogenesis D. Sweat secretion E. Thermoregulatory behavior

Stimulation of shivering During the rising phase of fever, the hypothalamic temperature set point (Tset) is greater than the body temperature (Tb). This the hypothalamus "thinks" that Tb is too low and stimulates thermoregulatory mechanisms to elevate Tb. This includes cutaneous vasoconstriction, decreased skin blood flow, decreased heat loss, decreased sweating and increased shivering.

Which of the following is most likely to occur during the rising phase of fever? A. Fall in core body temperature B. Increased skin blood flow C. Increased sweat secretion D. Stimulation of shivering E. Perception of being warm

Malignant hypothermia

hypermetabolic crisis characterized by excessive accumulation of calcium in skeletal muscle & resultant sustained contraction following exposure to certain volatile anesthetic agents in susceptible individuals A-Mild Hypothermia B-Malignant hypothermia C-Moderate hypothermia D-Severe Hypothermia

Evaporation

the primary mechanism of heat loss at high Ta & strenuous physical activity. Its rate depends on ambient humidity so increase in humidity decreases it A. Conduction B. Convection C. Radiation D. Respiration E. Evaporation

Non-shivering thermogenesis

the use of brown fat to increase heat production. Quantity does down with age with increase chronic exposure to cold. - Increase rate of heat production by 10-15% NE stimulates lipase & release FFAs. Thyroid hormone stimulates up-regulation of mitochondrial UPC1 A. Non-shivering thermogenesis B. Decreased hypothalamic temperature set point (Tset) C. Shivering D. Vasodilation of blood vessels in the skin