Thermoregulation Flashcards
What is normal body temperature and the acceptable range?
- normal: 36.7 degrees C (98.06 degrees F)
- range: 36.3-37.1 degrees C
What is the general control system of body heat?
controlled variable (e.g. core temp) is measured by
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sensor (thermometer)
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controller (establishes set point)
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effector (e.g. furnace, AC) which changes
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controlled variable
How does temperature vary based upon body part?
- core is the controlled variable (maintained across range of environmental temps)
- oral temp is closest to core temp
- hands and feet vary depending on environmental temp
How does body temp vary over a 24 hour period?
- varies ~1-2 degrees over 24 hr period
- temp is lowest in the mornings
- highest in the evening
- circadian rhythm infuences body temp
What is the purpose of maintaining a certain body temp?
- temp affects enzyme activity (w/ every 10 degrees of temp change), will change cellular function for better or worse (usually worse)
- environmental temp is a threat to temp since humans are always generating heat, heat loss is an issue
Where are thermoreceptors located and what is their specific function in each of these locations?
(thermoreceptors are the “sensors” in the thermoregulation pathway)
- brain (pre-optic and superoptic region of hypothalamus, core): neuron cell bodies sensitive to changes in temp, 3x as many warm sensitive, relay info to other areas of hypothalamus
- viscera (gut, core): senses core temp and threats to maintenance (food ingested that may change body temp, relays info to hypothalamus)
- skin (cutaneous thermoreceptors): often bimodal (e.g. temp and touch), may be warm or cold sensitive (10x cold sensitive), tell us about environmental conditions
(all of the above relay info to hypothalamus)
In terms of the thermoregulation, what structure is the controller (establishes set point)?
- hypothalamus is the “controller” in the thermoreg pathway
- has connections to control hormonal, autonomic, and behavioral changes that are part of thermoreg
How does hypothalamus control body temp?
1) determines set point
2) receives info about current temp
3) decides what to do and generates response that it relays to parts of brain that execute action
- anterior hypothalamus: responds to heat and controls heat loss behaviors
- posterior hypothalamus: reponds to cooling and controls heat production behaviors
- with sleep, temp decreases in set point
- with exercise, temp increase in set point (as high as 40 degrees C)
What is the effector (variable that causes changes to core temp) within the thermoreg system?
heat loss/heat production
What are the effectors for heat production and how is this process modulated?
- effectors: ANS (sympathetic), endocrine (thyroxin, epi), muscular activity (voluntary and involuntary), non-shivering thermogenesis (increase in metabolism not due to muscles, aka brown fat)
- modulated by control from the posterior hypothalamus when the body is abnormally cold
- muscular activity: shivering (dorsomedial posterior hypothalamus, increases motorneuron excitation) and increase in voluntary activity (via cortex, e.g. running/jumping)
- non-shivering thermogenesis: strong hormonal influence (sympathetic innervation of adipose tissue, thyroxin increases metabolic rate which cold is stim for TRH release; and epinephrine), increase in food intake (leads to increase in metabolism), and brown adipose tissue (adrenergic innervation for initiation)
What is the importance of brown adipose tissue in humans?
- low efficiency hydrolysis of ATP via uncoupling proteins leads to more heat production than otherwise
- brown fat is innervated by sympathetic fibers, also activated by circulating epinephrine
- importance: critical in infants due to their heat loss from high surface area; was originally thought to be non-functioning in adults, but recent info suggests white fat expresses right uncoupling proteins and can be activated by sympathetic innervation
How is heat loss modulated?
- modulated by the anterior hypothalamus when the body is abnormally hot
- evaporative heat loss: energy lost as water that evaporates, two types are insensible (respiratory) and sweating (controlled)
- convection: movement of molecules away from contact (air heating and rising)
- conduction: transfer of heat between objects in physical contact w/ another
- radiation: infared radiation transferring heat between 2 objects not in physical contact (example of babies in incubator that are double lined)
(convection, conduction, and radiation controlled through wearing clothes, feed forward behavior that prevents change in temp)
- blood to skin: determines how much heat moves from blood to external environment (blood moves away from skin (pale) when cold and blood moves toward skin (flushing) when hot)
What is the general structure of sweat glands and how are they innervated?
- sweat glands have lots of nearby blood vessels, a coiled region that starts sweat production, and a duct leading to skin
- sweat glands are innervated by sympathetic cholinergic neurons (Ach is NT) and binds to muscarinic receptor
- sweating is a form of evaporative heat loss that is not dependent on air temp
How is sweat produced?
- initially serum is filtrated from blood of plasma, ions (Na, Cl) and proteins
- serum moves to the coiled part of sweat gland
- as fluid travels up to the skin surface, water and Na+ are reabsorbed (back to the blood) in the duct of the sweat gland
- low flow rate (don’t need a lot of sweat): sweat is concentrated (little water due to reabsorption) and high Na+ (couldn’t follow water)
- high flow rate (need a lot of sweat): sweat is dilute due to lots of water (no time to reabsorb) and w/ acclimation low Na+ due to aldosterone action (increases temp = increases Na+ reabsorbed)
What is a fever defined as and what are its implications?
- fever: “controlled” increase in body temp
- implications: set point increases as body temp is doing what hypothalamus directs it to do
