Thermoregulation Flashcards
Where are thermoreceptors found?
Found in the skin, the viscera, and the brain
What thermoreceptors are in our “core”?
Brain and viscera
Describe cutaneous thermoreceptors
Often bimodal (temperature and touch sensitive); may be warm or cold sensitive; we have 10x as many cold sensitive receptors in the skin as we do warm sensitive receptors; these tell us about environmental conditions
Why do we have thermoreceptors in the gut?
Detect threats to maintenance; for example, food ingested may change body temperature, so they tell the hypothalamus about these potential threats
Describe thermoreceptors in the brain
Located mainly in anterior hypothalamus (pre-optic and superoptic regions of hypothalamus); these neuron cell bodies are sensitive to changes in temperature; we have 3x as many warm sensitive receptors in the brain than we do cold sensitive receptors; they relay their information to other areas of the hypothalamus
Why is the hypothalamus the controller of the body temperature or set point?
Has connections to control the hormonal, autonomic, and behavioral changes that are part of thermoregulation
What is the function of the hypothalamus in terms of thermoregulation?
Determines set point, receives info about the current temperature, and decides what to do
What happens to our temperature/set point when we sleep? During exercise?
Sleep: temperature decreases, which represents a decrease in set point
Exercise: temperature increases, which represents a increase in set point
What part of the hypothalamus is responsible for responding to heat? Cooling?
Heat: anterior hypothalamus controls heat loss behaviors
Cooling: posterior hypothalamus controls heat producing behaviors
What are the different mechanisms for heat production?
Autonomic nervous system (sympathetics), endocrine (secretion of thyroxin or epinephrine), muscular activity (shivering, moving), and non-shivering thermogenesis
What mediates shivering? What is the physiology behind shivering?
Mediated by dorsomedial posterior hypothalamus; caused by increased motorneuron excitation
What mediates an increase in voluntary muscle activity to produce heat?
Mediated by cortex; examples include jumping, running, etc
What are the mechanisms for non-shivering thermogenesis?
1) Secretion of thyroxin, which increases metabolic rate; cold is a stimulus for TRH release
2) Secretion of epinephrine, which causes us to increase food intake, which leads to increase in metabolism
3) Brown/white adipose tissue, innervated by sympathetics, hydrolyzes ATP through uncoupling proteins; under adrenergic innervation for its initiation (activated by circulating epinephrine)
What are the 2 kinds of evaporative heat loss?
Insensible (respiratory) and sweating (controlled)
What is convection as a way of heat loss?
Movement of molecules away from contact (air heating and rising)
What is conduction as a way of heat loss?
Transfer of heat between objects in physical contact with one another
What is radiation as a way of heat loss?
Infrared radiation transferring heat between 2 objects not in physical contact
How do we control the following forms of heat loss: convection, conduction, radiation?
By controlling how much blood is sent to the skin; sending blood to the skin allows for heat loss; bypassing the skin limits heat loss to the environment
Describe sweat glands and how they are under sympathetic cholinergic control and what makes them abnormal
Sweat glands are coiled and surrounded by blood vessels and they have a duct leading to the skin; they were identified as under sympathetic control because the fibers came from the thoracic/lumbar regions and they synapse in the sympathetic chain, however, it releases acetylcholine instead of norepinephrine at the tissues, which is abnormal
What does the acetylcholne released at a sweat gland bind to?
Muscarinic receptor
How is sweat filtered?
As fluid travels up to the surface of the skin, water and sodium are reabsorbed in the duct
What happens to sweat under low flow rates? High flow rates?
Low rates: sweat contains little water (most is reabsorbed), but it has high sodium because it couldn’t follow the water
High rates: sweat has lots of water (no time to be reabsorbed) and lots of sodium; after acclimated to heat, sweat contains little sodium because body reabsorbs it (can’t afford to keep losing large amounts of salt in sweat)
How does our body respond to low body temperatures?
Increase heat production, decrease heat loss
What is a fever?
Controlled increase in body temperature; set point increases (body temperature is doing what hypothalamus told it to do)
What is the major player in fevers?
Prostaglandin E2; increases hypothalamic set point for temperature
How does our body respond to produce a fever in response to an illness/infection?
Increase heat production, decrease heat loss
When the infection goes away, what happens to our set point?
In absence of endotoxins, hypothalamic set point returns to normal
With set point now returning to normal, how does our body respond to get rid of our fever?
Decrease heat production, increase heat loss
Note decreasing heat production usually causes decreased appetite, but so does being ill. When the illness goes away, our appetite returns, so decreased appetite is hard to correlate with a fever
