Hypothalamus Flashcards
What is a normal body temperature?
36.3 - 37.1 C
How does core temp vary throughout the day?
1-2 degrees
low at 6 am (drops at night)
Where are thermoreceptors and what are they?
found in skin, viscera, and brain
bare nerve endings w/ TRP receptors
What kind of system does your body use to regulate body temp?
feed forward system
air is cold –> take action now before the body temp drops
Where are thermoreceptors in the “core”?
brain
viscera
What are cutaneous thermoreceptors like?
often bimodal (temp and touch)
may be warm or cold sensitive
10X as many cold sensitive - bc cold is more threatening
tell us about environmental conditions
Why are there thermoreceptors in the gut?
not just sensing core temp
food ingested may change body T
tell hypothalamus about these threats
Where are the neurons sensitive to temp change located in the hypothalamus?
pre-optic and superoptic
*3x as many warm sensitive –> relay to other parts of hypoT
How do cutaneous thermoreceptors send info to the hypothalamus?
via anterolateral path
What does the hypothalamus do in relation to thermoregulation?
has the connections to control the hormonal, autonomic, and behavioral changes that are part of thermoregulation
What happens to body temp during sleep or exercise?
sleep: decrease in set point –> T decreases
exercise: increase in set point –> T increases (helps enzymes work better)
Where are heat loss and heat production behaviors controlled in the hypothalamus?
AL: anterior = heat loss behaviors
PHP: Posterior heat production
Why do babies lose heat easier than adults?
have high surface area compared to volume
What are the muscular muchanisms of heat production?
shivering (primarily during inspiration) – controlled by dorsomedial posterior hypothalamus
Increase voluntary activity – via cortex –> jumping, running
What are the non-muscular mechanisms of heat production?
Hormones: Thyroxin increases metabolic rate
epinephrine
Increase food intake –> increased metabolism
Brown adipose tissue: adrenergic I for initiation
How does cold relate to thyroxin?
Cold is a stimulus for TRH release –> TSH –> Thyroxine
How does brown fat produce heat?
low efficiency hydrolysis of ATP via uncoupling proteins –> more heat production
Innervated by sympathetic fibers
activated by circulating Epi
critical in infants; new research says white fat expresses right uncoupling proteins
What are the main ways the body can lose heat?
evaporative heat loss: insensible and sweating
convection: air heating and rising
conduction: transfer of heat btw objects in physical contact w/ one another
radiation: transfer btw 2 objects not in physical contact
How does bloodflow affect heat loss?
how much blood is sent to the skin determines how much heat moves from blood to ext environmnet
How are sweat glands innervated and how is heat loss promoted to occur?
Innervation: SNS –> Ach to muscarinic receptor
lots of blood vessels nearby, coiled region increases SA for heat loss to skin
What happens to sweat content in low and high flow rate sweating?
Low flow rate: concentrated sweat (most of water reabsorbed, but sodium couldn’t follow water)
High flow rate: lots of water (no time to reabsorb) with acclimation, little sodium due to aldosterone
How should your body respond to hypothermia?
Increase heat production
Set temp > body temp –> need to increase it
What is the definition of a fever?
controlled increase in body temp
set point increase by hypothalamus
How does a fever occur?
germ –> secretion of endotoxins
immune cells release cytokines, etc
major player = prostaglandin E2 –> increases hypothalamic set point for temp
Why do you shiver when you have a fever?
set temp > body temp initially (like in hypothermia)
shiver, non-shivering thermogenesis to get temp up
What occurs when an illness is vanquished and fever is no longer necessary?
no more activation of immune system –> hypothalamic set point returns to normal
Body temp > set point –> decrease heat production
sweat, don’t move as much
What is insensible heat loss?
loss through respiration
