Hypothalamus Flashcards
Difference between core temperature and skin temperature
Core temp is normally very steady except during fever; remains stable in environments of 55-130F (dry air), so it is only altered by extreme environments
Skin temp is very susceptible to fluctuations with the environment and exists within a range of normal limits
What are the sensors that detect core and environmental temp?
Thermoceptors = non-specialized receptor that codes absolute and relative changes in temp, primarily within the innocuous range
What happens to your core temp during sleep? How does this correlate with set point, metabolic rate, and heat loss mechanisms?
Decreases
Sleep is accompanied by lowering of the thermal set point. Metabolic rate reduces and heat loss increases via vasodilation/sweating
T/F: mild whole body warming ~2 hours before sleep promotes better sleep
True — d/t activation of thermoregulatory heat defense mechanisms
The goal during sleep is to maximize heat conservation despite lowering thermal set point
What happens to thermal set point in the body with high-intensity, long-duration exercise?
Set point increases
How does your core temp follow circadian rhythms? When is temp lowest vs. highest?
Temp varies +/- 1 degree celsius depending on time of day
Temp is lowest between 3-6am
Temp peaks between 3-6pm
What area of the brain governs the circadian rhythm-based changes in core temp?
Suprachiasmatic nucleus of anterior hypothalamus
3 hormones that influence body temperature
LH — body temp increase during ovulation
TRH — released in response to cold temps, effect is to increase cellular metabolic rate
Epinephrine — increases cellular metabolic rate
How does age affect ability to thermoregulate in terms of newborns vs. older age?
Newborns have large surface:mass ratio, do not readily sweat, large deposits of brown adipose, and have modest vasoconstriction ability to reduce heat loss when needed
Older age: progressive decline in thermosensation with age as well as reduced metabolic rate. Overall reduced ability to dissipate heat
Thermoreceptors consist of free nerve endings. What fiber types are associated with thermoreceptors for heat vs. cold?
Heat = C-fiber
Cool = C-fiber and A-delta fibers
There are 11 temperature sensitive TRP channels identified to date. What type of channels are these?
Non-specific, ligand gated ion channels
Name 2 TRP channels sensitive to cold and 1 TRP channel sensitive to heat
Cold = TRPA1 (allyl thiocyanate), TRPM8 (menthol)
Hot = TRPV1 (capsaicin)
Where is core temp detected in the brain
Hypothalamus
Which is more abundant as a thermoreceptor in the skin, those sensitive to cold or those sensitive to warm?
Cold»_space; warm-sensitive receptors
What are thermoreceptors in the viscera sensitive to?
Chemical heat signatures
May be from food ingested
Heat responsive nuclei in the brain
Anterior hypothalamic nucleus
Preoptic nucleus
Activation of heat responsive nuclei in the brain such as anterior hypothalamic nucleus and preoptic nucleus will activate what type of physiological behavior?
Heat loss behaviors
Cool responsive area of the brain
Posterior hypothalamus
Cool responsive areas of the brain such as posterior hypothalamus will initiate what type of physiological behavior?
Heat production behavior
The hypothalamus is what determines the set-point of the body. It is 3x more heat-sensitive than other body areas and integrates all other afferent detectors of heat to compare to the current set point.
What are the ways in which we generate heat?
Shivering (dorsamedial posterior hypothalamus — increases motor neuron excitation)
Voluntary muscle activity
Non-shivering thermogenesis (hormones, eating, brown adipose)
Brown adipose tissue is more abundantly found in infants, where is it typically maintained in adults?
Cervical and clavicular areas
Brown adipose tissue is characterized by ____ efficiency hydrolysis of ATP. Fatty acid metabolism in this type of adipose tissue is activated by _____ stimulation
low; sympathetic
4 mechanisms to dissipate heat
Evaporation (insensible = respiratory, sweat)
Convection (through air)
Conduction (through contact with object)
Radiation (infrared)
Influence of hotter temperatures on hypothalamus in terms of hormone release, metabolic rate, heat production, and overall effect
Hotter temperatures stimulate hypothalamus to inhibit TRH release —> decreases metabolic rate —> reduces heat production
Result is decreased body temp
Influence of colder temperatures on hypothalamus in terms of hormone release, metabolic rate, heat production, and overall effect
Colder temperatures cause the hypothalamus to stimulate TRH release —> increases metabolic rate of the body to generate heat production
Result is raised body temp
When the core temp increases (Tb>Tset-point), what happens with heat production vs. heat loss?
Decreased heat production — apathy, anorexia
Increased heat loss — vasodilation, sweating, panting
What happens with blood flow to the skin when the body temp decreases vs. increases?
When body temp decreases — there is vasoconstriction near skin surface
When body temp increases — there is vasodilation to dissipate the heat
Physiology of sweating:
_____ _____ fibers stimulate epithelial cells to secrete their fluid. The secretory portion produces the primary secretion
The product is similar to plasma but lacks _____. It is made up mainly of water, ____, and _____
Cholinergic (muscarinic) sympathetic
Proteins; Na; Cl
Compare low sweat rates with high sweat rates in terms of fluid flow, reabsorption, and osmotic pressure in duct
Low sweat rates:
Fluid flow is slow
Lots of reabsorption
Osmotic pressure in duct is low
High sweat rates:
Fluid flow is fast
Less reabsorption
Osmotic pressure in duct is higher
Describe acclimatization to hot environments
Occurs within 1-6 weeks of exposure to hot weather
Increases sweating capacity
What effect does aldosterone have on sweating?
Decreases the NaCl content in primary secretion —> helps conserve body salt
Fever is a controlled increase in the hypothalamic set-point. What types of conditions induce fever?
Pyrogens ike IL-1B
Induction of PGE2 (antipyretics target this)
Hypothalamic lesions
_____ = the point at which the actual body temp reaches the new set-point established by fever
Flush
Once “flush” is reached during fever conditions (body temp matches new raised set-point), what physiological changes occur?
Vasodilation
Sweating
[occurs as the set point is lowered again, and Tb>Tset-point]
How is fever different from hyperthermia?
Unlike fever, set-point remains normal in hyperthermia
In this case the environment exceeds hypothalamic ability to regulate body temp
A 44 y/o female presents to the ED with drowsiness and delirium which has progressed into a coma. Her body temp at the time of coma onset is 91.4F. There are no signs of infection and she has not been exposed to extreme environmental conditions. What could explain her condition?
Hypothalamic tumor has abolished her ability to thermoregulate
These tumors often result in fevers rather than hypothermia, however this particular one has simultaneously abolished the ability to secrete TSH, thus no thyroxin is produced. As a result, her BMR and heat production are very low. Her hypothalamus should compensate by generating heat-productive mechanisms but the tumor has diminished its overall function
The ______ is part of the central autonomic network and is considered the highest integrator of autonomic and endocrine functions
It has reciprocal connections with the nucleus _____ _____
Hypothalamus
Tractus solitarius (NTS)
Hypothalamic control of autonomics is in part due to its projections to pre-ganglionic visceral motor neurons via what 3 nuclei?
Vagal nuclei
Nucleus ambiguus
IML cell column
