Hypothalamus

Question 1

Difference between core temperature and skin temperature

Answer 1

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

Question 2

What are the sensors that detect core and environmental temp?

Answer 2

Thermoceptors = non-specialized receptor that codes absolute and relative changes in temp, primarily within the innocuous range

Question 3

What happens to your core temp during sleep? How does this correlate with set point, metabolic rate, and heat loss mechanisms?

Answer 3

Decreases

Sleep is accompanied by lowering of the thermal set point. Metabolic rate reduces and heat loss increases via vasodilation/sweating

Question 4

T/F: mild whole body warming ~2 hours before sleep promotes better sleep

Answer 4

True — d/t activation of thermoregulatory heat defense mechanisms

The goal during sleep is to maximize heat conservation despite lowering thermal set point

Question 5

What happens to thermal set point in the body with high-intensity, long-duration exercise?

Answer 5

Set point increases

Question 6

How does your core temp follow circadian rhythms? When is temp lowest vs. highest?

Answer 6

Temp varies +/- 1 degree celsius depending on time of day

Temp is lowest between 3-6am

Temp peaks between 3-6pm

Question 7

What area of the brain governs the circadian rhythm-based changes in core temp?

Answer 7

Suprachiasmatic nucleus of anterior hypothalamus

Question 8

3 hormones that influence body temperature

Answer 8

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

Question 9

How does age affect ability to thermoregulate in terms of newborns vs. older age?

Answer 9

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

Question 10

Thermoreceptors consist of free nerve endings. What fiber types are associated with thermoreceptors for heat vs. cold?

Answer 10

Heat = C-fiber

Cool = C-fiber and A-delta fibers

Question 11

There are 11 temperature sensitive TRP channels identified to date. What type of channels are these?

Answer 11

Non-specific, ligand gated ion channels

Question 12

Name 2 TRP channels sensitive to cold and 1 TRP channel sensitive to heat

Answer 12

Cold = TRPA1 (allyl thiocyanate), TRPM8 (menthol)

Hot = TRPV1 (capsaicin)

Question 13

Where is core temp detected in the brain

Answer 13

Hypothalamus

Question 14

Which is more abundant as a thermoreceptor in the skin, those sensitive to cold or those sensitive to warm?

Answer 14

Cold&raquo_space; warm-sensitive receptors

Question 15

What are thermoreceptors in the viscera sensitive to?

Answer 15

Chemical heat signatures

May be from food ingested

Question 16

Heat responsive nuclei in the brain

Answer 16

Anterior hypothalamic nucleus

Preoptic nucleus

Question 17

Activation of heat responsive nuclei in the brain such as anterior hypothalamic nucleus and preoptic nucleus will activate what type of physiological behavior?

Answer 17

Heat loss behaviors

Question 18

Cool responsive area of the brain

Answer 18

Posterior hypothalamus

Question 19

Cool responsive areas of the brain such as posterior hypothalamus will initiate what type of physiological behavior?

Answer 19

Heat production behavior

Question 20

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?

Answer 20

Shivering (dorsamedial posterior hypothalamus — increases motor neuron excitation)

Voluntary muscle activity

Non-shivering thermogenesis (hormones, eating, brown adipose)

Question 21

Brown adipose tissue is more abundantly found in infants, where is it typically maintained in adults?

Answer 21

Cervical and clavicular areas

Question 22

Brown adipose tissue is characterized by ____ efficiency hydrolysis of ATP. Fatty acid metabolism in this type of adipose tissue is activated by _____ stimulation

Answer 22

low; sympathetic

Question 23

4 mechanisms to dissipate heat

Answer 23

Evaporation (insensible = respiratory, sweat)

Convection (through air)

Conduction (through contact with object)

Radiation (infrared)

Question 24

Influence of hotter temperatures on hypothalamus in terms of hormone release, metabolic rate, heat production, and overall effect

Answer 24

Hotter temperatures stimulate hypothalamus to inhibit TRH release —> decreases metabolic rate —> reduces heat production

Result is decreased body temp

Question 25

Influence of colder temperatures on hypothalamus in terms of hormone release, metabolic rate, heat production, and overall effect

Answer 25

Colder temperatures cause the hypothalamus to stimulate TRH release —> increases metabolic rate of the body to generate heat production

Result is raised body temp

Question 26

When the core temp increases (Tb>Tset-point), what happens with heat production vs. heat loss?

Answer 26

Decreased heat production — apathy, anorexia

Increased heat loss — vasodilation, sweating, panting

Question 27

What happens with blood flow to the skin when the body temp decreases vs. increases?

Answer 27

When body temp decreases — there is vasoconstriction near skin surface

When body temp increases — there is vasodilation to dissipate the heat

Question 28

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 _____

Answer 28

Cholinergic (muscarinic) sympathetic

Proteins; Na; Cl

Question 29

Compare low sweat rates with high sweat rates in terms of fluid flow, reabsorption, and osmotic pressure in duct

Answer 29

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

Question 30

Describe acclimatization to hot environments

Answer 30

Occurs within 1-6 weeks of exposure to hot weather

Increases sweating capacity

Question 31

What effect does aldosterone have on sweating?

Answer 31

Decreases the NaCl content in primary secretion —> helps conserve body salt

Question 32

Fever is a controlled increase in the hypothalamic set-point. What types of conditions induce fever?

Answer 32

Pyrogens ike IL-1B

Induction of PGE2 (antipyretics target this)

Hypothalamic lesions

Question 33

_____ = the point at which the actual body temp reaches the new set-point established by fever

Answer 33

Flush

Question 34

Once “flush” is reached during fever conditions (body temp matches new raised set-point), what physiological changes occur?

Answer 34

Vasodilation
Sweating

[occurs as the set point is lowered again, and Tb>Tset-point]

Question 35

How is fever different from hyperthermia?

Answer 35

Unlike fever, set-point remains normal in hyperthermia

In this case the environment exceeds hypothalamic ability to regulate body temp

Question 36

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?

Answer 36

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

Question 37

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 _____ _____

Answer 37

Hypothalamus

Tractus solitarius (NTS)

Question 38

Hypothalamic control of autonomics is in part due to its projections to pre-ganglionic visceral motor neurons via what 3 nuclei?

Answer 38

Vagal nuclei

Nucleus ambiguus

IML cell column