Thermoregulation Flashcards
Function of cutaneous thermoreceptors
- May be warm or cold sensitive (10X as many cold sensitive)
- Tell us about environmental conditions
Function of central thermoreceptors
- Located at the pre-optic and superoptic regions of the hypothalamus
- Neuron cell bodies sensitive to changes in temperature (3X as many warm sensitive)
- Relay information to other hypothalamic areas
Function of visceral thermoreceptors
- Sense core temperature
- Detects foods ingested that can possibly change body temperature
- Sends that info to the hypothalamus
How does the hypothalamus control body temperature?
- Determines set point for core temperature
- Receives information about current temperature
- Decides what to do in response to current temperature and relays decision to parts of the brain that can actually mediate it
Name hypothalamus-mediated mechanisms of heat production
- Autonomic nervous system (especially sympathetic NS)
- Endocrine - mediated by Thyroxin and Epinephrine
- Muscular activity (voluntary vs involuntary/shivering)
- Non-shivering thermogenesis (increase metabolism NOT due to muscles)
Hypothalamus-mediated mechanisms of heat production: Muscular activity
- Shivering - mediated by the dorsomedial posterior hypothalamus and increases motoneuron excitation down the SC but not enough to activate the alpha-MN itself so if another input comes in the outflow is increased in a rhythmic fashion
- Increase voluntary activity - mediated via the cortex (e.g. jumping, running in place)
Shivering is mediated by which part of the brain?
Dorsomedial posterior hypothalamus
Hypothalamus-mediated mechanisms of heat production: Non-shivering thermogenesis
- Hormones:
- Throxin increases metabolic rate (cold is a stimulus for thyrotropin-releasing hormone release)
- Epinephrine - Increase food intake –> increased metabolism
- Brown adipose tissue - adrenergic innervation for initiation of low efficiency ATP hydrolysis via uncoupling proteins to increase heat production
Which parts of the hypothalamus responds to a) heating and b) cooling
a. Anterior hypothalamus to initiate heat loss behaviors
b. Posterior hypothalamus to initiate heat production behaviors
Heat loss techniques: Evaporative heat loss
- Energy (heat) lost as water evaporates (e.g. sweat, panting)
1. Insensible (respiratory) - always lose heat as we breath
2. Sweating (controlled)
Heat loss techniques: Convection
- Movement of molecules away from contact
- E.g. as air comes in contact w/ our skin, the air becomes hotter, rises and is replaced by cooler air
Heat loss techniques: Conduction
-Transfer of heat b/w objects in physical contact w/ one another (e.g. back touching chair and causing it to heat up)
Heat loss techniques: Radiation
- Infrared radiation transferring heat b/w 2 objects NOT in physical contact
- Losing heat to window b/c window very cold
Innervation of sweat glands
- Sympathetic cholinergic (ACh)
- Binds to a muscarinic receptor
How is sweat produced?
- Filtration of blood from BV into the sweat gland –> results in a serum which is high in Na+, Cl-, low in K+ and w/o proteins
- As fluid travels to skin surface via duct, the H20 and Na+ are reabsorbed to the blood but the amount that is reabsorbed depends on how much sweat we are producing:
a. Low flow rate - concentrated sweat w/ little water (lots reabsorbed) and high Na+
b. High flow rate - lots of water b/c no time to reabsorb it and while acclimating it will be less concentrated w/ Na+ due to aldosterone action (increases Na+ reabsorption and K+ secretion)
