What happens to core temperature, thermal set point, and metabolic rate during sleep?
- Sleep accompanied by lowering of the thermal set point
- Metabolic rate reduces
- Heat loss increases (vasodilation/sweat)
- Core temperature decreases
Exercise elevates what aspect of your body temperature?
Elevates core temperature
High intensity, long-duration exercise raises _______.
Core temperature follows a circadian rhythm, when is it lowest and highest?
- Lowest between 3-6 AM
- Peaks between 3-6 PM
What nucleus governs the circadian rhythm of core body temperature?
Suprachiasmatic nucleus of anterior hypothalamus
During what reproductive phase do you see a 0.5 °C increase in body temperature?
During what reproductive phase do you see a 0.3-0.5 °C increase in body temperature?
Cold temperature stimulate the release of what hormone, why?
- Thyroxine increases cellular metabolic rate
Which hormones increase cellular metabolic rate?
What factors influence thermoregulation in newborns?
- Large suface area:mass ratio (they lose heat better than adults!)
- Do not readily sweat
- Large deposits of brown adipose
- Modest vasoconstriction of skin to reduce heat loss when needed
What happens to thermosensation, heat dissipation, and metabolic rate as we age?
- Progressive decline in thermosensation w/ older age
- Reduced metabolic rate
- Reduce metabolic potential w/ diminished muscle mass
- Reduced ability to dissipate heat
Thermoreceptors for hot and cold sensations are made up of what kind of fibers?
- Heat = C-fiber
- Cold = C-fiber and Aδ fibers
What are the TRP channels for hot and cold sensation?
Cold = TRPA1 and TRPM8
Hot = TRPV1 (V = Vanilloid = capsaicin (hot peppers))
What kind of thermoreceptors found on the skin, characteristics, and which are more abundant?
- Warm or cold-sensitive (not both)
- Often polymodal (i.e., temperature and touch sensitive)
- Cold >> warm-sensitive receptors
- Cues atmospheric changes (tells us about enviornmental conditions)
What is the heat responsive portion of the hypothalamus and what is its function?
- Anterior hypothalamic nucleus and preoptic nucleus
- Heat loss behaviors
What is the cool responsive portion of the hypothalamus and what is its function?
- Posterior hypothalamus
- Heat production behaviors
How does temperature affect neurons of the hypothalamus and are there more heat or cold sensitive neurons?
- Neurons are excited or inhibited by temperature
- 3x more heat-sensitive (preoptic nuclei and anterior hypothalamic nuclei)
- There are more heat-sensitive because protecting your brain from overheating is MOST important
What are 3 ways we can generate heat?
1. Shivering (dorsomedial posterior hypothalamus)
2. Voluntary muscle activity (running, jumping, rubbing) via cortex
3. Non-shivering thermogenesis (hormones, eating, brown adipose)
What part of the hypothalamus induces shivering and how?
Dorsomedial posterior hypothalamus increases motorneuron excitation
Brown adipose is abundant in who and what is it responsible for; stimulated by what part of the ANS?
- High in infants; recent evidence shows existence in adults
- Low efficiency hydrolysis of ATP = heat production
- Sympathetics stimulation results in fatty acid metabolism
- Is considered low efficiency, which means its producing lots of heat!
What are the 4 ways to dissipate heat and how does each work?
1) Evaporation: insensible (respiratory) and sweat
2) Convection: dissipation through air
3) Conduction: dissipation through physical contact w/ an object
4) Radiation: infrared radiation transfers heat between objects NOT in physical contact
Colder temperatures cause the hypothalamus to stimulate the release of what hormone and why?
- Stimulate the release of thyroxin
- Increases metabolic rate to generate heat production
- Raises body temperature
Hotter temperatures cause the hypothalamus to inhibit the release of what hormone and why?
- Inhibits thyroxin release
- Decreases metabolic rate
- Reduces heat production (lower body temp)
When the core temperature increases (Tb >Tset-point) what occurs within the body?
Decreased heat production:
- Apathy (not activating skeletal muscle as much)
- Anorexia (decrease in eating behaviors)
Increased heat loss:
- Vasodilation (more blood sent to skin = more heat lost)
- Evaporative heat loss (sweat)
- Insensible heat loss (panting)
When the core temperature decreases (Tb < Tset-point) what occurs within the body?
- Increased heat production: shivering and non-shivering thermogenesis
- Decrease heat loss: vasoconstriction, decrease evaporative heat loss
What stimulates the epithelial cells to secrete their fluid for the process of sweating, what are the components of this fluid, and what produces the primary secretion?
- Cholinergic SYMPATHETIC fibers stimulate the epithelial cells
- Secretory portion produces the primary secretion
- Similar to plasma (lacks proteins)
- Mainly water, Na+ and Cl-
The postganglionic neuron for sweat gland innervation differs from other sympathetic postganglionic neurons in that it releases what NT to what receptor?
ACh (cholinergic) to act on a muscarinic receptor (mAChR)
What is fluid flow, reabsorption, osmotic pressure, and the reabsorption of water like during low sweat rates?
1. Fluid flow is slow
2. Lots of reabsorption
3. Osmotic pressure in duct is low
4. Most water gets reabsorbed; but the sweat will be high in Na+
What is fluid flow, reabsorption, osmotic pressure, and the reabsorption of water like during high sweat rates?
1. Fluid flow is fast
2. Less reabsorption
3. Osmotic pressure higher in duct
4. Less water is reabsorbed, so the sweat is very dilute (lots of water and little Na+)
Acclimatization to hot enviornments takes how long and what occurs?
- 1 to 6 weeks exposure to hot weather
- Increase sweating capacity