Lecture 13 - Temperature Regulation Flashcards
Heat is a ___ resulting from the ___ of the various metabolic pathways
metabolic byproduct
inefficiency
Factors that Determine Heat Production
- BMR (Basic Metabolic Rate)
- Muscle activity (i.e., shivering)
- Thyroxin
- Norepinephrine and epinephrine
- Increased cellular chemical activity
- Extra metabolism for digestion, absorption, and food storage
Factors that Determine Rate of Heat Loss
- How rapidly heat can be conducted from body core to skin
- How rapidly heat can be transferred from skin to surroundings:
- Skin and subQ especially act as heat insulators.
- Continuous venous plexus in subQ is supplied by inflow of blood from capillaries from dermis.
- Rate of blood flow into the plexus can be as great as 30% of total cardiac output.
A ___ amount of heat is transferred by the respiratory system.
small
How rapidly heat can be transferred from skin to surroundings
- About an 8x increase in conductance between fully vasoconstricted state to fully vasodilated state.
- Heat conduction to skin is controlled by: •Degree of vasoconstriction of arterioles and the arteriovenous anastomoses that supply blood to the venous plexus of the skin.
- Vasoconstriction is controlled almost entirely by sympathetic system in responses to core temperature and environmental temperature
Mechanisms of Heat Loss from Skin Surface
Radiation
Conduction
Convection
Radiation
- Loss in the form of infrared heat rays
- Radiated by all objects not at absolute zero
- If temperature of body is greater than ambient temperature, more heat is radiated from the body than to the body.
- Refers to thermal energy transferred to objects in the external environment.
- Amount transferred depends on temperature difference and ability of object to absorb energy
Conduction
Kinetic energy of the molecules of the skin is transferred to the air if the air is colder than the skin
•Transfer of energy from one body to another when they are in close contact.
Convection
Removal of heat from the body by convection air currents
•Heat is transferred between two objects by air or water (fluid).
Slide 8
body cooling via wind and circulation
Heat Loss by percentage
radiation: 60%
conduction to objects: 3%
conduction to air: 15%
evaporation: 22%
Note that heated air must be moved away from the skin for continued heat loss to occur through conduction to air
Evaporation
Heat is dissipated by the use of thermal energy to cause a change from fluid to gas
Stimulation of Sweating
- Stimulation of anterior hypothalamus-pre-optic area in the brain electrically or by excess heat
- Cholinergic sympathetic nerve fibers (muscarinic)
- Circulating epinephrine and norepinephrine
What effect does aldosterone have on sweat composition?
Increased resorption of sodium: sodium loss in urine is decreased under aldosterone stimulation. Increased resorption of water, with consequent expansion of extracellular fluid volume. This is an osmotic effect directly related to increased resorption of sodium.
Strong stimulation of sweat glands
- Large amounts of precursor secretion are formed.
- Ducts reabsorb only about half the sodium chloride
- Concentrations of sodium and chloride ions are about 50 to 60 mEq/L
- Little water is reabsorbed
Unacclimatizedperson normally produces about __ liter sweat per hour (or less).
one liter or less
Person exposed to hot weather for 1 to 6 weeks may produce__ liters of sweat per hour, increasing heat removal by factor of __.
2 to 3
10
Due to changes in internal sweat gland cells
(Climatization)
body core temp. is stable (98⁰F − 100⁰F between environmental temperature range of ___?
55F - 130F
Regulation of core body temperature is essential because…
most of the metabolic processes necessary for life are strongly temperature dependent.
What are the principal areas of the brain that affect body temperature?
•Anterior hypothalamic nuclei •Medial pre-optic area
Anterior preoptic hypothalamus
Anterior pre-optic area:
Contains warm-sensitive, cold-sensitive, and temperature insensitive neurons: •Warm sensitive neurons: •Increase firing rate 2-10x in response to a 10°C increase in body temperature. •Cold-sensitive neurons: •Increase firing rate when temperature falls
The hypothalamus is one of the few brain areas where neurons are found that are themselves directly sensitive …
to physical or chemical variables (i.e., temperature, plasma osmolarity, plasma glucose, and hormone levels).
Warm-sensitive neurons comprise __% of neuronal pool while cold-sensitive neurons comprise _%.
30, 5
The preoptic anterior hypothalamus is referred to as the ___, while the posterior hypothalamus is referred to as ___.
heat dissipation center
heat generation/conservation center
