Lecture 8.5 Thermoregulation Flashcards
What is extreme cold temp?
< 96 F
What temp can we reach when exercising?
104F
What temperature is higher when measured?
Rectal, which is about 1F higher.
How do we gain heat?
basal rate (metabolism)
activity (muscle activity/shivering)
Thyroxine/testosterone/GH (hormones)
EPOC (sympathetic stimulation/excess post-exercise oxygen consumption)
Dietary stimulation
How do we lose heat?
Radiation
Convection
Conduction
Evaporation
What organ has the worst heat conduction?
Skin, only 1/3 as fast.
Where does blood flow in the skin happen mainly in?
Arteriovenous anastomosis
How much blood flow does our skin use?
0-30% of our entire CO.
What controls heat transfer via the skin?
Sympathetic NS, which controls vasoconstriction.
Define radiation.
Infrared heat rays that we emit. (EM waves)
Responsible for 60% of heat loss!!!! (MOST)
Define conduction.
Physical contact with objects.
Responsible for 3% of heat loss (LEAST)
INCLUDES:
Physical contact with air (15% of heat loss)
Define convection.
An extension of conduction.
It is us conducting our heat to the air currents around us, which then carry that heat away.
15% of heat loss normally.
Wind increases loss.
Water is 20x more effective than air at conduction, so we lose heat rapidly in water.
Define evaporation.
Water heating up on the body’s surface and absorbing heat before it evaporates.
22% of heat loss.
Note:
At high air temps, it is the only means of losing body heat!!!!
What regulates sweating?
ANS, either by electrical stimulation or excess heat.
What innervates sweat glands?
Cholinergic fibers, but also from adrenal epi and NE.
What are the components of sweat glands?
The gland at the deep part, touching the nerve directly and makes the sweat. It is also coiled.
The duct, which leads to the pore in the epidermis.
Pore, which is the opening.
What is sweat similar to?
Plasma without proteins
What is contained in sweat when we are slow sweating? Fast sweating?
Slow sweating:
NaCl is FULLY REABSORBED in the duct.
High in urea, lactic acid, and potassium ions.
Fast sweating:
NaCl is 1/2 reabsorbed.
Note: If a person is losing excessive salt in their sweat, they are known as unacclimatized.
What is acclimatization?
Adapting to the environment.
How much do we sweat normally vs in hot weather?
1L/hr in normal.
2-3L/hr in extended hot weather 1-6 weeks.
However, heat loss increases by 10x.
What happens to someone who is acclimatized to hot weather?
Increased sweating.
Increased heat loss.
Decreased sodium lost in sweat
Increased aldosterone.
What regulates our body temperature?
Hypothalamus
If we are cold, what does our body do?
Shiver
Piloerection
Skin vasoconstriction
Increased thermogenesis
What are the 3 ways we can increase thermogenesis?
Shivering
Sympathetic excitation (uncoupling of oxidation and phosphorylation)
Thyroxine secretion
If we are hot, what does our body do?
Vasodilate skin blood vessels
Sweat
Decrease thermogenesis (depressed shivering and depressed chemical thermogenesis)
Do we have more cold or warm receptors?
Cold (10x) more
Where are the deep cold receptors found in our body?
Spinal cord
Abdominal viscera
Around the great veins
What is fever?
A body temperature greater than normal range.
What causes fever?
Abnormalities in the brain
Toxic substances affect the hypothalamus
What are pyrogens?
Things that cause fever.
What are the pyrogens?
Proteins
Breakdown products of proteins
Lipopolysaccharide toxins released from bacterial cell membranes
What is the main cytokine involved in fever?
IL-1
Why is aspirin an antipyretic?
It inhibits the formation of prostaglandins, which are pyrogens.
Why do we feel chills and flushed when we have a fever?
Our body feels cold because it is trying to reach the new higher set point.
