Thermoregulation

Question 1

What controls the core temperature of the body?

Answer 1

Hypothalamus

36°C - 37°C (97°F -99°F)

Question 2

What is the shell temperature?

Answer 2

Average of core and temperatures

Question 3

What are symptoms of excess of body heat?

Answer 3

Heart stroke, Brain lessions

Question 4

What are the temperature set points in the morning/afternoon?

Answer 4

Morning/night: cooler: 36.3
Afternoon: rises to normal: 37
Women have different set points within menstrual cycle

Question 5

What are the temperature set points for women?

Answer 5

Menstrual cycle:
Preovalutory: cooler
Postovalutory: warmer

Preganancy = Postovalutory: warmer

Question 6

How can we transfer (gain/lose) heat?

Answer 6

Gain and loss of heat:
-Conduction: direct molecular contact with something (hand on hot stove)
-Convection: with motion of gas or liquid across heated surface (cook food)
-Radiation: through electromagnetic waves (sun)

Loss of heat:
-Evaporation: we lose heat as fluid evaporates (sweat)

Question 7

How does thermoregulation occur?

Answer 7

-Central thermoreceptors: Abdomen and hypothalamus -> Feedback regulation -> respond to temperature change

-Peripheral thermoreceptors in the skin -> Feedforward (response before body temperature changes -> you walk into a cold room and start to shiver before body temperature drops)

Question 8

How does the body react in a cold environment - heat loss?

Answer 8

-Cutaneous (skin) vasoconstriction: increases resistance and decreases blood flow in the skin bc we lose heat there
-Shivering: muscle contraction (create heat) - spinal reflex

-Nonshivering thermogenesis:
Basic metabolic rate (BMR) goes up - through increase in Thyroid hormones
followed by Appetite -> effort to warm the body -> through sympathetic: Epi/NE

Question 9

How does the body react in a hot environment?

Answer 9

-Cutaneous vasodilation -> more blood flow to the skin->allow blood that carries heat to be decapitated through A-V anastomoses

-Sweating: evaporates
-Decrease thermogenesis: BMR, appetite, and muscle tone goes down
-remove clothes, shade

Question 10

Response to a cold environment (figure)?
SUMMARY

Answer 10

A signal from central (abdomen) or peripheral (skin) thermoreceptors to Hypothalamus

Skin arterioles: Vasoconstriction
Sweat gland: reduced production
Skeletal muscle: increased muscle tone (motor nerves)

Question 11

Response to a hot environment (figure)?
SUMMARY

Answer 11

Skin arterioles: Vasodilation
Sweat gland: increased production
Skeletal muscle: decreased muscle tone (via motor nerves)

Question 12

How does the body temperature change in a fever?

Answer 12

The set point rises to 38.7 while the body temperature is still at 37 -> the body assumes it is too cold -> so we shiver and vasoconstrict blood flow to the skin -> go through the sickness at a higher temperature

until the fever breaks -> set point gets back to normal -> sweat and skin vasodilation until body temperature gets back to normal

Question 13

What increases in response to endogenous pyrogens (inflammatory molecules)?

Answer 13

Prostaglandin E2 (PGE2) from CNS blood vessels -> responsible regulation of body temperature in the hypothalamus (shifts set point up)

Question 14

How does the body react to an increase in the set point?

Answer 14

The body assumes it is too cold as consequence of a high set point -> Skin vasoconstriction, Shivering

Question 15

What are the endogenous pyrogens?

Answer 15

Interleukins (IL-1, IL-6), are transported to Hypothalamus via vagus nerve and systemic circulation

Question 16

What is Hyperthermia and how is it different from fever?

Answer 16

Increase of body temperature with no change in hypothalamic set point - more thermal gain, too little thermal loss

-> caused by exercise, environment, some drugs (ecstasy, rising serotonin)

Question 17

What are the symptoms of Hyperthermia (Pathophysiology)?

Answer 17

Heat cramp -> loss of salts after exercise and skin moist (keep sweating)

Heat exhaustion: prolonged exposure to a hot environment
-> heat syncope (bc loss of water through sweat-> decrease in blood pressure (hypotension) until pass out),
skin moist, tachycardia, thirst, fatigue

Heat stroke: Life-threatening, core temperature more than 40°C
-> loss of ability to regulate that heat - the skin is dry (no sweating)
cardiovascular collapse, delirium, unconsciousness

Question 18

What are the symptoms of Hypothermia?

Answer 18

core temperature below 35°C
Loss of heat greater than production
caused by the environment (winter) or drugs (alcohol)

-> Shivering, slurred speech, low energy, memory loss, weak pulse,…