MNSR 23 - Thermoregulation

Question 1

Thermoregulation

Answer 1

Process of keeping the body at a constant temperature (37 C) in a constantly changing temperature of the environment
- in cold environments - conserves heat
- in hot environments - facilitates heat loss

Question 2

Thermoregulatory System Regulated by

Answer 2

• Neural negative feedback mechanisms which operate primarily through hypothalamus
• Input received from thermoreceptors in skin and body core

Question 3

Counter Current Heat Exchange

Answer 3

Exchange of heat between 2 vessels that
1) run in opposite directions/same direction
2) in close contact
Minimizes conductive and radiative heat loss in cold climates
* Heat lost by outgoing arterial blood re-heats returning venous blood, minimizes heat loss in limbs

(heat from hot blood vessel will go into the cold one - hot blood from body core pumped towards periphery/extremities, cold blood returns back to the core, warmed by hot blood vessel)

Question 4

Example of counter current heat exchange

Answer 4

Mechanism of keeping testes at optimum temperature
Optimum temp for producing healthy sperm is 3-4C lower than normal body temp

Question 5

Heat Production in Testes

Answer 5

As body temp increases, cremaster and dartos muscles relax
Lowers scrotum further away from the body and increases the effective length of the venous pampiniform plexus
Arterial blood passing through the elongated plexus is cooled more than usual, further reducing temperature of testes

Question 6

Heat Production / Conservation Mechanisms

Answer 6

• increased metabolic rate
• blood-flow redistribution (vasoconstriction)
• countercurrent blood flow
• shivering
• insulation (fat, feather, fur)
• behavior (huddling posture)

Question 7

Vasoconstriction

Answer 7

Decrease blood flow to the skin
Reduce heat loss to the environment
Make blood vessels smaller, by using:
- Sphincter muscles reduce the cross-sectional area of the vessel
- Shunt blood vessels that redirect blood flow

Question 8

Shivering

Answer 8

Bodily function in response to cold
An attempt to create warmth by expending energy
Involuntary contraction of muscles produces heat to warm the body

Question 9

Piloerection

Answer 9

“Goose bumps” created when tiny muscles at the base of each hair = arrector pili = contract and pull hair erect
Erect hair traps air to create layers of insulation
Warm air trapped against the skin
Retains heat, decreases blodo flow

Question 10

Frostbite

Answer 10

Local cold injury due to formation of ice crystals in the skin and other tissues
- Skin is exposed to temperature of 0°C or lower, resulting in vasoconstriction
- Decreases blood supply to extremities
- Ice can expand, causing cells to rupture
- Decrease in water reaching cells, leading to dehydration, hyperosmotic cell death (cells lose water until they die)
- Most effect treatment is warming of still frozen area by immersion in 40-42 C hot water following hospitalization

e.g. Beck Weathers spent 18 hrs lying in snow at -40 C at 800 m on Everest, amputated nose, lower right arm, all fingers on left hand

Question 11

Heat-Loss Mechanisms

Answer 11

• Blood flow redistribution (vasodilation)
• Perspiration (sweating)

Question 12

Vasodilation

Answer 12

Increase blood flow to the skin
Increase heat loss to the environment
Achieved using:
- Sphincter muscles increase cross-sectional area of vessel
- Shunt blood vessels into dilated vessels, that redirect blood flow towards extremities

Question 13

Perspiration

Answer 13

• Sweat glands found all over the body surface.
• Evaporative heat loss determined by the ability of ambient air to remove water vapor (convection).
• Allows heat to move from core to skin, to vaporize sweat
• Water has a high latent heat of vaporization, so a large loss of heat when sweat evaporates
• Less effective with high humidity, as sweat cannot evaporate
• Only cooling mechanism that works when outside temperature is greater than 37C
• Fever patients were sometimes (outdated - side effects) rubbed with isopropyl alcohol, lower BP than water so evaporates more vigorously at 37C
• Humans perspire more than any other mammal, seen as an evolutionary advantage allowing early ancestors to hunt prey by running them down over long distances without overheating (persistence hunting)

Question 14

Heatstroke / Sunstroke

Answer 14

• Body produces/absorbs more heat than it can dissipate
• Usually due to excessive exposure to heat
• Heat regulating-mechanisms become overwhelmed
• Body temperature climbs uncontrollable, core rectal temperature approaches 41 C
• Serious medical emergency, requires immediate medical attention

Question 15

Thermoregulatory processes in other species

Answer 15

• Dogs pant (sweat through tongue)
• Kangaroos lick their forearms (thin with large veins), saliva evaporates and cools the blood
• Pelicans open their bill and flutter the pouch, increasing blood flow, promoting heat loss through evaporative cooling
• Storks excrete onto their legs to prevent overheating - urohidrosis

Question 16

q) Thermoregulatory system acts to _________

Answer 16

Facilitate heat loss in hot environment