Thermoregulation

Question 1

Describe feedback system vs feed-forward system

Answer 1

Feedback: information is fed back to controller to report changes in controlled variable
Feed-forward: information is used to prevent changes in controlled variable

Question 2

Describe thermoreceptors

Answer 2

Neurons which change their firing rate in response to changes in local temperature
Presumed to be bare nerve endings (neurite complex)
May be warm or cold sensitive

Question 3

Describe warm sensitive thermoreceptors

Answer 3

4 channels: TRP-V1-4
Sensitive over different ranges
V=vanilloid=capsaicin (hot peppers)

Question 4

Describe cold sensitive thermoreceptors

Answer 4

Two receptors: TRPM8 (CMR-1), TRPA2
Also activated by menthol
Activation: opens as temperature decreases
Allows Na+ or Ca++ influx

Question 5

Where are thermoreceptors?

Answer 5

Found in skin, viscera, and brain

Different locations tell the brain about different temperatures

Question 6

What has connections to control the hormonal, autonomic, and behavioral changes that are part of thermoregulation?

Answer 6

Hypothalamus

Question 7

What part of the hypothalamus responds to heat vs cold?

Answer 7

Response to heat: anterior. Heat loss behaviors

Response to cooling: posterior. Heat production behaviors

Question 8

Describe body temperature changes with activity

Answer 8

With sleep, temperature decreases
Circadian influence (varies 1-2 degrees over 24 hr. Low at 6 am)
Set point decrease?

With exercise, temperature increases (as high as 40 C)
Increase heat production
Set point increase

Question 9

What determines the set-point for core temperature?

Answer 9

Hypothalamus

Question 10

Describe cutaneous thermoreceptors

Answer 10

Often bimodal (temperature and touch sensitive)
May be warm or cold sensitive
10x as many cold sensitive
These tell us about environmental conditions

Question 11

Why are thermoreceptors in the gut?

Answer 11

Not just for sensing core temperature
Threats to maintenance
-food ingested may change body temperature
-tell hypothalamus about these threats

Question 12

Describe central thermoreceptors

Answer 12

Location: pre-optic and superoptic region of hypothalamus
What: neuron cell bodies sensitive to changes in temperature
3x as many warm sensitive
They relay their information to other areas of the hypothalamus

Question 13

Describe heat production

Answer 13

1. Mechanisms
   - ans: sympathetic system
   - hormonal: thyroxin, epinephrine/norepi
2. Ways of producing heat
   - muscular activity
   - non-shivering thermogenesis (non-muscular)

Question 14

Describe muscular activity to produce heat

Answer 14

Shivering

• dorsomedial posterior hypothalamus
• increase motorneuron excitiation

Increase voluntary activity

• via cortex
• jumping, running

Question 15

Describe non-shivering thermogenesis

Answer 15

Hormonal influence is strong

• thyroxin increases metabolic rate (heat production; stimulus for TRH release is cold)
• epinephrine

Increase food intake
-increase metabolism

Brown adipose tissue

Question 16

Describe brown adipose tissue

Answer 16

1. Low efficiency hydrolysis of ATP (low efficiency = lots of heat production)
2. Sympathetic
   - innervation of brown fat
   - circulating epinephrine (catecholamine)
3. Importance in human
   - strong in infants
   - recent evidence shows existence in adults

Question 17

Describe ways for heat loss

Answer 17

Evaporative heat loss: energy (heat) lost as water evaporates
Two kinds: insensible (respiratory) and sweating (controlled)

Question 18

Compare convection, conduction, and radiation

Answer 18

Convection: movement of molecules away from contact (air heating and rising)
Conduction: transfer of heat between objects in physical contact with one another
Radiation: infrared radiation transferring heat between 2 objects not in physical contact

Question 19

Describe integrative responses to increased core temperature

Answer 19

Decrease heat production

• apathy/inertia
• anorexia

Increase heat loss

• blood to skin
• EHL (sweat)
• insensible heat loss (pant)

Question 20

Describe sweat gland and innervation

Answer 20

Lots of blood vessels nearby
Coiled region by vessels
Duct leading to skin

Innervation: sympathetic cholinergic (acetylcholine is neurotransmitter, binding to muscarinic receptor)

Question 21

Describe primary secretion of sweat gland

Answer 21

High in water and sodium

Water and sodium are reabsorbed in duct of sweat gland

Question 22

Describe low vs high flow rates of sweating

Answer 22

Low rate: concentrated; little water, high sodium

High rate: lots of water, little sodium

Question 23

Describe integrative responses to decreased core temperature

Answer 23

Increase heat production

• shivering
• non-shivering thermogenesis

Decrease heat loss

• blood away form skin
• decrease EHL (sweating)

Question 24

Describe fever

Answer 24

Controlled increase in body temperature

Implication: set point increase: body temperature is only doing what hypothalamus directs it to do

Question 25

How does a fever start?

Answer 25

“The bug” secretes endotoxins
Immune cells are activated by “bug” and then release cytokines
Major player: prostaglandin E2
Increase hypothalamic set point for temperature
Tb

Question 26

Describe hyper/hypothermia

Answer 26

Uncontrolled changes in body temperature
Implications:
Set point remains normal
Environmental stresses exceed body’s ability to regulate temperature
At extremes, hypothalamic regulation may be lost

Question 27

What is normal body temperature? What is the normal range?

Answer 27

36. 7 C (98.06 F)

36. 3-37.1