Thermoregulation

Question 1

Where are thermoreceptors found?

Answer 1

Found in the skin, the viscera, and the brain

Question 2

What thermoreceptors are in our “core”?

Answer 2

Brain and viscera

Question 3

Describe cutaneous thermoreceptors

Answer 3

Often bimodal (temperature and touch sensitive); may be warm or cold sensitive; we have 10x as many cold sensitive receptors in the skin as we do warm sensitive receptors; these tell us about environmental conditions

Question 4

Why do we have thermoreceptors in the gut?

Answer 4

Detect threats to maintenance; for example, food ingested may change body temperature, so they tell the hypothalamus about these potential threats

Question 5

Describe thermoreceptors in the brain

Answer 5

Located mainly in anterior hypothalamus (pre-optic and superoptic regions of hypothalamus); these neuron cell bodies are sensitive to changes in temperature; we have 3x as many warm sensitive receptors in the brain than we do cold sensitive receptors; they relay their information to other areas of the hypothalamus

Question 6

Why is the hypothalamus the controller of the body temperature or set point?

Answer 6

Has connections to control the hormonal, autonomic, and behavioral changes that are part of thermoregulation

Question 7

What is the function of the hypothalamus in terms of thermoregulation?

Answer 7

Determines set point, receives info about the current temperature, and decides what to do

Question 8

What happens to our temperature/set point when we sleep? During exercise?

Answer 8

Sleep: temperature decreases, which represents a decrease in set point

Exercise: temperature increases, which represents a increase in set point

Question 9

What part of the hypothalamus is responsible for responding to heat? Cooling?

Answer 9

Heat: anterior hypothalamus controls heat loss behaviors

Cooling: posterior hypothalamus controls heat producing behaviors

Question 10

What are the different mechanisms for heat production?

Answer 10

Autonomic nervous system (sympathetics), endocrine (secretion of thyroxin or epinephrine), muscular activity (shivering, moving), and non-shivering thermogenesis

Question 11

What mediates shivering? What is the physiology behind shivering?

Answer 11

Mediated by dorsomedial posterior hypothalamus; caused by increased motorneuron excitation

Question 12

What mediates an increase in voluntary muscle activity to produce heat?

Answer 12

Mediated by cortex; examples include jumping, running, etc

Question 13

What are the mechanisms for non-shivering thermogenesis?

Answer 13

1) Secretion of thyroxin, which increases metabolic rate; cold is a stimulus for TRH release
2) Secretion of epinephrine, which causes us to increase food intake, which leads to increase in metabolism
3) Brown/white adipose tissue, innervated by sympathetics, hydrolyzes ATP through uncoupling proteins; under adrenergic innervation for its initiation (activated by circulating epinephrine)

Question 14

What are the 2 kinds of evaporative heat loss?

Answer 14

Insensible (respiratory) and sweating (controlled)

Question 15

What is convection as a way of heat loss?

Answer 15

Movement of molecules away from contact (air heating and rising)

Question 16

What is conduction as a way of heat loss?

Answer 16

Transfer of heat between objects in physical contact with one another

Question 17

What is radiation as a way of heat loss?

Answer 17

Infrared radiation transferring heat between 2 objects not in physical contact

Question 18

How do we control the following forms of heat loss: convection, conduction, radiation?

Answer 18

By controlling how much blood is sent to the skin; sending blood to the skin allows for heat loss; bypassing the skin limits heat loss to the environment

Question 19

Describe sweat glands and how they are under sympathetic cholinergic control and what makes them abnormal

Answer 19

Sweat glands are coiled and surrounded by blood vessels and they have a duct leading to the skin; they were identified as under sympathetic control because the fibers came from the thoracic/lumbar regions and they synapse in the sympathetic chain, however, it releases acetylcholine instead of norepinephrine at the tissues, which is abnormal

Question 20

What does the acetylcholne released at a sweat gland bind to?

Answer 20

Muscarinic receptor

Question 21

How is sweat filtered?

Answer 21

As fluid travels up to the surface of the skin, water and sodium are reabsorbed in the duct

Question 22

What happens to sweat under low flow rates? High flow rates?

Answer 22

Low rates: sweat contains little water (most is reabsorbed), but it has high sodium because it couldn’t follow the water

High rates: sweat has lots of water (no time to be reabsorbed) and lots of sodium; after acclimated to heat, sweat contains little sodium because body reabsorbs it (can’t afford to keep losing large amounts of salt in sweat)

Question 23

How does our body respond to low body temperatures?

Answer 23

Increase heat production, decrease heat loss

Question 24

What is a fever?

Answer 24

Controlled increase in body temperature; set point increases (body temperature is doing what hypothalamus told it to do)

Question 25

What is the major player in fevers?

Answer 25

Prostaglandin E2; increases hypothalamic set point for temperature

Question 26

How does our body respond to produce a fever in response to an illness/infection?

Answer 26

Increase heat production, decrease heat loss

Question 27

When the infection goes away, what happens to our set point?

Answer 27

In absence of endotoxins, hypothalamic set point returns to normal

Question 28

With set point now returning to normal, how does our body respond to get rid of our fever?

Answer 28

Decrease heat production, increase heat loss

Note decreasing heat production usually causes decreased appetite, but so does being ill. When the illness goes away, our appetite returns, so decreased appetite is hard to correlate with a fever