8.10. Thermoreceptors. Thermoregulation. Regulation of the circulation of the skin.

Question 1

I. THERMORECEPTORS
1. Which system is responsible for the mediation of heat sensation (+ pain sensation)?

Answer 1

The anterolateral (spinothalamic) system

Question 2

I. THERMORECEPTORS
2. What is the role of The anterolateral (spinothalamic) system?

Answer 2

The anterolateral (spinothalamic) system is responsible for the mediation of heat sensation (+ pain sensation)

Question 3

I. THERMORECEPTORS
3. What types of fibers are heat and pain sensing fibers?

Answer 3

free nerve endings

Question 4

I. THERMORECEPTORS
4. What makes the free nerve endings specific to certain sensation?

Answer 4

• What makes the free nerve endings specific to a certain sensation are ion channels

Question 5

I. THERMORECEPTORS
5. What are the characteristics of TRP channels?

Answer 5

TRP channels = transient receptor potential channels
- TPR channels are cation channels => opened by hot temperatures + acidic pH

Question 6

I. THERMORECEPTORS
6. Describe non-adapting receptors that recognize thermal sensation

Answer 6

3 classes of non-adapting receptors recognize thermal sensation, which results from difference between external temperature of air and objects containing normal skin temperature (34 degrees)

Question 7

II. THERMOREGULATION
1. Is the temperature of body the same everywhere?

Answer 7

Temperature of the body is not exactly the same throughout

Question 8

II. THERMOREGULATION
2. Describe the core temperature?

Answer 8

• Core temperature = constant
• The brain, heart/chest, abdominal cavity have a core temperature of 37°C

Question 9

II. THERMOREGULATION
3. What happen to the temperature of body if you are in a cooler environment?

Answer 9

• Skin + extremities have lower temperatures (<37°C)
• The brain, heart/chest, abdominal cavity have a core temperature of 37°C

Question 10

II. THERMOREGULATION
4. What happen to the temperature of body if you are in a warmer environment?

Answer 10

If you are in a warmer environment, f.ex 30°C
=> large portion of body will also have same temperature as core temperature

Question 11

II. THERMOREGULATION
5. Why is thermoregulation important?

Answer 11

Thermoregulation is important in regulating the core temperature in presence of a variable environment

Question 12

II. THERMOREGULATION
6. Describe the 37 degree Celsius in terms of thermoregulation

Answer 12

37°C is the normal ‘’set-point value’’ that is encoded in the CNS as the optimal temperature value the body will strive to maintain
=> works like a thermostat

Question 13

II. THERMOREGULATION
7. What is the normal range of core temperature in order to be compatible with life?

Answer 13

Core temperature must be between 30 – 42°C in order to be compatible with life

Question 14

II. THERMOREGULATION
8. What happen if core temperature below 30°C?

Answer 14

Core temperature below 30°C:
=> primarily affects the function of heart – most sensitive to cold
=> different types of arrythmias will occur

Question 15

II. THERMOREGULATION
9. What happen if core temperature above 42°C?

Answer 15

Core temperature higher than 42°C:
=> primarily affects the function of the brain
=> abnormal reflexes occur + thermoregulation is further impaired due to CNS malfunction

Question 16

II. THERMOREGULATION - Processes leading to increased body temperature
10A. What are the 2 main processes leading to increased body temperature?

Answer 16

1. Chemical heat production
2. Physical heat uptake

Question 17

II. THERMOREGULATION - Processes leading to increased body temperature
10B. What is chemical heat production?

Answer 17

metabolism of the organism produces chemical heat

Question 18

II. THERMOREGULATION - Processes leading to increased body temperature
10B. What is chemical heat production?

Answer 18

metabolism of the organism produces chemical heat

Question 19

II. THERMOREGULATION - Processes leading to increased body temperature
10C. What are the 2 main chemical processes that produce heat?

Answer 19

1. Non-shivering heat production
2. Shivering heat production

Question 20

II. THERMOREGULATION - Processes leading to increased body temperature
10D. Describe non-shivering heat production

Answer 20

Non-shivering heat production: brown adipose tissue + major organs (heart, kidney, liver, brain)

1. Brown adipose tissue: professional heat-producing tissue. Brown adipocytes are more common in newborns, while beige adipocytes are more common in adults
2. Major organs: have a high BMR that contributes to core body temperature

Question 21

II. THERMOREGULATION - Processes leading to increased body temperature
10E. Describe shivering heat production

Answer 21

• Skeletal muscle is responsible for this.
• When core temperature drops, shivering reflex is triggered to maintain homeostasis.
• Skeletal muscle begin to shake in small movements -> increased muscular activity -> generation of heat

Question 22

II. THERMOREGULATION - Processes leading to increased body temperature
10F. Describe physical heat uptake

Answer 22

Requires higher air temperature than the temperature of skin
=> must be above 34°C (skin temperature) = only useful in hot environment

Question 23

II. THERMOREGULATION - Processes leading to decreased body temperature
11A. What are the 2 main processes leading to decreased body temperature?

Answer 23

1. Physical heat loss
2. Evaporation

Question 24

II. THERMOREGULATION - Processes leading to decreased body temperature
11B. Describe the physical heat loss

Answer 24

• Physical heat loss: these are passive processes. The determinant is the pressure gradient between environment and body.
• Heat will be transferred from higher to lower temperature

Question 25

II. THERMOREGULATION - Processes leading to decreased body temperature II. THERMOREGULATION - Processes leading to decreased body temperature 11C. What are the 3 main processes of physical heat loss?

Answer 25

1. Convective 2. Conductive 3. Radiation

Question 26

II. THERMOREGULATION - Processes leading to decreased body temperature 11C1. What is convective?

Answer 26

This is how the wind will cool the body down. => Moving air removes radiated heat

Question 27

II. THERMOREGULATION - Processes leading to decreased body temperature 11C2. What is conductive?

Answer 27

Heat is transferred to environment by direct contact

Question 28

II. THERMOREGULATION - Processes leading to decreased body temperature 11C3. What is radiation?

Answer 28

Emission of electromagnetic radiation

Question 29

II. THERMOREGULATION - Processes leading to decreased body temperature 11D. What is evaporation?

Answer 29

- Loss of heat by evaporation of water. - Does not depend on temperature gradient, but humidity of the air

Question 30

II. THERMOREGULATION - Processes leading to decreased body temperature 11E. What are the 2 main processes of evaporation?

Answer 30

1. Perspiration insensibles 2. Perspiration sensibles

Question 31

II. THERMOREGULATION - Processes leading to decreased body temperature 11F. What is Perspiration insensibles?

Answer 31

Perspiration insensibles: obligate heat loss we cannot regulate -> happens during breathing (15%) + skin (85%) -> about 1L of water/day evaporated

Question 32

II. THERMOREGULATION - Processes leading to decreased body temperature 11G. What is Perspiration sensible?

Answer 32

sweating (can be regulated)

Question 33

II. THERMOREGULATION - Heat balance 12. What is heat balance?

Answer 33

The processes that lead to increase of body temperature must be equal to processes that lead to decrease of body temperature => chemical heat production is equal to physical heat loss

Question 34

II. THERMOREGULATION - Heat balance 13. Describe isolation in heat balance

Answer 34

Isolation (adipose tissue, clothing hair): - If it is cold = isolation protects the core temperature and reduces heat loss - If it is warm = isolation may make things worse, but there are regulatory mechanisms in skin circulation -> the blood flowing to the skin will allow more heat to be transferred from body to environment

Question 35

II. THERMOREGULATION - Skin circulation 14. What are the important parameters of skin circulation?

Answer 35

1. Skin circulation: 100-300 mL/min, in warm environment it may rise to 8L/min 2. AVDO2 = 20-30mL/L

Question 36

II. THERMOREGULATION - Skin circulation 15A. Where can you find apical skin?

Answer 36

Apical skin: non-hairy, palms, lips, nose, ears, fingertips (vasoconstriction = conserve heat)

Question 37

II. THERMOREGULATION - Skin circulation 15B. Describe skin circulation of apical skin?

Answer 37

Apical skin: non-hairy, palms, lips, nose, ears, fingertips (vasoconstriction = conserve heat) - Apical skin has arteriovenous anastomoses (AVA), providing direct connection between arterial + venous systems - AVA has SYM innervation with basal tone leading to constriction - Highly sensitive to vasoconstrictors like NE => Plays a role in temperature regulation and constricts with increased SYM activity to conserve body heat

Question 38

II. THERMOREGULATION - Skin circulation 16A. Where can you find non-apical skin?

Answer 38

hairy skin, covers most of the body (vasodilation = dissipation of heat)

Question 39

II. THERMOREGULATION - Skin circulation 16B. Describe skin circulation of non-apical skin

Answer 39

Non-apical skin: hairy skin, covers most of the body (vasodilation = dissipation of heat) - Has arterioles with higher basal tone, lower neural tone -> normal SYM activity (NO AVA) - Sweat glands can be found here (cholinergic SYM innervation by mAChR)

Question 40

II. THERMOREGULATION - Skin circulation 17A. What is the main contributor to changes in cutaneous blood flow?

Answer 40

Thermoregulation

Question 41

II. THERMOREGULATION - Skin circulation 17B. How does vasoconstriction participate in thermoregulation in cutaneous blood flow?

Answer 41

Vasoconstriction: - Blood flow decrease in cold weather >7mL/min = sympathetic tone (conserve heat)

Question 42

II. THERMOREGULATION - Skin circulation 17C. How does Vasodilation participate in thermoregulation in cutaneous blood flow?

Answer 42

- Blood flow increases in hot weather >100L/min = to release heat (sympathetic tone inhibited, so vasodilation takes place for dissipation of heat) - Activation of sweat glands which make products that causes vasodilation

Question 43

II. THERMOREGULATION - Skin circulation 17D. How do emotions participate in thermoregulation in cutaneous blood flow?

Answer 43

Emotions: explained by vasodilatory mechanism, so there are CNS effects on skin circulation (especially in the face) - Fear -> pale skin due to poor skin circulation - Embarrassment -> flushing skin due to high skin circulation

Question 44

II. THERMOREGULATION - sweat glands and sweating 18. Where is sweat gland found? What does sweating depend on?

Answer 44

Sweat glands found in non-apical skin => sweating depends on the humidity of the air.

Question 45

II. THERMOREGULATION - sweat glands and sweating 19. What is sweat?

Answer 45

Sweat is a protein-free hypoosmotic fluid

Question 46

II. THERMOREGULATION - sweat glands and sweating 20A. What are the 2 main mechanisms of secretion of sweat glands?

Answer 46

1. Primary SECRETION in acinar cells – with concentrations similar to plasma (↑ in Na+/Cl-) 2. Secondary REABSORPTION of ductal cells – Na+-reabsorption is aldosterone dependent

Question 47

II. THERMOREGULATION - sweat glands and sweating 20B. Describe the mechanism of Primary SECRETION in acinar cells

Answer 47

Primary SECRETION in acinar cells – with concentrations similar to plasma (↑ in Na+/Cl-) 1) Na+/K+/2Cl—cotransporter moves these ions into the acinar cells from the basolateral side -> Cl—transporters move Cl- to the lumen 2) Paracellular Na+-transport + transcellular H2O transport into the lumen 3) Luminal fluid is initially plasma-like, but is modified later

Question 48

II. THERMOREGULATION - sweat glands and sweating 20C. Describe the mechanism of Secondary REABSORPTION of ductal cells

Answer 48

-Secondary REABSORPTION of ductal cells – Na+-reabsorption is aldosterone dependent 1) Cl- will follow based on electrochemical gradient 2) NO water reabsorptionhow the final product of sweat is hypoosmotic

Question 49

II. THERMOREGULATION - sweat glands and sweating 20D1. What do ionic components of sweat depend on?

Answer 49

Ionic components of sweat depends on rate of sweat flow

Question 50

II. THERMOREGULATION - sweat glands and sweating 20D2. Explain Ionic components of sweat in high sweat flow rate

Answer 50

High [Na+] + [Cl-], since there is less time for secondary reabsorption

Question 51

II. THERMOREGULATION - sweat glands and sweating 20D3. Explain Ionic components of sweat low sweat flow rate

Answer 51

Low [Na+] + [Cl-], since the ions are reabsorbed more effectively

Question 52

II. THERMOREGULATION - sweat glands and sweating 20D4. ExplainIonic components of sweat in cystic fibrosis

Answer 52

Cl--channel does not work => high [Na+] + [Cl-] in sweat

Question 53

II. THERMOREGULATION - sweat glands and sweating 21. Explain Vasodilatory mechanism of sweat

Answer 53

Vasodilatory mechanism of sweat: SYM cholinergic innervation - ACh activates sweat glands by activating PLC -> Ca2+-signal - The cells then produce kallikrein -> bradykinin -> vasodilation of local blood vessels in the skin - So, when sweat is activated, the skin circulation is also activated

Question 54

II. THERMOREGULATION - CNS center of thermoregulation 22. Which part of CNS is the most important part in thermoregulation? What is its role?

Answer 54

Hypothalamus = the most important regulator - Stimulating regional vasoconstriction -> ‘’cold centers’’ of the body - Stimulating regional vasodilation -> ‘’warm centers’’ of the body

Question 55

II. THERMOREGULATION - CNS center of thermoregulation 23A. What are the 2 types of receptors in CNS center of thermoregulation?

Answer 55

1. Central receptors 2. Peripheral receptors

Question 56

II. THERMOREGULATION - CNS center of thermoregulation 23B. Describe central receptors

Answer 56

Central receptors: sensitive to change of core temperature, because they are all located deep in the body (HT, liver, spinal bone marrow) => the most important thermoreceptors

Question 57

II. THERMOREGULATION - CNS center of thermoregulation 23C. Describe peripheral receptors

Answer 57

- Found in skin, oral cavity, etc. Play important role detecting air temperature. - Belong to TRP channel family -> sense the skin temperature. - Activation of peripheral thermoreceptors will regulate the set-point value, and impact the core temperature

Question 58

II. THERMOREGULATION 24. How does thermoregulation occur in warm environment?

Answer 58

Regulation in warm environment: meaning core temperature is getting higher - Decrease of isolation - Vasomotor activity decreases (decrease in SYM tone)vasodilation - Sudomotor activity increases (mAChR) -> sweating is activated - Complex behavioral change -> animal going to a colder place (ex: shadow

Question 59

II. THERMOREGULATION 25A. What are the 3 ways that thermoregulation occur in cold environment?

Answer 59

1. Decrease physical heat loss 2. Increase chemical heat production 3. Drinking alcohol will cause vasodilation

Question 60

II. THERMOREGULATION 25B. How does thermoregulation occur in cold environment if there is alcohol drinking?

Answer 60

Drinking alcohol will cause vasodilation -> peripheral heat receptors activated -> set-point temperature decreased -> lower core temperature (even though environment is cold)

Question 61

II. THERMOREGULATION 25C. What are the consequences of decreased physical heat loss in cold environment?

Answer 61

increase isolation by vasoconstriction of skin by increasing SYM activity

Question 62

II. THERMOREGULATION 25D. What are the consequences of Increased chemical heat production in cold environment?

Answer 62

Increase chemical heat production => SYM response: 1. Increase skeletal muscle activity (shivering, physical exercise) 2. Thyroid gland (slow effect, not so important) 3. Brown adipose tissue (mainly beige adipose tissue in adults)

Question 63

II. Problems that occur when thermoregulation does not work 1. What are the 4 problems that can occur when thermoregulation does not work?

Answer 63

1. Heat exhaustion 2. Hyperthermia 3. Fever 4. Hypothermia

Question 64

II. Problems that occur when thermoregulation does not work 2. What is Heat exhaustion?

Answer 64

- Warm temperature causes vasodilation and increased sweating -> hypovolemia (loss of blood volume) -> also lose Na+ + Cl- ions from sweating -> hypoosmotic hypovolemia -> decreased CO -> decreased arterial BP = circulatory shock - We need to drink more water + electrolytes to replenish what was lost in the sweat

Question 65

II. Problems that occur when thermoregulation does not work 3. What is Hyperthermia?

Answer 65

When sweating is not effective and the core temperature increases -> CNS function is impaired -> regulation of core temperature decreases -> even more increased core temperature -> may lead to death

Question 66

II. Problems that occur when thermoregulation does not work 4. What is fever?

Answer 66

- Different than hyperthermia, because thermoregulation is functioning and is causing the fever by increasing the set-point value - Fever induced by pyrogens (exogenous: bacteria/virus, endogenous: cells of immune system)

Question 67

II. Problems that occur when thermoregulation does not work 5. What is Hypothermia?

Answer 67

Core temperature decreases -> function of heart is impaired via arrythmias -> may lead to death

Question 68

II. Problems that occur when thermoregulation does not work 5. What is Hypothermia?

Answer 68

Core temperature decreases -> function of heart is impaired via arrythmias -> may lead to death

Question 69

IV. Extra 1. Make a schematic diagram of thermoregulation

Answer 69

Question 70

IV. Extra 2. Make a schematic diagram that demonstrate the relationship between O2 compensation and Tcore (heat production and heat loss)

Answer 70