L27 - Thermoregulation 2

Question 1

What must happen when body temperature decreases?

Answer 1

body heat must be conserved and additional heat (energy) must be produced

Question 2

What will happen to heart rate at low temperatures?

Answer 2

depends on the exact temperature and individual

Question 3

Why will decreased temperature result in decreased heart rate?

Answer 3

arterioles in the skin will constrict to conserve heat

this will increase TPR and as a result CO will decrease

Question 4

How does the body conserve heat?

Answer 4

sympathetic noradrenergic neurons cause cutaneous vasoconstriction (non-apical skin)
piloerection to increase insulating layer (largely ineffective in clothed individuals)

Question 5

What would happen to ventilation (at rest) at low temperature?

Answer 5

increase
this is because heat is produced through metabolism so in order to produce more heat metabolism ↑ and therefore ventilation ↑

Question 6

What are the different ways in which the body produces heat?

Answer 6

1. normal metabolism
2. skeletal muscles: shivering thermogenesis, voluntary movements (EAT and NEAT)
3. brown and beige adipose tissue (BAT): non-shivering thermogenesis

Question 7

What is EAT and NEAT?

Answer 7

exercise-associated thermogenesis and non-exercise activity thermogenesis

Question 8

Why does ventilation increase when there is overall increased metabolic activity?

Answer 8

increased O2 demand / CO2 production

Question 9

What are characteristics of shivering thermogenesis?

Answer 9

indicates maximum vasoconstriction, initiated by peripheral thermoreceptors (skin), activated by hypothalamus and motor cortex

Question 10

Where does non-shivering thermogenesis occur?

Answer 10

occurs in brown and beige adipose tissue (BAT)

Question 11

What does brown and beige adipose tissue contain?

Answer 11

high levels of uncoupling protein-1 which derails the electrochemical gradient for ATP synthesis in mitochondria, and causes the release of energy

Question 12

What is non-shivering thermogenesis regulated by?

Answer 12

thyroid hormone and sympathetic nervous system

Question 13

What are behavioural adaptations to cold?

Answer 13

warm clothing, “huddle up” to minimise exposed surface, seek shelter, stay well nourished

Question 14

What is fever?

Answer 14

↑ in set-point temperature induced by pyrogens
generally in response to pathology such as infection
aids to mobilise immune system

Question 15

What are exogenous and endogenous pyrogens?

Answer 15

endotoxins from bacteria are exogenous and cytokines are endogenous

Question 16

How do pyrogens result in fever?

Answer 16

pyrogens influence the hypothalamus resulting in an elevated thermoregulatory set point and fever

Question 17

What is the purpose of fever?

Answer 17

↑ T-cell generation and differentiation (enhances immune response)
may inhibit the function and spread of bacteria/viruses directly

Question 18

Is fever the enemy?

Answer 18

no, it is a response induced by the body to aid in the immune response
not harmful unless over 42˚C

Question 19

What is shivering a sign of?

Answer 19

the onset of fever

Question 20

What are chills (caused by fever)?

Answer 20

heating mechanisms activated as set-point rises (shivering)

Question 21

What happens when fever ends?

Answer 21

cooling mechanisms activated as set-point falls (sweating)

Question 22

What is there a conflict between during exercise in the heat?

Answer 22

skin blood flow, skeletal muscle blood flow and

fluid loss

Question 23

When exercising in the heat, fluid loss will result from:

Answer 23

sweating - 2-3 L/hour in trained individuals (~1 L/hour in untrained)
increased ventilation

Question 24

After significant fluid loss during exercise which parameters will decrease (compared to exercise at the same intensity before fluid loss)?

Answer 24

venous return, stroke volume, MAP, blood flow to inactive skeletal muscle and blood flow to skin

Question 25

If a person loses 6 litres of water through sweat and ventilation without consuming more water, how much will their plasma volume drop?

Answer 25

1/3 of body’s water is in the ECF and 1/4 of the ECF volume is plasma
therefore 6 x 1/3 x 1/4 = 0.5 L or 500 mL

Question 26

If a person loses 6L of water through sweat and ventilation during exercise, we would expect to see an increase in:

Answer 26

sympathetic nervous system activity, ANGII, aldosterone, vasopressin, sodium reabsorption, water reabsorption

Question 27

How is MAP restored?

Answer 27

increased SNS and decreased PNS activity resulting in increased CO (HR) and increased TPR

Question 28

How is plasma volume restored?

Answer 28

recruitment of the renin-angiotensin system which will lead to production of ANG II (↑ PCT reabsorption) and aldosterone (↑ Na+ reabsorption in the collecting duct)

Question 29

What stimulates activation of RAS?

Answer 29

the SNS

Question 30

What does it means if RAS is activated?

Answer 30

ANP is decreased resulting in increased Na+ reabsorption in the collecting duct

Question 31

What happens when water volume is low?

Answer 31

results in increased osmolarity and vasopressin release which is going to increase H2O reabsorption in the collecting duct

Question 32

What happens when water volume is particularly low?

Answer 32

ANGII will increase vasopressin release