Week 6 thermoregulation & homeostasis

Question 1

What is homeothermic?

Answer 1

Body temperature maintained within a narrow range

Question 2

What rhythm does human temperature display?

Answer 2

Diurnal rhythm:

lower in predawn hours, rises in afternoon

Question 3

Where is the thermo-regulating center?

Answer 3

Posterior hypothalamus

Question 4

What are peripheral thermoreceptors and central thermoreceptors? What are they detecting?

Answer 4

Peripheral thermoreceptors: detect skin temperature

1. cold receptors
2. warmth receptors

Central thermoreceptors: detect core body temperature

1. heat-sensitive neurons
2. cold-sensitive neurons

Question 5

2 factors determining rate of heat loss

Answer 5

1. How rapidly heat is conducted from core to skin by blood vessels
2. How rapidly heat can be transferred from surface of skin to surroundings

Question 6

What is core body temperature determined by?

Answer 6

balance between heat gain and heat loss

Question 7

Responses to heat

Answer 7

1. Increase heat loss
   a) vasodilation of cutaneous arterioles
   b) sweating
2. Reduce heat production

Question 8

Responses to cold

Answer 8

1. Reduce heat loss
   a) vasoconstriction of cutaneous arterioles
   b) piloerection
2. Increase heat production
   a) shivering thermogenesis
   b) non-shivering (chemical) thermogenesis - e.g. epinephrine, norepinephrine, thyroxine

Question 9

What is fever?

Answer 9

Pyrexia

Increased core body temperature caused by elevation of thermal set-point

Question 10

How is pyrexia caused?

Answer 10

1. Presence of pyrogens
2. Stimulates immune cells
3. Produce pyrogenic cytokines
4. Stimulates synthesis of prostaglandin E2 (PGE2) in hypothalamus
5. Elevation of thermal set-point
6. increase heat production and reduce heat loss

Question 11

Which substance is the direct cause of pyrexia? Where is it synthesized?

Answer 11

Prostaglandin E2 (PGE2) synthesized in hypothalamus

Question 12

When does heat stroke occur? What happens?

Answer 12

When body temperature reaches 41-42oC
thermoregulatory centre is depressed -> decrease sweating -> increase in core body temperature
(warm and dry skin)

Question 13

When does hypothermia occur?

Answer 13

Core body temperature <35oC

Question 14

What is homeostasis?

Answer 14

Maintenance of relatively constant conditions in the internal environment

Question 15

4 parameters determining cell functions

Answer 15

1. Quality of protein
2. Quantity of protein
3. Spatial (where protein is expressed)
4. Temporal (time when protein is expressed)

Question 16

Composition of body fluids

Answer 16

1. Intracellular fluids - 2/3 of all body fluids
2. Extracellular fluids - 1/3 of all body fluids
   a) Plasma - 1/4 of extracellular fluid
   b) Interstitial fluid - 3/4 of extracellular fluid