Ch. 7 Homeostasis of Body Temperature

Question 1

What causes slight variation in body temperature

Answer 1

o Activity or changes in external temp

o Characteristic daily body temp cycle

Question 2

why is a constant internal temp important and what occurs if temp not level

Answer 2

o Chemical reactions in cells are heat sensitive
♣ 37 degrees= optimum for cellular reactions
- If temp not lowered:
o nerve malfunction
o change in structure of proteins
o death

Question 3

Define thermoregulation

Answer 3

the regulation of body temperature; balance of heat gain and heat loss in order to maintain a constant internal body temperature independent of the external environment

Question 4

what three factors effect metabolic rate

Answer 4

exercise
stress (autonomic > noradrenalin)
body temp

Question 5

What are the two types of thermorecptors and where are they located

Answer 5

Peripheral- mucus membrane and skin

Central- hypothalamus

Question 6

What are the two types of peripheral thermorecpetors

Answer 6

♣ Cold receptors: stimulated by external temperatures lower than normal.
♣ If cold stimulated, hypothalamus receives info + initiates heat conservation + heat production mechanisms
♣ Heat receptors: detect external temperatures higher than normal
♣ If hot simulated, hypothalamus receives info + initiates mechanisms to reduce heat production and increase heat loss

Question 7

what are the diameter of vessels controlled by

Answer 7

sympathetic autonomic nerves

Question 8

when does sweating occur and what causes it

Answer 8

- large amounts of body heat must be lost and skin blood vessels already at max dilation
sweating occurs (production + transport stimulated by sympathetic nerves)

Question 9

How does sweat have a cooling effect

Answer 9

evaporation
Heat removed from skin when liquid sweat to changes into vapour
o Cooling of skin= cooling of the blood flowing through skin

Question 10

how is the hypothalamus involved in thermoregulation

Answer 10

• H monitors temp of blood + receives impulses from peripheral thermoreceptors
• Through neg feedback loops involving the autonomic NS, controls diameter of blood vessels, sweating, shivering, other mechanisms

Question 11

What re the 3 physiological and 2 behavioural responses to a increase in temp

Answer 11

1. Vasodilation
2. Sweating
3. Thyroxine

• Conscoius behaviour (cerebral cortex)
• E.g. removing clothing, AC
• Reduce physical activity therefor decreasing metabolic rate

Question 12

What re the 4 physiological and 2 behavioural responses to a decrease in temp

Answer 12

1. Vasoconstriction
2. Stimulation of Adrenal Medulla
3. Shivering
4. Increase Thyroxine
   - Conscoius behaviour (cerebral cortex)
   - E.g. adding clothing, sheltering
   - Increase physical activity therefore increasing metabolic rate

Question 13

Decrease in temp: explain Vasoconstriction

Answer 13

o Impulses from hypo stimulate sympathetic nerves> blood vessels constrict
o Constriction decreases flow of warm blood to skin from internal // decrease hear from internal to skin
o Skin becomes cooler (less warm blood blowing through it)
Less heat lost from body surface

Question 14

Decrease in temp: explain stimulation of adrenal medulla

Answer 14

o Imitated by hypothalamus to stimulate by sympathetic nerves
o Stimulation= medulla secrete adrenalin and noradrenalin into blood
♣ = increase in cellular metabolism= increase in heat production
o maintain internal temp in conditions with rapid heat loss

Question 15

Decrease in temp: explain shivering

Answer 15

o Heat produced
o Fall in temp= hypothalamus= stimuli to brain that increases skeletal muscle tone
o tremors= shivering (fast response + heat production)
o As no external work done, all energy liberated from metabolic activity= internal heat
o Shivering= primary control of hypothalamus, but conscious input from cerebral cortex can surpass urge to shiver

Question 16

Decrease in temp: explain thyroxine

Answer 16

o Hypothalamus > cause anterior lobe to secrete thyroid stimulating hormone (TSH) > thyroid gland release thyroxine into blood
o Increase thyroxine= increase metabolic rate (// increase body temp)
o Slower effect, but long lasting than other responses
o Small change in metabolic rate b/w summer and winter= result of this response

Question 17

Increase in temp: explain vasodilation

Answer 17

o	Increase blood flow to skin 
o	Skin=
♣	 turns red in colour,
♣	 surface temp rises, 
♣	greater heat loss through radiation + convection

Question 18

Increase in temp: explain sweating

Answer 18

o Above 28 degrees sweating needed to increase heat loss
o Cooling effect of sweating= only effective in dry environments (if humid= sweat cannot evaporate)
o In low humidity= affective sweating
o If temp greater than 37, heat gained from environment and evaporation of sweat= only avenue for heat loss

Question 19

Increase in temp: explain thyroxine

Answer 19

o Long term
o Decrease in metabolic rate = less heat production
o Reduction of secretion of thyroxine (less in winter than summer)

Question 20

Define heatstroke

Answer 20

the failure of a person’s temperature regulating mechanisms when exposed to excessive heat

Question 21

Define heat exhaustion

Answer 21

the collapse of a person after the exposure to heat, during which their body’s heat-regulating mechanisms continue to function normally

Question 22

Define hypothermia

Answer 22

abnormally low body temperature; the temperature drops below the level required to maintain normal body functions