5.1 Thermoregulation and Homeostasis

Question 1

What is being homeothermic

Answer 1

Maintaining a steady internal core temperature despite changes in external temperature

Question 2

What is the optimal temperature for body processes

Answer 2

about 37.8°C

Question 3

What is the core temperature

Answer 3

The temperature of the contents of the head, thorax and abdomen. It includes major organs, the central nervous system and some muscles

Question 4

What is the outer shell temperature

Answer 4

The skin temperature of the arms and legs (the subcutaneous fat)

Question 5

Does core temperature vary, if so how?

Answer 5

Core temperature varies a little. The average core temperature is 36.7°C. It is a little colder in the mornings (35.5°C) and a little warmer in the evenings (37.7°C).

Question 6

Out of hyperthermia and hypothermia, what is more dangerous for humans and why?

Answer 6

Hyperthermia is much more dangerous than hypothermia. At over 41°C, nerve and enzyme function are severely impacted and at 43.3°C there is death. Whereas, the body temperature can fall by 7°C and the body can still recover. It is only prolonged at below 27°C when people will die

Question 7

Does outer shell temperature vary?

Answer 7

Yes, it can vary from 20°C-40°C

Question 8

Give some common sites of temperature measurement

Answer 8

-under the tongue
-under the armpit
-the rectum
-the eardrum

Most of these give values slightly below the core temperature other than the rectum that gives a value slightly above

Question 9

Describe the pills that accurately measure core temperature

Answer 9

Ingestible pills with a bluetooth connection to an outside device. The pill has a thermocouple measuring device and radio ink inside. It can give an accurate measurement but it is very expensive.

Question 10

Why do we allow for a small rise in core temperature

Answer 10

Because we can counteract this with sweating (this sweating also causes an imbalance of water homeostasis by raising serum osmolarity)

Question 11

Generally speaking, how is heat gained and lost in the body.

Answer 11

Heat is produced from metabolic processes. Heat is lost by radiation, conduction, convection and evaporation

Question 12

What decides whether there is a net gain or loss of heat from the body

Answer 12

The external temperature, this is because heat always flows from hot to cold

Question 13

Describe how the body detects temperature

Answer 13

The body has thermoreceptors that sensor temperature, they are very sensitive and can detect changes in core temperature down to 0.01 of a degrees. They are in the skin and the CNS (mostly the hypothalamus). Humans have many more cold receptors than heat receptors. The afferents from the thermoreceptors go to the hypothalamus (where there are different centres for heat and cold)

Question 14

Following a drop in core temperature, what are some skeletal muscle mechanisms to increase heat production

Answer 14

-increased voluntary activity of skeletal muscle
-increased muscle tone and shivering
-stimulation of the adrenergic pathway from hypothalamus to muscle
These can all increase muscle heat production 5x within seconds

Question 15

Give 2 non skeletal muscle involved mechanism to increase core temperature

Answer 15

non shivering thermogenesis - metabolism of fats in brown adipose tissue is stimulated by adrenaline and thyroid hormone

in response to chronic cold, an increased metabolic rate is stimulated by thyroxine

Question 16

What is a major variable in controlling heat loss

Answer 16

Blood flow

Question 17

What controls the mechanisms of blood flow

Answer 17

Blood flow is controlled by the vasodilation/constriction of arterioles in the skin. Hot conditions cause vasodilation of skin arterioles to bring blood towards the skin so that heat can be lost. The vasomotor control of skin arterioles is controlled in the hypothalamus via adrenergic nerves

Question 18

Where is there a potential conflict in terms of adrenergic control of arterioles

Answer 18

The hypothalamus send stimuli to down the adrenergic nerves to the arterioles in response to temperature. However blood pressure is controlled by the medulla which can also dictate vasoconstriction/dilation. But in cases of conflict (deciding whether to control temperature of blood pressure) the hypothalamus over rides the medulla.

Question 19

Give some common responses to cold exposure

Answer 19

-increased heat production from metabolic processes
-behavioural adaptations such as moving, putting on clothes, changing posture, food choices etc
-piloerection via the sympathetic nervous system (although this is better for furry animals)

Question 20

What are common problems associated with temperature regulation

Answer 20

-fever
-exercise induced hyperthermia
-pathological hyperthermia
-excess thyroid or adrenal hormones

Question 21

What is allostasis

Answer 21

When the body learns from previous experiences, to give predictive anticipatory responses to external condition changes. The levels are continuously adjusted and the needs are anticipated before they arise.