Physiology - Viral Diseases

Question 1

Critical body core temperature

Answer 1

37.1°C

Question 2

What is the critical body temp determined mainly by

Answer 2

Degree of activity

Heat temp receptors in the anterior hypothalamic preoptic area

Question 3

Core temp is dependent upon

Answer 3

Time of day (circadian rhythm)
Stage of menstrual cycle
Level of physical activity/exercise

Question 4

What does core temp deviations challenge

Answer 4

Body’s thermoregulatory mechanisms

Question 5

What causes skin temp to rise and fall

Answer 5

Change in temp of surroundings

Question 6

Consequences of body temp of 40-44°C

Answer 6

Heat stroke

Brain lesions

Question 7

Consequences of body temp of 38-40°

Answer 7

Fever

Exercise

Question 8

Temp of mild hypothermia

Answer 8

34-36°C

Question 9

Core body temp of 27-29°c

Answer 9

Cardiac fibrillation

Question 10

Heat production of the human body

Answer 10

Basal rate of metabolism
Dietary thermogenesis
Non-shivering thermogenesis
Shivering thermogenesis
External work

Question 11

Heat loss in the body

Answer 11

Radiation
Conduction
Evaporation
Convection

Question 12

Radiation

Answer 12

50-70% of leat loss from nude person sitting inside at normal room temp (25°c)
Loss of heat by infrared heat rays

Question 13

Conduction

Answer 13

Direct conduction from body surface to solid objects is small (3%)
Conduction to air under normal conditions (15%)
Kinetic energy of molecular motion

Question 14

Convection

Answer 14

Removal of heat from the body by convection air currents
Heat most be conducted first
Affected by wind velocity

Question 15

Evaporation

Answer 15

Occurs when water evaporates from body surface

600-700ml/day lost from skin and lungs -cannot be regulated

Question 16

Role of hypothalamus

Answer 16

Heat loss centre —preoptic and anterior

Heat conservation centre - posterior hypothalamic

Question 17

How do we know role of hypothalamus

Answer 17

When preoptic area is heated, body immediately breaks out into profuse sweat, skin blood vessels dilate and observe effects of destructive lesions

Question 18

Heat sensitive necrons

Answer 18

Increase firing rate 2-10 fold in response to a 10 degree Celsius increase in body temp

Question 19

Cold-sensitive neurons

Answer 19

Increase firing rate in response to a fall in body temp

Question 20

Peripheral receptors

Answer 20

Skin has both warmth and cold receptors
Detect changes in skin temp
10x as many cold receptors than warm

Question 21

Where are deep body receptors found

Answer 21

Brain
Spinal cord
Abdominal viscera
In and around Upper abdomen and thorax

Question 22

Deep body receptor

Answer 22

Detect changes in core temp
Defect mainly cold rather than warmth
Concerned w/ preventing hypothermia

Question 23

Response when body is cold

Answer 23

Skin vasoconstriction throughout body
Piloerection
Increase in thermogenesis

Question 24

Skin vasoconstriction

Answer 24

Constriction of arterioles

Stimulation of posterior hypothalamic sympathetic centres

Question 25

Piloerection

Answer 25

Sympathetic stimulation causes erector pilli muscles attached to hair follicles to contract Allows thicker layer of insulating air to be trapped next to skin

Question 26

Increase in thermogenesis

Answer 26

Shivering Chemical excitation of heat production Thyroxine increases heat production

Question 27

Why do we shiver

Answer 27

Body heat production can rise 4-5x as normal

Question 28

Where is the primary motor centre for shivering located

Answer 28

In posterior hypothalamus near. wall of 3rd ventricle Inhibited by signals from heat centre in anterior hypothalamic-preoptic area Excited by cord signals from skin and spinal cord

Question 29

Descending tract for shivering

Answer 29

Signal transmitted down bilateral tracts of brain stem into lateral columns of spinal cord to anterior motor neurons

Question 30

When does shivering begin

Answer 30

By facilitating activity of anterior motor neurons, when tone rises above certain critical level shivering begins

Question 31

Thyroxine-stimulated heat production

Answer 31

Cooling anterior hypothalamic -preoptic area also leads to increase in production of TRH Leads to stimulation of TSH TSH stimulates thyroxine release from thyroid gland Takes place over weeks not immediate

Question 32

TRH

Answer 32

Thyrotropin releasing hormone

Question 33

TSH

Answer 33

Thyroid stimulating hormone

Question 34

Function of thyroxine

Answer 34

Increasing of cellular metabolism throughout body - another mechanism of chemical thermogenesis

Question 35

Response when body is too hot

Answer 35

Vasodilation Sweating Decrease in heat production

Question 36

Vasodilation

Answer 36

Dilation of arterioles | Stimulation of anterior and preoptic hypothalamic neurons

Question 37

Sweating as a response when the body is too hot

Answer 37

Evaporative heat loss increases dramatically above 37°c

Question 38

How is heat production decreased

Answer 38

Chemical thermogenesis and shivering strongly inhibited