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MBBS - Year 1 > Physiology - Viral Diseases > Flashcards

Physiology - Viral Diseases Flashcards

1
Q

Critical body core temperature

A

37.1°C

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2
Q

What is the critical body temp determined mainly by

A

Degree of activity

Heat temp receptors in the anterior hypothalamic preoptic area

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3
Q

Core temp is dependent upon

A

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

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4
Q

What does core temp deviations challenge

A

Body’s thermoregulatory mechanisms

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5
Q

What causes skin temp to rise and fall

A

Change in temp of surroundings

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6
Q

Consequences of body temp of 40-44°C

A

Heat stroke

Brain lesions

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7
Q

Consequences of body temp of 38-40°

A

Fever

Exercise

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8
Q

Temp of mild hypothermia

A

34-36°C

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9
Q

Core body temp of 27-29°c

A

Cardiac fibrillation

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10
Q

Heat production of the human body

A 
Basal rate of metabolism
Dietary thermogenesis
Non-shivering thermogenesis
Shivering thermogenesis
External work
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11
Q

Heat loss in the body

A

Radiation
Conduction
Evaporation
Convection

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12
Q

Radiation

A

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

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13
Q

Conduction

A

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

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14
Q

Convection

A

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

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15
Q

Evaporation

A

Occurs when water evaporates from body surface

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

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16
Q

Role of hypothalamus

A

Heat loss centre —preoptic and anterior

Heat conservation centre - posterior hypothalamic

17
Q

How do we know role of hypothalamus

A

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

18
Q

Heat sensitive necrons

A

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

19
Q

Cold-sensitive neurons

A

Increase firing rate in response to a fall in body temp

20
Q

Peripheral receptors

A

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

21
Q

Where are deep body receptors found

A

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

22
Q

Deep body receptor

A

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

23
Q

Response when body is cold

A

Skin vasoconstriction throughout body
Piloerection
Increase in thermogenesis

24
Q

Skin vasoconstriction

A

Constriction of arterioles

Stimulation of posterior hypothalamic sympathetic centres

25
Q

Piloerection

A

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

26
Q

Increase in thermogenesis

A

Shivering
Chemical excitation of heat production
Thyroxine increases heat production

27
Q

Why do we shiver

A

Body heat production can rise 4-5x as normal

28
Q

Where is the primary motor centre for shivering located

A

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

29
Q

Descending tract for shivering

A

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

30
Q

When does shivering begin

A

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

31
Q

Thyroxine-stimulated heat production

A

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

32
Q

TRH

A

Thyrotropin releasing hormone

33
Q

TSH

A

Thyroid stimulating hormone

34
Q

Function of thyroxine

A

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

35
Q

Response when body is too hot

A

Vasodilation
Sweating
Decrease in heat production

36
Q

Vasodilation

A

Dilation of arterioles

Stimulation of anterior and preoptic hypothalamic neurons

37
Q

Sweating as a response when the body is too hot

A

Evaporative heat loss increases dramatically above 37°c

38
Q

How is heat production decreased

A

Chemical thermogenesis and shivering strongly inhibited

MBBS - Year 1 (93 decks)

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