Energy balance 2 Flashcards
Why is temperature regulation important?
Is overheating more serious than cooling?
As Humans we are constantly losing heat. Heat production ultimately depends on the oxidation of metabolic fuel derived from food. Changes in body temperature are critical for cellular activity. Overheating is more serious than cooling.
Defininitions of body temperature:
- Define Homeothermic, what is its opposite?
- What is normal body temperature?
- What is the average temperature over a period of time?
- What is hypothermia?
- What is hyperthermia?
- What is basal body temperature?
- Homeothermic = warm-blooded (organisms that generate heat from metabolic reactions in their own body. Opposite is ectotherms (an animal that is dependent on external sources such as sunlight to generate body heat e.g. fish and reptiles)
- Normal body temperature = 36-37.2°C
- 37°C is the average over a period of time.
4 .Hypothermia = temperature <35°C
- Hyperthermia/pyrexia = temperature >38°C
- Basal body temperature (BBT) – temp while sleeping
What is thermoregulation?
Thermoregulation is the maintenance of internal body temperature within a physiological range (Independent of outside temperature)
What is normal body temperature in the morning compared to the evening?
- Normal Body Temp = 37.8°C
- in the morning 35.5°C
- in the evening 37.7°C
Body temperature can mean several different things
- Core temp – most important, narrow range (abdominal and thoracic organs, CNS and skeletal muscles)
- Shell temp – can vary widely, provides regulatory mechanism (skin, subcutaneous fat, extremities)
- Both comply with homeostatic mechanisms
Why is heat balance key?
- Balance between loss and gain
- Body produces 1kcal/kg/hour at rest
- <1kcal/kg needed to increase body temperature by 1°C
- Without heat loss body would get warmer by 1°C per hour!
Internal core temperature is homeostatically maintained at:
•100°F (37.8°C)
What are the sites for monitoring body temperature?
- Rectal
- Oral
- Axillary
- Eardrum
- Temporal
What is the temperature of the core or extremities in warm compared to cold environments?
- Your core temperature stays at 37°C in both environmnts
- In cold environments: Core and shell temperature are different (e.g 28ºC in your hands 34ºC in your thighs) Colder hands and feet reflects activation/tension because in fight/flight blood flow is directed to vital organs
- In warm environments: Core and shell temperature are very similar (warmer hands and feet indicate realxation)
What happens when body temperature rises above 37ºC?
When does it become fatal?
Hot
- 37°C (98.6°F) - Normal body temperature (which varies between about 36.12-37.5°C (96.8-99.5°F)
- 38°C (100.4°F) - Sweating, feeling very uncomfortable, slightly hungry.
- 39°C (102.2°F) - Severe sweating, flushed and very red. Fast heart rate and breathlessness. There may be exhaustion accompanying this. Children and people with epilepsy may be very likely to get convulsions at this point.
- 40°C (104°F) - Fainting, dehydration, weakness, vomiting, headache and dizziness may occur as well as profuse sweating.
- 41°C (105.8°F) - (Medical emergency) - Fainting, vomiting, severe headache, dizziness, confusion, hallucinations, delirium and drowsiness can occur. There may also be palpitations and breathlessness.
- 42°C (107.6°F) - Subject may turn pale or remain flushed and red. They may become comatose, be in severe delirium, vomiting, and convulsions can occur. Blood pressure may be high or low and heart rate will be very fast.
- 43°C (109.4°F) - Normally death, or there may be serious brain damage, continuous convulsions and shock. Cardio-respiratory collapse will likely occur.
- 44°C (111.2°F) or more - Almost certainly death will occur; however, patients have been known to survive up to 46.5°C (115.7°F).
Core temperatures need to be elevated and sustained for a period of time for it to be fatal
What happens when body temperature falls below 37ºC?
Cold
- 37°C (98.6°F) - Normal body temperature (which varies between about 36-37.5°C (96.8-99.5°F)
- 36°C (96.8°F) - Mild to moderate shivering (it drops this low during sleep). May be a normal body temperature.
- 35°C (95.0°F) - (Hypothermia) is less than 35°C (95.0°F) - Intense shivering, numbness and bluish/grayness of the skin. There is the possibility of heart irritability.
- 34°C (93.2°F) - Severe shivering, loss of movement of fingers, blueness and confusion. Some behavioural changes may take place.
- 33°C (91.4°F) - Moderate to severe confusion, sleepiness, depressed reflexes, progressive loss of shivering, slow heart beat, shallow breathing. Shivering may stop. Subject may be unresponsive to certain stimuli.
- 32°C (89.6°F) - (Medical emergency) Hallucinations, delirium, complete confusion, extreme sleepiness that is progressively becoming comatose. Shivering is absent (subject may even think they are hot). Reflex may be absent or very slight.
- 31°C (87.8°F) - Comatose, very rarely conscious. No or slight reflexes. Very shallow breathing and slow heart rate. Possibility of serious heart rhythm problems.
- 28°C (82.4°F) - Severe heart rhythm disturbances are likely and breathing may stop at any time. Patient may appear to be dead.
- 24-26°C (75.2-78.8°F) or less - Death usually occurs due to irregular heart beat or respiratory arrest; however, some patients have been known to survive with body temperatures as low as 14.2°C (57.5°F)
Describe normal variations in core temperature
- Core temperature normally varies about 1.8°F (1°C) during the day
- Women experience a monthly rhythm in core temperature
- Core temperature increases during exercise
- Older is colder
- Core temperature may vary slightly with exposure to extremes of temperature
Variations in Core Temperature: Daily rhythm (circadian rhythm)
Describe the function of the suprachiasmatic nucleus or nuclei (SCN)
•Temperature follows a circadian rhythm (physical, mental and behavioural changes that roughly follow a 24 hour cycle and respond too light and darkness within an organisms environment)
- The suprachiasmatic nucleus or nuclei (SCN) a tiny region of the brain in the hypothalamus, situated directly above the optic chiasm. It is responsible for controlling circadian rhythms by responding to light detection.
- Falls through early morning (6-7am)
- Rises in evening and after meals (5-7pm)
Variations in Core Temperature: Menstrual Cycle
- ↑oestrogen circulating during follicular phase ↓ BBT
- ↑progesterones released by the ovaries (builds up uterus lining) found in luteal phase and causes↑ BBT set point by up to 0.5°C this helps with insemination
- Rise occurs day after ovulation
- Used to facilitate conception
Variations in Core Temperature: Exercise and Meals
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- Strenuous exercise can ↑ temperature up to almost 40°C
- Depends on level of hydration (sweat) and clothing
- Eating increases temperature (DIT)
- Depends on meal size and nutrients
Heat input must balance heat output to maintain a stable core temperature:
How does heat input occur?
How does heat output occur?
How does heat exchange occur?
–Heat input occurs by heat gain from the external environment and internal heat production
–Heat output occurs by heat loss from exposed body surfaces to the external environment.
•Heat exchange takes place by radiation, conduction, convection, and evaporation
The body uses four mechanisms of heat transfer: Describe them
• The body uses four mechanisms of heat transfer:
- Radiation (The transfer of heat energy from a warmer object to a cooler object in the form of electromagnetic waves; allows you to gain heat by absorbing electromagnetic waves from the sun)
- Conduction (The transfer of heat from a warmer to a cooler object that is in direct contact with the warmer one; the heat is transferred through the movement of thermal energy from molecule to adjacent molecule)
- Convection (transfer of heat energy by air or water currents. Cool air is warmed by the body through conduction rises and is replaced by the forced movement of air across the body surface)
- Evaporation (conversion of a liquid such as sweat into a gaseous vapour, a process that requires heat which is absorbed from the skin)
Describe physiological control of temperature
- Thermoregulation excellent example of physiological ‘setpoints’
- Variety of systems can compensate to maintain 37°C setpoint
- Set by hypothalamus (sensitive to 0.01°C change)
Anterior hypothalamic nucleus
- Hypothalamus needs constant central & peripheral information
- Thermoregulation not just central!
Describe the process of Shivering Thermogenesis
What allows non-shivering thermogenesis?
What happens when the Hypothalamus detects a drop in temperature?
•Shivering is the primary involuntary means of increasing heat production.
–Adjustments in heat production by skeletal muscles
•Shivering: rhythmic, oscillating skeletal muscle contractions that occur at a rapid rate of 10 to 20 per second
–Nonshivering thermogenesis by brown fat
•Increased heat production stimulated by brown adipose tissue, which is capable of converting chemical energy from food into heat.
When the hypothalamus detects a drop in temperature it fires AP’s down neurons that terminate on motor neurons controlling skeletal muscles which contract and relax rapidly to generate heat
(More irosin=more brown fat)
Draw a diagram to show the physiological control of temperature
What are the bodys natural responses to cold and heat exposure?
How does Fever and Hyperthermia occur?
How do macrophages respond to an elevation in temperature as a result of an infection?
Why do you feel cold when you are ill?
•During a fever, the hypothalamic thermostat is “reset” at an elevated temperature
–Fever: elevation in body temperature as a result of infection or inflammation.
•Hyperthermia can occur unrelated to infection
It could be due to abnormally high circulating levels of hormones such as adrenaline
–Pathological hyperthermia
–Heat exhaustion/heat stroke
Macrophages release proinflammatory cytokines endogenous pyrogen this cascades of events acts on the hypothalamus and it raises body temperature. The brain thinks this elevated temperature needs to be maintained so the hypothalamus engages in heat generating behaviours (shivering thermogenisis, vasoconstriction, Piloerection)
This aims to prevent bacterial proliferation.
When you start taking medication the pyrogen levels decrease and the pro inflammatory cytokines decrease and body temperatures comes back to set point
Describe Hyperthermia in Sustained Exercise
- At the onset of exercise, the rate of heat production initially exceeds the rate of heat loss so the core temperature rises.
- When heat loss mechanisms are reflexly increased sufficiently to equalize the elevated heat production, the core temperature stabilizes slightly above the resting point for the duration of the exercise.
