Homeostasis refers to the body's ability to maintain a stable internal environment despite changes in external conditions.
The regulation of internal body temperature is crucial for optimum conditions for enzyme-catalysed reactions.
Normal Body Temperature: 37°C.
Consequences of Temperature Changes:
Above 37°C:
Enzymes denature (lose structure and function).
Metabolic pathways are blocked.
Below 37°C:
Metabolism slows.
Can affect brain function.
Heat transfer through infrared electromagnetic rays.
Body radiates heat; loses heat if the surrounding temperature is lower than body temperature.
About 60% of total heat loss in a nude person occurs via radiation.
Heat exchange between objects in direct contact.
Minimal heat loss from contact with solid objects (3%).
Larger heat loss occurs through conduction to air.
Heat removal through air currents.
Heat must be conducted to air first, increasing removal ceiling.
12% of body heat is lost via this method; wind increases heat loss significantly.
Water evaporates from skin/lungs, even without sweating (approx. 600 ml/day).
Sweating is a key regulated heat loss method.
Heat loss occurs primarily through evaporation when other methods are ineffective.
Humidity decreases evaporation efficiency.
Small heat loss through urine and faeces.
Hypothalamus: Contains Thermoregulatory Centre that monitors blood temperature.
Acts as a thermostat set to 37°C.
Receives input from skin thermoreceptors.
Feedback System: Cycle of monitoring and evaluation affecting body conditions.
Receptor: Sensors that respond to changes (stimuli).
Control Centre: Sets range of values, evaluates inputs, and sends outputs.
Effector: Receives output from control centre and produces response.
Detection: Thermoreceptors in hypothalamus respond to high body temperature.
Responses:
Vasodilation: Blood vessels widen, increasing blood flow toward skin surface.
Sweating: Heat energy converts sweat into vapor, cooling the body.
Detected by thermoreceptors in the hypothalamus.
Responses:
Vasoconstriction: Blood vessels constrict, reducing blood flow to skin.
Decreased sweating.
Shivering: Muscle contractions generate heat.
Piloerection: Hair muscles contract to insulate by trapping a layer of warm air.
Not very effective in humans; creates goosebumps instead.
Human behavior adapts to temperature changes:
Cold: Add clothing, seek heat sources, exercise.
Hot: Remove layers, hydrate with cold drinks, reduce physical activity.
Occurs when cooling mechanisms fail, leading to very high body temperature.
Can cause unconsciousness and potentially death if untreated.
Results from dehydration due to extreme sweating and exercise.
Decreased blood volume can lead to collapse from low blood pressure.