Human Body Temperature Regulation

Temperature Homeostasis

Definition: Temperature homeostasis is the ability of the body to maintain a constant internal temperature, despite changes in the external environment.

Importance: Temperature homeostasis is crucial for proper bodily functions, as enzymes and other biological molecules are sensitive to temperature changes.

Normal Body Temperature: The normal body temperature range is 36.5°C to 37.5°C (97.7°F to 99.5°F).

Regulation of Body Temperature: The body regulates temperature through a negative feedback loop, involving the following components:

• Hypothalamus: The part of the brain that acts as the thermostat, sensing changes in body temperature.
• Thermoreceptors: Specialized nerve endings that detect temperature changes in the skin.
• Effectors: Muscles, sweat glands, and blood vessels that respond to temperature changes.

Mechanisms of Temperature Regulation: The body uses the following mechanisms to regulate temperature:

1. Vasoconstriction: Blood vessels constrict to reduce blood flow to the skin, conserving heat.
2. Vasodilation: Blood vessels dilate to increase blood flow to the skin, releasing heat.
3. Sweating: Evaporation of sweat cools the body.
4. Shivering: Muscles contract to generate heat.
5. Behavioral responses: Seeking shade, removing clothing, or using external heat sources.

Fever: A fever is an elevated body temperature, usually above 37.5°C (99.5°F), in response to an infection or inflammation. The hypothalamus resets the body's temperature setpoint to fight the infection.

Hypothermia: Hypothermia is a body temperature below 35°C (95°F), usually caused by exposure to cold temperatures. The body's metabolic rate slows down to conserve energy.

Clinical Significance: Temperature homeostasis is critical in medical settings, as abnormal body temperatures can indicate underlying illnesses or complications.

Temperature Homeostasis

• Temperature homeostasis is the ability of the body to maintain a constant internal temperature, despite changes in the external environment.

Importance of Temperature Homeostasis

• Temperature homeostasis is crucial for proper bodily functions.
• Enzymes and other biological molecules are sensitive to temperature changes.

Normal Body Temperature

• The normal body temperature range is 36.5°C to 37.5°C (97.7°F to 99.5°F).

Regulation of Body Temperature

• The body regulates temperature through a negative feedback loop.
• The hypothalamus acts as the thermostat, sensing changes in body temperature.
• Thermoreceptors detect temperature changes in the skin.
• Effectors such as muscles, sweat glands, and blood vessels respond to temperature changes.

Mechanisms of Temperature Regulation

• Vasoconstriction: Blood vessels constrict to reduce blood flow to the skin, conserving heat.
• Vasodilation: Blood vessels dilate to increase blood flow to the skin, releasing heat.
• Sweating: Evaporation of sweat cools the body.
• Shivering: Muscles contract to generate heat.
• Behavioral responses: Seeking shade, removing clothing, or using external heat sources.

Fever and Hypothermia

• A fever is an elevated body temperature, usually above 37.5°C (99.5°F), in response to an infection or inflammation.
• The hypothalamus resets the body's temperature setpoint to fight the infection during a fever.
• Hypothermia is a body temperature below 35°C (95°F), usually caused by exposure to cold temperatures.
• The body's metabolic rate slows down to conserve energy during hypothermia.

Clinical Significance

• Temperature homeostasis is critical in medical settings, as abnormal body temperatures can indicate underlying illnesses or complications.

Temperature Homeostasis

• The body's ability to maintain a stable internal temperature despite changes in the external environment is crucial for proper bodily functions.

Vasodilation

• Widening of blood vessels to increase blood flow to the skin, allowing heat to be lost.
• Triggered by increased body temperature, which stimulates the hypothalamus to release vasodilatory signals.

Sweat Regulation

• Process of producing and regulating sweat to cool the body through evaporation.
• Controlled by the hypothalamus, which stimulates sweat glands to produce sweat in response to increased body temperature.
• Factors influencing sweat rate include humidity, temperature, and individual differences in sweat gland function.

Hyperthermia

• Body temperature above 37°C (98.6°F) caused by high environmental temperature, intense physical activity, and certain medical conditions.
• Symptoms include headache, nausea, fatigue, and heat stroke.
• Can lead to heat stroke, organ damage, and even death if left untreated.

Hypothermia

• Body temperature below 35°C (95°F) caused by exposure to cold temperatures, wet conditions, and certain medical conditions.
• Symptoms include shivering, confusion, drowsiness, and loss of consciousness.
• Can lead to organ failure, cardiac arrest, and even death if left untreated.

Thermoregulation

• Process of maintaining a stable body temperature through mechanisms such as vasodilation, sweat regulation, and shivering.
• Essential for maintaining proper bodily functions, including enzyme activity, metabolism, and nerve function.
• Regulated by the hypothalamus, which acts as the body's thermostat.

Temperature Homeostasis

The Hypothalamus

• Regulates body temperature, acting as the body's thermostat
• Receives temperature information from thermoreceptors in the skin and internal organs
• Sets a temperature setpoint of around 37°C (98.6°F) and compares it to the current body temperature
• Triggers responses to maintain homeostasis when there's a discrepancy between the setpoint and current temperature

Mechanisms to Generate Heat

• Shivering: a mechanism that generates heat when body temperature drops below 35°C (95°F)
  • Muscles contract and relax rapidly, producing heat through muscle activity
  • Can increase heat production by up to 5 times the basal metabolic rate
• Vasoconstriction: the constriction of blood vessels to reduce blood flow to the skin
  • Decreases heat loss by reducing blood flow to the skin, where heat is lost to the environment
  • Occurs when body temperature drops, and is more pronounced in cold environments
  • Can also occur in response to emotional stress or fear

Mechanisms to Lose Heat

• Sweat Evaporation: a mechanism that loses heat when body temperature rises above 37°C (98.6°F)
  • Sweat glands produce sweat, which evaporates and takes heat away from the body
  • Evaporation of 1 liter of sweat can remove approximately 580 kcal of heat

Thermoreceptors

• Specialized sensory neurons that detect changes in temperature
• Found in the skin and internal organs
• Can detect changes in temperature as small as 0.1°C (0.18°F)
• Send signals to the hypothalamus to trigger responses to maintain temperature homeostasis

Homeostasis

Negative Feedback

• Reverses the direction of a change to maintain homeostasis
• Examples:
  • When body temperature rises, sweat glands are activated to cool the body
  • When blood glucose levels increase, insulin is released to decrease glucose levels

Set Point

• Predetermined range of values for a physiological parameter (e.g. body temperature, blood pressure)
• Normal or ideal value for a particular parameter
• Body strives to maintain the set point through homeostatic mechanisms

Receptors

• Specialized cells or molecules that detect changes in the internal environment
• Examples:
  • Thermoreceptors detect changes in temperature
  • Baroreceptors detect changes in blood pressure
• Trigger a response to maintain homeostasis when a change is detected

Stimulus Response

• Stimulus: a change in the internal environment that triggers a response
• Response: an action taken to maintain homeostasis
• Examples:
  • Stimulus: increase in blood glucose levels
  • Response: release of insulin to decrease glucose levels

Feedback Mechanisms

Negative Feedback

• Reverses the direction of a change
• Examples:
  • Thermoregulation
  • Blood glucose regulation

Positive Feedback

• Amplifies the direction of a change
• Examples:
  • Childbirth
  • Blood clotting

Feedforward Mechanisms

• Predicts and prepares for a change
• Examples:
  • Anticipatory responses to stress
  • Circadian rhythms