Homeostasis in the Human Body

Homeostasis

• Homeostasis is the maintenance of a stable internal physiological state despite external changes
• A narrow range of physical and chemical conditions allows optimal body function
• This includes glucose, ion levels, osmotic pressure (water and solute amounts), CO2 levels, and temperature
• Homeostasis is a dynamic process, maintaining a steady state within set parameters
• Internal environments of animals are relatively stable, shielding cells from harmful external conditions.
• E.g., humans: approximately 60% water—around 60% present in cells. The remaining 40% is extracellular fluid, with 20% plasma and 80% interstitial fluid
• This stable internal environment allows animals to thrive in a variety of habitats
• Homeostatic control utilizes corrective mechanisms that maintain balance in the body.

Homeostatic Control Mechanisms

• Excess detected -> Corrective mechanism -> Norm set point -> Negative feedback
• Deficiency detected -> Corrective mechanism -> Norm set point -> Negative feedback.

Control of Blood Glucose

• Blood glucose levels must remain constant
• Glucose is absorbed from the small intestine and enters the bloodstream, eventually reaching the liver
• The liver responds to blood glucose levels, either:
  • Performing cell respiration (producing water and CO2)
  • Converting glucose to glycogen for storage
  • Converting glucose to fat for storage
  • Releasing glucose into the bloodstream as needed.
• Hormone control dictates which process occurs depending on the blood glucose level.

Control of Blood Glucose by Hormones

• Insulin:
  • Released when blood glucose is high.
  • Causes body cells to absorb more glucose, lowering blood glucose levels.
• Glucagon:
  • Released when blood glucose is low.
  • Causes the liver to break down glycogen and release glucose into the blood, raising blood glucose levels.

Temperature Sensitivity

• Cells need a temperature range between approximately 0°C and 40°C
• Physiological processes vary in temperature sensitivity.
• Not all biochemical reactions change at the identical rate with temperature changes.

Control of Body Temperature

• Animals obtain heat from the sun (solar energy) and cellular respiration
• "Warm-blooded" (endotherms) vs "cold-blooded" (ectotherms)
  • Ectothermic animals gain heat from their environment
  • Endothermic animals generate their own heat internally.
• Ectothermic animals generally require less food and have a lower metabolic rate for maintaining a consistent body temperature
• Endothermic animals typically need more food and a higher metabolic rate for temperature maintenance.
• Aquatics vs Terrestrial Ectotherms
  • Aquatic ectothermic animals generally have body temperatures similar to the water's temperature.
  • Terrestrial ectothermic animals can adjust their body temperature based on their surroundings.

Heat Exchange in Ectotherms

• Convection: Heat exchange through a current of air or water
• Radiation: Heat transfer via electromagnetic waves
• Evaporation: Heat loss by converting liquid to vapor
• Conduction: Heat transfer through direct contact

Endotherms and BMR

• Endotherms can adjust their metabolic rate to maintain their body temperature
• Thermoneutral zone: A range where metabolic rate is low and independent of ambient temperatures
• Basal metabolic rate (BMR): The metabolic rate of a resting animal in the thermoneutral zone.
• Endotherms have differing BMRs correlated with their respective body masses

Behavioral Mechanisms Outside of the Thermoneutral Zone

• Endotherms use behavioral mechanisms to regulate body temperature, including:
  • Warming: Huddling, seeking shelter, clothing
  • Cooling: Seeking shade, wallowing in water, removing clothing
• This helps maintain homeostasis when outside the thermoneutral zone.

Physiological Mechanisms Outside the Thermoneutral Zone

• Endotherms use physiological mechanisms to regulate body temperature, including:
  • Warming: Vasoconstriction, piloerection (raising hair), shivering, increased metabolic rate
  • Cooling: Sweating, vasodilation (widening blood vessels), decreased metabolic rate.

Vasodilation and Vasoconstriction

• Vasodilation: Increases blood flow to the skin, facilitating heat loss to the environment
• Vasoconstriction: Decreases blood flow to the skin, reducing heat loss

Hypothalamus Regulation of Temperature

• Hypothalamus acts as the thermostat, regulating body temperature.
• Both behavioral and physiological mechanisms are triggered in response to body temperature deviations from the set point to maintain homeostasis

Summary of Homeostatic Control by Negative Feedback

• The hypothalamus and skin detect temperature changes
• The body responds to these changes with physiological responses and behavioral changes.
• Signal transmission to the brain and regulatory mechanisms help maintain ideal internal body conditions.

Test your knowledge on homeostasis and its key concepts related to the human body. This quiz covers various aspects, including physiological responses, body composition, and the role of the nervous system in regulating internal conditions. Challenge yourself and see how well you understand the mechanisms that maintain a stable internal environment.