Homeostasis: Feedback Mechanisms and Thermoregulation

Homeostasis: Feedback Mechanisms and Thermoregulation

• Homeostasis is the process that maintains internal physical and chemical conditions within a tolerable range, despite external changes.
• Tolerable ranges for internal conditions can vary.
• Walter Cannon, a physiology professor, discovered in 1932 that when animals were frightened, their digestive processes stopped.
• The internal environment includes extracellular fluid (interstitial fluid), surrounding cells and tissues, and blood plasma.
• In adults, extracellular fluid makes up about 20% of the body mass. It has 15 litres of fluid.
• Extracellular fluid transfers energy, transports chemicals, and eliminates waste.

Organ Systems Involved

• Several organ systems contribute to homeostasis including: nervous, endocrine, muscular, integumentary, excretory, and reproductive.

How Homeostasis is Regulated

• The excretory system removes waste and maintains water balance.
• The endocrine system controls hormone levels.
• The circulatory system delivers hormones and chemicals and distributes thermal energy.
• The immune system protects against infection.
• Digestive system detoxifies (mainly the liver).
• The Integumentary system helps maintain body temperature.

Detoxification Pathways

• The liver is a key organ in detoxification.
• Pollutants, contaminants, pesticides, insecticides, food additives, drugs, alcohol, and phytochemicals are among substances the liver helps eliminate.
• These substances are often eliminated via the bowel actions or by kidneys in the form of urine.

Dynamic Equilibrium

• Our bodies adjust to maintain stable internal conditions in response to a changing environment.

Methods of Regulation - Negative Feedback

• Negative feedback is a mechanism that restores conditions to their original state.
• This is the preferred method in homeostasis, like a thermostat.
• Negative feedback mechanisms have four major components, Stimulus, Sensor, Integrator, and Effector.

Negative Feedback Mechanisms

• Stimulus: An environmental change (e.g., cold outside temperature).
• Sensor: Detects changes in the stimulus (e.g., cold sensors in the skin).
• Integrator: Compares existing conditions with ideal conditions (control center, e.g., brain).
• Effector: A system that returns the system to optimal state (e.g., muscles).
• Response: The effector returning the system to the desired point (e.g., shivering).

Thermostat Example

• The thermostat monitors temperature and sends a signal to the furnace to turn it on when the temperature drops below a set point.
• The furnace produces heat, making the room warmer. When the required temperature is reached the signal turns it off.

Positive Feedback Examples

• Positive feedback amplifies small effects; it's less common than negative feedback in the body.
• Examples include birth (oxytocin release) and blood clotting.

More Positive Feedback Examples

• Platelets clump together to form clots by activating other platelets.
• Lactation in breastfeeding activates the release of more milk.
• During the follicular stage, estrogen thickens the uterine lining.

Thermoregulation

• Internal temperature regulation occurs through negative feedback mechanisms.
• Homeotherms have a stable body temperature (e.g., humans).
• Poikilotherms have a variable body temperature (e.g., fish).

Ectotherms vs. Endotherms

• Ectotherms absorb heat from their surroundings (e.g., fish, reptiles).
• Endotherms generate their own heat (e.g., mammals, birds).

Example of Ectotherm/Endotherm

• An endotherm's metabolism increases at low temperatures to create heat.
• An ectotherm's metabolism decreases at low temperatures to conserve energy.

Special Behavioral Adaptations for Thermoregulation

• Torpor: Sleep-like state with decreased metabolic rate and body temperature.
  • Examples include hummingbirds and some ground squirrels
• Hibernation: A period of dormancy with significantly reduced metabolic rates and body temperature. Triggered by seasonal changes.
  • Examples include Arctic ground squirrels.
• Estivation: A form of torpor in response to harsh summer conditions, often involving reduced metabolism and environmental seclusion from environmental dangers.
  • Examples include ground squirrels and other ectothermic organisms.

Other Thermoregulation Structures and Behaviours

• Large external surfaces (e.g., ears) or specialized body structures that radiate or absorb heat.
• Behavioral changes like positioning yourself for heat conservation ,and panting or sweating to dissipate heat
• The hypothalamus, which contains thermoreceptors. It coordinates nerve and hormone function to control body temperature.

Human Body Temperature Control

• Temperature sensors in the skin send signals to the brain (hypothalamus).
• The hypothalamus regulates responses to increase or decrease body temperature appropriately.
• Body temperature responses vary according to the need - heating and cooling systems in the body turn on or off as required.