Feedback Loops and Homeostasis

Feedback Loops and Homeostasis

  • Feedback loops are mechanisms that maintain balance (homeostasis).
  • Homeostasis involves various cells, systems, and organs constantly maintaining physiological factors.
  • Processes that fix physiological factors are known as feedback loops.

Negative Feedback

  • Negative feedback corrects deviations from a normal range.
  • Example: Core body temperature regulation.
  • If body temperature deviates from the normal range, a process ensues to fix it.
  • Once the temperature is back in a stable range, the feedback loop ends.

Thermoregulation (Negative Feedback Example)

  • Thermoregulation for hot and cold.
  • Experiencing both hot and cold triggers actions.
  • When hot: Sweating and skin flushing.
  • When cold: Shivering.
  • Negative feedback counteracts deviations from the normal range.

Positive Feedback

  • Positive feedback reinforces a stimulus.
  • Example: Childbirth.
  • During childbirth, hormone release causes contractions.
  • Instead of the body trying to remove the hormone, more is released until birth.
  • The mechanism either corrects the range (negative) or influences it in a direction (positive).

Examples of Feedback Loops

  • Negative feedback: Thermoregulation.
  • Positive feedback: Childbirth and paper cuts (acute inflammation).
  • Breastfeeding is a positive feedback loop (more breastfeeding leads to more milk production).

Thermoregulation in Detail

Range

  • Normal body temperature range: 97.8 to 99 degrees Fahrenheit.
  • Receptors receive information and send it to the brain (control center).
  • The brain checks the information against the range and determines if action is needed.
  • If the temperature is within range, nothing happens.

Too Cold

  • Shivering, piloerection (goosebumps), and vasoconstriction occur.
Shivering
  • Rapid muscle contractions generate heat through friction.
  • Shivering also causes rapid muscle contraction, which burns ATP.
  • When ATP is broken down, heat is generated, warming the body.
  • Work (muscle contraction) burns ATP, and when ATP is broken down, heat is generated.
Vasoconstriction
  • Blood vessels constrict to reduce blood flow to the extremities.
  • Most body heat is maintained through water in the tissues (high heat capacity).
  • Directing blood flow influences heat maintenance.
  • Reduced blood flow to extremities reduces heat loss to the environment, maintaining core body temperature.
  • Vasoconstriction reduces blood flow to the extremities, reducing heat loss to the environment and maintaining core body temperature.
Piloerection (Goosebumps)
  • Each hair is connected to a piloerector muscle.
  • Contraction moves hairs from a flat to an upright position.
  • Piloerection creates pockets of air that trap and warm air against the skin, providing insulation.

Too Hot

  • Sweating, vasodilation, and pilorelaxation occur.
Vasodilation
  • Increases blood flow to the extremities, increasing contact with the environment.
  • Increased heat loss to the environment.
  • Increased blood flow due to vasodilation leads to increased heat loss.
Sweat
  • Sweat glands create sweat, which is primarily water.
  • Evapotranspiration: Water on the skin evaporates into the environment, creating a cooling sensation.
  • Sweat absorbs heat from the body, and vasodilation moves heat to the skin.
Pilo relaxation
  • Hairs lay flat, reducing trapped air and heat retention.
  • Keeps sweat held to the skin a little bit longer, therefore it can absorb heat from the body.

How Negative Feedback Works

  • Receptors detect temperature and send information (a number) to the brain.
  • The brain checks the number against its range.
  • If the temperature is out of range, mechanisms like sweating, vasodilation, and pilorelaxation start.
  • Once the temperature is back in range, the loop ends.

Hypothermia

  • In extreme cases, vasoconstriction stops, turning into vasodilation.
  • Individuals may feel warm due to full relaxation of vessels, leading to removal of clothing.
  • Prolonged vasoconstriction can cause tissue death due to limited blood flow.

Positive Feedback Examples

Paper Cuts

  • Platelets show up to the area of the cut and send out chemicals signaling more platelets to come.
  • Blood flow increases to get platelets to the area.
  • Once enough platelets clot the area, the feedback loop stops.

Childbirth

  • Pressure from the baby on the cervix releases oxytocin.
  • Oxytocin aids in smooth muscle contraction in the uterus.
  • More pressure on the cervix leads to more oxytocin release, resulting in strong contractions.
  • This continues until birth, and then the feedback loop ends.
  • In a C-section, oxytocin is triggered until the baby is out, stopping the loop.
  • Braxton Hicks contractions do not lead to active labor because the baby hasn't dropped yet.
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