Notes on Homeostasis and Feedback Mechanisms

Homeostasis and Feedback

• Homeostasis: The state of relatively stable internal conditions within the body.
  • Organisms detect and respond to stimuli, maintaining balance.
  • Achieved through feedback loops.

Set Points and Their Importance

• Set Points: Values for various physiological conditions that the body strives to maintain.
  • Example: Body temperature.
  • Set Point: 98.6℉ (37°C)
  • Normal Range: 97℉ to 99℉

Thermoregulation in Humans

• Nervous System Role: Sends signals to skin and muscles in response to temperature changes.
  • Too Hot:
  • Body temperature rises.
  • Blood vessels dilate (vasodilation).
  • Sweat glands secrete sweat leading to heat loss.
  • Body temperature drops toward normal.
  • Too Cold:
  • Body temperature drops.
  • Blood vessels constrict (vasoconstriction).
  • Muscles contract to shiver, generating heat.
  • Body temperature rises toward normal.

The Role of the Brain in Homeostasis

• Hypothalamus: Detects glucose levels in the blood and regulates hormone release to either release or store glucose.
  • Hormones: Chemical signals affecting changes in body and cellular functions.
  • Examples: Insulin, testosterone, estrogen.

Components of the Nervous System

• Functions:

  • Regulates body functions and maintains homeostasis.
  • Responds to external stimuli by sending signals to the body.
  • Involved in voluntary movements (e.g., muscle control).

• Parts:

  • Brain: Controls all functions and interprets external signals.
  • Spinal Cord: Transmits messages between the brain and body.
  • Neurons: Specialized cells sending and receiving signals.

Excretory System

• Kidneys:
  • Regulate water balance and eliminate waste.
  • Urea: Nitrogenous waste product removed from the body.
• Bladder:
  • Stores and releases urine.

Integration of Systems

• Nervous System, Circulatory System, and Excretory System:
  • The nervous system detects changes and releases hormones in response.
  • Circulatory system transports blood to and from kidneys which control urine composition through osmosis.

Feedback Loops

• Two Types:
  • Negative Feedback:
  • Most common; reduces the effect of the stimulus.
  • Examples: Sweating, blood sugar regulation, breathing rate.
  • Illustrative Example: Temperature regulation with sweating.
  • Positive Feedback:
  • Increases the effect of the stimulus.
  • Examples: Childbirth, blood clotting, fruit ripening.
  • Illustrative Example: Childbirth - stretching cervix induces oxytocin release, stimulating contractions.

Circadian Rhythms and Homeostasis

• Body functions vary throughout the day in a cycle.
• Melatonin secretion and body temperature fluctuate based on time of day.

Homeostatic Imbalances

• The inability of the body to maintain homeostasis can result from:
  • Genetic disorders.
  • Drug/alcohol abuse.
  • Extreme environmental conditions.
• Diseases:
  • Cancer: Causes uncontrollable growth of cells.
  • Diabetes: Impairs blood glucose regulation.

Cell Signaling in Homeostasis

• Cells communicate through signal transduction pathways to maintain homeostasis in multicellular organisms.