Homeostasis and Negative Feedback

Homeostasis

Homeostasis is the ability of the body to maintain a stable internal environment despite changes in the external environment.

Negative Feedback

• A mechanism used to maintain homeostasis
• Involves a response to a change in the body that reverses the change
• Three components:
  1. Sensor: detects the change in the body
  2. Integrator: interprets the signal from the sensor and sends a response
  3. Effector: carries out the response to reverse the change
• Examples:
  • Thermoregulation: when body temperature rises, sweat glands are activated to cool the body
  • Blood glucose regulation: when blood glucose levels rise, insulin is released to lower levels

Blood Glucose Regulation

• Maintaining a stable blood glucose level is crucial for proper bodily function
• Regulation involves a negative feedback loop:
  • Sensor: pancreatic cells detect changes in blood glucose levels
  • Integrator: pancreatic cells interpret the signal and send a response
  • Effector: insulin is released to lower blood glucose levels, or glucagon is released to raise levels
• Insulin:
  • Lowers blood glucose levels by facilitating glucose uptake in cells
  • Stimulates glycogen synthesis in the liver
• Glucagon:
  • Raises blood glucose levels by stimulating glycogen breakdown in the liver
  • Stimulates glucose release from stored glycogen

Osmoregulation

• Maintaining a stable balance of water and electrolytes in the body
• Regulation involves a negative feedback loop:
  • Sensor: osmoreceptors in the hypothalamus detect changes in blood osmolality
  • Integrator: hypothalamus interprets the signal and sends a response
  • Effector: ADH (antidiuretic hormone) is released to regulate water reabsorption in the kidneys
• ADH:
  • Stimulates water reabsorption in the kidneys to decrease blood osmolality
  • Inhibits water reabsorption in the kidneys to increase blood osmolality

Thermoregulation

• Maintaining a stable body temperature (around 37°C) is crucial for proper bodily function
• Regulation involves a negative feedback loop:
  • Sensor: thermoreceptors in the hypothalamus detect changes in body temperature
  • Integrator: hypothalamus interprets the signal and sends a response
  • Effector: sweat glands, shivering, and vasodilation/vasoconstriction are activated to cool or warm the body
• Cooling mechanisms:
  • Sweating: evaporation of sweat cools the body
  • Vasodilation: increased blood flow to the skin surface cools the body
• Warming mechanisms:
  • Shivering: muscle contraction generates heat
  • Vasoconstriction: decreased blood flow to the skin surface conserves heat

Hormonal Regulation

• Hormones play a crucial role in maintaining homeostasis
• Endocrine glands produce hormones that regulate various bodily functions
• Examples of hormonal regulation:
  • Insulin and glucagon regulate blood glucose levels
  • ADH regulates water reabsorption in the kidneys
  • Thyroid hormone regulates metabolic rate
• Hormonal regulation involves a negative feedback loop:
  • Sensor: detects changes in the body
  • Integrator: interprets the signal and sends a response
  • Effector: hormone is released to reverse the change

Homeostasis

• Ability of the body to maintain a stable internal environment despite changes in the external environment

Negative Feedback

• Mechanism used to maintain homeostasis
• Involves a response to a change in the body that reverses the change
• Three components: sensor, integrator, and effector

Blood Glucose Regulation

• Maintaining a stable blood glucose level is crucial for proper bodily function
• Regulation involves a negative feedback loop with pancreatic cells as sensors, integrators, and effectors
• Insulin lowers blood glucose levels by facilitating glucose uptake in cells and stimulating glycogen synthesis in the liver
• Glucagon raises blood glucose levels by stimulating glycogen breakdown in the liver and glucose release from stored glycogen

Osmoregulation

• Maintaining a stable balance of water and electrolytes in the body
• Regulation involves a negative feedback loop with osmoreceptors in the hypothalamus as sensors, hypothalamus as integrator, and ADH as effector
• ADH stimulates water reabsorption in the kidneys to decrease blood osmolality and inhibits water reabsorption to increase blood osmolality

Thermoregulation

• Maintaining a stable body temperature (around 37°C) is crucial for proper bodily function
• Regulation involves a negative feedback loop with thermoreceptors in the hypothalamus as sensors, hypothalamus as integrator, and sweat glands, shivering, and vasodilation/vasoconstriction as effectors
• Cooling mechanisms: sweating, vasodilation
• Warming mechanisms: shivering, vasoconstriction

Hormonal Regulation

• Hormones play a crucial role in maintaining homeostasis
• Endocrine glands produce hormones that regulate various bodily functions
• Examples of hormonal regulation: insulin and glucagon regulate blood glucose levels, ADH regulates water reabsorption in the kidneys, thyroid hormone regulates metabolic rate

Homeostatic Mechanisms

Thermoregulation

• The body maintains a constant temperature of around 37°C despite changes in environmental temperature.
• Negative feedback mechanisms regulate body temperature:
  • Heat loss occurs through sweating and vasodilation.
  • Heat gain occurs through shivering and vasoconstriction.
• The hypothalamus acts as a thermostat to regulate body temperature.

pH Regulation

• The body maintains a narrow pH range of 7.35-7.45.
• Buffering systems help maintain pH balance:
  • Bicarbonate-carbonic acid buffer.
  • Phosphate buffer.
  • Protein buffers.
• The respiratory system regulates CO2 levels to maintain pH.
• The renal system regulates H+ ion excretion to maintain pH.

Water Balance

• The body maintains proper water balance through the regulation of water intake and excretion.
• The hypothalamus and kidneys work together to regulate water balance.
• Osmoreceptors in the hypothalamus monitor blood osmolality.
• Antidiuretic hormone (ADH) and aldosterone regulate water reabsorption in the kidneys.
• The thirst mechanism stimulates water intake when blood osmolality increases.

Osmoregulation

• The body maintains proper osmotic balance through the regulation of solute and water levels.
• The kidneys and hypothalamus work together to regulate osmotic balance.
• Osmoreceptors in the hypothalamus monitor blood osmolality.
• ADH regulates water reabsorption in the kidneys to maintain osmotic balance.
• Sodium and potassium ion balance also play a crucial role in osmoregulation.

Gas Exchange

• The body exchanges oxygen and carbon dioxide with the environment through the respiratory system.
• Chemoreceptors in the carotid and aortic bodies monitor CO2 and O2 levels.
• Negative feedback mechanisms regulate gas exchange:
  • Increased CO2 levels stimulate increased ventilation rate.
  • Decreased O2 levels stimulate increased ventilation rate.