Biology Homeostasis Overview

Homeostasis

• Homeostasis is the maintenance of a steady internal state, regardless of external environment changes.
• Examples include blood pressure, body temperature, blood glucose, pH levels, and fluid balance.

Maintaining Homeostasis

• Dynamic equilibrium is maintained through three components:
  • Receptor/Sensor: Detects changes in the internal or external environment.
  • Control Center: Processes information from the receptor and decides on a response.
  • Effector: Carries out the response determined by the control center.

Homeostatic Control System

• Input: Information from the receptor/sensor is sent to the control center.
• Change Detected: The receptor detects a change in the variable.
• Imbalance: The variable is out of homeostasis.
• Output: Instructions from the control center to the effector.
• Response: The effector carries out the response.
• Influence: The response influences the magnitude of the stimulus and returns the variable to homeostasis.

Feedback Systems

• A cycle of events where a variable (e.g., body temperature, blood glucose, blood pH) is continuously monitored, assessed, and adjusted.
• This involves a sensor, a control center, and an effector.

Types of Feedback Systems

1. Negative Feedback

• A process where a mechanism is activated to restore conditions to their original state.
• Example: Thermoregulation; when body temperature increases, cooling mechanisms like sweating are activated. Conversely, when temperature decreases, mechanisms like shivering are used to increase the core temperature.

2. Positive Feedback

• A process where a small effect is amplified, moving the controlled variable further away from a steady state.
• Example: Childbirth; uterine contractions initiating during labor, leading to more contractions.

Thermoregulation

• Ectotherms: Organisms that depend on external sources of heat to regulate body temperature, e.g. fish, amphibians, and reptiles.
• Endotherms: Organisms that maintain a constant internal temperature. Mammals and birds regulate their body temperature through internal mechanisms, e.g., shivering, sweating, and adjusting blood vessel diameter.

Core Temperature

• The temperature of the internal organs, such as the liver and heart.
• Most constant, usually between 36.5°C and 37.5°C.

Peripheral Temperature

• The temperature of the body extremities, like fingers and toes.
• Can fluctuate and be as much as 4°C lower than the core temperature on cold days.

Heat and Cold Stress

• The body is exposed to both heat and cold stress.
• Heat stress can lead to excessive core temperature, while cold stress can lead to hypothermia from dropping core temperature.

Regulating Temperature

• The hypothalamus coordinates nerve and hormone functions, regulates body temperature.

Response to Extreme Cold (Hypothermia)

• Core body temperature drops below normal range and can trigger coma or death.
• The body tries to retain heat by diverting it from the periphery to the core.

Metabolism of Brown Fat

• Brown fat is dark adipose tissue with many blood vessels.
• Used for heat production during cold stress.
• Present in hibernating animals and human babies, possibly also in some adults.

Freezing Cells

• The body tries to prevent freezing by doing as much as it can.
• Ice crystal formation can damage cell membranes, while thawing can cause cells to burst.