Animals maintain a stable internal environment through homeostasis, keeping physiological parameters within narrow ranges. This process is crucial for proper cell function and involves various body systems working together to regulate conditions like temperature and water balance.

Organisms respond to environmental changes through stress responses and adaptations. These mechanisms help animals cope with challenges and survive in diverse habitats. Understanding these processes is key to grasping how animals function and thrive in different environments.

Homeostasis and Internal Environment

Maintaining a Steady Internal State

• Homeostasis refers to the maintenance of a relatively stable internal environment despite changes in the external environment
• Involves keeping physiological parameters within a narrow range of values known as the steady state
• The internal environment consists of the fluid surrounding the cells (interstitial fluid) and the fluid inside the cells (intracellular fluid)
• Homeostasis is critical for proper functioning of cells, tissues, and organs (enzymes, membranes, and biochemical reactions)

Physiological Systems and Setpoints

• Various physiological systems work together to maintain homeostasis (nervous, endocrine, cardiovascular, respiratory, and excretory systems)
• Each physiological parameter has a specific setpoint, which is the optimal value for that parameter
• Setpoints are maintained by negative feedback loops that detect deviations and initiate corrective responses
• Physiological parameters also have a tolerance range, which is the range of values that can be tolerated without causing significant harm to the organism

Regulation and Adaptation

Osmoregulation and Thermoregulation

• Osmoregulation is the regulation of water and solute balance in the body
• Involves the control of water intake, excretion, and distribution between compartments (intracellular and extracellular fluids)
• Thermoregulation is the maintenance of a relatively constant body temperature
• Achieved through behavioral and physiological mechanisms (sweating, shivering, vasodilation, and vasoconstriction)

Stress Response and Adaptation

• The stress response is a set of physiological changes that occur in response to a stressor (physical or psychological challenge)
• Involves the activation of the sympathetic nervous system and the release of stress hormones (cortisol and epinephrine)
• The stress response prepares the body for "fight or flight" by increasing heart rate, blood pressure, and blood glucose levels
• Adaptation refers to the long-term adjustments made by an organism in response to changes in its environment
• Can involve changes in physiology, behavior, or morphology that improve the organism's ability to survive and reproduce in its environment (acclimatization to high altitudes or cold temperatures)