Homeostasis and Negative Feedback

• Organisms maintain stable internal conditions via structures and processes that regulate temperature, osmotic balance, and glucose levels.

Homeostasis

• Homeostasis refers to the relatively stable state inside the body of an animal.
• Animal organs and organ systems constantly adjust to internal and external changes in order to maintain the steady state.
• Stable conditions are maintained through physiological processes resulting in negative feedback relationships.
• The goal of homeostasis is to maintain equilibrium around a specific value, known as the set point.
• While there are fluctuations from the set point, the body usually tries to return to it.
• A stimulus, detected by a receptor, prompts a system response to adjust a parameter toward the set point.

Negative Feedback

• Negative feedback loops change the direction of the stimulus in a homeostatic process.
• This increases or decreases the stimulus, preventing it from continuing as before.
• If a level is too high, the body lowers it; if too low, the body raises it.

Example of Homeostasis

• Beta cells in the pancreas release insulin when blood glucose levels rise.
• Insulin prompts the liver to take up glucose and store it as glycogen, and body cells take up glucose.
• As blood glucose levels decline, alpha cells in the pancreas release glucagon.
• Glucagon causes the liver to break down glycogen, which then releases glucose.

Positive Feedback

• Positive feedback loops maintain and potentially accelerate the stimulus.
• Uterine contractions during childbirth exemplifies positive feedback.
• Oxytocin, from the endocrine system, stimulates uterine contractions.
• The nervous system senses this process, producing pain.
• More oxytocin is produced, not less, until contractions are strong enough for childbirth.

Thermoregulation

• Thermoregulation is the control of body temperature.
• Some animals maintain constant body temperature, while others' varies with the environment.
• Ectotherms do not control their own body temperature, thus relying on external temperatures.
• Homeotherms maintain a constant body temperature despite environmental changes.
• Endotherms rely on internal sources for body temperature and can have extremes in temperature.
• Endotherms maintain activity at cooler temperatures due to differing enzyme activity levels.

Nervous System and Thermoregulation

• The nervous system is important in thermoregulation and temperature control.
• Homeostasis and temperature control are centered in the hypothalamus of the brain.
• The hypothalamus maintains a set point, using vasodilation/vasoconstriction reflexes for shivering or sweating.
• Increased body temperature conserves iron, suppressing bacterial growth.
• Higher body heat increases animal enzyme and protective cell activity, inhibiting invading microorganisms.
• Heat itself can kill pathogens.
• Fevers are a normal defense mechanism.
• Normal body temperature is around 37C (98.6F).

Osmotic Balance

• Osmosis involves diffusing water across a membrane due to osmotic pressure from molecular imbalances.
• Osmoregulation maintains salt and water balance through membranes within body fluids.
• Body fluids are a mix of water, electrolytes, and non-electrolytes.