The environment can have major influences on human physiology. Environmental effects on physiology are numerous; one of the most carefully studied effects is the alterations in thermoregulation in the body due to outside stresses. This is necessary because in order for enzymes to function, blood to flow, and for various body organs to operate, temperature must remain at consistent, balanced levels.

To achieve this, the body alters three main things to achieve a constant, normal body temperature:

• Heat transfer to the epidermis
• The rate of evaporation
• The rate of heat production

The hypothalamus, or "master gland", plays an important role in thermoregulation. It connects to thermal receptors in the dermis, and detects changes in surrounding blood to make decisions of whether to stimulate internal heat production, or to stimulate evaporation.

There are two main types of stresses that can be experienced due to extreme, environmental temperatures; heat stress and cold stress . Heat stress is physiologically combated in four ways; by radiation, conduction, convection, and evaporation. Cold stress is physiologically combated by shivering, accumulation of body fat, circulatory adaptations (that provide an efficient transfer of heat to the epidermis), and increased blood flow to the extremities.

There is one part of the body fully equipped to deal with cold stress. The respiratory system protects itself against damage by warming the incoming air to 80-90 degrees Fahrenheit before it reaches the bronchi. This means that not even the most frigid of temperatures can damage the respiratory tract.

In both types of temperature related stress, it is important to remain well hydrated. Hydration reduces cardiovascular strain, enhances the ability of energy processes to occur, and reduces feelings of exhaustion.

Extreme temperatures are not the only obstacles that humans face. High altitudes also pose serious physiological challenges on the body. Some of these effects are reduced arterial P02, the rebalancing of the acid-base content in body fluids, increased hemoglobin, increased RBC synthesis, enhanced circulation, and lower levels of 2,3 DPG.

Environmental factors can play a huge role in the human body's fight for homeostasis. Fortunately, humans have found ways to adapt, both physiologically and tangibly.