Traditionally, the body is divided into different systems according to their specific functions. However, the ultimate purpose of each system is to maintain a constant internal environment for each cell to enable it to survive.

The human body is exposed to a constantly changing external environment. These changes are neutralised by the internal environment of blood, lymph and tissue fluids that bathe and protect the cells.

System level (digestive system)

Fig 1.1 Levels of structural organisation in the body

Body parts function efficiently only when the concentrations of water, food substances, oxygen and the conditions of heat and pressure remain within certain narrow limits. The process by which the body maintains a stable internal environment for its cells and tissues is called homeostasis.

Homeostasis is like a fine-tuning mechanism that your body goes through automatically in order to restore balance among the body's systems.


When the body's systems are imbalanced through stress, pain, infection or depleted oxygen levels, the body's cells do not work at their optimal level and therefore signs of disorder and disease may be seen.

The body and its systems are constructed in such a way that all systems work synergistically with each other with one overall aim — to maintain homeostasis. Examples of homeostatic mechanisms in the body include the regulation of:

• body temperature

• blood pressure

• blood sugar levels

The part of the brain called the hypothalamus is significant in maintaining homeostasis. Throughout the body, receptors in the blood vessels detect pressure, temperature, glucose levels and pH levels in the blood. These receptors send a signal through the nervous systems to the hypothalamus to initiate changes in the body to bring the body back to balance (an example of this is the secretion of insulin if the blood sugar levels get too high).

The Smoker's Sanctuary

The Smoker's Sanctuary

Save Your Lungs And Never Have To Spend A Single Cent Of Ciggies Ever Again. According to a recent report from the U.S. government. Centers for Disease Control and Prevention, more than twenty percent of male and female adults in the U.S. smoke cigarettes, while more than eighty percent of them light up a cigarette daily.

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