Role of Water in Human Biology

Water is the one of the most significant components of the human body; it plays a crucial role in several physiological activities because of its unique physicochemical properties. Importantly, it helps to regulate body temperature and is the chief component of several body fluids.

Water's Solvent Properties

Since water is a polar molecule with slightly positive and slightly negative charges, ions and polar molecules can readily dissolve in it. Therefore, it is referred to as a solvent, a substance capable of dissolving other polar molecules and ionic compounds. The charges associated with these molecules will form hydrogen bonds with water, surrounding the particle with water molecules. This is called a sphere of hydration, or a hydration shell. It serves to keep the particles separated or dispersed in the water.

Water's High Heat Capacity

Water has a higher specific heat capacity than most other liquid substances, due to its unique arrangement of hydrogen bonds. Specific heat is defined as the amount of heat one gram of a substance must absorb or lose to change its temperature by 1° Celsius. For water, this amount is one calorie. Therefore, it takes water a greater amount of time to heat and then cool than something with a lower specific heat. Due to its high heat capacity, water is used by warm-blooded animals to disperse heat more evenly in their bodies. In this case, water can be compared to a car's cooling system, transporting heat from warm places to cool places, helping the body maintain a more even temperature.

Water's Heat of Vaporization

Water also has a high heat of vaporization, meaning the energy required to change one gram of a liquid substance into a gas. A considerable amount of heat energy is needed to accomplish this change in water. This process occurs on the surface of the water. As liquid water heats up, hydrogen bonding makes it difficult to separate the water molecules from each other in their liquid state. As a result, water acts as a heat sink or reservoir that requires much more heat to boil than a liquid such as ethanol, where hydrogen bonding between molecules is weaker. Eventually, as the water reaches its boiling point of 100° Celsius (212° Fahrenheit), the heat breaks the hydrogen bonds and the kinetic energy allows the water molecules to escape in the form of gas.

This text is adapted from Openstax, Biology 2e, Section 2.2: Water

Water constitutes 50-60% of the total body weight in humans and plays many crucial roles in their physiology.

First, it provides a suitable medium for most biochemical reactions in the body due to its excellent solvent properties. It also directly participates in many important chemical reactions, such as the breakdown of complex food molecules.

Second, water is the main component of body fluids, such as saliva, blood, and tears.

While saliva aids in swallowing and digestion of food, blood facilitates the transport of nutrients and elimination of toxic wastes from the body.

Tears help to flush out irritants from the eyes and keep them lubricated. Similarly, water also serves as a lubricant in joints, protecting them from friction.

Third, water has a high heat capacity that helps to regulate body temperature. It absorbs and redistributes the heat throughout the body via blood.

When the body temperature rises, the heat is released from the body via sweat, which is mainly composed of water. This helps to bring down the temperature.

Finally, water also acts as a shock absorber. For example, as part of the amniotic fluid, it helps to protect the developing fetus from physical trauma.