Human Physiology

Lesson 04 : Water Compartment & Homeostasis


Water is the main solvent of the human body.
Some Physical Characteristics:
Water has several important physical characteristics that make it extremely useful solvent for the body.

  • As a fluid, it has the capacity to flow between various compartments.
  • Being a "universal solvent" it can dissolve so many substances within itself, thus making it an excellent vehicle for the circulatory systems.
  • Water is very useful in the temperature control mechanisms of the body. This is because of its heat-carrying capacity (high specific heat) and its tendency to remove large numbers of calories during evaporation.

Water input: The human body obtains water in two primary ways:

  • Most items that humans drink or eat consist largely of water (Oral input).
  • A second source of water is metabolic oxidation. This water is referred to as metabolic water. As various food substances are oxidized within the individual cell, water is one of the main by-products.

Water output: The human body looses water in following ways:

  • Perspiration: Water is continuously lost from the body in the form of perspiration or sweat. With high surrounding temperatures and/or vigorous exercise, the sweating is obvious. This is called sensible perspiration. Otherwise, in the absence of sweating there is a low level of water loss from skin surface called insensible perspiration.
  • Respiration: The surfaces of the lungs must be moist to ensure the passage of gases to and from the blood. Air is moistened within the respiratory passages and the alveoli of the lungs. Thus, moisture passes out of the body along with the exhaled breath.
  • Urination: Water is also lost from the body in the form of urine. Urine carries nitrogenous wastes of protein metabolism dissolved in the water.
  • Vomiting and diarrhea: During vomiting and diarrhea, the body loses large quantities of water and dissolved electrolytes. In infants and the elderly, this loss of water and electrolytes can be very dangerous. Sometimes, even death may result.

In spite of continuous input and output of water from the body, the volume of volume of various fluid compartments is maintained. Quantity of water in extra cellular fluid is regulated by Antidiuretic hormone or vasopressin secreted from posterior pituitary.

Last modified: Tuesday, 10 April 2012, 5:12 AM