AJ-5-Physiology-of-the-human-body

5) PHYSIOLOGY OF THE HUMAN BODY

The human energy system is composed of several systems of the body: the respiratory system provides oxygen needed for the burning of the fuel; the cardiovascular system delivers the oxygen and fuel to the muscles; and energy conversion systems in the muscles convert the oxygen and fuel into the muscular activity. There is in addition the digestive system, which of course provides the fuel, but its functioning processes are not dealt with in this chapter.

RESPIRATORY SYSTEM
The respiratory system is an organ system which is used for breathing. This action is achieved by ventilation, which involves two acts: inhalation (inspiration) and exhalation (expiration). The respiratory system consists of the upper and lower airways, the lungs, and the respiratory muscles that mediate the movement of air into and out of the body. The upper airway is formed by the nose, mouth, pharynx and larynx. The lower tract consists of trachea, bronchi and two lungs.

Air moves through the body in the following order:

The major function of the respiratory system is gas exchange. Upon inhalation, air enters the body through the nose and mouth and travels down the trachea, through the bronchial tubes, and finally into the lungs. Once in the lungs, the air is drawn into an enormous number of sacs (alveoli) richly supplied with capillaries. The alveolar walls are extremely thin, and are permeable to gases. The alveoli are lined with pulmonary capillaries, the walls of which are also thin enough to permit gas exchange. All gases diffuse from the alveolar air to the blood in the pulmonary capillaries, as carbon dioxide diffuses in the opposite direction, from capillary blood to alveolar air. At this point, the pulmonary blood is oxygen-rich, and the lungs are holding carbon dioxide. Exhalationfollows, thereby ridding the body of the carbon dioxide and completing the cycle of respiration. The respiration is under the control of the respiratory centre in the medulla of the brain and is affected by many factors such as exercise, emotional reactions, pain, elevated temperature, shock, or certain drugs.

There are two ways in which the lungs can respond to the body’s increased demand for oxygen. They can pump faster or they increase the volume of air they pump with each breath. It is more efficient to increase the volume rather than the rate. The average male has a total lung capacity of around 6 litres. If he tried to breathe all the air out, he would still have around 1.2 litres of air left in his lungs, which is his residual volume. The difference between the total capacity and the residual volume is termed vital capacity, which is usually 4-5 litres for men and 3- 4 litres for women. However, elite endurance athletes may have vital capacities of 6 – 7 litres.

VO2 MAX

Fitness can be measured by the volume of oxygen you can consume while exercising at your maximum capacity. VO2 max is the maximum amount of oxygen in milliliters, one can use in one minute per kilogram of body weight.