Body & Mind Training Center

Gaseous Exchange in the Lungs :


The main function of the respiratory system is gaseous exchange. This refers to the process of Oxygen and Carbon Dioxide moving between the lungs and blood.

Diffusion occurs when molecules move from an area of high concentration (of that molecule) to an area of low concentration.
This occurs during gaseous exchange as the blood in the capillaries surrounding the alveoli has a lower oxygen concentration of Oxygen than the air in the alveoli which has just been inhaled.
Both alveoli and capillaries have walls which are only one cell thick and allow gases to diffuse across them.
The same happens with Carbon Dioxide (CO2). The blood in the surrounding capillaries has a higher concentration of CO2 than the inspired air due to it being a waste product of energy production. Therefore CO2 diffuses the other way, from the capillaries, into the alveoli where it can then be exhaled.

To demonstrate the use of Oxygen and Carbon Dioxide in respiration you can look at the amounts of both gases which we inhale and then exhale. The air we breathe contains approximately 21% Oxygen and 0.04% Carbon Dioxide. When we exhale there is approximately 17% Oxygen and 3% Carbon Dioxide. This shows a decrease in Oxygen levels (as it is used in producing energy) and an increase in Carbon Dioxide due to it being a waste product of energy production.

VO2 Max :


VO2 max is the measure of the peak volume of Oxygen (VO2) you can consume and use in a minute. It is measured in ml/kg/min and so you can see that it is also relative to body weight.

As we already know, Oxygen is needed to produce energy. The harder you exercise the more Oxygen you use in order to produce sufficient energy. However, everybody has a maximum level (their VO2 Max), where Oxygen utilisation is at its peak

If exercise intensity increases beyond this point then the anaerobic energy systems must be used to supply the additional energy. However, anaerobic metabolism produces lactic acid which causes fatigue and so cannot be sustained. Anaerobic energy production also results in Oxygen Debt.

Your VO2 Max can be increased through training, as this causes adaptations within the cardiovascular, respiratory and muscular systems which make the processes of gas exchange, Oxygen transport and aerobic metabolism more efficient.

There are a number of ways of testing your VO2 max. The most accurate is in a laboratory, where exhaled Oxygen and Carbon Dioxide levels are measured whilst running on a treadmill. This allows us to see how much of the Oxygen inhaled (we know 21% of the air we inhale is O2) is used for energy production. VO2 can also be estimated using tests such as a bleep test, or Balke test.

Results vary depending on fitness level, sex, age and genetics. The older you are the lower your VO2 Max is estimated to be. An average score for a twenty-something male would be 40 ml/kg/min with an excellent score being 52 ml/kg/min. An average score for a female of the same age would be 30 ml/kg/min and an excellent score would be 41 ml/kg/min. Some prefoessional sports people (involved in endurance activities) have scores in the 80's!

The Human Digestive System



The Functions of the Digestive Syste :

The primary function of the digestive system is to break down food both mechanically and by the use of enzymes, so that it can be used by the body for energy and cell growth and repair. The human digestive system consists of a large number of organs and processes with the combined functions of breaking down our food into smaller molecules which can be used to produce energy and for other nutritional purposes; and excreting the waste consumed and produced by the system.


What is the Digestive System ?

How does the Digestive System work ? Digestion essentially occurs in a series of tubes such as the Oesophogus and Intestines as food passes through the body. A number of other organs contribute to digestion by providing enzymes for the breakdown of food. The anatomy of the digestive system can be seen in the diagram below.





Digestive System Organs :

Mouth: The mouth is the starting point of digestion. Here the process of chewing starts to break down food and enzymes such as salivary lipase and amylase also start to chemically break down the food.

Oesophagus: Once you swallow the food moves into the Oesophagus where continual waves of involuntary contraction push the food into the stomach.

Stomach: The stomach has both a mechanical and a chemical function in digestion. The upper part of the smooth (involuntary) stomach muscle relaxes to allow a large volume of food to be stored. The lower muscle then contracts in a rhythmical manner in order to churn the food inside and mix it together with the gastric acid (mainly hydrochloric acid) and digestive enzymes Pepsin, Gelatinase and Gastric Amylase and Lipase which break it down further. The stomach must then empty its contents into the small intestine.

Small Intestine: Whilst in the small intestine food is subjected to yet more enzymes, those from the Pancreas and from the glands within the intestine walls which break down carbohydrates and proteins. It is also mixed with a product of the liver which is stored and released into the intestine by the gall bladder. This is commonly known as bile. Bile works to dissolve fat so that it can be digested by the other enzymes. Rhythmic smooth muscle contraction continues within the small intestine and pushes the digesting food through its narrow tube.

Once the food is completely broken down into its individual components it is absorbed through the intestinal walls, into the blood flow of the capillaries which surround the intestine. To make this process faster and more efficient the intestinal walls contain numerous folds which are covered in finger-like projections called villi. This vastly increases the surface area of the intestine wall for molecules of digested food to pass through.


Large Intestine : The large intestine continues the foods journey and is the bodies last chance to absorb any water and minerals still remaining. The rest of the contents of the large intestine is waste such as undigestable pieces of food and fiber. This is passed through to the rectum where it is stored until you go to the toilet!