2 2 4 Describe The Main Changes In The Chemical Composition

The transport system within the body is involved in moving gases (carbon dioxide and oxygen), nutrients, wastes and hormones

The changing chemical composition of blood

The difference in the chemical concentration of blood entering or leaving an organ, depends on the function of the organ. External gaseous exchange occurs in the lungs (carbon dioxide is released from the blood and oxygen in picked up). Internal gaseous exchange occurs in all organs of the body and is the result of cellular respiration (oxygen combines with glucose to make energy, with carbon dioxide as a waste product). Absorption of nutrients into the bloodstream takes place in the digestive tract (particularly the small intestine). Nitrogenous waste is produced in the liver and is excreted by the kidneys. Hormones are secreted into the blood by glands and then travel to where they are required and used up by the target tissue.

Change in carbon dioxide and oxygen content of blood

The lungs are the organs of external gaseous exchange. Deoxygenated blood arrives at the lungs and it releases carbon dioxide and picks up oxygen. The haemoglobin binds with the oxygen, forming oxyhaemoglobin. Most oxygen (98.5%) travels as oxyhaemoglobin only 1.5% travels as dissolved in the plasma. The oxygenated blood is returned to the heart where it is pumped to other tissues of the body, where oxygen is released and used for cellular respiration.

Internal gaseous exchange occurs in the tissues of the body as a result of cellular respiration. Cells release carbon dioxide which diffuses into the capillaries in the tissues. When carbon dioxide enters the blood, some dissolves into the plasma, some is carried by haemoglobin, the rest is transported as bicarbonate ions. This forms the deoxygenated blood returning back to the lungs.

Changes in other chemicals in blood

- An increase in oxygen and a decrease in carbon dioxide is evident when the blood passes through the lungs
- A decrease in oxygen and increase in carbon dioxide is noted when the blood passes through any organ other than lungs
- An increase in digestive end products is evident in blood that passed through an organ involved in absorbing digested food (small intestines). These products travel into the bloodstream directly into the liver
- A decrease in digestive end products (glucose, fatty acids, amino acids) is evident as blood leaves the liver, as it is the center of food metabolism
- An increase in nitrogenous wastes as the blood leaves the liver, as it is the organ in which proteins are de-aminated
- A decrease in nitrogenous wastes as the blood passes through the kidneys, since they filter the wastes and excrete them