Respiration And Acid Base Balance

BIOSCIENCE MODULE TASK I

RESPIRATION AND ACID BASE BALANCE

Questions: 1. Explain the diffusion mechanism of O2 from the atmosphere to the tissue

and diffusion of CO2 from the tissue to atmosphere! 2. Give one example that cause respiratoric acidosis and explain the mechanism of respiratoric acidosis in the example! 3. Give one example that cause respiratoric alkalosis and explain the mechanism of respiratoric alkalosis in the example!

By Theo Dapamede. 2009.

Answers: 1. There are two main principles that are present in the diffusion of O2 from the atmosphere to the tissue. First, oxygen diffuses from a high PO2 (partial pressure of oxygen) to a lower PO2. Second, oxygen is transferred in two ways: as soluble O2 gas in blood (plasma) and transported by Hb (haemoglobin). Oxygen is first taken into the lungs, where the PO2 is 107 mmHg. Blood oxygenation takes place in the lung capillaries.

Oxygenated blood is

brought to the left atrium where the pressure drops to 40 mmHg. The blood is pumped to the whole body by the left ventricle, which increases the PO2 to 100 mmHg. Along the arteries, the PO2 decreases to 40 mmHg. This large difference of pressure is known to happen because based on the longitudinal and radial oxygen gradients data in the arteriolar blood vessels of most tissues; a significant amount of oxygen is lost from these vessels.1 In tissue capillaries, the PO2 is approximately 20 mmHg. This value indicates that the oxygen is being consumed by the tissue for the synthesis of ATP at the cellular level.

In the diffusion of CO2, the cell produces CO2 as a waste product of cell respiratory. CO2 is diffused to the blood in the tissue capillaries, which is carried by Hb. The PCO2 in the tissue capillaries is 60 mmHg. In the veins, the partial pressure decreases to about 46 mmHg. Along the way to the lungs, the PCO2 slowly decreases to 40 mmHg. In the lungs, PCO2 is about 36 mmHg, where it is released by Hb into the form of gas, and exhaled out of the body and diffuses into the atmosphere, dropping its PCO2 to 0.3 mmHg.

1 Tsai, A.G., Johnson, P.C., Intaglietta, M., Oxygen Gradients in the Microcirculation (Physiological Reviews, 2003), p. 959.

By Theo Dapamede. 2009.

2. Respiratoric acidosis occurs when the level of carbonic acid (H2CO3) is above normal, thus decreasing the pH of the blood below 7.4.

The

increase level of H2CO3 is due to the increase of PCO2 in the blood caused by insufficient removal of CO2 by the body.

One of the causes of

respiratoric acidosis is the obstruction of the respiratory system. According to its name, obstruction of the respiratory system happens because there is an obstruction happening to a part of the respiratory system that decreases the ability for the body to exhale CO2 normally. The obstruction could occur because of microbial infection (i.e. pneumonia), choking on a foreign object, (i.e. Corpus alienum), asthma, etc. With only little ability to exhale CO2, there will be an accumulation of CO2 in the blood. Through a reaction with water in the body, this accumulation of CO2 will produce H2CO3; hence lowering the pH of the blood and therefore respiratoric acidosis would occur. 3. Respiratoric alkalosis occurs when the level of carbonic acid (H2CO3) is lower than normal, thus increasing the pH of the blood above 7.4. The decrease level of H2CO3 is commonly due to a sudden drop of PCO2 in the blood caused by over expiration of CO2 by the body. One of the causes of respiratoric alkalosis is the hysteric reaction. When a person is having a hysteric reaction, which could be caused by a fright, or overwhelm of joy, his/her breathing will increase rapidly. This rapid breathing will exhale a large amount of CO2, causing a sudden drop of PCO2 in the blood. Without sufficient CO2, carbonic acid levels will also decrease, therefore the acidity in the blood will drop and the blood will become alkaline (pH > 7.4), hence resulting in respiratoric alkalosis.

By Theo Dapamede. 2009.

Reference Law, R., Bukwirwa, H. 1999. The Physiology of Oxygen Delivery. World Anaesthesia Online. http://www.nda.ox.ac.uk/wfsa/index.htm. [accessed 4 November 2009]. Setyohadi. 2009. Respiration. Lecture notes on Biochemistry, Brawijaya University, Malang. (not published). Tsai, A.G., Johnson, P.C., Intaglietta, M. 2003. Oxygen Gradients in the Microcirculation. Physiological Reviews 83: 933-963. Wang, W., Winlove, C.P., Michel, C.C. 2003. Oxygen partial pressure in outer layers of skin of human finger nail folds. J Physiol 543(3): 855-863.

By Theo Dapamede. 2009.