Mechanism of Regulation and the Importance of Blood PH - Essay Example

HUMAN BIOSCIENCE Human Bioscience Introduction Maintenance of the pH of the blood is an important process which has to be regulated strictly by the human body. The normal blood pH ranges from 7.35 to 7.45 and deviations from the normal range can lead to hazardous outcomes as the functions of the body are very sensitive to the pH. A blood pH which is below 7.2 has serious consequences such as reduced growth, a decline in cardiac output, resistance to insulin; a lower than normal blood pressure and raised blood potassium levels (hyperkalemia). On the other hand, a pH above 7.6 leads to low calcium in the body causing tetany and abnormalities in the hearth rhythm. pH has a direct effect on the structure of proteins in the human body as pH aberrations lead to either excess protonation or deprotonation of the proteins. This has a direct effect on the protein structures making them less functional. Proteins form the major component of bodily structures, enzymes and chemical components, and their chemical sensitivity to pH leads to an increased demand for regulator mechanisms so that pH can be maintained within the required ranges. pH maintainence is important mainly in the blood or the extracellular compartment, however, several cells of the body and even the brain require a proper maintainence of intracellular pH levels. Intracellular compartments are mainly more acidic than the extracellular compartments because of the negative charges on the inside of the cells. Cells also contain hydrogen pumps such as H-ATPase and Na/H exchanger pumps which are crucial in maintaining the pH inside the cells and keep in metabollicaly active (Seifter, et al., 2005 pg.392). pH of the blood is susceptible to changes in response to several physiological as well as pathological processes and body mechanisms work in conjunction regulate the ranges. pH ranges are subjected to alterations after increased acid or basic food intake, excessive exercise or in conditions such as alcoholism, salicylate poisoning, diabetes or hyperventilation. These are only some of the examples which alter the pH levels and require prompt compensations. Body responds by its chemical buffering system, respiratory mechanisms and renal compensations mainly to keep the pH withing the normal ranges. Mechanism of Regulation of Blood PH The acid base homeostasis of the body is maintained by body buffers, chemosensors present in the brain as well as the circulation, the kidneys and the lungs. These components form the basic acid-base apparatus of the human body. The buffers present in the body include bicarbonate, proteins, phosphate and other chemicals. Bicarbonate is a significant buffering system through the important chemical equation where carbonic acid can be shifted to its two sets of breakdown products. It can either form carbon dioxide and water or hydrogen ions (H+) and bicarbonate ions (HCO3-). The chemical buffers form the first line of defence of the body to acid base changes however; they do not remove the acid or base from the body. Lungs act as second line of defence and the renal compensation is a late response (Seifter, et al., 2005, pg 393; Rhoades & Bell, 2009, pg. 457; Johnson & Byrne, 2003, pg. 296). Physiological Sources of Acid Ou body has two main sources of acid. First category is of the volatile or gaseous sources such as carbon dioxide which is produced as an end product of body metabolisms of the dietary carbohydrates and fats. All aerobic cells undergo metabolism and produce carbondioxide. Increased carbon dioxide increases the amount of H+ ions in the body hence lowering the body pH. The non-volatile sources of acid is through the metabolism of the amino acids. The end products of amino acid metabolism is mainly HCl and H2SO4 which increase the hydrogen ions in the body has shifting the carbonic acid equation towards carbon dioxide and lowering the bicarbonates (Seifter, et al., 2005. Pg 393). Changes in the systemic pH also controls the rate of endogenous acid production, which is both rapid and reversible. Keto acids and lactic acids are endogenously produced in our body, and are products of body metabolism. Lactic acid is an important source of energy during exercise and keto acids serve as significant sources of energy during conditions of fasting or starvation. A low pH inhibits the production of glycolytic metabolism producing lactic acids and a high pH stimulates it (Hood & Tannen, 1998, pg. 820-822). Blood pH Buffer Systems Major chemical pH buffers in the body are in the form of acid-base conjugates and regulate the pH. In the ECF important buffers are bicarbonate/carbon dioxide, inorganic phosphate, plasma proteins and in the ICF the important chemical buffers include cell proteins such as haemoglobin, organic phosphates and bicarbonate/carbon dioxide. Bone also plays a significant role in buffering system and has mineral phosphates and mineral carbonates to regulate pH (Rhoades & Bell, 2009. Pg. 455). It has been shown through research that during pH aberrations both during acute and chronic conditions, activate the buffering system in the bones. Low pH levels lead to loss of calcium from the bone, buffering of the hydrogen ions by the bone, bringing the pH to normal levels. The response of bone buffers is more active during metabolic acidosis as compared to respiratory acidosis. Bone is an important reservoir of carbon dioxide in the form of carbonates and during metabolic acidosis it leads to active release of carbonates into the blood (Kidney International, 1991, pg. 14-16). Renal Compensation Kidney performs its major role in regulating acid base balance by controlling the amount of bicarbonate concentration in the body. Kidneys can either reabsorb the bicarbonate to prevent its depletion in cases such as metabolic acidosis or excrete greater amounts of bicarbonate ions in situations such as metabolic alkalosis. Proximal convoluted tubule is the principal site of ninety percent of the reabsorption of bicarbonates. Bicarbonate is however not directly reabsorbed. First it combines with the hydrogen ions to form carbonic acid which is then acted upon by the carbonic anhydrase enzyme present in the brush borders of the proximal cells. It is converted to carbon dioxide which diffuses across the cell membrane into the cell and again forms carbonic acid and them bicarbonate ions. The bicarbonate ion from here is reabsorbed into the blood capillaries (Lee & Pharmacists, 2009, pg 180). Respiratory Compensation Lungs maintain the pH of the blood mainly by regulation of PCO2. Chemoreceptors in the medulla of the brain and also the arteries of the brain are highly sensitive to the blood pCO2 levels and can respond by increasing or decreasing the ventilation. Increased ventilation decreases the carbon dioxide while decreased ventilation increases the carbon dioxide levels in the blood. Lungs are therefore capable of responding quickly to changes in blood pH. Ventilation is increased by increasing the rate of respiration (Lee, et al, 2009, pg 181). ECF Potassium Changes Maintenance of a normal extracellular potassium range is important for various normal body functions, most importantly for the electrical activity of the heart muscles. A metabolic acidosis leads to shift of potassium from the intracellular compartment to the outside of the cell leading to hyperkalemia. On the other hand, in alkalosis, there is a net shift of potassium from the ECF to the inside of the cell leading to hypokalemia. Most of the exchange takes place through the K-H exchange pump present in several cells. In acidosis, increased number of hydrogen ions is shifted into cell with a net shift of potassium outwards and the opposite happens in alkalemia (Aronson, 2011, pg. 1981-1982). There is no change in the ICF voltage of the cells in patients with respiratory acid-base disturbances because in these conditions, movement of Na and Cl across the cells is minimal and hence no net effect on potassium (Halperin, et al., 2010, n.p.) Acid-Base Imbalances Metabolic acidosis is characterized by decreased plasma pH, less than 7.35 and decreased plasma bicarbonate levels (less than 22mmol/L) which can be because of gain of hydrogen ions or loss of bicarbonate ions (Porth, et al., 2010, pg 785). Metabolic alkalosis is characterized by an increase in plasma pH and an increase in plasma bicarbonates. It can be caused by increased intake of bicarbonates, increased loss of hydrogen ions, increased bicarbonate retention or contraction alkalosis (Porth, et al., 2010, pg.786). Respiratory acidosis is characterized by a rapid increase in arterial PCO2, a minimal decrease in plasma bicarbonate and an increase in plasma pH. It can be caused by a depression in respiratory centre, any lung disease such as emphysema or pneumonia, airway obstruction or disorder of chest wall or respiratory muscles leading to hypoventilation and it can also result as long-term breathing in air with high CO2. Respiratory alkalosis is also called as hypocapnia because of fall in arterial PCO2, a minimal rise in plasma bicarbonates and a rise in plasma pH. Causes of respiratory alkalosis include conditions which lead to hyperventilation such as anxiety, hypoxia, lung disease, stimulation of respiratory centres, salicylate toxicity and fever (Porth, et al., 2010, pg787-789). Summary Regulation of pH in the blood is governed by several mechanisms which are activated at various stages of time or according to severity of the deviations from the normal ranges. Body functions and protein structure are highly sensitive to changes in pH levels and hence, body systems are activated as soon as deviations are detected. Chemical buffer systems composed of proteins, phosphates and bicarbonates are the first line of defence against pH aberrations. Lung is a significant part of maintaining blood pH by detection through chemoreceptors in brain and is highly sensitive to changes in blood PCO2 which leads to quick changes in ventilation. Kidney’s primary function is to control blood pH through excretion or reabsorption of bicarbonates. Bone also buffers the increased or reduced pH through its carbonate reserves and calcium release or absorption. References Aronson, P. S., 2011. Effects of pH on Potassium: New Explanations for Old Observations. Journal of the American Society of Nephrology, 22(11), pp. 1981-1989. Halperin, M. L., Goldstein, M. B. & Kamel, K. S., 2010. Fluid, Electrolyte and Acid-Base Physiology: A Problem-Based Approach. Philadelphia, PA: Saunders/Elsevier. Hood, V. L. & Tannen, R. L., 1998. Protection of Acid-Base Balance by pH Regulation of Acid Production. The New England Journal of Medicine, 10(339), pp. 819-826. Johnson, L. R. & Byrne, J. H., 2003. Essential medical physiology. Amsterdam; Boston: Elsevier Academic Press. Kidney International, 1991. Role of Bone in regulation of systemic acid-base balance. Kidney International, Volume 39, pp. 9-26. Lee, M. & Pharmacists, A. S. o. H.-S., 2009. Basic Skills in interpreting laboratory data. Bethesda: American Society of Health System Pharmacists. Porth, C., Hannon, R. A. & al, e., 2010. Porth Pathophysiology: Concepts of Altered Health States. Philadelphia, PA: Wolters Kluwer Health/ Lippincott Williams & Wilkins. Rhoades, R. & Bell, D. R., 2009. Medical physiology; principles for clinical medicine. Philadelphia: Lipponcott Williams & Wilkins. Seifter, J., Sloane, D. & Ratner, A., 2005. Concepts in Medical physiology. Philadelphia: Lippincott Williams & Wilkins. Read More