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PHYSIOLOGICAL EFFECT OF METABOLIC RATE ON ACID-BASE BALANCE 4 Essay Example

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Physiological Effect of Metabolic Rate on Acid-base Balance

Introduction

Acidosis and alkalosis are terms used to describe the abnormal conditions in the human body resulting from change in blood pH caused by imbalance of acid and alkali. The normal blood pH should be regulated within a narrow range of 7.35 – 7.45 to enable proper functioning of metabolic processes and sufficient delivery of oxygen to the body tissues. Excess acid in the body causes the blood pH to fall below 7.35, and excess of base increases the blood pH to above 7.45. There are two categories of acidosis and alkalosis according to the cause of each of the two conditions; metabolic acidosis or alkalosis and respiratory acidosis or alkalosis (Thomson, Adams, & Cowan, 1997). Metabolic acidosis is a result of all conditions that cause the blood pH to fall below 7.35, except conditions that result from altered respiratory functioning. As the level of hydrogen ion concentration increases, buffers work to resist a fall in pH. If the buffers fail to compensate for the increase in hydrogen ions, the respiratory center is stimulated by the reduced blood pH, which responds by hyperventilation and increases the rate at which CO2 is eliminated from the blood. Removal of CO2 results to elimination of excess hydrogen (Schrier, 2010). Metabolic alkalosis is as a result of all conditions that cause the blood pH to rise above 7.35, except conditions that result from altered respiratory functioning. As the level of hydrogen ion concentration decreases in the body, buffers work to resist a rise in the pH of the blood. If the buffers fail to compensate for the decrease in the level of hydrogen ions, the respiratory center is stimulated to help in regulation of the blood pH back to the normal range. Respiratory acidosis is caused by inadequate ventilation of the lungs, a condition that reduces the rate at which CO2 is eliminated from the blood. This causes an increase in the concentration of CO2 in the body which react with water to form carbonic acid. The carbonic acid dissociate to form carbonate and hydrogen ions. Increased concentration of the later leads to a rise of blood pH (Truchot, 2012). Respiratory alkalosis is as a result of hyperventilation of the lungs. It increases the rate at which CO2 is expelled from the blood, causing a decrease in the concentration of CO2. The decrease in the concentration of CO2 results in the formation of carbonic acid as carbonate ions react with hydrogen ions. As the concentration of hydrogen ions in blood reduces, the pH of the blood rises. The major organs involved in regulation of blood pH are the kidneys and the lungs. The kidneys compensate for respiratory alkalosis by excreting excess acids in the urine and also regulating the concentration of HCO3 (bicarbonate; a base) in the blood. In the kidneys, the rates at which hydrogen ions are secreted into the urine and reabsorption of bicarbonate ions are reduced. The lungs remove acid from the blood by exhaling CO2 gas. Lowering or increasing the rate of respiration alters the amount of CO2 gas exhaled and this can affect the pH of the blood within a few minutes. Buffering systems in the blood, such as hemoglobin, plasma proteins, phosphates and bicarbonates, resist changes in blood pH and contribute to regulation of acid-alkali balance (Barash, 2009).

In this lab experiment, the physiological effect of metabolic acidosis and alkalosis was investigated using a laboratory simulator consisting of a heart pump, a lung chamber and an oscilloscope to observe timing of breathing volume. The figure 1 below shows the experimental set up that was used to collect the experimental data.Metabolic Acidosis

Figure 1: Experimental Set-Up for Testing the Effect of Metabolic Acidosis and alkalosis

The experiment was performed with cell metabolic rates of: 50kcal/hr (normal), 60kcal/hr, 80kcal/hr, 20kcal/hr and 40kcal/hr.

Results and Interpretation

The figures shown below from 2 – 6, show the results obtained from the oscilloscope for each metabolic rate.

Metabolic Acidosis  1Metabolic Acidosis  2

Metabolic Acidosis  3Metabolic Acidosis  4

Metabolic Acidosis  5

Table 1: Data Recorded for Metabolic Rate, Respiration, and Acid-Base Balance

Metabolic Acidosis  6

Respiration is a biochemical reaction process that enables body cells to release chemical energy from food. Breathing, controlling body pH and temperature, contraction of muscles, blood circulation and nerve function are some of the metabolic processes that the body needs for normal functioning. The speed at which such reaction processes take place is referred to as the metabolic rate of the body. The respiratory system provides the oxygen required by the cells to burn food nutrients to energy and removing some of the metabolic wastes from the bloodstream, such as CO2. In figures 2 – 4, it can be seen that more food is broken by cells at a higher rate to provide more energy as the metabolic rate increases from 50kcal/hr to 80kcal/hr. As the metabolic rate falls as denoted in figures 5 – 6, the amount and rate of food breakdown by cells also reduces.

When the metabolic rate increases, as it happens during a workout, the body cells burn more food nutrients to cope up with the energy demand. More oxygen supply is required, and more CO2 is produced as a waste, which the body must get rid of. As a result of this, the breathing rate increases and the lungs respond by working faster. In table 1 above, when the metabolic rate was increased from 50kcal/hr to 60 kcal/hr, the number of breaths per minute increased from 15 BPM to 17 BPM. The breathing rate further increased to 21 BPM as the metabolic rate increased to 80kcal/hr. The concentration of CO2 produced also increases as the metabolic rate increases. Conversely, as the metabolic rate reduces, body cells burn fewer nutrients because the amount of energy required is reduced. The cells need less oxygen and produce less CO2. The lungs have to work more slowly, and the rate of breathing is therefore, reduced. That is why the rate of breathing falls to 9 BPM when the metabolic rate reduced to 20kcal/hr.

Increase in the metabolic rate increases the amount of CO2 produced. This causes an increase in the concentration of CO2 in the body which react with water to form carbonic acid. The carbonic acid dissociate to form carbonate and hydrogen ions. This results to increase in concentration of hydrogen ions in the blood, leading to a fall in the blood pH. It can be seen in table 1 that the blood pH falls from 7.41 to 7.27 when the metabolic rate increases from 50kcal/hr to 80kcal/hr. The end result of all this is the development of respiratory acidosis. The initial compensation step for metabolic acidosis is cellular buffering followed by renal compensation in the kidney. Conversely, when the metabolic rate is reduced, less CO2 is produced and the little that is generated is expelled from the blood system. As the concentration of CO2 falls (from 55mmol/l to 31mmol/l), more carbonic acid is formed as carbonate ions react with hydrogen ions. This reduces the concentration of hydrogen ions in the blood (from 14.5mmol/l to 30mmol/l, and increases the concentration of bicarbonate ions. This causes a rise in the pH of the blood, and subsequently, the development of respiratory alkalosis. The initial compensation step for metabolic alkalosis is cellular buffering followed by respiratory compensation through a slower breathing rate to retain more CO2 (hyperventilation) in the lungs. This is the main compensation mechanism.

Metabolic acidosis can be caused by ketones and lactic acid in the body. Ketones cause ketoacidosis, which is a condition resulting from burning of fats for energy instead of carbohydrates in a diabetic body with insufficient insulin and dehydration. Increased amount of ketones in the body turns into acid. Lactic acidosis occurs when there is anaerobic respiration (little oxygen is available for the body cells), especially during intense exercise. When this acid builds up in the body, it causes lactic acidosis.

Two possible causes of metabolic alkalosis are chloride depletion and hyperaldosteronism. Chloric metabolic alkalosis is caused by loss of gastric juice and diuretics. Gastric alkalosis is mostly associated with vomiting due to obstruction or pyloric stenosis because the vomitus contains acidic gastric juice. This results in variation in the acid-base balance in the body. Diuretic therapy using thiazides and frusemide interfere with reabsorption of sodium and chloride ions in the kidney. As a result of this condition, more chloride is lost through urinal system compared to bicarbonate. Administration of chlorides can correct these disorders. In the case of hyperaldosteronism, renal loss of H+ occurs when excess aldosterone accelerates the activity of sodium-hydrogen exchange protein inside the kidney. As a result of this, more sodium ions are retained and more hydrogen ions are pumped into the renal tubule. The increased sodium creates more extracellular volume whilst the loss of H+ causes metabolic alkalosis.

Conclusion

Blood pH in a healthy human body is maintained within a range of 7.35 – 7.45, and since pH is the negative log of [H+], a decrease in [H+] indicates an increase in pH and vice versa (Thomson, Adams, & Cowan, 1997). A decrease in [H+] leads a rise in blood pH and subsequent development of alkalosis while an increase in [H+] leads a fall in blood pH and subsequent development of acidosis (Hills, 2008). Metabolic rate of the body cells affects the acid-base balance. An increase in the metabolic activity causes a decrease in blood pH below the normal, while a decrease in metabolic activity leads to an increase in blood pH.

References

Barash, P. G. (2009). Clinical Anesthesia. London: Lippincott Williams & Wilkins.

Disorders, R. a. (2010). Robert W. Schrier. London: Lippincott Williams & Wilkins.

Hills, A. G. (2008). Acid-base Balance; Chemistry, Physiology, Pathophysiology. Michigan University: Williams & Wilkins.

Thomson, W. S., Adams, J. F., & Cowan, R. A. (1997). Clinical Acid-base Balance. London: Oxford University Press.

Truchot, J.-P. (2012). Comparative Aspects of Extracellular Acid-Base Balance. 2012: Springer Science & Business Media.