Blood pH - There is a complex relationship between the pH levels and fundamental biochemical functions in the human body.

Homeostasis

Introduction:

There is a complex relationship between the pH levels and fundamental biochemical functions in the human body. pH is the measurement of acidity or alkalinity of a substance, in this instance blood. pH stands for ‘potential Hydrogen’. The pH scale runs from 0 to 14 and is the indicator of the level of free protons (H+) in a system. At the lower end of the scale indicates a strong, complete acid that that is saturated with highly reactive free protons. At the higher end of the scale it indicates a strong, complete alkali with virtually no free protons and is saturated with highly reactive hydroxide ions (OH-). In the middle of this pH scale at 7 indicates that it is neutral, neither acid or alkaline. The pH scale is logarithmic so each number step up the scale is a tenfold increase.

The human body functions at its best in a slight alkaline environment. The acid/alkaline balancing mechanisms are what is needed to for a healthy body chemistry.

The blood pH in a healthy human body is kept within a very narrow range of 7.35 and 7.45. It is the lungs and the kidneys that are the most responsible organs in keeping blood pH at a reasonable level between 7.35 and 7.45.The kidneys through their complex filtration functions are able to cleanse the excess venous acids an remove them from the body via the urinary tract. The kidneys are responsible for releasing ammonia into the blood as a buffer to bring the blood to normal pH levels. Oxygen that has been absorbed through the lungs also helps in pH balance. Oxygen combines with carbon in certain proteins to produce carbonates, these are buffering agents that prevent acidic build-up.

The Importance of the system:

The importance of maintaining this system is to prevent the blood pH either raising above or below the necessary 4.35-4.45. If however, the system does not function properly this will result in illness and perhaps in death.

If there is too much acid in the blood the definition is acidosis and if there is not enough and the blood is too alkaline, this is known as alkalosis. Acidosis and alkalosis can result from metabolic or respiratory causes. Respiratory acidosis and alkalosis are the result of abnormal breathing patterns. Alkalosis is caused by hyperventilation that accompanies hysteria, anxiety, or prolonged crying. Acidosis can result from hypoventilation brought on by such factors as an overdose of depressant narcotics or anesthesia. Metabolic acidosis can result from the metabolic production of acids in the body or the elimination of alkaline materials as ...

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Firstly the term acidosis will be evaluated. Acidosis is a condition characterized by excessive acid in the body fluids. The acid/base status of the body (pH) is regulated by the kidneys and the lungs. Acidosis is caused by an accumulation of acid or a significant loss of bicarbonate. The major categories of acidosis are and .

The human body is programmed to correct for either or metabolic acidosis to maintain normal pH. For example, if the acidosis was caused by excessive carbon dioxide (which is an acid) the body will correct the pH by retaining bicarbonate (a base).

Respiratory acidosis develops when there are excessive amounts of carbon dioxide in the body, primarily caused by decreased breathing. Other names for this include hypercapnic acidosis and carbon dioxide acidosis.

There are several types of metabolic acidosis. (also called and ) develops when ketone bodies accumulate during uncontrolled .

Hyperchloremic acidosis results from excessive loss of sodium bicarbonate from the body, like in severe diarrhea for example. Lactic acidosis is an accumulation of . This can be caused by many conditions, including prolonged lack of oxygen, certain diseases, prolonged , , and medications such as oral medications used to treat . www.nlm.nih.gov

Alkalosis is a condition of excess base (alkali) in the body fluids. This is the opposite of excess acid (), and can be caused by many different conditions.

The lungs and kidneys regulate the acid/base status of the body. Decreased carbon dioxide or increased bicarbonate levels create an excessive alkaline state called        alkalosis.

is caused by lower carbon dioxide levels. () causes the body to lose carbon dioxide. Altitude or a disease that causes reduced oxygen in the blood triggers the individual to breathe faster. This reduces carbon dioxide levels which        results        inrespiratory        alkalosis.

Metabolic alkalosis is caused by an excess of bicarbonate in blood. Hypochloremic alkalosis is caused by an extreme lack or loss of chloride (may be caused by prolonged ). The kidneys compensate for the chloride loss by conserving        bicarbonate.

Hypokalemic alkalosis is caused by the kidneys' reaction to an extreme lack or loss of potassium which may be caused by some diuretic medications.

Compensated alkalosis is caused when the body has partially compensated for alkalosis, returning the acid/base balance to normal, even though bicarbonate and carbon dioxide levels remain abnormal. www.nlm.nih.gov

The Monitoring and Control of the System:

Metabolic reactions in the body are highly sensitive to pH or Hydrogen ion concentration. Hydrogen ions change the shape of proteins and this includes enzymes, so H+ changes in the blood can greatly effect the chemical reactions in the human body.

H+ ions are created and destroyed all of the time. Because of this the body needs to maintain a narrow range of free H+ concentration to function properly.

Even though the strong acids and bases are continually taken into and formed by the body, the pH of the blood remains almost constant. To keep it constant is the presence of buffer systems, which function to convert strong acids or bases into weak acids or bases. Strong acids or bases, ionise easily and contribute many H+ or (OH-) to a solution.These can change the pH drastically which will disrupt the body’s metabolism. Weak acids or bases do not ionise as much and contribute fewer H+ or (OH-). These have less effect on the pH. The chemical compounds that can convert a strong acid or base into a weak one is called a buffer.

Besides buffers, H+ levels are controlled by the lungs. When H+ is high the lungs reflexively increase their ventilation and this blows off CO2, decreasing PCO2 and decreasing H+.

Homeostasis of H+ by the kidneys: The kidney can correct any imbalances by removing excess acid (hydrogen ion) or bases (bicarbonate) in the urine and restoring the bicarbonate concentration in the blood to normal. The kidney cells produce a constant amount of hydrogen ion and bicarbonate because of their own cellular metabolism (production of carbon dioxide). Through a carbonic anhydrase reaction similar to the red blood cells, hydrogen ions get produced and secreted into the lumen of the nephron. Also, bicarbonate ions get produced and secreted into the blood. In the lumen of the nephron, filtered bicarbonate combines with secreted hydrogen ions to form carbon dioxide and water (carbonic anhydrase is also present on the luminal surface of the kidney cells). Whether the kidney removes hydrogen ions or bicarbonate ions in the urine depends upon the amount of bicarbonate filtered in the glomerulus from the blood relative to the amount of hydrogen ions secreted by the kidney cells. If the amount of filtered bicarbonate is greater than the amount of secreted hydrogen ions, then bicarbonate will be lost in the urine. Likewise, If the amount of secreted hydrogen ion is greater than the amount of filtered bicarbonate, then hydrogen ions will be lost in the urine (i.e. acidic urine). By excreting a bicarbonate (HCO3) in the urine results in free H+ in the plasma because an HCO3 that would bind H+ has been eliminated. When H+ is lowered in the body, alkalosis, the kidney excretes HCO3 to free up H+ in the plasma. When H+ is raised in the body, acidosis, the kidney tubules produce bicarbonate and add it to the urine. One important buffer system in the body is the carbonic acid-bicarbonate buffer system. Carbonic acid H2CO3 can act as a weak acid and the bicarbonate ion can act as a weak base.

If there is an excess of H+ , HCO3 can function as a weak base and remove the excess H+, as follows:

H+ + HCO3 ➔ H2CO3 ➔ H2O + CO2

If there is a shortage of H+, H2CO3 can function as a weak acid and provide need H+ as follows:

H2CO3 ➔ H+ + HCO3

Bibliography and References:

Tortora, Grabowski, 2002, Principles of Anatomy and Physiology, US

Roberts, Reiss, Monger, 2000, Advanced Biology, UK