Bicarbonate ions blood

The enzyme carbonic anhydrase promotes the hydration of COg. Many of the protons formed upon ionization of carbonic acid are picked up by Hb as Og dissociates. The bicarbonate ions are transported with the blood back to the lungs. When Hb becomes oxygenated again in the lungs, H is released and reacts with HCO3 to re-form HgCOj, from which COg is liberated. The COg is then exhaled as a gas. 

A 0-9% salt solution is considered to be isotonic with blood. Other electrolytes present include bicarbonate ions (HCOj ) and small amounts of potassium, calcium, magnesium, phosphate, sulphate and organic acid ions. Included among the complex compounds and present in smaller amounts are phospholipids, cholesterols, natural fats, proteins, glucose and amino acids. Under normal conditions the extracellular body fluid is slightly alkaline with a pH of 7-4. ... 

The remaining 60% of carbon dioxide is transported in the blood in the form of bicarbonate ions. This mechanism is made possible by the following reaction ... 

The carbon dioxide produced during cellular metabolism diffuses out of the cells and into the plasma. It then continues to diffuse down its concentration gradient into the red blood cells. Within these cells, the enzyme carbonic anhydrase (CA) facilitates combination of carbon dioxide and water to form carbonic acid (H2C03). The carbonic acid then dissociates into hydrogen ion (H+) and bicarbonate ion (HC03). 

This entire reaction is reversed when the blood reaches the lungs. Because carbon dioxide is eliminated by ventilation, the reaction is pulled to the left. Bicarbonate ions diffuse back into the red blood cells. The hemoglobin releases the hydrogen ions and is now available to load up with oxygen. The bicarbonate ions combine with the hydrogen ions to form carbonic acid, which then dissociates into carbon dioxide and water. The carbon dioxide diffuses down its concentration gradient from the blood into the alveoli and is exhaled. A summary of the three mechanisms by which carbon dioxide is transported in the blood is illustrated in Figure 17.8. 

In a similar way, blood does not change its pH because it contains suitable concentrations of carbonic acid and bicarbonate ion, which act as a buffer, as below. 

Overall, for each bicarbonate ion filtered, one has been returned to the blood that is sodium bicarbonate has been reabsorbed and the glomerular filtrate leaving the PCT has a greatly reduced bicarbonate concentration. The relatively small amount of proton secreted by the PCT cell and not used to protonate filtered bicarbonate... 

Bicarbonate ions secreted into the blood stream help maintain the normal plasma bicarbonate concentration of approximately 25 mmol/1, whilst the two protons are secreted into the lumen of the proximal tubule in exchange for sodium via a Na+/H+ antiport. 

M. L. Anthony, E. Holmes, P. C. R. McDowell, T. J. B. Gray, M. Blackmore, J. K. Nicholson, ll NMR Spectroscopic Studies on the Reaction of Haloalkylamines with Bicarbonate Ions Formation of IV-Carbamates and 2-Oxazolidones in Cell Culture Media and Blood Plasma , Chem. Res. Toxicol. 1995, 8, 1046 - 1053. 

Another important diuretic contains both triamterene and hydrochlorothiazide. Triamterene is a diuretic and is known to increase sodium and chloride ion excretion but not potassium ion. It is used in conjunction with a hydrothiazide, which is an excellent diuretic but also gives significant loss of potassium and bicarbonate ions. If the triamterene were not included potassium chloride would have to be added to the diet. Hydrochlorothiazide is an antihypertensive agent as well but, unlike other antihypertensives, it lowers blood pressure only when it is too high, and not in normotensive individuals. These two drugs are made by a number of different manufacturers and do not appear in our top 35 list, but they would rank high if all brands were combined. 

Carbonic Anhydrase (MW2 = 30,000, 1 Zn) This enzyme occurs in red blood cells and catalyse the dehydration of bicarbonate ion and hydration of CO2. 

Mechanism of Action An alkalinizing agent that dissociates to provide bicarbonate ion. Therapeutic Effect Neutralizes hydrogen ion concentration, raises blood and urinary pH. 

The human body is a remarkable machine. It relies on a variety of safeguards to keep blood pH constant. Our blood constitutes a buffer system — meaning, it has components that can react with excess base or excess acid. Carbon dioxide, which is produced by the metabolism of food, dissolves in blood to produce carbonic acid, and carbonic acid can neutralize any excess base. The bicarbonate ion, also present in blood, will promptly take care of any surplus acid. The level of carbon dioxide in the blood adjusts to a body s rate of respiration. If blood pH drops — which actually means that the blood has... 

Carbonic acid in the blood readily dissociates into hydrogen and bicarbonate ions. If the serum pH of... 

In mammals the bicarbonate ion, IICOT, is used as a buffer in blood and is catalysed by the zinc-containing enzyme carbonic anhydrase ... 

Bicarbonate ions are freely filtered by the glomerulus. The concentration of bicarbonate in the tubular fluid is equivalent to that of plasma. If bicarbonate were not reabsorbed the buffering capacity of the blood would rapidly be depleted. 

Metabolic acidosis involves a build-up of hydrogen ions in the blood, thus lowering blood pH. Under normal physiological conditions, the kidneys excrete excess hydrogen ions, and release more bicarbonate ions into the bloodstream to buffer the excess acid. However, in renal failure, or in diabetic ketoacidosis, this mechanism either fails, or is unable to compensate to an adequate extent. Hence, metabolic acidosis is usually treated with sodium bicarbonate, either intravenously (1.26% or 8.4% i.v. solution) or orally (typically 1 g three times a day). Sodium bicarbonate 1.26% intravenous solution is isotonic with plasma (and with sodium chloride 0.9%), so may be given in large volumes (1-2 L) by peripheral venous catheter to correct metabolic acidosis and provide fluid replacement at the same time. Sodium bicarbonate 8.4% may only be given by central venous catheter. 

Bicarbonate ion (production catalysed by carbonic anhydrase) exits the cell on the basolateral surface, in exchange for chloride. The outflow of hicarhonate into hlood results in a slight alkalinity of the blood, known as the alkaline tide . 

Methods for Reducing Toxic Effects. Uranium forms complexes with the bicarbonate ion (Cooper et al. 1982) and has been administered prophylactically after uranium exposure (Fisher et al. 1991). Bicarbonate can alkalize the blood to a degree that facilitates the excretion of uranium via the kidneys. This in turn, can prevent uptake by and deposition in critical tissues (kidney, bone). Chelation has been tested in animals and found to have a limited potential, though possibly valuable, role in reducing acute uranium toxicity. Further research is needed to validate, refute, or refine method(s) for reducing the toxic effects of uranium compounds. No verified methods for reducing the toxic effects of long-term exposure to uranium are currently available. 

Carbon dioxide is a major end product of aerobic metabolism. In complex organisms, this carbon dioxide is released into the blood and transported to the lungs for exhalation. While in the blood, carbon dioxide reacts with water. The product of this reaction is a moderately strong acid, carbonic acid (pAT = 3.5), which becomes bicarbonate ion on the loss of a proton. 

The blood must not be allowed to become too acidic or too basic— the pH of the blood must not be allowed to go too high or too low—so the carbonate and bicarbonate ions must be carefully regulated. If there is too much carbonate, it will be skimmed off and removed, and if there is too little, there is a mechanism for restoring this equilibrium, too. 

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