Acids and bases in the body

In this chapter you will learn that the danger associated with acids and bases is a function of their concentration and identity. Most acids and bases are not inherently dangerous. They are all around us. The acid-base balance in our blood is critical to good health and many biological reactions depend on acids and bases in the body. The acid content of our rainfall (and other forms of precipitation) has a critical role in determining the health of our rivers and forests and our ability to raise the foodstuffs upon which we depend. Acids and bases are key components of many manufacturing processes. In fact, sulfuric acid is required by so many industrial processes that the amount of it sold each year is taken as a measure of a nation s economy. 

Another mechanism for regulating acids and bases in the body is the chemical buffer system. Chemical buffers are substances that combine with H and remove it or release H+ when it dissociates to allow more H+ to roam free in the bloodstream. Two major chemical buffers are phosphate and protein. The phosphate system is a solution of HPO and H PO ... 

The kidneys and lungs play major roles in regulation of the levels of acids and bases in the body thus anything that damages or inhibits the function of the kidneys or lungs affects the acid-base balance in the body. 

Most drugs, such as the analgesic aspirin and the decongestant ephediine, are weak organic acids or bases. In the body they switch between the ionized and neutral forms, depending on pH. This abihty is cmcial to their potency The neutral form diffuses more readily across nonpolar cell membranes to get to the target receptor site, but its ionized counterpart is more soluble in the aqueous blood plasma for distribution throughout the body. 

One bodily function that relies on acids and bases is the process of digestion. During digestion, food is broken down into small molecules that the body can use. Digestion begins in the mouth when food comes into contact with an enzyme called amylase found in the saliva. Enzymes are the body s catalysts. They speed up chemical reactions that would otherwise be too slow to be useful to the body. Amylase breaks down starch molecules and converts them into sugars. 

Drugs may be formulated as their salt forms (i.e., hydrochloride salt for base, sodium salts for acids) that dissociate in the body, or they may be formulated as the free acid or base. The fraction of the drug absorbed can be difficult to predict, as it is influenced by many factors. The extent and rate of absorption are partly determined by the physicochemical properties of the drug. Favorable absorption is related to lipid solubility, nonpolarity, and small molecular size. Reduced absorption is often observed for highly polar, non-lipid-soluble, and large-molecular size drugs. 

ELECTROLYTE IMBALANCE Improper proportions of acids, bases, salts, and fluids in the body. Electrolytes include the salts sodium, potassium, magnesium, chloride chlorine. They can conduct electricity, and therefore are essential in nerve, muscle, and heart function. 

Organs and tissues in the body can have very different pHs. The pH of blood is 7.4. The stomach can be as low as 1, while the small intestine is slightly basic at about 8. Functional groups, especially carboxylic acids, can lose or gain a charge as they move from one part of the body to another. If the solution pH and pKa of the acid are known, then the relative concentrations of the acid and its conjugate base can be calculated through the Henderson-Hasselbalch equation (Equation 9.1). 

Vitamins are substances essential for a healthy life humans must ingest vitamins via their diet because there is no mechanism for their biosynthesis in the body. There are 14 vitamins - the name was coined when the first vitamin chemically identified (vitamin Bi in 1910) turned out to be an amine - a vital amine. A typical vitamin is folic acid, a complex molecule in which the functionally important unit is the bicyclic pyrazino[2,3- f pyrimidine (pteridine) ring system, and its arylaminomethyl substituent. Folic acid is converted in the body into tetrahydrofolic acid (FH4) which is crucial in carrying one-carbon units, at various oxidation levels, for example in the biosynthesis of purines, and is mandatory for healthy development of the foetus during pregnancy. Other essential co-factors that contain pteridine units must and can be biosynthesised in humans - without them we cannot survive - aud are incorporated into oxygen-transfer enzymes based on molybdenum, in which the metal is liganded by a complex ene-dithiolate. 

The examination of the students learning was based on a range of questions (approximately 50-60 per semester) that were dealt with in their tutorial groups - for example Explain how the acidity of blood is affected by respiration, a) in the lungs and b) in the body. These questions would then form the final examination of students in this course, This form of assessment was quite deliberate and consistent with Barry s purpose for the course as being to educate these students in appropriate fundamental chemical ideas, and not just train them for a particular vocation. ... 

Bicarbonate ion (HC03 ) that forms from the dissociation of carbonic acid (H COj) acts as a weak base. Bicarbonate ion is a very important base in the body and is abundant in blood. 5... 

The CO2 content is an indirect measure of bicarbonate in the blood. Since most of the CO2 in the body is in the form of HCO3, the CO content indicates the status of base in the body. The venous CO level is commonly included when routine electrolyte levels are measured and should not be confused with the Pco that is found in arterial blood and measures respiratory acid. The normal range for CO content is 23-30 mEq/L (or mmol/L) for adults, 20-28 mEq/L (or mmol/L) for infants and children, and 13-22 mEq/L (or mmol/L) for newborns. The CO level, as an indication of the bicarbonate level, is regulated by the kidneys. An elevated CO2 level indicates metabolic alkalosis, whereas a decreased CO level indicates metabolic acidosis. 

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