Acids and Bases in the Human Body

Acids and bases can be dangerous chemicals outside of the body, but there are plenty of acids and bases inside the human body as well. Not only are these acids and bases not harmful to the body, but also they are absolutely necessary for it to function properly. 

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. 

After the food is swallowed, the digestive process continues in the stomach where the food is attacked by stomach acid. In fact, stomach acid is concentrated hydrochloric acid. The hydrochloric acid, along with an enzyme called pepsin, breaks down proteins in the food. Pepsin can only function in the low pH environment of the stomach. The hydrochloric acid is needed to maintain the low pH that pepsin needs to function. 

Bicarbonate is only one of the digestive chemicals that get secreted into the small intestines. Bile acids play a role as well. Bile is made in the liver, stored in the gallbladder, and, when needed, secreted into the small intestines via the bile duct. Bile plays an essential role in the breakdown of fat by dissolving it in the small intestine, much like soap dissolves oil on a frying pan. This breaks the fat down into small droplets. These fat droplets are broken down even further by other intestinal enzymes so that they can be absorbed by the body. 

Despite the bad press, the body needs cholesterol. In fact, cholesterol is a key ingredient in bile. The more bile the body makes, the lower the amount of cholesterol in the bloodstream. 

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Figure 6.1 Acids and bases exist in the human body and are necessary for its proper function, including the function of the digestion process. When food is swallowed, it is attacked by stomach acids. The stomach acids need to be neutralized before food can continue down the digestive tract. A hormone called secretin monitors the pH balance in the small intestine and sends chemical signals to other parts of the body, thereby regulating pH balance.

Along with stomach, bile, and lactic acids, there are many other acids in the human body These include, but are not limited to, nucleic acids, amino acids, fatty acids, and vitamins such as folic and ascorbic acids. Nucleic acids, including RNA (ribonucleic acid) and DNA (deoxyribonucleic acid), are long chains of phosphates and sugar to which nucleotide bases are attached. The phosphate molecules in the backbone of RNA and DNA are derived from phosphoric acid. Therefore, DNA is very weakly acidic. 

Nanosized objects perform various functions in the biomedical field. In the human body, nanosized particulate substances behave very differently from larger particles. In 1986, Maeda et al. found that the stained albumin, having a size of several nanometers, naturally accumulates in the region of cancerous tissues, which is now well known as the enhanced permeability and retention (EPR) effect. Many studies in the field of nanoparticles are based on this finding. Another application of nanoparticles is the delivery system using various polyplexes that are composed of carrier molecules and plasmid DNA or nucleic acid drugs such as antisenses and siRNA. In addition, nanofibers are mainly used for biodegradable scaffolds in tissue... 

One of the most important buffer systems in the human body is that which keeps the pH of blood around 7.4. If the pH of blood fall below 6.8 or above 7.8, critical problems and even death can occur. There are three primary buffer systems at work in controlling the pH of blood carbonate, phosphate, and proteins. The primary buffer system in the blood involves carbonic acid, H COj and its conjugate base bicarbonate, HCO3. Carbonic acid is a weak acid that dissociates according to the following reaction ... 

Polyfunctional acids and bases play important roles in many chemical and biological systems. The human body contains a complicated system of buffers within cells and within bodily fluids, such as human blood. The photo is a scanning electronmicro-... 

Rubidium typically exists in the human body at the level of only 1/1,000 of 1 percent, and cesium content is even lower. Rubidium and cesium are both absorbed from soil by plants and are, therefore, present in small quantities in vegetables and up the food chain to meat products and humans. Rubidium is known to stimulate mammalian metabolism, probably because of its physical and chemical similarity to potassium, which plays a crucial role in electrical pulse transmission along nerve fibers protein synthesis acid-base balance and formation of collagen, elastin, and muscle. Its likeness to potassium may be the reason rubidium enhances growth in some plants. For particular insects, however, the introduction in the laboratory of rubidium to the bloodstream has been shown to drastically reduce fluid secretion and to change the electric potential across cell membranes. Excess rubidium is almost never encountered, however, in nature. 

A buffer solution is a solution of(l)a weak acid or a weak base and (2) its salt both components must be present. The solution has the ability to resist changes in pH upon the addition of small amounts of either acid or base. Buffers are very important to chemical and biological systems. The pH in the human body varies greatly from one fluid to another for example, the pH of blood is about 7.4, whereas the gastric juice in our stomachs has a pH of about 1.5. These pH values, which are crucial for proper enzyme function and the balance of osmotic pressure, are maintained by buffers in most cases. 

One of the most important applications of the acid-base chemistry is the buffer capacity. A buffer solution is a solution that counteracts an external action affecting pH. Some of the most well-known buffer solutions are found in the human body where they help to protect the pH of the blood from external actions and to keep the blood at constant pH levels. It is essential for the human body to be able to maintain the pH of the blood at fairly constant levels as certain types of cell only may survive in a close pH window. 

Protein is found in all cells and has multiple functions in the human body including structural, hormonal, enzymatic, immunologic, and regulation of acid-base balance. Protein contains 16 % nitrogen. There are 20 amino acids used for protein function in humans. These are divided into three categories indispensable amino acids (also called essential amino acids) that cannot be synthesized in the body and must be supplied from the diet, dispensable (also called nonessential... 

Steroids and bile acids. The third major class of lipids is steroids. The structure of steroids is based on the cyclopentanoperhydrophenanthrene moiety (see Figure 12.5). Steroids exist in free form or as a conjugate of various molecules such as fatty acids, sulfuric acid, glucorinic acids, sugars, and amino acids. The most abundant steroid in the human body is cholesterol, which serves as a membrane component. It also acts as a precursor for the synthesis of other steroid hormones. Other known members of the steroid family are bile acids they are also derivative of cholesterol. 

Vitamin Bg consists of pyridoxine (PN) and five related compounds, namely pyridoxal (PL), pyridoxamine (PM) and their respective 5 -phosphates (PEP, PNP and PMP). PLP is the major form in the human body (Figure 42.1). Vitamin Bg functions as a coenzyme in more than 100 enzymatic reactions involved in the metabolism of amino acids, glycogen and sphingoid bases. 

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