Absorption circulation

B14. Bjorn, B., Hellstrom, K., and Rosen, A., Fate of orally administered H digitoxin in man with special reference to the absorption. Circulation 43, 852-861 (1971). 

The human body is about 70 percent water. Water is involved in nearly every body process, including digestion, absorption, circulation, and excretion. Blood is about 90 percent water it transports nutrients to the cells and washes out lactic acid and other waste products. 

So far studies on the absorption, circulation, metabolism and excretion of vitamin Bg have been performed by feeding or injecting high amounts of radiolabelled PN. However, the contents of PN in the foods examined were low compared with those of the other vitamin Bg forms. Thus, information on the absorption, circulation, metabolism and excretion of vitamin Bg when animals or human consume usual foods should be obtained using enzymatic HPLC assay. 

Investigations on the absorption, circulation, distribution, and excretion of radioiodide are discussed in the monographs of Salter (155) and the author (84). 

Normal blood plasma or semm levels of the mineral nutrients and the usual form ia circulating blood are given ia Table 2. Modes of absorption and excretion are summarized ia Table 3. Standard treatises on mineral nutrients (r4—r6, rlO—r21) and standard sources of nutrient composition (22,23) are available ia the Hterature. 

Most ozone is formed near the equator, where solar radiation is greatest, and transported toward the poles by normal circulation patterns in the stratosphere. Consequendy, the concentration is minimum at the equator and maximum for most of the year at the north pole and about 60°S latitude. The equihbrium ozone concentration also varies with altitude the maximum occurs at about 25 km at the equator and 15—20 km at or near the poles. It also varies seasonally, daily, as well as interaimuaHy. Absorption of solar radiation (200—300 nm) by ozone and heat Hberated in ozone formation and destmction together create a warm layer in the upper atmosphere at 40—50 km, which helps to maintain thermal equihbrium on earth. 

Gas leaving the economizer flows to a packed tower where SO is absorbed. Most plants do not produce oleum and need only one tower. Concentrated sulfuric acid circulates in the tower and cools the gas to about the acid inlet temperature. The typical acid inlet temperature for 98.5% sulfuric acid absorption towers is 70—80°C. The 98.5% sulfuric acid exits the absorption tower at 100—125°C, depending on acid circulation rate. Acid temperature rise within the tower comes from the heat of hydration of sulfur trioxide and sensible heat of the process gas. The hot product acid leaving the tower is cooled in heat exchangers before being recirculated or pumped into storage tanks. 

Materials may be absorbed by a variety of mechanisms. Depending on the nature of the material and the site of absorption, there may be passive diffusion, filtration processes, faciHtated diffusion, active transport and the formation of microvesicles for the cell membrane (pinocytosis) (61). EoUowing absorption, materials are transported in the circulation either free or bound to constituents such as plasma proteins or blood cells. The degree of binding of the absorbed material may influence the availabiHty of the material to tissue, or limit its elimination from the body (excretion). After passing from plasma to tissues, materials may have a variety of effects and fates, including no effect on the tissue, production of injury, biochemical conversion (metaboli2ed or biotransformed), or excretion (eg, from liver and kidney). 

The processes using physical absorption require a solvent circulation proportional to the quantity of process gas, inversely proportional to the pressure, and nearly independent of the carbon dioxide concentration. Therefore, high pressures could favor the use of these processes. The Recitsol process requires a refrigeration system and more equipment than the other processes. This process is primarily used in coal gasification for simultaneous removal of H2S, COS, and CO2. 

Of the three categories, the packed column is by far the most commonly used for the absorption of gaseous pollutants. Miscellaneous gas-absorption equipment could include acid gas scrubbers that are commonly classified as either wet or diy. In wet scrubber systems, the absorption tower uses a hme-based sorbent liquor that reacts with the acid gases to form a wet/solid by-product. Diy scrubbers can be grouped into three catagories (1) spray diyers (2) circulating spray diyers and (3) dry injection. Each of these systems yields a diy product that can be captured with a fabric filter baghouse downstream and... 

Cooler Absorbers When the absorption of a gas is accompanied by the evolution of heat, an important function of the absorption equipment is the removal of the heat generated. This may be accomplished by using a number of towers in series, the liquid from each tower being circulated through an external cooler. There are different types of cooler-absorbers in which processes of this type can be carried out in a single unit. The materials of which these cooler-absorbers are constructed should be of high thermal conductivity and resistant to corrosion by the substances used in the process. As an example, in the manufacture of hydrochloric acid of the... 

Spray Towers A spray tower consists of an empty shell into the top of which the liquid is sprayed by means of nozzles of various kinds the droplets thus formed are then allowed to fall to the bottom of the tower through a stream of gas flowing upwards. The use of sprays appears to offer an easy way of greatly increasing the surface area exposed to the gas, but the effectiveness of the m.ethod depends on the production of fine droplets. These are difficult to produce and suffer from the disadvantage that they are liable to entrainment by the gas even at low gas velocities. The surface area may also be reduced as a result of the coalescence of the droplets first formed. As a consequence of these effects, the large increase in surface area expected may not be achieved, or if achieved m.ay be accompanied by serious entrainment and internal circulation of the liquid so that true counter-current flow is not obtained. A single spray tower is suitable for easy absorption duties. For difficult duties, a number of towers in series can be used. 

Other important determinants of the effects of compounds, especially solvents, are their partition coefficients, e.g., blood-tissue partition coefficients, which determine the distribution of the compound in the body. The air-blood partition coefficient is also important for the absorption of a compound because it determines how quickly the compound can be absorbed from the airspace of the lungs into the circulation. An example of a compound that has a high air-blood partition coefficient is trichloroethane (low blood solubility) whereas most organic solvents (e.g., benzene analogues) have low air-blood partition coefficients (high blood solubility). 

Anthropologic features of humans, their physical activities, ventilation capacities, and the state of their circulation all affect exposure to chemical compounds. Some of the physiological determinants of exposure will be dealt with below. Exercise typically increases cardiac output, facilitates circulation, increases the minute volume of ventilation, is associated with vasodilation of the skin circulation, and increases perspiration and secretory activity of the sweat glands. All of these changes tend to facilitate the absorption of chemicals through multiple routes. 

Chemicals have to pass through either the skin or mucous membranes lining the respiratory airways and gastrointestinal tract to enter the circulation and reach their site of action. This process is called absorption. Different mechanisms of entry into the body also greatly affect the absorption of a compound. Passive diffusion is the most important transfer mechanism. According to Pick s law, diffusion velocity v depends on the diffusion constant (D), the surface area of the membrane (A), concentration difference across the membrane (Ac), and thickness of the membrane (L)... 

After absorption, a chemical compound enters the circulation, which transfers it to all parts of the body. After this phase, the most important factor affecting the distribution is the passage of the compound through biological membranes. From the point of view of the distribution of a chemical compound, the organism can be divided into three different compartments (1) the plasma compartment (2) the intercellular compartment and (3) the intracellular compartment. In all these compartments, a chemical compound can be bound to biological macromolecules. The proportion of bound and unbound (free) chemical compound depends on the characteristics of both the chemical... 

The absorption occurs as a result of the driving force of the partial pres-Miie from the gas to the liquid. The reactions involved are reversible bv changing the system temperature or pressure, or both. Therefore, die at[ueous base solution can be regenerated and thus circulated in a contin nous cycle. The majority of chemical solvent processes use either an amine or carbonate solution. 

The oldest kind of gas plants are absorption/lean oil plants, where a kerosene type oil is circulated through the plant as shown in Figure 9-1. The lean oil is used to ab.sorb light hydrocarbon components from the gas. The light components are separated from the rich oil and the lean oil is recycled. 

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