Limb absorption

After oral ingestion, ethanol pharmacokinetics must take into account (1) Absorption from the gastrointestinal tract. Since ethanol is absorbed most efficiently from the small intestines, the rate of gastric emptying is an important factor that governs the rate of rise of blood alcohol concentration (BAC), i.e., the slope of the ascending limb of the BAC-time curve, and the extent of first pass metabolism of ethanol by the liver and stomach. (2) Distribution of ethanol in the body. Ethanol distributes equally in total body water, which is related to the lean body mass of the person, and (3) the elimination of ethanol from the body, which occurs primarily by metabolism in the liver, first to acetaldehyde and then to acetate [7]. 

The rate of absorption from an SC injection site may be retarded by immobilization of the limb, local cooling to cause vasoconstriction, or application of a tourniquet proximal to the injection site to block the superficial venous drainage and lymphatic flow. In small amounts, adrenergic stimulants, such as epinephrine, will constrict the local blood vessels and, therefore, slow systemic absorption. Conversely, cholinergic stimulants (such as methacholine) will induce very rapid systemic absorption subcutaneously. Other agents may also alter their own rate of absorption by affecting local blood supply or capillary permeability. 

Even when administered by intramuscular or subcutaneous injection the rate of absorption of drugs from their site of administration varies, not only from individual to individual, but from site to site in the same subject (B13). For the few drugs studied in this way absorption and distribution was quicker and higher blood levels achieved when injections were given into upper rather than lower limbs and proximal to the trunk than distally. 

The thick ascending limb is a major site of salt absorption and a principal locus of action of an important group of diuretics. Approximately 25% of the filtered sodium is reabsorbed by the thick ascending limb of Henle s loop. Sodium transport in this nephron segment is mediated by Na+-K+-2C1 cotransport (Fig. 21.3). This transporter is present only on the apical, or urine, side of the tubule cells. Although K+ is taken up by the transporter, little net K+ reabsorption occurs in the thick ascending limb because much of the absorbed K+... 

Oral bioavailability is only 15% but after SC injection absorption is rapid and complete. It is metabolized by MAO-A isoenzyme and metabolites are excreted in urine. Adverse effects include tightness in head and chest, paresthesia in limb, dizziness, rise in BP and bradycardia. Rarely seizures and hypersensitivity reactions occur. 

Therefore, ground-based measurements are restricted to atmospheric windows where the water vapour absorptions are relatively small. For limb space-based atmospheric sounding, this is less of a problem but retrieval of trace gases in the upper troposphere are restricted to a limited number of candidates. For many gases such measurements are optimal for sounding the stratosphere and mesosphere. For the lower stratosphere and upper troposphere, some interesting possibilities exist, but the range of application is more restricted. 

Both absorption and emission experiments have been made using a number of different instruments. The Limb Radiance Inversion Radiometer (LRIR) and Limb Infrared Monitor of the Stratosphere (LIMS) are both infrared radiometers which were flown aboard Nimbus 6 and 7, respectively, and recorded data in 1978 and 1979 (Gille et al., 1980 Gille and Russell, 1984). The six channels of LIMS observed emission by C02, HN03,03, H20 and N02 from 15-65 km. 

Soda lime E is usually employed for the absorption of C02, an indicator being sometimes added to show when it is exhausted. The soda lime is carried in tubes (Fig. 64) similar to Fig. 63, except that no glass bulb, B, is required. Two soda lime tubes (in series) are used in every combustion. If the combustion has been properly carried out there ought to be no increase in weight of the second tube. Since H20 vapour may be evolved in the absorption of the C0a by the soda lime, a small 1 rap of CaCla is inserted (C) in the exit limb of each tube to prevent loss of this HaO. Glass wool plugs A retain the absorbents in position. 

A U-tube containing calcium chloride in one limb and soda-lime in the other, to protect the absorption apparatus from the carbon dioxide of the air and from the moisture of the aspirator. 

Loop diuretics selectively inhibit NaCl reabsorption in the thick ascending limb of the loop of Henle. Due to the large NaCl absorptive capacity of this segment and the fact that diuresis is not limited by development of acidosis, as it is with the carbonic anhydrase inhibitors, these drugs are the most efficacious diuretic agents available. 

The dusts irritate the nose and eyes and may cause nausea and abdominal pain by absorption. The metal on contact with moist skin produces a white film of the hydroxide. Skin absorption of the soluble salts and ingestion may cause nausea, vomiting, abdominal pains, weakness of the legs, and mental confusion. Prolonged exposure to small amounts of the dust or solutions may result in loss of appetite, loss of hair, pain or weakness of limbs, insomnia, and mental disturbance. Avoid breathing dust. Avoid contact with skin and eyes.2 TLV-TWA 0.1 mg/m3.3... 

Essential oils enter the body through the skin by the ducts of the sweat glands and the hair follicles. The permeability of the skin at various locations in the body can be linked to the number of available ducts acting as entry points. Sites such as the palms of the hands, soles of the feet, armpits, genitals, forehead and scalp are quite permeable to absorption of essential oils, while the limbs, buttocks, abdomen and trunk are relatively impermeable. 

Apart from occasional cases of skin irritation, adverse effects have been few. The efficiency of skin absorption is not known. Absorbed benzyl benzoate is rapidly biotransformed to hippuric acid which is exacted in the urine. When given in large doses to laboratory animals, benzyl benzoate causes excitement, incoordination, paralysis of the limbs, convulsions, respiratory paralysis, and death. No human poisonings have been reported. 

Fig. 3. Idealized Cotton effect at an isolated, optically active absorption band with its maximum at X<. If the positive limb of the rotatory dispersion is to the high wavelength side of the band, the Cotton effect is termed positive if the negative limb is at higher wavelength, the effect is negative. In regions distant from the absorption band, the rotatory dispersion approaches simple Drude behavior.

---