Total skin

In the simplest case, for a pressure drawdown survey, the radial inflow equation indicates that the bottom hole flowing pressure is proportional to the logarithm of time. From the straight line plot ot pressure against the log (time), the reservoir permeability can be determined, and subsequently the total skin of the well. For a build-up survey, a similar plot (the so-called Horner plot) may be used to determine the same parameters, whose values act as an independent quality check on those derived from the drawdown survey. 

As mentioned previously, the other term for characterizing skin moisture is skin wettedness (w) or the size of the water film as a fraction of total skin area that is necessary to account for the observed evaporative heat loss from the skin... 

Patients with photodamage can apply a lotion containing 25% glycolic acid for 6 months. In such cases an increase in total skin thickness of approximately 25% was reported, accompanied by an increased thickness of viable epidermis and dermis, an increased content of acid mucopolysaccharides, a greater collagen density and an improved quality of the elastic fibers. This could be defined as self-treatment. 

Routine self-examination of the skin is a method in which individuals can take responsibility for identifying MM early when it is curable. Pamphlets and online information describing the method of skin self-examination are available from agencies such as the American Cancer Society (www.cancer.org), the American Academy of Dermatology (www.AAD.org), and the Skin Cancer Foundation (www.skincancer.org). Patients should be given the following instructions for doing total skin self-examination 36... 

The skin not only is a barrier to restrict diffusion of chemicals into the body, it is also an organ that can metabolize a variety of topically applied substances before they become systemically available. The skin has many of the same enzymes as the liver. The activities of several cutaneous enzymes in whole skin homogenates have been measured and compared to hepatic activity in the mouse. The activities of the enzymes in the whole skin homogenates were typically 2-6% of the hepatic values. However, there is evidence that the enzymes are present primarily in the epidermis. Because the epidermis makes up only 2-3% of the total skin, the real activities may range from 80% to 240% of those in the liver. Enzyme systems present include a qrtochrome P-450 system and a mixed-function oxidase system. 

Prednicarbate is a topical glucocorticoid that seems to have an improved benefit-harm balance, as has been shown in 24 healthy volunteers (7 men, 17 women, aged 25-49 years) in a double-blind, randomized, placebo-con-trolled study of the effects of prednicarbate, mometasone furoate, and betamethasone 17-valerate on total skin thickness over 6 weeks (175). On day 36, total skin thickness was reduced by a mean of 1% in test fields treated with vehicle the relative reductions were 13,17, and 24% for prednicarbate, mometasone furoate, and betamethasone 17-valerate respectively. There were visible signs of atrophy or telangiectasia in two subjects each with betamethasone 17-valerate and mometasone furoate, but not with prednicarbate or its vehicle. 

Although it is generally believed that electroporation involves the creation of aqueous pathways (pores) in the stratum corneum [24], this mechanism remains somewhat controversial. These proposed channels have not yet been identified in any microscopic study due to their small size (about 10 nm), sparse distribution (<0.1% of the total skin area), and shortlived nature (millisecond to second) [16,25]. 

Cutaneous biotransformation is mostly associated with the stratum basale layer where there can be phase I and phase II metabolism. However, the skin is not very efficient, compared to the liver. The epidermal layer accounts for the major portion of biochemical transformations in skin, although the total skin activity is low (2-6% that of the liver). Where activity is based on epidermis alone, that layer is as active as the liver or, in the case of certain toxicants, several times more active. For some chemicals, metabolism can influence absorption, and transdermal delivery systems of drugs utilize this activity. For example prodrug such as lipid esters are applied topically, and cutaneous esterases liberate the free drug. These basal cells and extracellular esterases have been shown to be involved in detoxification of several pesticides and bioactivation of carcinogens such as benzo(a)pyrene. For rapidly penetrating substances, metabolism by the skin is not presently considered to be of major significance, but skin may have an important first-pass metabolic function, especially for compounds that are absorbed slowly. 

Patches to collect measurements of dermal exposure were attached to clothing on the chest, back, thighs and forearms of each individual. To calculate total dermal exposure, the concentration of 2,4,5-T detected on the patch area was multiplied by the total skin area exposed (Lavy, 1978). 

Phillips, L.J., R.J. Fares and L.G. Schweer (1993). Distributions of total skin surface area to body weight ratios for use in dermal exposure assessments, J. Expo. Anal. Environ. Epidem., 3, 331-338. 

Scheuplein (1) concluded that diflFusion rates are high but transport capacities are limited in hair and ducts because these structures occupy only one-thousandth of the total skin surface area. The present data suggest that intercellular cement and desmosomes occupy 0.001-0.004 of the remaining area. Accordingly, penetration through the interspaces will be limited by their relatively small area for exposure. However, the interspace route could be significant for molecules that penetrate SC cells poorly. As with asphalt tile, properties of the solvent and composition of the cellular tile must be considered. 

Thermal burns are classified by the amount of damage done to the skin and other body tissue. The surface area of the skin ranges from 0.2 to 0.3 m in an average newborn, and 1.5-2.0m in an adult. The skin consists of two layers the epidermis, ranging from 0.05 mm thickness (in such areas as the eyelids) to over 1 mm thickness on the soles and the dermis, usually at least 10 times thicker than the associated epidermis. An average total skin depth is 1-2 mm. Males generally have thicker skin than... 

Henriques treated the skin as a semi-infinite body in which all skin layers have the same thermal properties, and the total skin thickness is far greater than that heated by the thermal source. Based on this assumption, he obtained the following formula for the temperature of the basal epidermal layer as a function of time ... 

Distribution Factors for Total Skin Surface Area/Body Weight Ratio by Age... 

Ultimate bearing capacity is the summation of total skin resistance and bearing force at base, that is... 

Fig. 12.22 Relationship between skin penetration and transdermal delivery of vitK at 12 h post-applieation using different fcnmulations. a Relationship between vitK eoneentration in the stratum eomeum (SC) and epidermis without SC + dermis ( E + D]). b Relationship between vitK eoneentration in the reeepUn phase (an index of transdermal delivery) and total skin (an index of skin penetration). The number of repheates is 6—8 per experimental group. (Taken from [17])...

Third degree Pearly white or brown opaque gray firm leathery, dry No sensation Total skin loss includes all appendages heals by scar formation if small... 

The principle of iontophoresis is that ionized drug molecules can be driven into the skin when an electrical potential is apphed across the skin by placing two electrodes on the skin in electrolyte solution, one of which contains the drug. The ionic current flow in the skin seems to take place at discrete pores, which have been identified mainly to be the sweat glands and hair follicles (Cullander, 1992 Scott et al, 1993). Human skin contains 40 to 70 hair follicles and more than 200 sweat ducts per square centimeter, but these appendages occupy only 0.1% of the total skin surface (Chien, 1991). Additional pores may, however, be created by the apphed current (Amsden andGoosen, 1995). 

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