Percutaneous absorption

Clinical effectiveness of topically applied medications depends on the ability of the active ingredient to leave its vehicle and penetrate into the epidermis. The stratum corneum is that layer of the epidermis which functionally is the most important in limiting percutaneous absorption, showing the characteristics of a composite semipermeable membrane. A mathematical expression of transepidermal diffusion may be derived from Fick''s Law of mass transport; factors altering the rate of diffusion are discussed.     

Intestinal absorption of fat

Summary It is generally accepted that between 50 and 70% of the fatty acids of ingested triglycerides are hydrolyzed prior to absorption and yet migration between the 2 and 1,3 positions is minimal. The occurrance of the monoglyceride pathway for triglyceride biosynthesis provides a logical explanation for these findings. In addition, this sequence provides a logical explanation of the particulate and lipolytic theories. Triglycerides are hydrolyzed at the 1 and 3 positions giving rise to fatty acids and 2-monoglycerides, which in combination with bile salts form micelles and penetrate the intestinal membrane. The fatty acids are activated to the respective CoA derivatives and acylate the 2-monoglyceride forming triglycerides. The triglyceride thus synthesized, has a similar chemical structure with regard to the 1,3 and 2 position as the original triglyceride. The triglyceride is coated with a-lipoprotein and is transformed into chylomicrons which enter the thoracic duct lymph.It is suggested that this mechanism be referred to as the PARLIP sequence since, particles in the form of micelles are involved in the absorption, and in addition a considerable amount of lipolysis occurs. This terminology would represent a scientific merger of the particulate and the lipolytic theories into a common sequence, while maintaining some identity in recognition of the numerous investigations that have occurred in the past 100 years to support these two basic postulates.     

Stability and absorption of chromium and absorption of chromium histidinate complexes by humans

Increased intake of chromium (Cr) often leads to improvements in glucose, insulin, lipids, and related variables in studies involving humans and experimental and farm animals. However, the results are often variable, depending not only on the selection of subjects but also dietary conditions and the form of supplemental Cr used. Our objective was to find a Cr supplement suitable for humans that was absorbed better than any of those available. Chromium absorption by six adult subjects, three males and three females, was determined based on the amount of Cr excreted in the urine in the initial 2 d following intake of 200 μg of Cr of the various forms of chromium tested. The absorption of the newly synthesized complexes was greatest for those containing histidine. Urinary Cr losses for six control subjects consuming 200 μg of Cr as Cr histidinate increased from basal levels of 256±48 to 3670±338 ng/d compared with 2082±201 ng for Cr picolinate, the currently most popular nutrient supplement, in the 48h following Cr consumption. Chromium histidinate complexes were stable and absorption was similar to the initial values after more than 2 yr. Mixing of some of the complexes with starch, which was postulated to improve Cr absorption, was shown to essentially block Cr absorption within 1 mo. These data demonstrate that urinary Cr losses need to be determined because stability and absorption of the Cr complexes varies widely and could be responsible for the variability in some of the Cr supplementation studies. Chromium ***DIRECT SUPPORT *** A02Q2015 00003 histidinate complexes are absorbed better than any of the Cr complexes currently available and need to be evaluated as Cr nutritional supplements.     

On the theory of cyclotron absorption at the wing of the absorption line

It is shown that, at the wing of the cyclotron absorption line, the relativistic effects associated with the dependence of the gyrofrequency on the particle energy can play an important role even far from the relativistic cyclotron cutoff region, i.e., even when the resonance lines in velocity space are mainly determined by the nonrelativistic Doppler synchronizm. Simple relationships for the relativistic absorption coefficient and power deposition profile in a nonuniformly magnetized plasma slab, as well as a new condition, which was not discussed earlier, for the applicability of the nonrelativistic approximation, are derived from illustrative physical considerations.     

Intestinal iron absorption

Intestinal iron absorption is a critical process for maintaining body iron levels within the optimal physiological range. Iron in the diet is found in a wide variety of forms, but the absorption of non-heme iron is best understood. Most of this iron is moved across the enterocyte brush border membrane by the iron transporter divalent metal-ion transporter 1, a process enhanced by the prior reduction of the iron by duodenal cytochrome B and possibly other reductases. Enterocyte iron is exported to the blood via ferroportin 1 on the basolateral membrane. This transporter acts in partnership with the ferroxidase hephaestin that oxidizes exported ferrous iron to facilitate its binding to plasma transferrin. Iron absorption is controlled by a complex network of systemic and local influences. The liver-derived peptide hepcidin binds to ferroportin, leading to its internalization and a reduction in absorption. Hepcidin expression in turn responds to body iron demands and the BMP-SMAD signaling pathway plays a key role in this process. The levels of iron and oxygen in the enterocyte also exert important influences on iron absorption. Disturbances in the regulation of iron absorption are responsible for both iron loading and iron deficiency disorders in humans.