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Disorders of the renal system
Published in Judy Bothamley, Maureen Boyle, Medical Conditions Affecting Pregnancy and Childbirth, 2020
Selective reabsorption, as the term implies, allows the filtered constituents that are needed to maintain fluid/electrolyte balance and pH back into the bloodstream. In the proximal tubule solutes, nutrients, electrolytes and proteins are reabsorbed, followed by the loop of Henle, where a concentration of the urine occurs as water is reabsorbed.
The renal system, hypertension and pre-eclampsia
Published in Judy Bothamley, Maureen Boyle, Medical Conditions Affecting Pregnancy and Childbirth, 2020
Selective reabsorption, as the term implies, allows those filtered constituents that are needed to maintain fluid and electrolyte balance to be reabsorbed into the bloodstream. In the proximal tubule, solutes, nutrients, electrolytes and proteins are reabsorbed, followed by the loop of Henle, where a concentration of the urine occurs as water is reabsorbed.
Clinical anatomy of the newborn
Published in Prem Puri, Newborn Surgery, 2017
Mark D. Stringer, S. Ali Mirjalili
At birth, the kidneys are about 4–5 cm in length compared to a mean length of 11 cm in adults. Fetal lobulation of the kidneys is still present at birth. Individual nephrons consist of a renal corpuscle with (i) a central glomerulus concerned with plasma filtration and (ii) a renal tubule that produces urine by selective reabsorption of the filtrate. At birth, there are about 1 million renal corpuscles in the cortex of each kidney. Postnatally, cortical nephron mass increases but no new nephrons are made. The glomerular filtration rate (GFR) is low in newborns, particularly in the premature, but in the term infant, the GFR doubles by 2 weeks of age and reaches adult values (120 mL/min per 1.73 m2) by 1–2 years.47
Effect of different bile acids on the intestine through enterohepatic circulation based on FXR
Published in Gut Microbes, 2021
Junwei Xiang, Zhengyan Zhang, Hongyi Xie, Chengcheng Zhang, Yan Bai, Hua Cao, Qishi Che, Jiao Guo, Zhengquan Su
Under physiological conditions, the taurine/glycine conjugates in the side chain of BAs can be removed under the action of intestinal microorganisms.72 Intestinal microorganisms can oxidize or dehydroxylate the hydroxyl groups at C3, C7 and C12 in the BA molecular structure to form unsaturated BAs, and can also convert BAs via carbonyl reduction or epimerization.31,73 CA is converted into DCA; CDCA is coverted to LCA; α-MCA and β-MCA in mice are converted to ω-MCA, HCA, and HDCA; et al.74 Two main mechanisms control the reabsorption of BAs in the intestine. The first is active transport, which occurs mainly in the distal ileum, by which BAs can be effectively recovered by ASBT.75 Almost all types of BAs are transported through this mechanism, but the absorption rates are different; these differences may depend mainly on the number of hydroxyl groups and molecular states of different BAs. The second mechanism is passive transport, which occurs mainly in the small intestine and colon. The rate of passive selective reabsorption depends on the degree and polarity of ionized. Unconjugated BAs and glycine conjugates of dihydroxy BAs (nonionized form) can also be reabsorbed by simple diffusion through the membrane of the small intestine can occur in any part of the small intestine. In summary, different BAs have different physical and chemical properties in the enterohepatic circulation, and the degree of action may be altered accordingly.
Metabolism and disposition of the SGLT2 inhibitor bexagliflozin in rats, monkeys and humans
Published in Xenobiotica, 2020
Wenbin Zhang, Xiaoyan Li, Haifeng Ding, Yuan Lu, Geoff E. Stilwell, Yuan-Di Halvorsen, Ajith Welihinda
The kidney functions by a default elimination process in which all of the contents of the plasma below ∼50 kDa in mass are excreted, followed by the selective reabsorption of the constituents that are beneficial to retain. The latter consist of nearly all of the water and electrolytes, as well as metabolically important small molecules, such as sugars, vitamins and amino acids. Glucose is a sufficiently important resource that the kidneys devote a tandem two-stage recovery process to its retention. In the first stage, in the pars convoluta of the proximal tubule (Vallon et al., 2011; Vrhovac et al., 2015), SGLT2 retrieves glucose by concentrative co-transport of one glucose molecule and one Na+ ion from the filtrate into the tubular epithelium (Ghezzi et al., 2018). Because there is a substantial transmembrane electrochemical potential for Na+ ions, glucose can be concentrated in the tubular epithelial cells even when found in a lower concentration in the extracellular fluid than in the epithelial cytoplasm (Ghezzi et al., 2018). In the second stage of reabsorption, in the pars recta of the proximal tubule (Vrhovac et al., 2015), the remaining glucose is taken up by the related transporter SGLT1, which co-transports one glucose molecule for every two Na+ ions (Ghezzi et al., 2018).
Bioengineering strategies for nephrologists: kidney was not built in a day
Published in Expert Opinion on Biological Therapy, 2020
Anna Julie Peired, Benedetta Mazzinghi, Letizia De Chiara, Francesco Guzzi, Laura Lasagni, Paola Romagnani, Elena Lazzeri
The pioneering work by Humes et al. has opened a new perspective not only for improving renal replacement treatment, but also for moving dialysis patients outside the clinic. Indeed, the growing evidence for the efficacy and safety of longer and more frequent dialysis treatment has led a multitude of studies and new prototypes, the so-called Portable and Wearable Artificial Kidneys (PAK, WAK). The development and challenges of such highly engineered, non-cell based, technologies go beyond the scope of this review and have been recently reviewed elsewhere [62–64]. Combining the first experiences with RAD bioengineering and new advances in miniaturization technology, a project for an Implantable RAD, or implantable bioartificial kidney, was described by Fissel and Roy [65,66]. The two main challenges that hinder engineering of an implanted system are i) to reduce the large size and replicate the high permeability coefficient of conventional hemofilters, and ii) to overcome the need for a great amount of dialyzate. The first challenge was tackled by the use of microelectromechanical system technology and the creation of silicon nanopore membranes capable of designing highly uniform pores [67]. This technology guaranteed higher permeability and selectivity, mimicking the glomerulus basement membrane structure, and allowed to both reduce the filter size and the required pressure ahead of the filter taking advantage only of the arterial-venous pressure differential, with no need of a mechanical pump [66,67]. This silicon nanotechnology has been successfully tested in large animals [68,69]. The second challenge could be tackled by placing a system of selective reabsorption in series the filtering unit permitted, by mimicking the nephron anatomy, to overcome the need for a large volume of dialysate. This could be possible by taking advantage of the bioartificial kidney technology developed by Humes et al. in the RAD and the BRECS, by seeding and differentiating human epithelial cells over silicon and thin-film material substrates and microelectromechanical system materials [70]. Despite limitations and challenges, mostly represented by high costs of production and storage, the ability to reabsorb a great volume of water and solutes from the filtrate, and the durability of the implanted device, this bioengineered artificial kidney could represent a feasible alternative to renal replacement therapy and transplantation.