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The patient with acute renal problems
Published in Peate Ian, Dutton Helen, Acute Nursing Care, 2020
This is a large straight tubule that extends down from the cortex of the kidney into the medullary section. On its route through the kidney, it is joined by the distal tubules of several nephrons. The collecting duct then joins larger ducts and eventually forms a renal pyramid, and these structures finally converge to form a tube that enters into the small calyces. From here, the filtrate, now called urine, drains into the renal pelvis and then into the bladder.
Renal Drug-Metabolizing Enzymes in Experimental Animals and Humans
Published in Robin S. Goldstein, Mechanisms of Injury in Renal Disease and Toxicity, 2020
The kidney is composed of the cortex and medulla, which contain several cellular structures where both transport and metabolism of xenobiotics can occur. Thus, the nephron has been divided into 11 morphologically and functionally distinct units: proximal convoluted tubules, proximal straight tubules, descending and ascending thin limbs, medullary and cortical thick ascending limbs, distal convoluted tubule, connecting tubule, cortical collecting tubule, and inner and outer collecting ducts (Bulger and Dobyan, 1982). In the rat, rabbit, and dog the proximal tubules have been subdivided into Sb S2, and S3 segments. Sj comprises the beginning and middle portion of the convoluted part, S2 the final portion of the convoluted part and the beginning of the straight part, and S3 the remaining portion of the straight part (Maunsbach, 1966; Jacobsen and Jorgensen, 1973; Tisher and Madsen, 1991). The cortex has a high oxygen consumption and is particularly susceptible to chemicals that produce anoxia, especially in the S3 segment (eg., Venkatchalam et al., 1978).
Functions of the Kidneys and Functional Anatomy
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
The proximal tubule, consisting of a coiled or convoluted tubule followed by a proximal straight tubule, collects the large volume of filtrate from Bowman's capsule and reabsorbs some 60% of it back into the bloodstream. The proximal tubule reabsorbs water, sodium, chloride, potassium, bicarbonate, calcium, glucose, urea, phosphate and any filtered proteins. Substances secreted from the blood into the lumen by the proximal tubule include hydrogen ions, ammonium, urate and organic anions and cations.
Advances in understanding vertebrate nephrogenesis
Published in Tissue Barriers, 2020
Joseph M. Chambers, Rebecca A. Wingert
By the time the nephron is fully developed, it will contain a number of unique cell-types that each need to have the appropriate gene expression to complete their vital functions (Figure 1). The nephron begins with the blood filter, or renal corpuscle encompassing the glomerulus and Bowman’s capsule. This contains a number of cell types including capillaries, mesangium, podocytes, and parietal cells. Next, the tubule contains the proximal convoluted tubule, proximal straight tubule, the Loop of Henle (including descending limb, thin ascending limb, thick ascending limb), distal convoluted tubule, and connecting tubule. The proximal tubule functions in absorption and secretion in an effort to regulate pH of the filtrate. Largely, the Loop of Henle functions to concentrate the filtrate by reabsorbing water. The distal tubule ensures proper ion transport occurs to fine-tune the filtrate by regulating potassium, sodium, and calcium levels. Each unique segment is needed to maintain blood homeostasis by completing these functions. Nephron cells must acquire a number of features to be generally considered terminally differentiated, including proper epithelization, cilia formation, and expression of functional proteins such as tight junctions and solute transporters.
Outer Retinal Tubulation in Subretinal Neovascularization Associated with Macular Telangiectasia Type 2
Published in Seminars in Ophthalmology, 2018
Duc Anh Hua, Giulio Barteselli, Jay Chhablani
With the widespread adoption of spectral domain optical coherence tomography (SD-OCT) in diagnosing and following up retinal diseases, outer retinal tubulations (ORTs) have become a better-characterized feature in eyes with disruptions of the outer retina.1–4 Outer retinal tubulations are defined as round or ovoid hyporeflective spaces with hyperreflective borders on B-scan SD-OCT sections, generally situated in the outer nuclear layer of the retina.4They have a single straight tubule or branching tubules to complex networks, as made visible by en-face SD-OCT C-scan.5 “Pseudodendritic” types of ORTs develop next to fibrotic scars, while “perilesional” types develop at the edge of atrophic areas.5The underlying pathogenesis for ORT development is not yet completely understood; however, it is likely the result of a long-lasting retinal degenerative process.4 It has been hypothesized that ORTs derive from the rearrangement of photoreceptor cells and Müller cells in a reparative attempt to retinal degenerative processes or as a response to injury.4 Lately, Schaal et al. compared optical coherence tomography (OCT) and histology of outer retinal tubulation (ORT) secondary to advanced age-related macular degeneration (AMD) in patients and in postmortem specimens, with particular attention to the basis of the hyperreflective border of ORT. They concluded that the defining OCT features of ORT are location in the outer nuclear layer, a hyperreflective band differentiating it from cysts, and retinal pigment epithelium that is either dysmorphic or absent. Histologic and OCT findings of outer retinal tubulation corresponded in regard to composition, location, shape, and stages of formation. The reflectivity of ORT lumenal walls on OCT apparently does not require an outer segment or an inner/outer segment junction, indicating an independent reflectivity source, possibly mitochondria, in the inner segments.6