Lumen tubule

ENaC mediates Na+ entry from the tubule lumen at the apical membrane and the Na+/K+ ATPase extrudes Na+ at the basolateral side. K+ channels are present on the basolateral and apical membrane. K+ channels at the apical membrane mediate K+ secretion into the tubular lumen. 

The kidney contains the major site of renin synthesis, the juxtaglomerular cells in the wall of the afferent arteriole. From these cells, renin is secreted not only into the circulation but also into the renal interstitium. Moreover, the enzyme is produced albeit in low amounts by proximal tubular cells. These cells also synthesize angiotensinogen and ACE. The RAS proteins interact in the renal interstitium and in the proximal tubular lumen to synthesize angiotensin II. In the proximal tubule, angiotensin II activates the sodium/hydrogen exchanger (NHE) that increases sodium reabsorption. Aldosterone elicits the same effect in the distal tubule by activating epithelial sodium channels (ENaC) and the sodium-potassium-ATPase. Thereby, it also induces water reabsotption and potassium secretion. 

Ryanodine Receptor. Figure 1 Three-dimensional architecture of the RyR1 by cryo-electron microscopy, (a), top view (from the T-tubule) (b), bottom view (from the SR lumen) (c), side view (parallel to the SR membrane). The binding sites of FKBP12, apo-CaM and Ca -CaM are indicated in the side view. Courtesy of Dr. M. Samso (modified from Samso etal. (2005) Nat Struct Mol Biol 12 539-544). 

Renal 1.9 3.9 (yellow protein in tubule lumen eosinophilic droplets in cells of proximal convoluted tubules increased kidney weights) 23.4 M (proteinuria) ... 

Sodium SGLTl -dependent unidirectionai transporter Small intestine and kidney Active uptake of glucose from lumen of intestine and reabsorption of glucose in proximal tubule of kidney against a concentration gradient... 

Aldosterone acts on the distal tubule of the nephron to increase sodium reabsorption. The mechanism of action involves an increase in the number of sodium-permeable channels on the luminal surface of the distal tubule and an increase in the activity of the Na+-K+ ATPase pump on the basilar surface of the tubule. Sodium diffuses down its concentration gradient out of the lumen and into the tubular cells. The pump then actively removes the sodium from cells of the distal tubule and into the extracellular fluid so that it may diffuse into the surrounding capillaries and return to the circulation. Due to its osmotic effects, the retention of sodium is accompanied by the retention of water. In other words, wherever sodium goes, water follows. As a result, aldosterone is very important in regulation of blood volume and blood pressure. The retention of sodium and water expands the blood volume and, consequently, increases mean arterial pressure. 

More simply, in the early regions of the tubule (proximal tubule and Loop of Henle), Na+ ions leave the lumen and enter the tubular epithelial cells by way of passive facilitated transport mechanisms. The diffusion of Na+ ions is coupled with organic molecules or with other ions that electrically balance the flux of these positively charged ions. In the latter regions of the tubule (distal tubule and collecting duct), Na+ ions diffuse into the epithelial cells through Na+ channels. 

An essential requirement for diffusion of Na+ ions is the creation of a concentration gradient for sodium between the filtrate and intracellular fluid of the epithelial cells. This is accomplished by the active transport ofNa+ ions through the basolateral membrane of the epithelial cells (see Figure 19.4). Sodium is moved across this basolateral membrane and into the interstitial fluid surrounding the tubule by the Na+, K+-ATPase pump. As a result, the concentration of Na+ ions within the epithelial cells is reduced, facilitating the diffusion of Na+ ions into the cells across the luminal membrane. Potassium ions transported into the epithelial cells as a result of this pump diffuse back into the interstitial fluid (proximal tubule and Loop of Henle) or into the tubular lumen for excretion in the urine (distal tubule and collecting duct). 

A strong surface charge on the halloysite tubules has been exploited for designing nano-organized multilayers using the layer-by-layer (LbL) method of Lvov et al. [8,13,14]. The lumen of the halloysite has been used as an enzymatic nano-reactor by Shchukin et al. [15] The biocompatible nature of the halloysite was... 

Nanoassembly on Tubules and at the Lumen Opening 429 % Releases of proteins from Halloysite assisted with PEI... 

No adverse effects in 40 mg/kg BW group. High dose groups had skin damage (atrophy, acanthosis, hyperkeratinization) and testicular damage (abnormal seminiferous tubules, tubular lumens filled with degenerated sperm)... 

Nephrotic syndrome (loop diuretic protein binding in tubule lumen)... 

Bicarbonate ions secreted into the blood stream help maintain the normal plasma bicarbonate concentration of approximately 25 mmol/1, whilst the two protons are secreted into the lumen of the proximal tubule in exchange for sodium via a Na+/H+ antiport. 

Amino add reabsorption in the renal tubules Amino acids are small, easily filtered molecules. Efficient reabsorption mechanisms are vital to conserve amino acids which are metabolically valuable resources. Transport of individual amino acids and small peptides is symport carrier mediated mechanisms in which sodium is co-transported. The process is indirectly ATP dependent because Na is returned to the lumen of the nephron by the sodium pump , Na+/K+ dependent ATPase. 

Hemoglobinuria and hematin casts in the distal convoluted tubules and tubular lumens located in the medulla and papilla were reported in rats after a single dermal exposure to 107.1 mg/kg liquid phenol (Conning and Hayes 1970). These phenomena are probably related to red blood cell lysis and increased glomerular filtration of hemoglobin. Hemoglobinuria is characteristic of lethal or near-lethal exposures by the dermal route. 

The endoplasmic reticulum (ER) is responsible for the production of the protein and lipid components of most of the cell s organelles. The ER contains a large number of folds, but the membrane forms a single sheet enclosing a single closed sac. This internal space is called the ER lumen. The smooth endoplasmic reticulum (ER) in muscle cells contains the vesicles and tubules that serve as a store of calcium ions. These are released as one step in the muscle contraction process. Calcium pumps, Ca +-ATPases, serve to move the calcium from the cytoplasm to the ER or SR lumen. 

The blood first reaches the glomerulus, the filter unit of the nephron. The glomerular filtrate, i.e. blood deprived of macromolecules and blood cells, passes through the tubular lumen. The blood which is not filtered, flows through the efferent arteriole into the network of capillaries around the tubules suppl5dng the proximal and distal tubules with blood. 

---