113116PathwayKidney Function - Descending Limb of the Loop of HenleThe loop of Henle of the nephron can be separated into an ascending limb and the descending limb. The ascending limb is highly impermeable to water, but permeable to solutes. Conversely, the descending limb is highly impermeable to solutes such as sodium, but permeable to water. As solutes are being actively transported out of the ascending limb, the solutes cause in increase in osmotic pressure. This, combined with the ability for water to move freely out of the descending limb, leads to a water reabsorption into the adjacent capillary network and a high concentration of sodium in the filtrate at the descending Limb. Water moves from the descending loop to the capillary network through aquaporin channels in the cell membrane.PhysiologicalPW122276CenterPathwayVisualizationContext12255215382620#000099PathwayVisualization112979113116Kidney Function - Descending Limb of the Loop of HenleThe loop of Henle of the nephron can be separated into an ascending limb and the descending limb. The ascending limb is highly impermeable to water, but permeable to solutes. Conversely, the descending limb is highly impermeable to solutes such as sodium, but permeable to water. As solutes are being actively transported out of the ascending limb, the solutes cause in increase in osmotic pressure. This, combined with the ability for water to move freely out of the descending limb, leads to a water reabsorption into the adjacent capillary network and a high concentration of sodium in the filtrate at the descending Limb. Water moves from the descending loop to the capillary network through aquaporin channels in the cell membrane.Physiological12795685460286Kokko JP: Sodium chloride and water transport in the descending limb of Henle. J Clin Invest. 1970 Oct;49(10):1838-46. doi: 10.1172/JCI106401.113116Pathway2795754427415Pennell JP, Lacy FB, Jamison RL: An in vivo study of the concentrating process in the descending limb of Henle's loop. Kidney Int. 1974 May;5(5):337-47.113116Pathway1CellCL:00000005HepatocyteCL:00001824CardiomyocyteCL:00007463NeuronCL:00005407Epithelial CellCL:00000661Homo sapiens9606EukaryoteHuman2Bacteria2ProkaryoteBacteria3Escherichia coli562Prokaryote12Mus musculus10090EukaryoteMouse5Bos taurus9913EukaryoteCattle17Rattus norvegicus10116EukaryoteRat19Schizosaccharomyces pombe4896Eukaryote24Solanum lycopersicum4081EukaryoteTomato4Arabidopsis thaliana3702EukaryoteThale cress18Saccharomyces cerevisiae4932EukaryoteYeast21Xenopus laevis8355EukaryoteAfrican clawed frog6Caenorhabditis elegans6239EukaryoteRoundworm25Escherichia coli (strain K12)83333Prokaryote49Bathymodiolus platifrons220390EukaryoteDeep sea mussel10Drosophila melanogaster7227EukaryoteFruit fly23Pseudomonas aeruginosa287Prokaryote60Nitzschia sp.0001EukaryoteNitzschia45CytoplasmGO:00057376LysosomeGO:00057644PeroxisomeGO:00057773Mitochondrial MatrixGO:00057592MitochondrionGO:000573910Cell MembraneGO:000588611Extracellular SpaceGO:000561516Lysosomal LumenGO:00432027Endoplasmic Reticulum MembraneGO:00057891CytosolGO:000582918Melanosome MembraneGO:003316213Endoplasmic ReticulumGO:000578325Golgi ApparatusGO:000579414Mitochondrial Outer MembraneGO:000574112Mitochondrial Inner MembraneGO:000574320Endoplasmic Reticulum LumenGO:000578821SynapseGO:004520215NucleusGO:000563431Periplasmic SpaceGO:000562035ChloroplastGO:000950736MembraneGO:001602053Endoplasmic Reticulum BodyGO:001016834Plant-Type VacuoleGO:000032540PeriplasmGO:004259738Apical cell membraneGO:001632456Basal Cell MembraneGO:00099251LiverBTO:00007597294Adrenal MedullaBTO:000004971825IntestineBTO:000064828StomachBTO:0001307155267Nervous SystemBTO:00014848Blood 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is a chemical substance that is essential to all known forms of life. It appears colorless to the naked eye in small quantities, though it is actually slightly blue in color. It covers 71% of Earth's surface. Current estimates suggest that there are 1.4 billion cubic kilometers (330 million m3) of it available on Earth, and it exists in many forms. It appears mostly in the oceans (saltwater) and polar ice caps, but it is also present as clouds, rain water, rivers, freshwater aquifers, lakes, and sea ice. Water in these bodies perpetually moves through a cycle of evaporation, precipitation, and runoff to the sea. Clean water is essential to human life. In many parts of the world, it is in short supply. From a biological standpoint, water has many distinct properties that are critical for the proliferation of life that set it apart from other substances. It carries out this role by allowing organic compounds to react in ways that ultimately allow replication. All known forms of life depend on water. Water is vital both as a solvent in which many of the body's solutes dissolve and as an essential part of many metabolic processes within the body. Metabolism is the sum total of anabolism and catabolism. In anabolism, water is removed from molecules (through energy requiring enzymatic chemical reactions) in order to grow larger molecules (e.g. starches, triglycerides and proteins for storage of fuels and information). In catabolism, water is used to break bonds in order to generate smaller molecules (e.g. glucose, fatty acids and amino acids to be used for fuels for energy use or other purposes). Water is thus essential and central to these metabolic processes. Water is also central to photosynthesis and respiration. Photosynthetic cells use the sun's energy to split off water's hydrogen from oxygen. Hydrogen is combined with CO2 (absorbed from air or water) to form glucose and release oxygen. All living cells use such fuels and oxidize the hydrogen and carbon to capture the sun's energy and reform water and CO2 in the process (cellular respiration). Water is also central to acid-base neutrality and enzyme function. An acid, a hydrogen ion (H+, that is, a proton) donor, can be neutralized by a base, a proton acceptor such as hydroxide ion (OH-) to form water. Water is considered to be neutral, with a pH (the negative log of the hydrogen ion concentration) of 7. Acids have pH values less than 7 while bases have values greater than 7. Stomach acid (HCl) is useful to digestion. However, its corrosive effect on the esophagus during reflux can temporarily be neutralized by ingestion of a base such as aluminum hydroxide to produce the neutral molecules water and the salt aluminum chloride. Human biochemistry that involves enzymes usually performs optimally around a biologically neutral pH of 7.4. (Wikipedia).7732-18-5C0000196215377937OH2OInChI=1S/H2O/h1H2XLYOFNOQVPJJNP-UHFFFAOYSA-N18.015318.010564686FDB013390Dihydrogen oxide;Steam;[oh2];Acqua;Agua;Aqua;Bound water;Dihydridooxygen;Eau;H2o;Hoh;Hydrogen hydroxide;WasserPW_C001420H2O55894910951394151316214481135261562428652106912077033823188382109431137749146554159043201824253222267860272746277817280529314370316472363461459836472737494193503027515675195975214100522794523610352971055319111534311353551125402110547012354831255492126550712755341305537114554112955911355608118562210856916575914057781015841143585314658771075890955910147594015160321556059157608716161231636133159621516218166647717865071806600152671311768401886888160716220571812077193206721121172282137238214724321572951987350216738821074012127467222749222475001907588170820122582372268414162926526118502771192216412011281122132851225028612264287123272491252022712632651269329012705291127152921300729813019300130253011303730213261223133272941534030842327315426953184369132276914293770192537710213277131133772151347737833177397332774713337751611577536334776283367772233777759341778163437798234778071329782353527824235378270356791133608001436880039370805912288065611993830383947943841105573901106393911158443981198792321199151221199634061200084071200464081201131241203654121204304051204384091206064151207944141211584251212404291213511211213814191216074341221183821223844361227531201227973741228044431230124461230643761230721371231314471231421361231624481232314511233844501237304601238104641239404551241654691246703991249384711249454721253052971253534791253864811254244821254802991256824831257074781257454871260544901262384951262734841267644801268965011269635021270173881271772081271992091272275041275065071275765151278363891280823951281765131406747901406758341407551854860Aquaporin-1P29972Forms a water-specific channel that provides the plasma membranes of red cells and kidney proximal tubules with high permeability to water, thereby permitting water to move in the direction of an osmotic gradientHMDBP10782AQP17p14AC00469118459141362902301363756812136Aquaporin-2P41181Forms a water-specific channel that provides the plasma membranes of renal collecting duct with high permeability to water, thereby permitting water to move in the direction of an osmotic gradientHMDBP02881AQP212q12-q13AF14709311362982301401403081401427821402278311402308321422068341422089972004Aquaporin-3Q92482Water channel required to promote glycerol permeability and water transport across cell membranes. Acts as a glycerol transporter in skin and plays an important role in regulating SC (stratum corneum) and epidermal glycerol content. Involved in skin hydration, wound healing, and tumorigenesis. Provides kidney medullary collecting duct with high permeability to water, thereby permitting water to move in the direction of an osmotic gradient. Slightly permeable to urea and may function as a water and urea exit mechanism in antidiuresis in collecting duct cells. 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