肾单位

title: 组织机制.
content: 肾元可分为近皮质肾元(cortical nephron)和近髓质肾元(juxtamedullary nephron)两类。近皮质肾元的肾丝球位于皮质的外围,占肾元85%肾元总数,近髓质肾元的肾丝球接近皮质与髓质的交接处,占15%肾元总数,且含有亨利氏环(loop of Henle),长度较长,浓缩尿液功能较好。  肾小体位于皮质区,是由鲍氏囊和肾丝球组成,鲍氏囊为双层壁构造,外层为单层鳞状上皮,内层为特化上皮(足细胞(podocytes))。鲍氏囊将肾丝球包住。  Nephron Remodeling( 肾元重塑 ) Loop diuretics主要抑制盐分在粗上升支上的再吸收,但它们不能增加NaCl的排泄,因为它们间接刺激肾元较远端处(例如远曲小管)的再吸收速率,因此不能完全抑制NaCl的再吸收。接着NaCl的净排泄反映出利尿作用主要部位的抑制与远端(或近端)刺激之间的平衡,持续使用利尿剂会引起其他变化,包括显著的远端肾小管的remodeling,这些作用涉及运输钠离子的细胞,但也涉及其他intercalated cells,这些细胞参与NaCl的再吸收和酸碱平衡。 RAS系统是促进nephron remodeling的信号途径。long-term furosemide的注射会导致thiazide-sensitive sodium chloride cotransporter (NCC)的活化,而此活化部分是由aldosterone调控的,且aldosterone亦活化了epithelial sodium channel。第二种机制涉及增加向远端肾元段的管腔溶质和液体的运送,这增加了通过上皮的溶质量,并且根据实验研究结果显示,这些远端肾元段细胞中可见转录的增加 。第三种机制为利尿剂使用对全身代谢的影响,包括代谢性碱中毒和低钾血症。血浆中钾浓度即使只有一点降低也与预后不良有关 。低钾血症会强烈活化sodium–chloride cotransporter,并与远distal convoluted tubule remodeling有密切关系。最后,在心衰竭患者中,经由肾丝球过滤的circulating proteases(如furin, plasmin, and plasminogen)可以直接活化epithelial sodium channel。

Summary: 肾单位又称肾元(英语:Nephron),是肾制造尿液的基本功能单位,人体的肾脏中,约含200万个肾元,每一个肾元是由肾小体和肾小管所组成,肾小体包含肾丝球(glomerulus)和鲍氏囊(Bowman's capsule)。肾元的主要功作是利用超滤作用,调节血液中的水分和溶解物质,重新吸收有用的物质,并将剩余的部分以尿液的形式分泌出去。肾元的功能除了将身体的废物排出,还可以调节血量和血压,控制电解质和代谢,并调节血液的酸碱值。它对生命的维持具有重要性。肾元会受到抗利尿激素、醛固酮(aldosterone)和副甲状腺素(parathyroid hormone)等荷尔蒙的影响,

Nephron: The nephron is the microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and an encompassing Bowman's capsule. The renal tubule extends from the capsule. The capsule and tubule are connected and are composed of epithelial cells with a lumen. A healthy adult has 1 to 1.5 million nephrons in each kidney. Blood is filtered as it passes through three layers: the endothelial cells of the capillary wall, its basement membrane, and between the foot processes of the podocytes of the lining of the capsule. The tubule has adjacent peritubular capillaries that run between the descending and ascending portions of the tubule. As the fluid from the capsule flows down into the tubule, it is processed by the epithelial cells lining the tubule: water is reabsorbed and substances are exchanged (some are added, others are removed); first with the interstitial fluid outside the tubules, and then into the plasma in the adjacent peritubular capillaries through the endothelial cells lining that capillary. This process regulates the volume of body fluid as well as levels of many body substances. At the end of the tubule, the remaining fluid—urine—exits: it is composed of water, metabolic waste, and toxins. The interior of Bowman's capsule, called Bowman's space, collects the filtrate from the filtering capillaries of the glomerular tuft, which also contains mesangial cells supporting these capillaries. These components function as the filtration unit and make up the renal corpuscle. The filtering structure (glomerular filtration barrier) has three layers composed of endothelial cells, a basement membrane, and podocytes (foot processes). The tubule has five anatomically and functionally different parts: the proximal tubule, which has a convoluted section the proximal convoluted tubule followed by a straight section (proximal straight tubule); the loop of Henle, which has two parts, the descending loop of Henle ("descending loop") and the ascending loop of Henle ("ascending loop"); the distal convoluted tubule ("distal loop"); the connecting tubule, and the collecting ducts. Nephrons have two lengths with different urine concentrating capacities: long juxtamedullary nephrons and short cortical nephrons.