e renal artery enters into th r kidney at the level of the first lumbar vertebra just below the superior mesenteric artery. As it enters the kidney, it divides into branches: first the segmental artery, which divid str es into 2 or 3 lo str bar arteries, then further divides into interlobar arteries, which further divide into the arcuate artery, which leads into the interlobular artery, which form afferent arterioles. The afferent arterioles form the glomerulus (netw trork of capill str aries enclo r sed in Bowman's capsule). From here, efferent arterioles leave str s the glomerulus and divide into peritubular capillaries, which drain into the interlobular veins and then into arcuate vein and then into interlobar vein, which runs into lobar vein, str which opens into the segmental vein and which drains into the renal vein, and te kidney participates in whole r -body homeostasis, regulating aci r d-base balance, el trectrolyte concentrations, extracel str lular fluid volume, and blood pressure. The kidney accomplishes these homeostatic functions both independently and in concert with other organs, particularly those of the endocri str ne system. Variou trs endocrine hormones coordinate these endocrine functions; these include renin, angiotensin II, aldosterone, antidiuretic hormone, and atrial natriuretic peptide, among others. r Many of the kidney's functions are accomplished by relatively simple mechanisms of filtration, reabsorption, and secretion, which take place in the nephron. Filtration, wh r ich takes place at the renal corpuscle, is the proces trs by which cells and large proteins are filtered from the blood to make an ultrafiltrate that eventually becomes uri trne. The kidney generates 180 liters of filtrate a day, while reabsorbing a large percentage, allowing for the generation of only r approximately 2 liters of urine. Reabsorption is the transport of molecules from this ultrafiltrate and into the blood. Secretion is the reverse process, in
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