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(BQ) Part 2 book "Harrison's nephrology and acid-base disorders" presents the following contents: Glomerular and tubular disorders, renal vascular disease, urinary tract infections and obstruction, urinary tract infections and obstruction. | SECTION IV GLOMERULAR AND TUBULAR DISORDERS CHAPTER 15 GLOMERULAR DISEASES Julia B. Lewis Eric G. Neilson Two human kidneys harbor nearly 1.8 million glomerular capillary tufts. Each glomerular tuft resides within Bowman s space. The capsule circumscribing this space is lined by parietal epithelial cells that transition into tubular epithelia forming the proximal nephron or migrate into the tuft to replenish podocytes. The glomerular capillary tuft derives from an afferent arteriole that forms a branching capillary bed embedded in mesangial matrix Fig. 15-1 . This capillary network funnels into an efferent arteriole which passes filtered blood into cortical peritubular capillaries or medullary vasa recta that supply and exchange with a folded tubular architecture. Hence the glomerular capillary tuft fed and drained by arterioles represents an arteriolar portal system. Fenestrated endothelial cells resting on a glomerular basement membrane GBM line glomerular capillaries. Delicate foot processes extending from epithelial podocytes shroud the outer surface of these capillaries and podocytes interconnect to each other by slit-pore membranes forming a selective filtration barrier. The glomerular capillaries filter 120 180 L d of plasma water containing various solutes for reclamation or discharge by downstream tubules. Most large proteins and all cells are excluded from filtration by a physicochemical barrier governed by pore size and negative electrostatic charge. The mechanics of filtration and reclamation are quite complicated for many solutes. For example in the case of serum albumin the glomerulus is an imperfect barrier. Although albumin has a negative charge which would tend to repel the negatively charged GBM it only has a physical radius of 3.6 nm while pores in the GBM and slit-pore membranes have a radius of 4 nm. Consequently variable amounts of albumin inevitably cross the filtration barrier to be reclaimed by megalin and cubilin receptors along the .
