Renal Vasculature

Renal Vasculature - 1 Renal Vasculature Blood reaches the...

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1 Renal Vasculature Blood reaches the kidneys via the renal arteries. In the hilum, the renal artery gives off branches, called interlobar arteries , which run through the medulla adjacent to the medullary pyramids. At the junction of the medulla and cortex, the arteries arch to form arcuate arteries . Arcuate arteries give off branches, called interlobular arteries whic h will form the afferent artery of the glomerulus, the capillary bed that filters the blood to start the process of forming urine. The glomerulus is a fenestrated capillary but has a thick basement membrane (that is not fenestrated) that is formed by the endothelial cells of the capillary AND special cells that are attached to the outside of the capillary wall. These special cells are the podocytes. Think of podocytes as cells sitting in Bowman’s space and sending out numerous cytoplasmic processes (feet, pedicels) which are attached to the basement membrane of the glomerular capillary. The pedicels (feet) of adjacent podocytes interdigitate but between the digitations there is space. These spaces are the filtration slits . The slits have a diaphragm which prevents passage of proteins. Podocytes can contract and thus slow glomerular filtration rate. Another function of the podocytes is simply support to the delicate fenestrated capillary. The fused basal lamina of the podocytes and the endothelial cells as well as the diaphragms of the filtration slits constitutes the filtration membrane .
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2 The wall of the afferent artery contains specialized smooth muscle cells, called J-G cells (juxtaglomerular cells). These smooth muscle cells make and secrete the hormone renin. The J-G cells in the wall of the afferent artery plus the macula densa cells of the distal convoluted tubule constitute the juxtaglomerular apparatus. (see below). The glomerulus is an “arterial” portal system. After blood flows through the capillary bed of the glomerulus, it leaves via the efferent artery. Blood leaving in the efferent artery is thicker because of the loss of water and other substances during the trip through the glomerulus (but most of these substances will be reabsorbed from the proximal convoluted tubule). Blood from the efferent artery enters the peritubular capillaries OR the vasa recta. Peritubular capillaries surround the proximal and distal convoluted tubules in the cortex of the kidney and eventually return blood to the interlobular veins. Vasa recta come off efferent arteries that come from glomeruli that lie deep in the cortex close to the medulla. They are basically capillaries (large ones) that give nourishment and oxygen to the medulla and they parallel the course of the loops of Henle that extend deep into the medulla.
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Renal Vasculature - 1 Renal Vasculature Blood reaches the...

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