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BIOL 302 - Urinary System

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BIOL 302
Mungo Marsden

Urinary System – BIOL 302 Functions  Salt/water balance  Acid/base balance  Nutrient conservation  Excretion of waste  Production of urine – 180L/day. Filtration, resorption and secretion.  Endocrine glands depend on kidneys Kidney  Two zones: o Cortex  Outside  Consists of renal corpuscles (glomerulus and Bowman’s capsule) for filtering  Medullary rays break up the cortex into segments. o Medulla  Inside  Pyramidal areas that tubules and blood vessels pointing in one direction that empty into the papilla  Outer, more dense, darker layer consists of proximal and distal tubules  Inner, looser lighter layer consists of loop of Henle, collecting ducts, papillary ducts  The kidney is divided into lobes. Lobes are defined as a pyramidal shape Calyxes at the small end of the pyramid join to form the renal pelvis.  The renal artery and renal vein supply blood to the kidney. Nephron is the functional unit of the kidney. The glomeruli and the tubular system are both parts of the functional unit. It consists of the renal corpuscle, proximal convoluted tubule, loop of Henle, and distal convoluted tubule. Uriniferous Tubules  The uriniferous tubule is divided into the proximal tubule, the intermediate (thin) tubule, the distal tubule and the collecting duct. Renal Corpuscle  Vascular pole: o Blood supply o Big afferent arteriole o Glomerulus o Small efferent arteriole  Urinary pole: o Proximal convoluted tubule continuous with the parietal layer of Bowman’s capsule  Bowman’s capsule: o Visceral layer is against capillaries with podocytes (supporting cells)  Podocytes have pedicels (end feet that interdigitate with filtration slits)  Basal lamina is thick, shared endothelium, and acts as a filter o Parietal layer against Bowman’s (urinary) space Proximal Tubule  Simple cuboidal epithelium, microvilli in lumen, small lumen  Convoluted portion: o In cortex o Coils close to the glomerulus in the cortex. o Their walls are formed by a simple cuboidal/columnar epithelium, with round nuclei. o The eosinophilic cells of the epithelium have a wide brush border and are active in endocytosis. They almost completely resorb substances of nutritional value from the glomerular filtrate (glucose, amino acids, protein, vitamins etc.). o In the proximal tubules the volume of the glomerular filtrate is reduced by about 75%. Sodium ions are actively resorbed from the glomerular filtrate. They are followed by passively diffusing chloride ions and the osmotic absorption of water. o The straight portion of the proximal tubule descends towards the medulla.  Straight portion: o In medullary ray and medulla o The straight portion of the proximal tubule merges with the intermediate tubule (thin segment of the loop of Henle). o A flattened, only ~1-2 µm high epithelium forms the intermediate tubule, which is only ~15 µm wide. o Descending parts of the straight proximal and intermediate tubules are permeable to water but not to solutes. Loops of Henle  In medulla  Simple squamous epithelium  For osmotic balance and to create a sodium gradient  Consists of a descending thin segment, a loop, and a ascending thin segment Distal Tubule  Simple cuboidal epithelium, low or flattened nuclei on apical side, large lumen  Straight portion o In medulla and medullary ray o The straight portion of the di
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