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14. Urinary System.pdf

12 Pages

Anatomy & Cell Biology
Course Code
ANAT 261
Craig Mandato

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Naveen Sooknanan McGill Fall 2011 Urinary System (Kidneys): The urinary system is made up of the kidneys, ureters, urinary bladder and the urethra In this course, we will only study the kidneys and the urinary bladder The urinary system contributes to: o Excretion of metabolic waste products (such as urea) This is done through a filtration process, during which proteins such as albumin are recovered o Regulation of total body water Highly regulated and can vary greatly depending on how much water you consume o Regulation of electrolyte balance Retains sodium and other ions to a constant level o Endocrine secretion of Renin and Erythropoietin Renin is an enzyme released into the blood which controls blood pressure Erythropoietin stimulates RBC production (modern name is Erithrogenin) The kidney is shaped like a kidney bean (which was named after it) It has two borders: o The concave border, called the hilium, is where the renal pelvis is located This structure is funnel shaped and is continuous with the ureters At this level, there is also the entrance of renal arteries and the exit of renal veins o There is a convex lateral portion The human kidney is big enough to be divided into lobes and lobules o A mouses kidney is unilobar The capsule is made of tough dense irreg. CT rich in collagen fibers and fibrocytes o Very eosinophilic, easy to identify The cortex is located immediately below the capsule, and looks grainy due to the presence of tiny little spheres The cortico-medullary junction is where the cortex stops and the next part, the medulla begins The medulla is a striated structure which have straight ducts travelling all the way to the draining points (called calices, or calix in singular) o Each lobe contains a group of straight ducts making the a medullary pyramid (a mouse only has one pyramid) o The medulla can also be separated further into lobules Medullary rays are projections of the medulla into the cortex o They have the exact same structure as the upper medulla, as we will look at later 1 Naveen Sooknanan McGill Fall 2011 Dividing each lobe are columns of Bertin, which is the equivalent of interlobular CT in other structures (it is made of CT) All of these medullary pyramids drain through openings known as the area cribosae o There are around 25 of these regions in each renal pyramid These collections then get dumped into the minor calix, which are small pockets in front of the AC These minor calices then converge to form the major calix, which turns into the renal pelvis o The renal pelvis is continuous with the ureters The ureter will go all the way to the urinary bladder The main filtration unit of the kidney is called the nephron, and is located between the medulla and cortex Each kidney is comprised of 1-4 million nephrons Blood comes into the nephron and gets filtered into urine through a series of tubules o In the cortex, blood enters the renal corpuscle, which is a dilated tuft, and gets filtered o Still in the cortex, the urine then enters the proximal convoluted tubule (PCT) which is very twisted o The PCT then penetrates into the medulla and straightens out, becoming the straight thick descending limb (SD) It is structurally identical to the PCT except its straight and in the medulla o Next, the SD turns into the thin limb, which does a U turn in the lower medulla and starts coming back up (towards the cortex) o The TL then turns into the straight thick ascending limb (SA) which penetrates back into the cortex o The SA, once in the cortex, becomes the distal convoluted tubule, which is very twisted like the PCT The SA and DCT are structurally the same as well o The SD, TL and SA together are known as the loop of Henle (because of the U turn) This point marks the END of the nephron, from here on, the urine is no longer inside the nephron o The DCT is connected to a collecting tubule, which collect urine from different nephrons and merge as they penetrate into the medulla o In the deeper medulla, the collecting tubules begin to thicken and become collecting ducts of Bellini 2Naveen Sooknanan McGill Fall 2011 o The CD of B then drain into the area cribosa, through the minor and major calices, and to the ureters The renal corpuscle consists of a double walled-epithelium containing a glomerular tuft of capillaries The unit is surrounded by a capsule called Bowmans capsule, which contains two layers: the inner visceral layer and the outer parietal layer o These layer do not touch, the space between them is known as Bowmans space or capsular space o The visceral layer has cells called podocytes with a lot of indentations and processed, whereas the parietal layer is similar to a simple squamous epithelium resting on a BM The parietal layer is also surrounded by reticular fibers (type III collagen) The squamous cells and podocytes are embryologically related The renal corpuscle is polarized (not electrically). This just means is has two different poles: the vascular pole and the urinary pole o The vascular pole contains afferent and afferent arterioles Like the portal venule in the liver, these BVs are functional (get filtered) and are not for nutrition o The afferent arteriole contains a region of modified SMCs in the media whi
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