Renal Physiology summary

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University of Toronto Scarborough
Biological Sciences
Stephen Reid

Renal Physiology Kidney Anatomy The kidneys are located just above the pelvis on either side of the body. Directly above then are the adrenal glands. Each kidney is connected to the bladder by a ureter. The kidney receives blood from the renal artery while the renal vein carries blood from the kidneys back to the heart. In cross section you see that the kidney is composed of an outer region called the renal cortex and an inner region called the renal medulla. Furthermore, the kidney consists of repeating segments called renal pyramids. Within each renal pyramid there are numerous nephrons (the functional unit of the kidney). Fluid (urine) from the collecting ducts of nephrons within any given renal pyramid drains into a minor calyx. The urine then flows into the central region of the kidney (the renal pelvis) before entering the ureter which drains urine from the kidney to the bladder . The Nephron The functional unit of the kidney is the nephron. The majority of nephrons are found in the renal cortex and are called cortical nephrons. However, the collecting ducts from the cortical nephrons extend into the renal medulla before emptying into the minor calyx. Some nephrons are contained primarily within the medulla (although part of them is in the cortex). These are called juxtamedullary nephrons and they play an important role in establishing the conditions required for the formation of a concentrated urine. A nephron begins with a dense capillary bed called the glomerulus which is surrounded by Bowmans capsule. The glomerulus receives blood from the afferent glomerular arteriole and is drained by the efferent glomerular arteriole. Together, the glomerulus and Bowmans capsule are called the renal corpuscle. From Bowmans capsule, fluid flows into the proximal convoluted tubule and then into the proximal straight tubule . From there fluid enters the descending Loop of Henle and then the thin and thick ascending Loop of Henle. Fluid leaves the Loop of Henle and enters the collecting tube. The collecting tubes from many nephrons connect to a collecting duct which drains into the minor calyx. The function of the glomerulus and Bowmans capsule is to filter the plasma to create the initial fluid that will become urine. The proximal tubule is the primary site of bulk reabsorption of water, ions, glucose, etc that occurs without any hormonal regulation. The Loop of Henle (particularly of the juxtaglomerular nephrons) is involved in creating the conditions necessary for the production of a concentrated urine. The distal convoluted tubule is a site of regulated ionwater reabsorption. The collecting tube and collecting duct are the site of regulated water uptake.
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