human anatomy and physiology here we are in the urinary system focused on the kidney in episode 7 the kidney's primary function is around processing blood plasma for the purpose of urine formation now the kidneys function is derived from the actions of the nephrons which are the functional units of the kidney let's take a look in the next series of slides at the major structures involved in this process at a very basic level here you can see the two kidneys one on the left and one on the right side they are protected by the ribs and as well by fat uh tissue as well now what you can't see though is that the kidney has many many functions owing to the nephrons and there are over a million nephrons that act as the functional units of the kidney to process the blood plasma and form the urine the urinary system also plays a crucial role as you are aware from our preceding lecture episodes on fluid and electrolyte balance and uh subsequent lecture episodes will focus on acid base balance as well now if we continue to go on uh we can look now uh at an image of the kidney and focus in on some of the key structures most notably we have renal arteries and renal veins the oral arteries arise directly from the abdominal aorta to allow blood to make its way into the kidney where filtration can occur following the filtration of the blood blood is able to exit each kidney through a renal vein these renal veins drain directly into the inferior vnea there are additional structures on this slide uh which we will uh go into more detail in a few minutes but I will highlight them here we have both a minor and major calic and these structures are responsible for allowing the urine to collect SCT after it has uh been uh formed the filtrate has been formed in the nefron so first the urine will enter or the filtrate will enter into the minor calx and then make its way down to the major calx before entering the renal pelvis it is at the point of the renal pelvis where the urine starts to collect essentially in a funnel uh or a funnel shaped uh structure known as that renal pelvis whereby urine will then exit the urer and make its way to the urinary bladder where it can be stored this diagram also nicely highlights the two main uh layers of the kidney or how we can divide it we have the renal cortex which is that outer layer compared to the renal medulla which is the inner layer it is at the inner layer where those structures such as the calluses and the pelvis will exist now let's focus more so on those functional units of the kidney known as the nefron the nefron consists of a series of structures the two main parts of the nefron are the renal corpal and the renal tual notably the renal corpal is composed of a glomeris which essentially is uh the tuft of capillaries shown at the the top left of this figure and Bowman's capsule which is the C shaped or the cup-shaped structure that surrounds the glomeris this capsule helps a glomeris to filter blood small molecules from the blood are able to pass free freely into B's uh capsule or into the space and this EX as long as the K kidney is working normally thereby preventing cells and larger proteins from leaving the blood larger proteins or larger part particles will stay in the blood so this filtration process is all based on particle size so we've talked talked about the renal corpal including the glomeris and the Bowman's capsule the second part of the nefron remember there's two parts the ren renal corpal and then the renal tual so the second part is known as the renal tual and that extends from the capsule and is made up of the three segments including the proximal convoluted tual which you can see extends directly from the capsule and that is followed by the nefron loop sometimes known as the loop of Henley and then the third and final segment is the distal convoluted tual notably the proximal and distal convoluted tubal are winding and convoluted portions of the tual it is in the proximal convoluted tual where you have the greatest absorption and secretion absorption and secretion can continue in the distal convoluted tubal but to a lesser extent than in the proximal convoluted tual the loop of Henley consists of a very thin walled limb a sharp turn and a thick ascending limb and its length helps to determine the concentration of urine so that's the loop of the nefron that we're looking at on the middle of your diagram and then we also have a collecting duct and you can see that that runs um in a single Direction uh and it's a straight duct that is joined by the renal tubal of several nephrons at the renal pyramid to form one tube that can then open at the renal pill and make its way into the minor CX notably each collecting duct will collect the forming urine from several nephrons and but it is also um able to respond to the hormone anti-diuretic hormone anti-diuretic hormone as you may recall helps to modulate water reabsorption high levels of ADH like to hold on to excess water it can accomplish this within the collecting ducts there are uh aquaporin water channels that can be inserted into the cell membrane to help with the recovery of water when ADH is present this next slide just compares the renal corpal to the renal tual so this is just an enlargement of the diagram we saw in the preceding slide you'll recall that the renal corpal and the renal tual are the two main structures that form the nefron once again the nefron being the functionalit unit of the kidney so what you can see here is the glomeris and Bowman's capsule those two structures make up the renal corpal the renal tual uh can be observed as that is the tube uh that extends from uh Bowman's capsule and makes its way uh to the proximal convoluted tual Loop of hen also known as the loop of the nefron as well as a distal convoluted tual so well filtration tends to occur at the renal corpal where you have the glomeris and Bowman's capsule the actual reabsorption secretion and excretion occur further down with the renal tual now you may be wondering well how exactly uh can filtration occur and there are structures known as pites and these poyes help with filtration of substances in a similar way to fenestrations in fact there are cell processes known as pedia cells and these are extensions of the poyes which are packed closely together to form filtration slits this allows for fluid and smaller solutes to leave the capillaries but prevents those larger cells and macro molecules from leaving the glomeris this next diagram just uh reiterates uh the uh fenestrations that can exist uh within capillaries and allow substances to diffuse from the blood based primarily on the particle size