chapter 26 lecture two is on the nephron a nephron consists of the renal corpuscle and the renal tubule renal corpuscle is where the filtration occurs and then the renal tubule is where the fluid passes through and where tubular reabsorption and tubular secretion occur the tubule consists of proximal convoluted tubule or pct the loop of henle or the nephron loop and a distal convoluted tubule or dct the distal convoluted tubules of a number of different nephrons are going to drain into one single collecting duct and then many collecting ducts drain into a smaller number of papillary ducts papillary ducts are found at the tip of the renal pyramid and that's called the papilla the loop of henle has a descending limb a thin ascending limb and a thick ascending limb there are two different kinds of nephrons based upon the differences in their loop of henle as well as their function there's cortical and juxtamedullary this shows the cortical this makes up the vast majority of nephrons about 80 to 85 percent and here you can see the nephron sits up in the cortex hence the name cortical and a small a small amount of the loop of henle sits down in the medulla inside the the renal pyramid a juxta medullary has a very very long loop of henle and most of which is in the renal medulla and it goes nearly down to where the papilla is this only makes up about 15 to 20 percent of all nephrons so when we look at a nephron we have the renal corpuscle which consists of the glomerulus which is the capillary and then the capsule around it and we have the proximal convoluted tubule which is always attached to that renal core puzzle we have the descending loop of henle and then the thin and the thick ascending limbs then we have the distal convoluted tubule and that feeds right into the collecting duct we have a number of different kinds of cells that we find here we have uh in the proximal convoluted tubule and most of these are going to be those um cuboidal epithelial cells simple cuboidal epithelium some are going to have more microvilli than others but that's the main type of cells that you're going to find there you can also find in the nephron loop you can find some simple squamous epithelium as well as the cuboidal simple cuboidal epithelium and this is showing the cortical nephron next to the juxtamedullary they're both going to have the dct the pct and the glomerulus and renal capsule are always going to be in the cortex it's just how much of the loop of henle goes down into the medulla the blood vessels around the nephron the afferent arteriole is going to take blood to the renal corpuscle the efferent takes blood away and this is where filtration occurs when you're looking at pictures remember the afferent is always going to be bigger in diameter than the efferent so that there's more pressure as it goes through as the blood is being filtered then the peritubular capillaries are where the reabsorption and secretion occur the vasarecta we'll speak about a little bit so you can see the peritubular capillaries are all around the tubules now remember the the way that you find the proximal convoluted tubule is it's attached to that renal corpuscle the distal convoluted tubules can be over here um in this picture it's over here as well but sometimes they have the distal convoluted tubule right next to they show it right next to the renal corpuscle all right so here we have the afferent notice it's bigger in diameter the efferent and then we have the peritubular capillaries okay and then down here we have the vasa recta which is around the loop of henle so the kidney has over a million nephrons the renal corpuscle again is the site of plasma filtration renal tubules where reabsorption occurs and secretion and then the collecting ducts and the papillary ducts are involved in urine drainage to the renal pelvis and ultimately the ureter urinary bladder and urethra the capsule which is also called bowman's capsule or the glomerular capsule has visceral and parietal layers remember the terms visceral and parietal visceral means it's going to adhere to the organ or structure parietal means it's going to be superficial to that so the visceral layer consists of potasites the parietal layer is simple squamous epithelium and that's the outer wall the area in between is the capsular space and that's where the fluid is going to to flow so here we can see and now here is the afferent is down here and the efferents up there and this is that little knot of capillaries called glomerulus surrounding the capillary are these cells called the podocytes the parasites again this is going to be the visceral epithelium the parietal epithelium is just simple squamous epithelium those flat floor tile like like cells um the little slits in between the extensions that come out from the podocytes are called pedicils and that is that third filtration layer i spoke of in class this shows the distal convoluted tubule right butted against the um afferent nephron arterial and then this would be the proximal because it's attached uh there are two areas here that we're going to talk more about later and these make up the the juxtaglomerular apparatus or you could say complex uh there are cells in the afrin arterial that are called juxtaglomerular cells and there are cells in an area of the distal convoluted tube you'll call the maculidensa and together they make up the jga which is going to be involved in regulating the glomerular filtration rate this is just a scan electron micrograph showing the glomeruli there are as i said before there's distinctive features that you find in each of the regions most of these are going to be simple cuboidal epithelium um there's these cells are going to have hormone receptors on some of them there are going to be microvilli on some of them particularly the proximal convoluted tubule has lots of microvilli the pct is where the majority of secretion and reabsorption occurs so these microvilli give it an increased surface area here is a potasite and you can see the pedicels the little feet it puts out and the gaps between the toes are the filtration slits uh as i mentioned the jga or the juxtaglomerular apparatus consists of the adjusted glomerular cells that are found in the aferin arterial and the macula densa which is in the distal convoluted tubule this helps to regulate blood pressure and the rate of filtration in the the distal convoluted tubule most of the cells are called principal cells principal cells have receptors for antidiuretic hormone and aldosterone antidiuretic hormone is involved in concentrating urine when you're dehydrated and it returns water to the blood by the insertion of proteins called aquaporins so the way that adh acts on these principal cells is it causes them to produce and insert aquaporin proteins into their membranes so that they can reclaim so that water can be reclaimed back to the blood from the filtrate the receptors for aldosterone are involved in sodium balance and we'll talk about those a little bit later there are also intercalated cells and intercalated cells are important in the homeostasis of blood ph so you should make sure you know all the different types of cells the podocytes we'll talk about mesengeal cells principal cells intercalated cells and what they do and how they function the number of nephrons that we have is constant from the time we're born they can increase in size but they don't increase in numbers so if you have a disease that kills nephrons you're going to have decreased kidney function so here we see bowman's capsule or the glomerular capsule we have here we have the bigger diameter so this is the afferent arterial the smaller diameter is efferent you can also tell by the arrows this is the glomerulus the capillary bed and the potasites with their pedicels and the filtration slits surrounding the glomerulus and remember this is the visceral peritoneum the parietal peritoneum is up here making the capsule over here we have the macula densa and the juxtaglomerular cells smushed right against each other and that helped to form the jga and in the proximal convoluted tubule you can see the simple cuboidal epithelium with the microvilli so in the proximal convoluted tubule we have simple cuboidal cells with microvilli so they have that brushed border in the descending loop of henle simple squamous epithelium the ascending loop of henle it can be simple cuboidal to columnar and the distal convoluted tubule collecting ducts simple cuboidal okay the juxta glomerular cells that we find in the afrin arteriole are modified muscle cells the macula densa is is a thickened part of the ascending limb henle out of the ascending limb of family or sometimes we talk about that as being part of the distal convoluted tubule then as i said the number of nephrons is constant from birth if they're injured you don't have a replacement and dysfunction is not evident until the function of the kidney declines by about 25 of normal because the other nephrons pick up the slack if you remove a kidney you it can cause enlargement of the remaining one until it can filter about 80 percent of the normal rate of the two kidneys the goals for this lecture are to draw and label the parts of nephron describe what the two types of nephrons are describe what is the jga and describe the location function the following types of cells potasite cells in the macula densa juxtaglomerular cells principal cells intercalated cells i forgot to talk about the mesengeal cells but these uh i'll talk about in an upcoming lecture these are involved in um these are found between the capillaries in the cells of the glomerulus and they help to regulate the glomerular filtration rate