Nephron Types

Filtration

I love coffee.  I am not awake enough in the morning. I cannot pour scalding hot waterThe universal solvent essential for life. over grinds like this person here.  This little coffee maker, and all coffee makers are basically filtrationThe process by which fluid moves out of capillaries into surrounding tissues due to hydrostatic pres membranes.  Coffee grinds and water enter into the filtration membrane. Only the water and the lovely essence of coffee leave into my coffee cup.  The same thing is happening in the kidney. 

Whole blood enters the kidney to curve around a medullary pyramid. It flows into an arcuate arteryArteries that curve over the base of the renal pyramids, supplying blood to the kidney cortex. and then perfuses into a cortical radiate artery. Here, it branches off into an afferent arterioleThe small artery that carries blood into the glomerulus of the nephron. that feeds a nephronThe functional unit of the kidney that filters blood and produces urine. for filtering.  At that point, there are two filtration events that separate waste products from the whole blood.  The filtered whole blood returns to circulation via a venule, just like any other capillary bed.  The waste products leave via urineThe liquid waste excreted by the kidneys.. They weep from this renal papillaThe tip of a renal pyramid where urine drains into the minor calyx. here into a minor calyxA small cavity in the kidney where urine from a renal pyramid collects before moving to the major ca, then into a major calyxA large cavity in the kidney where urine from the minor calyces collects before entering the renal p, and the renal basin. From there, they continue to other urinary organs until excreted from the body.

Nephron Parts

Let’s try to put all these parts together and in perspective.  This is one medullary pyramid with blood vessels, nephrons, and a collecting ductA duct in the nephron that collects urine from multiple nephrons and adjusts water reabsorption..  Blood comes in via this interlobar arteryArteries that run between the renal pyramids and supply blood to the kidney.. It then curves around and hugs the border between the cortex and the medullary pyramid.  The arcuate artery and vein are on that border of the cortex and the medullary pyramid. You can use them as landmarks in pictures.  I’ve placed a few nephrons coming off one cortical radiate artery.  Please understand that there are numerous nephrons coming off of one cortical radiate artery.  You have many cortical radiate arteris in one pyramid and you have a few pyramids, right?  So, you have a lot of nephrons.  A lot. 

Right now, I want you to focus on two parts of a nephron. These are the renal corpuscleThe structure in the nephron that consists of the glomerulus and Bowman’s capsule, where filtration and the renal tubule.  The renal corpuscle are these knots of a capillary here, surrounded by this little cup of the nephron.  These renal corpuscles are all in the cortex.  On this microscopic picture of the kidney, we can see all the renal corpuscles in the cortex.  Deep to the cortex is thee medullary pyramid, which is made up of the tubule parts of the nephrons. 

Some nephrons have tubules that dip very deeply into the medullary pyramid

Nephron Types

textA nephron consists of the renal corpuscle and a renal tubule, both discussed in more detail in other mini-lectures.  A nephron contains filtrateThe fluid that is filtered from the blood into the nephron and will eventually become urine. not urine.  Filtrate is still in the process of exchanging with a capillary bed. No matter what type of nephron we talk about, the renal corpuscles are always in the cortex. The renal corpuscles are basically serous membranesThin tissues that line body cavities and secrete fluid. surrounding a fenestrated capillaryCapillaries with pores (fenestrations) that allow rapid exchange of fluids and small solutes (found called the glomerulusA network of capillaries in the nephron where blood filtration occurs..  In both types of nephrons pictured here, the renal tubule drains the capsular spaceThe space between the glomerular capsule and the glomerulus where filtrate collects. of the renal corpuscle. 

Urine then travels through these nephrons to connect to a collecting duct that drains many nephrons.  This collecting duct, along with others, weeps urine from the renal papilla of the medullary pyramid. 

Cortical nephrons do not dip deepAway from the surface of the body. into the medullary pyramids, giving them the name cortical.  Juxtamedullary nephrons have this component that dips deep into the medulla.  These are the nephrons that save your life in times of severe dehydrationA condition in which fluid loss exceeds intake, leading to a decrease in total body water..