 Hey everybody, Dr. O here. I'm just going to introduce the nephron, I'm not going to talk about what the proximal convoluted tubule does in this video, but I just want you to understand what they are. So the microscopic, your own production occurs in these microscopic nephrons. Like you see in the picture, it's been blown up so you can see it, but these are microscopic. There's 1.25 million of them in each kidney, which ends up being about 85 miles. There's about 85 miles of nephrons in your body, and these nephrons are going to be where we... We filter things out of the urine, we reabsorb things that we want to keep, we secrete things we have to get rid of, and we concentrate our urine. But the main thing I wanted to show you with this video is that there are two types of nephrons. Let me show you this image here. There are 85% of the nephrons are what are called cortical nephrons, and they're going to have short loops of Henley, that loop that travels down and back up. They're going to be short, so the huge majority of your nephrons are cortical nephrons. These nephrons are primarily going to be responsible for the reabsorption and secretion of materials. The second kind of nephron is called a juxtamedulary nephron, and the loop of Henley is much longer and it travels farther down into the cortex. So even though they're only 15% of your nephron, so they don't play a big role in absorption and secretion, but these long loop of Henley allow you to reabsorb a lot more water, which is why these juxtamedulary nephrons are responsible for making sure you make concentrated urine, and you're not losing any more urine than you have to. So that's very, very important. As far as how much flows through these nephrons, a healthy kidneys should be able to receive about 1200 milliliters of blood every minute. About 20%, 25% of your cardiac output goes to your kidneys, and all that fluid is going to be filtered through these nephrons. So you're going to filter 50 gallons of fluid a day out, and then you're going to reabsorb all the solutes you need and reabsorb all the water that you can or need to because of these nephrons. Just quickly again, cortical nephrons, most common, 85% of nephrons, they play a big role in absorption and secretion. Juxtamedulary nephrons, less common, only 15%, but because their loop of Henley is so long, they play a huge role in concentrating your urine. All right, that's a quick intro to the nephrons. We'll cover the parts of the nephron in the next video. I hope this helps. Have a wonderful day. Be blessed.