Overview: Proximal Vs. Distal Nephron

by Carlo Raj, MD

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    00:00 In this section, we’ll take a look at transport mechanisms. Its overview is what we’ll take a look at first and just kind of give you a tease as to what happens in different parts of the nephrons at this point.

    00:12 I want you to dive into the glomerulus and take a lovely little bath in one’s urine.

    00:19 Proximal, what does that mean to you, PCT, proximal convoluted tubule? What you want to pay attention to in this picture is there are two nephrons here.

    00:32 Do not get accustomed to only one image, one graph. What I mean by that is it’s all about perspective.

    00:40 Here, you're looking at the glomerulus. Right beyond it, you hit the PCT. Then you go through the thin portion. The thin portion in your mind, you're thinking well, you’re creating what kind of urine? Hypertonic urine. How can you confirm then? Well, when you get to the medullary loop of Henle, then you know that you can have your urine osmolarity, urine osmolarity. Being above 300? Definitely.

    01:09 600, 900, potentially, potentially, up to 1200. Now clinically, when we walk through some important pathologies including things like diabetes insipidus, then the urine osmolarity and its measurement becomes really important for us. Right now, we're reabsorbing the water, aren't we, along with this? Obviously, there is going to be two-thirds of many of your electrolytes that is also being reabsorbed. The distal portion, well here, we’ll begin our discussion now looking at our thick ascending limb. Thick ascending limb, of course, having the most important symport known as your sodium-potassium two chloride. We’ll be spending time with this region at a later lecture, DCT, cortical collecting tubule. DCT has a thiazide-sensitive removing sodium, 25% or so, and then also your chloride, and also responsible for your PTH receptors reabsorbing your calcium. The cortical collecting tubule and medullary, we’ll group them together.

    02:20 As a whole, we'll call that the collecting duct. With the collecting duct, here we have, well, depending as to what kind of effect took place in the DCT which is known as your diluting segment, isn’t it? Because you’re moving your solute and you’re creating what kind of water? Free water versus obligated water. You've heard of such things in physio. You've heard of such references in nephrology. Free water will be completely free of solute creating diluted urine.

    02:55 Depending as to what kind of modification took place, well, whether or not there was ADH and such will make sense as to what kind of tonicity of the urine that you have by the time you travel through the distal tubule and the collecting duct. Nice, little overview here as to what you can expect.

    03:13 I've given you little tidbits of information so that you're not blindly going through here.

    03:17 Everything that we're going to do, you give it some type of medical piece of tag, clinical application, and you create a perspective as to what happens now.

    About the Lecture

    The lecture Overview: Proximal Vs. Distal Nephron by Carlo Raj, MD is from the course Diseases of the Nephron.

    Included Quiz Questions

    1. 300-1200 mOsm/kg
    2. 0-300 mOsm/kg
    3. 1000-1200 mOsm/kg
    4. 300-800 mOsm/kg
    5. 800-1200 mOsm/kg
    1. Only juxtamedullary nephrons have proximal convoluted tubules.
    2. Juxtamedullary nephrons have longer loops of Henle compared to cortical nephrons.
    3. Peritubular capillaries surround the tubules of both classes of nephrons.
    4. Juxtamedullary nephrons are responsible for development of osmotic gradients in the renal medulla.
    5. Bowman’s space of both juxtamedullary and cortical nephrons are always located in the cortex.

    Author of lecture Overview: Proximal Vs. Distal Nephron

     Carlo Raj, MD

    Carlo Raj, MD

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