Reabsorption in the Distal Tubule

by Thad Wilson, PhD

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    Let's continue our reabsorption. Now, we are gonna talk about the distal tubule and the collecting ducts. For here, we need to think about the various segments of the nephron again. So remember, we start it off in Bowman's space or the glomerular capsule, we went into the proximal convoluted tubule, the proximal straight, then we went into the thin descending limb, around the hairpin turn, thin ascending limb, thick ascending limb and then into the distal convoluted tubule, to the cortical collecting ducts and then down to the medullary collecting ducts. Let's begin with calcium. Calcium is a divalent cation. It will travel across the apical membrane by itself meaning that it does not require cotransport. The transporter that is important for this process is a TRPV5 channel. This TRPV5 channel allows calcium across the apical membrane and calcium can't be in high concentration in the cytosol because it is cytotoxic. Therefore we need to bind it to something, and that substance is calbindin. So, calbindin mops up the free calcium within the cyctosol and then translocate it over towards the basolateral membrane. It can then be released from the calbindin and moved across the basolateral membrane by the calcium ATPase, or be exchanged with sodium. Either of these processes will get the calcium across the basolateral membrane into the interstitial space. What governs the control of how much calcium gets moved across the apical membrane, mainly involves parathyroid hormone. So parathyroid hormone, when it's bound, allows for both the up-regulation of adenylyl cyclase increasing also phospholipase C activity. These involve a protein cascade that phosphorolizes these TRPV5 channels, allowing for more calcium to move across the apical membrane, so parathyroid hormone up-regulates the calcium transport. Another divalent cation magnesium also gets transported across the apical membrane. This...

    About the Lecture

    The lecture Reabsorption in the Distal Tubule by Thad Wilson, PhD is from the course Renal Physiology.

    Included Quiz Questions

    1. TRPV5
    2. TRPM6
    3. Calcium ATPase
    4. Sodium-calcium exchanger

    Author of lecture Reabsorption in the Distal Tubule

     Thad Wilson, PhD

    Thad Wilson, PhD

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