Movement of Large Molecules Across Membranes: Transcytosis

by Richard Mitchell, MD, PhD

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    00:01 Finally, a big concept, and then I think we will finish for this particular topic, is transcytosis.

    00:08 We're gonna move big things all the way across cells.

    00:12 So, what's shown here are two endothelial cells, and they're held together at their tight junction.

    00:18 And that forms a pretty good barrier.

    00:20 There are lots of blue balls outside that we might wanna get across into the other side of the endothelium. How do we do that? We could try to do it by a kind of, piecemeal endocytosis where we have a little bit of cell drinking, and then it internalizes, and then it moves across, and it dumps its contents into the other side of the endothelial cell.

    00:47 Conversely, what we can do is fuse endosomes and bake one big, gigantic pore.

    00:53 And it turns out, transcytosis, moving across a cell like this, happens both ways, but the most efficient way to get things across very quickly in large amounts is fusing the endosomes to make these pores.

    01:06 It plays a role in placental transport. So, babies? Very metabolically active. You wanna get as much across as you possibly can.

    01:13 Mom's circulation allows a great delivery of nutrition, but we have to get it across the baby's endothelial cells to get it into their bloodstream, and that happens by transcytosis.

    01:26 The blood-brain barrier transport.

    01:28 Normally, we have a very tight barrier, but sometimes, we wanna move things at higher volumes, and we will use this progressive endocytosis and/or fused endosomes to accomplish that.

    01:40 Thyroid epithelium will transport its thyroxin content out in exactly the same way.

    01:47 Certain infections will take advantage of this transcytosis pathway to get across barriers.

    01:53 And vascular permeability in tumors.

    01:55 Tumors are incredibly edematous.

    01:59 They're very, very leaky, and it's because those tumors drive this process quite efficiently.

    02:04 So, with that, we've actually kind of looked at getting things across membranes.

    02:09 Membranes are great barriers, but now we have to move things in and out across them. Enjoy.

    About the Lecture

    The lecture Movement of Large Molecules Across Membranes: Transcytosis by Richard Mitchell, MD, PhD is from the course Cellular Housekeeping Functions.

    Included Quiz Questions

    1. Its efficiency is increased by the fusion of the endosomes.
    2. It plays a defensive role against the spread of cancer cells.
    3. It involves breaking down and/or recycling the content of the endosome.
    4. The parathyroid gland uses this method to secrete its hormone into the circulation.
    5. It transports specific molecules directly into the nucleus.

    Author of lecture Movement of Large Molecules Across Membranes: Transcytosis

     Richard Mitchell, MD, PhD

    Richard Mitchell, MD, PhD

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