Fenestration & Endothelial Transport

by Thad Wilson, PhD

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    00:01 Endothelial transport is much different than epithelial transport.

    00:08 It also though has tight junctions.

    00:12 The tight junctions though can be very tight such as in the blood-brain barrier when there’s no movement of fluid, or in capillaries they sometimes have fenestrations, pores, or sometimes even clefts that will allow things to travel through.

    00:33 So, endothelial transport is going to rely less on specific transporters than epithelial transport does.

    00:43 You’re going to utilize things like pressure and osmolality to move various solutes and solvents around.

    00:53 It is primarily a variable associated with the flux of the substance.

    01:00 So you will filter certain things, hydrostatic pressure is highly involved, and osmotic and oncotic pressures.

    01:10 Remember, osmotic pressures have to do with the ion differences and oncotic pressures have to do with protein differences to draw fluid.

    01:23 This is an example of how pressure can move fluid out of a capillary bed.

    01:30 The higher the amount of pressure, the more fluid travels through.

    01:36 Other examples determine about how much the fenestrations are in terms of their width.

    01:43 Some will allow more fluid to travel out and some will allow less.

    01:47 The other issue that we need to think about with endothelium versus epithelium is that we sometimes turn the membranes a little bit differently.

    01:58 The terminology used for the inside surface is the luminal surface rather than the apical membrane.

    02:07 In terms of the outside is termed the basal surface rather than the basolateral membrane.

    02:15 But if you keep those linked together, you’ll be better off and able to think about the differences between epithelial and endothelial surfaces.

    02:26 Let’s look at how fenestrations can be regulated because normally you think of a pore either being open or being closed, but you can modulate this in certain tissues.

    02:38 The lymphatic is a great example of this.

    02:42 So you can have some constriction and have the pores closed.

    02:47 And then, after constricting these, you can open them up.

    02:54 This then will allow fluid to transport between the lymphatic circulation.

    03:01 Then when you have smooth muscle constriction, you close them up.

    03:06 Good examples of how you can modulate these fenestrations.

    03:11 Now, many tissues you don’t have the modulatory ability because either they are open or closed, but you do have some regulation of fenestration widths.

    03:22 Let’s summarize now the different ways you’re going to move a solution, a substance, or a gas across the endothelial wall.

    03:35 The first thing you could do is use something called pinocytosis, which is the actual pinching off of a small vesicle that contains a solute and solvent.

    03:47 It moves from the luminal surface to the basal surface and then releases it out.

    03:55 Another way you could get fluid through is by fenestrations, either fluid travels through or sometimes solutes travel along with the fluid.

    04:07 The fenestration width will be dependent upon what molecules can make it through.

    04:12 Water will always be able to make it through, but sometimes larger substances like big proteins, maybe like albumin, have a harder time in moving through these fenestration slits so they get stuck on one side or the other.

    04:27 A primary variable is the pressure at which is in the hydrostatic, which is inside the vessel to push fluid through.

    04:39 And that helps with the bulk transport driven by the pressure change.

    04:46 You also have diffusion that is capable of moving a solute through these fenestration slits.

    04:53 So this is based upon a concentration gradient.

    04:57 The bigger the concentration gradient, the more solute is allowed to travel through.

    05:03 Other items, such as gases or other things that are very soluble might be able to make it through the endothelial cell all on its own, without a fenestration slit, without pinching off the particular portion of the membrane and having it travel through.

    05:21 These substances are usually more lipophilic in nature and therefore can travel through the membrane on their own.

    About the Lecture

    The lecture Fenestration & Endothelial Transport by Thad Wilson, PhD is from the course Membrane Physiology.

    Included Quiz Questions

    1. It relies on hydrostatic pressure to transport solutes across.
    2. It relies on specific transporters.
    3. It relies on vector transport.
    4. It relies on voltage differences between the two sides of the cell membrane.
    5. It has impermeable tight junctions throughout the body.
    1. Protein concentration
    2. Ion differences
    3. Ion-derived voltage differences
    4. Protein derived voltage differences between the two sides of the endothelium
    5. Types of ions
    1. Luminal surface
    2. Basal surface
    3. Apical membrane
    4. Basolateral membrane
    5. Luminal membrane
    1. Hydrostatic pressure
    2. Pinocytosis
    3. Osmosis
    4. Simple diffusion
    5. Passage through the cell membrane
    1. Arteriolar side of the capillary
    2. Venous side of the capillary
    3. Second third of the capillary
    4. Last part of the capillary
    5. Middle of the capillary
    1. They are open in the expansion phase.
    2. They are open in the compression phase.
    3. They are always open.
    4. They are open when the secondary lymph valves are open.
    5. They are closed when the secondary lymph valves are closed.

    Author of lecture Fenestration & Endothelial Transport

     Thad Wilson, PhD

    Thad Wilson, PhD

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    Dr. Wilson is awesome!
    By Mirela P. on 23. August 2022 for Fenestration & Endothelial Transport

    Thank you for this lecture. Very good explanation, excellent structure! Dr. Wilson, you are awesome!!!

    Like all Dr. Wilson's lectures
    By Wei Z. on 13. December 2017 for Fenestration & Endothelial Transport

    All Dr. Wilson's lectures are great. Good contents presented in a clear and interesting manner.