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Hindgut – Autonomic Nerves of Abdominopelvic Organs

by James Pickering, PhD
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    00:01 The hindgut, exactly the same but it's just work through the para-sympathetic and sympathetic input to this hindgut, really the large intestine.

    00:13 Its going to be from the inferior mesenteric plexus distributed via those periarterial branches around the inferior mesenteric artery because that's the perfect way to distribute them to their organs.

    00:28 Now, for the para-sympathetic, this isn't via the vagus nerve.

    00:34 The vagus nerve only does foregut and midgut. Now we are looking at our sacral outflow.

    00:40 Remember parasympathetic was craniosacral. We are now going to our sacral outflow and specifically S2, S3, S4.

    00:49 Those spinal cord segments are giving rise to pelvic splanchnic nerve.

    00:55 Parasympathetic. Previously we spoke about greater, lesser, least splanchinc nerves, they were sympathetic.

    01:03 This time it's the pelvic splanchnic nerve and its a parasympathetic.

    01:08 So these has an input into the inferior mesenteric plexus and we can actually see that the pelvic splanchnic nerves can follow the arteries back up into the inferior mesenteric plexus. They can do in that way. Or they can actually run up what's called the hypogalstric plexus to the inferior mesenteric plexus and do it that way. We will explore the hypogastric plexus in a moment.

    01:40 The sympathetic input to the inferior mesenteric plexus is going to be via lumbar splanchnic nerves.

    01:47 And these lumbar splanchnic nerves come from the lumbar portion of the sympathetic chain. Come from the lumbar region and they pass through L1, L2, L3.

    01:58 So pre-ganglionic fibers from L1-3 pass through the sympathetic chain and go towards the inferior mesenteric ganglia where they then synapse, post-ganglionic fibers to run in the periarterial branches that go and supply the hindgut.

    02:18 So hopefully that's made the autonomic nerve supply to the foregut, midgut and hindgut slightly more straight forward.

    02:27 If you remember the arterial supply to it, then it will be via the corresponding plexus that these parasympathetic and sympathetic fibers gets to their destination.

    02:39 Okay, let's have a look at the autonomic innervation for some specific organs within the pelvis and let's starts with the bladder and the sphincters that surrounds the urethra.

    02:53 Now here we can see the bladder, positioned directly behind the pubic symphysis.

    02:58 And then in the male we can see the postrate and we have an internal urethral sphincter and we have an external urethral sphincter. And in the female we don't really have a very clear internal urethral sphincter. It's not very well identified. But you have an external urethral sphincter.

    03:18 Now the parasympathetic input to the bladder is going via these pelvic splanchnic nerves via the left and right inferior hypogastric plexuses. Now pelvic splanchnic nerves leave from S2, S3, S4 and they pass out of the sacrum and they run to the branches of the internal iliac artery.

    03:46 And around the branches of internal iliac artery do we have the inferior hypogastric plexus.

    03:53 The inferior hypogastric plexus associated with the internal iliac artery is going to receive pelvic splanchnic nerves from the S2, 3, 4.

    04:06 These are parasympathetic. So they are going to contract the detrusor muscle. This is going force micturition to occur.

    04:15 For that to happen at the same time as contracting the detrusor muscle they relax or they inhibit the internal urethral sphincter.

    04:25 This allows urine to pass through.

    04:29 Sympathetic is going to come from T12-L2 region.

    04:35 So that's going to be via the lower, least splanchinc nerves. The greater, lesser, least, the lower one of these three.

    04:44 and some lumbar splanchnic nerves. And they all pass through the superior mesenteric plexus.

    04:50 That will then follow the aorta into the pelvis and it does this by running down to the bifurcation of the aorta and there we have the superior hypogastric plexus.

    05:05 The superior hypogastric plexus then follows the common iliac arteries as hypogastric nerves.

    05:13 And these hypogastric nerves then blend with the inferior hypogastric plexus.

    05:20 So this inferior hypogastric plexus now has parasympathetic from pelvic splanchnic and it has sympathetic from about T12-L2.

    05:29 This is going to do the opposite of the parasympathetic. So it's actually going to relax the detrusor muscle and allows it to fill with urine and its going to contact the internal sphincter.

    05:42 So we have parasympathetic that's going to force micturition to occur and you got sympathetic that's going to prevent it.

    05:50 However, this is in unconscious nervous system. We are not control of this.

    05:58 Except as adults, we don't just spontaneously micturate. We don't just spontaneously urinate.

    06:07 We have a level of conscious control and that is due to the contribution of the pudendal nerve.

    06:15 That can control the external urethral sphincter.

    06:21 So, the somatic contribution.

    06:24 If you have the urge to go to the toilet then you will somatically, consciously contract your external urethral sphincter.

    06:33 So when the parasympathetic is pushing the urine down you recognize this urge to go to the toilet and you constrict, you contract your external urethral sphincter.

    06:45 The ability to relax and control that is down to the pudendal nerve and only when you are in a suitable environment, when you are at the toilet, can you then control the external urethral sphincter and you can go to the toilet.


    About the Lecture

    The lecture Hindgut – Autonomic Nerves of Abdominopelvic Organs by James Pickering, PhD is from the course Pelvis.


    Included Quiz Questions

    1. Thoracic and lumbar only
    2. Thoracic and cervical only
    3. Thoracic and sacral only
    4. Thoracic and coccygeal only
    1. Lumbar
    2. Greater
    3. Lesser
    4. Least
    1. Inferior hypogastric
    2. Celiac
    3. Superior mesenteric
    4. Inferior mesenteric
    5. Pelvic splanchnic
    1. Contraction of external urethral sphincter
    2. Contract external anal sphincter
    3. Contract internal anal sphincter
    4. Contract internal urethral sphincter
    5. Ejaculation

    Author of lecture Hindgut – Autonomic Nerves of Abdominopelvic Organs

     James Pickering, PhD

    James Pickering, PhD


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