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Transport of sperm via erection and ejaculation

Created by Vishal Punwani.

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  • primosaur ultimate style avatar for user Simchak
    when the sperm enters the female why dosn't the female immune system kill the sperm cells
    (30 votes)
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    • duskpin ultimate style avatar for user Medical  Mermaid
      Interesting question!

      I looked up some information on this and found that usually the female immune system will be inhibited by immunosuppresive components found in the seminal plasma, which is part of semen. This protects the sperm from being attacked by inhibiting most components of the immune system, such as complement.

      However, these seminal components can be picked up by macrophages/dendritic cells and can lead to an inflammatory response. In most cases, though, this response does not last long and the sperm is able to escape and fertilize an egg if present.
      I am sure there are cases where the immune system will fully attack the sperm and result in an all-out immune response if recognition happens quick enough, but this is likely very rare.

      Hope that helps! :)
      (30 votes)
  • mr pink red style avatar for user Austin Clark
    I thought that nor epinephrine stimulated the sympathetic (fight or flight) system. Why does the sympathetic system keep the penis flaccid then?
    (11 votes)
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    • orange juice squid orange style avatar for user lafrelke
      You can kind of think of it this way:
      So the Sympathetic nervous system (SNS) uses Epinephrine and Norepinephrine (NE) to shunt blood to places where its most needed (so lots of vasoconstriction going on). At times of great stress, you want blood in your skeletal muscle to be ready to move, and your blood pressure, breathing and heart rate to increase, etc. Your body isn't concerned with extra blood in your penis because its not essential for staying alive at that moment. That's why NE is used to inhibit an erection. On the other hand, Nitric Oxide (NO) is used via the Parasympathetic Nervous System to create an erection. The end of the video does get a little confusing when he mentions that NE is used for ejaculation, but remember that the SNS = vasoconstriction! So the SNS will send that signal of NE close to ejaculation to constrict those vessels to prepare to expel the semen out.
      I hope that helps explain it from another perspective :)
      (33 votes)
  • piceratops ultimate style avatar for user Oshien
    So, just to clarify the concept, would something like Viagra contain nitric oxide to cause erection?
    (9 votes)
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  • leaf green style avatar for user Richa Kumari
    So lets say there is a pair of male twins named Miles and Joe. And a pair of female twins called Margo and Kate. So they grow up, and Mark marries Margo and Joe marries Kate. So if Mark and Margo have a girl would they be identical to Joe and Kate’s girl?
    (7 votes)
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    • aqualine ultimate style avatar for user michelle
      Technically the girls would be cousins. Their fathers as a pair and mothers as a pair share identical DNA though, so genetic the girls would share the same % of DNA as sisters would.

      They would however never be identical. Just like children born to one set of parents (who have the same DNA as them selfs) are never identical unless they are identical twins. Think groups of siblings they can be a lot alike, but they will never be exactly the same.
      (12 votes)
  • male robot johnny style avatar for user ranaajrawat
    Could you please clarify whether it is Nitrus Oxide from the Parasympathetic nervous system or Norepinephrine from the Sympathetic nervous system that is released to cause an erection? The answers below are not clear and do not clearly state which stimulating hormones are responsible and from what part of the nervous system. It would be great if Vishal Purwani himself could actually clarify this question thoroughly.
    (4 votes)
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    • mr pink red style avatar for user Johnatan
      NE is responsible for constricting vessels.
      1) by contricting the BLOODvessels it hinders blood from entering these vessels, hence the flacid state.
      2) When there is an erection and it's time for the ejaculation, NE is produced --> it once again constricts vessels (this time the vas deferens, the different glands and a few muscles) to shoot the semen out --> ejaculation.

      You are correct in saying that NO causes the erection (NO causes vessels to dilate, one of the reasons it is used in e.g. agina pectoris) but to actually cause ejaculation. the vessels need to constrict. Thats where NE comes in play.
      (18 votes)
  • leaf green style avatar for user Richa Kumari
    Where does the blood come from when a female gets her period?
    (4 votes)
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  • leafers ultimate style avatar for user Sneha Rajendran
    Around , Vishal says that the sympathetic nervous system is responsible for stimulating the various reproductive structures by releasing norepinephrine, but didn't we learn that norepinephrine is responsible for keeping the penis flaccid, whereas NO from the parasympathetic nervous system is responsible for the aroused state of an erection?
    (5 votes)
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    • blobby green style avatar for user jassimranb
      @Sneha, what you said is correct. However, the SNS/PNS play different roles in ERECTION and EJACULATION. In order to cause an ERECTION, the PNS is responsible. So when NO is released from a Parasympathetic neuron onto the arterioles and vessels of the penis, you get vasodilation and engorgement which results in an erection. Similarly, when NE is released from a sympathetic post neuron, you get vasoconstriction of the spinchters around the arteries decreasing blood flow to the penis and resulting in a flaccid/non-erect penis. Here's where things can get confusing. For EJACULATION, the SNS (sympathetic nervous system) is responsible for emission of sperm and not the PNS. So when NE is released from the SNS, you get contraction of the muscles around the vas deferens, etc, while NO from the PNS will inhibit this.
      (3 votes)
  • blobby green style avatar for user Soumaneel Konar
    isn't an orgasm and an erection basically the same thing?
    (3 votes)
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    • aqualine seedling style avatar for user SpinosaurusRex
      An orgasm is a climax of sexual excitement, characterized by feelings of pleasure centered in the genitals and (in men) experienced as an accompaniment to ejaculation. An erection is a physiological phenomenon in which the penis becomes firmer, engorged and enlarged. I hope this helps!
      (4 votes)
  • winston baby style avatar for user Jonathan
    Does urine and semen come out of the same "hole" in the penis or different?
    (3 votes)
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  • blobby green style avatar for user sourish.rathi
    From to 10, the teacher explains that NE is needed for contraction of things to release sperm which I get but how are you able to keep a erection during ejaculation if NE is present since NE also causes Arteries to constrict ?
    (4 votes)
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Video transcript

- [Voiceover] We're gonna talk about the transport of sperm. I just mean how it gets transported out of the male reproductive tract, and into the female reproductive tract, where it can hopefully fertilize an egg, and result in a pregnancy. To do this, we're gonna first look at a sagittal view of the male reproductive system. I'll just show you what a sagittal view is. Basically, if we were to look at this blue guy over here, and if we said this is his left side and this is his right side, we would make a cut down his midline, like so, and we would sort of cut away everything on one of the sides. In this case, we're gonna cut away everything on his left side. Then we're gonna look, here's an eye here, we're gonna look at his right side of his cut surface on the right side here. When we do that, we find that we see something like that. This is what we call a sagittal view. Just to remind you, this would be his right leg. The bottom line is that sperm needs to be transported out of our bodies. We do that, in males, via a two-step process. The first step is called erection. An erection is basically when the penis goes from having very little blood within its core, a state called flaccidity, and I'll write that out, to a state where it's filled with blood, and we call that an erection, when it's filled with blood. The second step in our two-step process is called ejaculation. Ejaculation is basically the expulsion of sperm out of the reproductive tract. Let's go into the mechanisms of how this happens. Before we talk about how an erection happens, let's briefly discuss why an erection happens. Let's just clear off some of this stuff here. Believe it or not, an erection actually starts in your brain. Here we have a brain. When you're physically or mentally sexually stimulated by sights or sounds, or smells, or even thoughts, your brain sends signals to your penis, and it can cause an erection. It does that by sending signals to the blood vessels in the penis, and those signals cause those blood vessels to open up, and allow blood into the penis. So it's this filling of the penis with blood which results in an erection. We'll expand on that in a moment. First, we'll talk about some regional anatomy of the penis. The base of the penis, here, that's called the base, or the root. This area here, is known as the body. This area here is called the head, or, the glans. What we'll do next is look at a more detailed view of the anatomy of the inside of the penis. The best way to visualize that is if we did something called a transverse view. Transverse view is basically a cut that goes this way across the penis. We'll put our little eye here and we'll look up at this cut surface here. When we do that, you'll find that it looks something like this. Again, this is called a transverse view. Just to orient you, this transverse view is of two different penises, side by side. The one on the left is a flaccid penis, It's not filled with blood. You can tell because it's got a lot more visible blue veins, which you don't see in erection. Over on the right we have an engorged, erect penis. You can see the veins have been compressed to the sides. So that one's erect. I'll explain all that in a minute. In this view, it's quite easy to see the three cylindrical vascular compartments that get filled with blood during an erection. These vascular compartments, or chambers, are called the corpora cavernosae, and you have two of those, one on each side here, and the corpus spongiosum, which you have down here. By the way, this is the bottom of the penis, the underside, and this is the top of the penis. Also, this structure here in the center, this tube, is the urethra. Blood normally flows into these vascular chambers via both dorsal arteries and cavernosal arteries. Here's a dorsal artery, and here's a cavernosal artery here. When the penis is filling with blood, blood actually leaks out of these cavernosal arteries and into these purple circles that you see called lacunar spaces. These lacuner spaces run the entire length of these vascular chambers, so there are a lot of spaces there for blood to leak out into. That's what causes the penis to get engorged. Blood is normally drained out of these chambers by veins with the same name. So, dorsal veins and cavernous veins. But under normal conditions, i.e, when you do not have an erection, the blood flow into the penis equals the blood flow out of the penis, so there's no actual net change in erection status. Let's just label these here. This one on the left here is flaccid. This one over here on the right is erect. The reason why the one on the left is flaccid, is because it has arterials that are constricted. These red arterials, when they're constricted, they don't actually allow much blood into the penis. Over here on the right, the erect penis is sexually excited. So you can see visually that the arterials on this side are much more dilated, that is, they let in a lot more blood, thus can cause an erection. What's keeping this penis flaccid? What is keeping these arterials from opening up? Well, It turns out that it has to do with your brain. Normally, little chemical signals from the brain, called norepinephrine, cause the arterials to stay constricted. We can see a neuron here, leaving the spinal cord, and sending a signal to the arterial, to keep it small. By the way, a neuron is a cell of the nervous system responsible for sending messages. Over on the other side, on the erect side, there's another neuron, actually a different type of neuron, that actually sends a different signal to the arterials, and results in them opening up and allowing blood into the penis. The signal that this neuron is sending, it's called norepinephrine. What norepinephrine is, it's a little chemical signal from a division of the nervous system called the sympathetic nervous sytem, or the SNS. That'll become important later on. The signal that this neuron is sending is NO, or nitric oxide. This neuron is actually from a division of the nervous system called the parasympathetic nervous system, or the PSNS. As these arterials dilate and allow lots of blood into these sinuses here, they actually fill so much that they push outward against the edges and compress the veinous drainage of the penis. That basically prohibits flaccidity, thus, it results in an erection. Just to be complete, an erection is reversed when the inflow of blood is stopped, and the veins are then allowed to open up and allow the blood back out of the sinuses. Then you go flaccid again. That might happen when the nitric oxide from those green parasympathetic neurons stop being produced. One last thing before we move on. You might be thinking, "Vish, you told us that "these arterials dilate and allow blood "into the vascular chambers." Well, what's to stop the penis from filling up indefinitely? We actually have, if you look at these yellow circles here, the three of them, they surround our vascular chambers and they prevent them from over-expanding. These wrappings are called the tunica albuginea, and they're just a supportive structural tissue. Let's just clear off some of this stuff and move on to the second phase, which is ejaculation. We'll start with a definition. What is ejaculation? Ejaculation is the discharge of semen from the penis. You normally discharge about three to five milliliters per ejaculation. In that three to five milliliters, you actually pack about 300 million sperm. An ejaculation happens when, basically, a critical level of sexual excitement has been reached. Sexual stimulation actually causes nerves in the penis to send chemical signals to the spinal cord and brain. The brain and the spinal cord send messages back to the penis to cause ejaculation. There's two phases to ejaculation in itself. We'll start with our erect penis because now we're sexually excited. Remember, now that we're erect, we've filled these vascular chambers here with blood. The first part is sympathetic nervous system stimulated. Remember, in red we drew these neurons, the sympathetic nervous system neurons. They're gonna release norephinephrine, which I'll abbreviate as NE, onto all of the following structures: the epididymis, the vas deferens, the accessory glands, and the ejaculatory duct, which is here sitting inside the prostate gland. To respond to that norepinephrine, these structures that I mentioned here, actually contract and emit semen into the beginning part of the urethra. In the second phase, the semen is now sitting here at the beginning part of the urethra. The smooth muscle of the urethra itself, all along its length, and this muscle at the base of the penis called the bulbospongiosum muscle, they then contract and expel the semen from the urethra out of the tip of the urethra, called the meatus. That's basically the process of ejaculation. All of these muscular contractions are associated with a feeling of extreme pleasure. You also get full body physiological changes. For example, you see a decrease in heart rate and blood pressure after ejaculation. In some, the process of ejaculation and the whole body physiological changes, is called an orgasm.