 Hey everybody, Dr. O here. Let's talk about the scrotum here primarily. So why are the testicles outside the body? That's a very common question I get. Why are they not protected? Well, I'll explain why they can't be physically protected in the way that other body parts are like your heart. But they are protected. They're primarily protected by pain, right? There are so many pain fibers that are so pain sensitive that people avoid damaging them. So pain in itself can be a protection. But let's go ahead and dive in. So here we see the skin covered sac, the scrotum, which is its job is to protect the testicles or cover and protect the testicles outside of the body. So why? Why is this location so important? Here's the key thing to remember, sperm production occurs most efficiently at a temperature that's between 2 and 4 degrees Celsius below our body temperature. I generally think about the number being about 2 degrees Fahrenheit. So if your testicles are inside the body, it's too warm and sperm production doesn't occur efficiently. I wish they were encased in bone and they were protected, but they can't. The price we have to pay for having the testicles be at the appropriate temperature, and I can't say why the temperature is appropriate, is having them outside the body. That's number one. Number two, we have to control where they are outside the body. And that's why the most important thing with the scrotum is these muscles. So first we see the dartose muscle. It's what gives the scrotum that core gait appearance, and it can contract or relax to help pull the scrotum together and up towards the body or let it drop away. Then they have the cremaster muscles. They're going to be like these big muscular nets that hold the testicles. So let's say you go outside or you're in a cold environment. When it's cold, the cremaster and dartose muscles are going to contract, pulling the testicles closer to your body to keep them warm, to keep the temperature of the testicles up. If it's warm, then these muscles are going to relax and the testicles are going to drop away from the body in order to keep the temperature stable. So the reason that the testicles are outside the body and in the scrotum instead of protected like your skull protects your brain is because of this temperature thing. The temperature of the testicles has to be around two degrees cooler than the rest of the body. But we have these muscles that then control how close to the testicles are to the body or how far away they are. So that's going to be the cremaster and dartose muscles, their primary jobs and why that's so important. But you can also see here on the right hand side, we have what's called the spermatic cord. We'll talk about this in the testicles in just a second. Because the spermatic cord is going to have the vast deference or ductus deference we covered in the last video, the actual tube carrying sperm into the body, but then we have the testicular arteries, veins and lymphatic vessels as well and nerves. So that the spermatic cord has to come from the abdominal pelvic cavity, from the peritoneal cavity into the scrotum. Let's talk about why. So we already said the testicles have to be on the outside, but about the seventh month of fetal development, the testicles are going to descend outside of the body. So when we all were a few cells and we all started to develop, we all had a basic female body plan and then the production of fetal testosterone leads to the conversion of boys to the male body plan. So the reason that our testicles start in the abdominal pelvic cavity and drop is because they started where the ovaries are and they descend into the scrotum. So this descent of the testicles into the scrotum occurs about the seventh month of development. If it doesn't occur, it's called crypt orchidism and if one of them doesn't potentially drop and several, you know, five to 15% depending on you ask of babies in different parts of the world have this issue where one or both testicles don't descend, that can lead to sterility, especially if both. If both testicles do not descend in the scrotum, they will not produce sperm functionally. Okay, the other big thing to note here is right at the top of this image, the inguinal canal. So the hole that's created as the testicles descend in the scrotum and the spermatic cord travels with it is running through the inguinal canal. Now it normally should be closed, but because of this weak spot created by the spermatic cord, men are more likely to develop inguinal hernias right at this location. So there's a weak spot. So like I used to, I've done hundreds or if not thousands of sports physicals and one of the things you do when you're doing a sports physical on a boy or a man is to look for these inguinal hernias and this would be when people think of with a sports physical where you turn your head and cough. So my job was to take my pinky finger behind the testicles in the scrotum and find the, or into the scrotum and find the end of this inguinal canal. And then you have the person cough to increase abdominal pressure. If something were to bump into my finger, that would mean that there's an inguinal hernia and abdominal pelvic contents are bumping into my finger. That's why you have them cough to increase abdominal pressure. The reason they turn their head and cough is so they don't cough on the top of your head. There's nothing significant about that. Okay. So that is the scrotum and the muscles that control where the scrotum sits. That's why it's important that the testicles are outside the body because they need that lower temperature. And here's this anatomical weak spot created by this permatic cord, which carries the nerves, blood vessels and lymphatics to and from the testicles. I hope this helps. Have a wonderful day. Be blessed.