Membranes and Diaphragm

Greetings, my name is Gil Hadley, and I'd like to thank you for joining us today. And thank you for your interest in the Integral Anatomy Series. I intend to reveal and explore with you in this volume the layers of the human form which follow and build on our discoveries in volume 1, Skin and Superficial Fascia, and volume 2, Deep Fascia and Muscle. The human form is an integrated whole. There are no parts to the living form. Parts are merely the renderings of the inquiring mind and artifacts of the anatomist scalpel which reduce the form to its bare bones and the quest for understanding what lay beneath the skin.

My ultimate goal is to create a deeper, felt and lived experience of the whole, more so than to measure the parts. As we sharpen our perception and appreciation of the details of whole body layers, continuities of texture, and the repeating patterns of our form, we increase our range of motion and maximize the potential of our human experience. We take a moment now to express our gratitude to the donors and their families who make study at this level possible. The relentless stream of abundance which blesses our creative endeavors here waits only for our readiness to step into it and receive what is prepared for us. One form follows upon another, and there is truly nothing to fear in what lies ahead or in what has been left behind.

In Volume 1 of the Integral Anatomy series, I introduced the onion tree as a way of modeling the textural continuities of the human body, which you encounter as you drop in layer by layer. I suggested the body could be understood as a series of thin, fibrous covering layers and thicker, fluffy layers, all related and interpenetrated by tree-like neurovascular branchings. So the skin would be the relatively thin, outermost covering layer, overlying the relatively fluffy superficial fascia, which itself overlies the thin, fibrous deep fascia, which in turn covers and invests the relatively fluffy muscle layer. Superficial fascia and muscle are shaping layers of the body, the mass of which can change considerably over a lifetime. These thicker layers can grow and diminish in thickness substantially, so that any given person's overall shape is defined by them more or less.

In the membranous wrappings of the organs and central nervous tissues, and in these viscera themselves, we have yet another reiteration of the pattern of thin covering layer and a relatively thick covered layer. The membranes are thin, the organs relatively thick or fluffy, and greatly changeable in dimension over time. Of course, every layer actually consists of multiple layers at a cellular level, and here this is so even at a gross level. The multiple wrappings of our organs and central nervous tissues share common textures and patterns and define several important potential spaces within our form. These fibrous and membranous layers of the cranial and visceral spaces have earned their very own volume in this series due to their relative complexity as a layer, and due to the fact that they have gotten so little clear attention otherwise.

It is very difficult to figure out these truly bag-like balloon-like layers from book descriptions and still imagery, and even in the dissection lab they are easy enough to miss in the pursuit of structures whose fame surpasses them. Yet these tissues are incredibly important to our experience of overall health, and they are easily affected by our every movement and touch. I present them here as an invitation to integrate them into your general understanding and vision of the whole human body and your internal experience of yourself. Let's introduce the fibrous and membranous layers of the visceral spaces with a diagram. Now, I use the word visceral generally to even include the brain.

The word viscus is from the Latin. It means a large organ. So I speak for simplicity generally of the viscera and include the central nervous system when I do so. Embryologically it's a little different, but in terms of the basic anatomical schema it's very similar, and that's why I diagram it in this way. So far we've explored the layers of the skin, then the superficial fascia on volume one, the deep fascia and dropping in deeper the muscle on volume two. At the end of that volume we encountered bony layer as well as the fibrous coverings of the viscera themselves.

Now it's our turn to explore those, and because they're slightly more complicated in their layering, I've decided to diagram it here for you to make understanding more simply. So let's look at this black layer here. The black layer will represent that first fibrous layer of fascia that one encounters. It's like a balloon. One encounters sort of a fibrous, literally just like a balloon. We take a balloon here and we can imagine as we're dropping in skin, superficial fascia, deep fascia, muscle, and then we saw, for instance, the posterior rectus sheath, that fibrous fascia.

Or in the chest area we have the endothoracic fascia and the cranium. We have the dura, or surrounding the heart, the fibrous pericardium. Now immediately deep to that, it's like balloons within balloons. So immediately deep to the fibrous layer, whatever it's called in whichever visceral space, we have here, you see, immediately adhering, stuck to, literally stuck to the fibrous layer, we have a serous membrane. Now the serous membrane has slightly different anatomical and physiological properties relative to the fibrous membrane.

And again, it will have a different name depending upon which visceral space we're in. But for now, let's just get the lay of the land. The idea that there are these one, two, three fascial and membranous layers surrounding each of our visceral spaces. So we have the fibrous layer, then the membranous layer. Now what's interesting about the membranous layer is it sort of double backs upon itself.

So it's like if you had a balloon, you push your fist into it. You could imagine that then there would be sort of two balloon shapes. So the outer balloon would be the outer layer of the serous membrane. And then this inner layer, I call it, well, the inner serous membrane or the skin of the organ. When you're doing dissection, you cut deeply into the body and you encounter the organs, whether it's the brain or the heart or the lungs or the abdominal viscera, the abdominal organs.

Now when you see those organs, what you're actually seeing is their covering layer. And their covering layer is the doubling back of the serous membrane. So we see the organ layer here in blue. And we'll call the inner serous membrane the skin of the organ. It doesn't matter which organ, the skin of the organ.

And the skin of the organ immediately adheres to the organ. But the organ itself, with its skin, does not adhere to the outer serous membrane. It's actually a slick sliding surface, so we'll let this little white area here represent the place where the serous fluids lie. And which creates a sliding surface between these two serous layers so that the organs can move happily between themselves. So we have here the outer layer.

The outer serous layer is adhered to the fibrous layer. And then we have a sliding surface between the two serous layers, the outer and the inner. Now the outer layer, well you can see how it sort of hugs the perimeter or hugs the wall. So it's like the wall layer we'll call it. In Latin we use the word parietal to reference the wall layer.

So this layer could be the parietal pericardium or the parietal peritoneum or the parietal pleura, meaning the outer layer or the wall layer of the serous membrane. And then this layer here we would call the visceral layer because it adheres to the viscous, the organ. It adheres to the organ. So this visceral layer, this could be the visceral peritoneum in the belly or the visceral pericardium, that surface of the heart, the skin of the heart, or the visceral pleura, the skin of the lung. And in the case of the brain we have the pia.

Now it's one thing to demonstrate and grasp the idea of the fascial and membranous layers that surround the viscera on the whiteboard. And it's another altogether to demonstrate them on the cadaver form. Following the careful dropping down through the layers, I decided to remove as a unit the bony ribbasket and shoulder girdle to expose as much of the sacking around the organs as possible. In doing so, I had to work through some of the fibrous inner lining of the thorax, the endothoracic fascia. Here, focusing our attention on the space between the 11th and 12th ribs from the back, I reflect the outer layer of muscle from between the ribs, the intercostal muscle.

Deep to that we see the very fibrous layer of the endothoracic fascia. The endothoracic fascia invests and coats all of the ribs and the muscle between the ribs from the inside. Just as the fibrous deep fascia coats the outside of the ribcage. Coming from the outside into the body then, the endothoracic fascia is that first fibrous fascia layer inside the thorax which surrounds the contents of the thorax and contains them within itself. So this fibrous inner lining of the thorax is not an independent structure.

It invests the inner layer of the intercostal muscles here. This orange layer is invested within it. So we encounter the endothoracic fascia. We've also encountered the inner layer of the intercostal muscles. Immediately deep to this fibrous endothoracic fascia, we encounter the parietal layer of the pleura, the outermost serous membrane of the thorax within which the lungs enjoy their motion.

So this is parietal pleura and if we really get fancy, because we're local to the ribs, we call it the costal pleura. So I'm going to cut away this layer of pleura that we've identified now. And when I do so, I'm dropping into thoracic space. Now, of course, I'm just cutting a little strip out of the pleura. The pleura is a balloon that coats the entire space there.

So we can see the pleura here. It's tough. It's not tough like the endothoracic fascia in the sense that it's not filled with strapping tape. At the same time, it has a definite integrity. If you punctured it with a needle, you'd feel a little pop as you went through it.

It's a durable bag because you breathe 20,000 times a day. And this thing is going with the flow of that breath. Here, though, we look inside and what do we see? You can say, hey, that doesn't look like a lung. Well, it's not a lung.

Any more than when we look over here, we see a lung. Instead, we see the diaphragm. But the diaphragm is covered with pleura as well. Remember, the pleura is folding its way and coating every surface inside the thorac. So this is pleura here.

And I can't pass my finger through from the 12th rib into the abdominal space or vice versa. See? I get stuck. I can't go through. So is this like a balloon that's stuck to the ribs or is it in between each rib? Do you know what I'm saying?

The balloon inflates. If you had a Mr. Bones model and you stuck a balloon in it and go... and you blew it up from the inside, there would be no place that the pleura doesn't cover. The balloon would completely fill the thorax. So, yes, if I stroke here on the inside margin of the rib, I'm touching the pleura.

If I stroke here, I'm touching the pleura. And when I come to the 12th rib, I get a barrier. I have to turn and it doubles back on itself. I'm coating the outside coating of the rib cage here, coating that with pleura. And then I come down to the 12th rib and it doubles back on itself.

It turns back up and then covers the diaphragm. It goes this way and then, whoa, it comes back this way. From this angle, we can see the parietal pleura backlit where it doubles back at the 12th rib. Structural distortion in the relative position here will consequently have a direct impact in the shape of the thoracic space and the dynamics of breathing. The parietal pleura, because that wall is a complicated one as many surfaces, we divide those surfaces geographically to help indicate exactly which area of the parietal pleura that we're talking about.

So these are the four areas, the costal pleura, the diaphragmatic pleura, the mediastinal pleura, and the pleura of the cupola. So those would be the four regions. The cupola would be the peak or dome of the thorax here, like the dome of a church, the cupola of St. Peter's Cathedral. Here we have the cupola of our thorax. So the pleura of the cupola would indicate this region within our body.

Then the mediastinal pleura, well, all of these structures within the middle, which aren't lung, here's lung, here's lung, and within we have the heart and the aorta coming from it and the thoracic duct and all sorts of other structures in that we'll explore later. So all those things which stand in the middle are in the mediastinal space, and the mediastinum references the space that's created by the non-touching of the pleura on either side. So the two pleural sacs, one for each side, don't actually touch each other, but there's a space in between them, and everything that's within that space, those structures are mediastinal. So the structure, the space is the mediastinum, and the structures within it are mediastinal structures, and the pleura, which is surfacing those structures as it comes around, would be the mediastinal pleura. Now, finally, we have a costopleura, and that's the pleura which we've already encountered in the dissection as we dropped through the endothoracic fashion and encountered that pleura, and we've even seen the light passing through it.

That would be the pleura that surfaces all the rib surfaces. So we have costopleura, the diaphragmatic pleura, the pleura that's surfacing the domes of the diaphragm, the mediastinum pleura, the pleura that brushes up against the structures in the middle and creates the mediastinal space, and then finally the pleura of the cupola. I've taken away the intercostal muscles, the endothoracic fascia, the fibrous layer as well, and now I've got my fingers on the diaphragm, but the diaphragm itself is coated with the pleura, the pleura coats everything in the thoracic space. That's the potential space to realize. Although my fingers can fit in here now in the living, there is no space here.

There's no space. The organs fill the space. We breathe and we fill the space. The air fills the lung, not the intervening space. If you had space in here, it would hurt. We can see how round and domed shaped the diaphragm is.

Can I say, what do you mean the diaphragm? That can't be the diaphragm. Well, that is the shape of the diaphragm. The diaphragm is filled like bubbles on either side with the contents of the abdominal viscera bulging upward. They're bulging upward into thoracic space.

They don't pass into thoracic space because the balloons prevent the contents. The balloons and the muscle prevent the contents of the diaphragm, the contents below the diaphragm, from entering there. Lift up a little higher in the lung. You go over the hill here and it's just round and round. It's like a parachute on either side, a parachute. A diaphragm here is covered with a film.

That film is the plura, the diaphragmatic plura because we're looking at the diaphragm from the thoracic space. It's on the northern side, on the head side, on the thoracic side of the diaphragm. The diaphragm is painted over, covered with a cirrus membrane called the plura there. It's called the parietal plura because it's covering all the wall. More particularly at that point, it's called the diaphragmatic plura.

It's all just the same skin, balloon skin. Either way, you slice it. The line of the 12th rib where the plura here, the plura is covering the diaphragm and then scrolling back like an ocean wave here, like an ocean wave. It curls back over and paints the endothoracic fascia of the fibrous covering of the rib cage. That's the terminus of the thoracic space right there.

That's the end of the road. That's the end of the thorax. On the far side of it, we have the abdominal territory here. As I sweep my hand in, I come over the diaphragm on either side, over the diaphragm in this great arc. Then, of course, we have our lungs here. Our lungs are huge.

You're going to pull these ribs back. You can see we're on the right side. We have this big joint. There's a joint in the lung that enables it to spiral on itself in the breath motion. Down here, we see the plura come off in a sheet, which will anticipate our anterior view.

The rest of it we cut away as we went through the ribs and the other tissues. It's pretty amazing to be able to see the immensity of the lungs from the side here. From the side view, you see these giant lobes. When you get an anterior view, it's very superficial. You only see the superficial projection of the lungs.

But plura means side. Plura means side. It's a Greek word, plura. It's really a side organ, and it fills in your whole side. It's huge. The lungs are huge.

The parietal peritoneum here, which we can see out puffing when I move the organs around, this filmy layer here puffing up and down, that layer has the kidney underneath it. Here we marked out the border of our liver and then our kidney. Here we had our spleen. A little spleen here. The shape of the spleen through the diaphragm and the shape of the great liver here, leaving the kidneys running down the middle.

Here we have our spleen. Here we have our spleen. We're looking at the transversalis fascia here. It's a great sheet of fascia. We can see that this sheet of fascia doesn't go over the ribcage.

It actually goes under it. Because this transversalis fascia that invests the transversus abdominis muscle, this layer here, filling in the groove, attaching to the 12th rib again, along the margin of the ribcage here, this muscle layer with its great tendon that passes over the belly here, which is now like a loose bag, this transversalis fascia, has adhered on its opposite side. On its deep side is adhered the peritoneum, the parietal peritoneum, the wall layer of the peritoneum, that cirrhosec in which the abdominal organs are carried. So we see the action of the... I'm just moving things around here so you can see this fringe of muscle fiber with its great sheath.

It's on both sides. It's a little green here because of the gallbladder. So I can pull across here. You can see how the shortening of the fibers of the transversus abdominis muscle would create a tension in this sheet over the guts, over the viscera of the abdomen. That's this rib here.

And these ribs are going to be free now because they're freed from their musculo attachment here, and in the back they're freed from the spine as well. So I pry up here and see... cool. See that? The continuity of the transversus abdominis muscle with the diaphragm. This is my diaphragm.

This is my transversus abdominis. Look, like one big bag. The only difference is that the diaphragmatic pleura that's covering here has come down to this point and doubled back here. We've cut through the pleura. What I just did was cut through the pleura that was attaching here and cutting away the attachment of the diaphragm to the ribcage.

So although it appears to be a complete continuity, what we can't tell basically is that the pleura has been cut. The pleura has been cut here. And that's what defines this space in terms of the continuity of the material. Look at the diaphragm and the transversus abdominis are a union. But I'm wanting to pull the pleura.

See, I'm pulling the pleura away from the... lay it back down, if I can. See, that's pleura. And the pleura is adhered to the ribcage, right? And I'm just...

Can you hear that? Yeah, that's the... Now, that's an adhesion that belongs there. See, now we're looking at the abdominal contents, right, held back by the diaphragm from emerging into thoracic space. This is great.

This is about the coolest way I've ever done this. As I work to peel back as much of the parietal pleura as possible, I encounter areas of scar tissue adhesions, the aftermath of an old bypass surgery. Ultimately, with the ribs disarticulated from behind and the chest wall and shoulder girdle freed as a whole, we have a unique insight into the intimate relationship of our arms with the whole basket of breath, as it were. This approach also affords us a chance to look at the chest wall, literally from the inside out, while also preserving all of the organs in their relationship to each other and to the respiratory diaphragm. Looking now at the chest wall from the inside, we see the internal thoracic artery and vein coming into view, also known as the mammary artery and vein, which circulate blood to the anterior chest and the breasts.

These vessels are now commonly borrowed to bypass coronary vessels during an open heart surgery. The surgeons peel them from the chest wall and sew them onto the heart. Scar tissue will then cause the injured layers to adhere. We see some lung tissue against the thoracic wall. It would adhere the pleura, not only the parietal pleura, but also the visceral pleura.

The lung was stuck to the wall of the thorax, which can happen during inflammatory processes. It gets stuck, and then the lung gets carried along with the movements of the ribcage in a way that it normally would have a sliding surface. As we look inside the wall here, we see the fibrous layer covering the intercostal muscles and, exactly, covering the intercostal muscles as well as the bone. So in the same way that the fibrous deep fascia covers the outside of the thorax, the fibrous endothoracic fascia surfaces the inside of the thorax. So we've worked our way now through the bony form and the fibrous lining of the thorax, and can turn our attention at last to the membranous layers surrounding the lungs.

While we dissected the parietal pleura away in the back, in the front we've tried to peel it away as best we can from the endothoracic fascia and demonstrate this first layer of serous membrane in relationship to the visceral pleura and lungs deep to it. At the belly we still have the entire transversalis fascia, the fibrous layer, still intact to explore a bit later. So we have our fibrous transversalis fascia here. The peritoneum is adhered to the other side, and here we have our pleura. Now, at this point I can see that this parietal pleura, this wall layer of the pleura that was peeled from the thorax, it was peeled from the endothoracic fascia.

Look at that. See how it's tacked down onto the lung? I can pick up the lung. That shouldn't be. This is a sliding surface. This two serous membranes, the parietal layer and the visceral layer, are designed to be slick against each other, just like my two gloves with a little bit of butter between them.

So the serous fluid is minimal, but sufficient to create a slick sliding surface between the parietal layer and the visceral layer. But here we have adhesion. They're stuck to each other. We have more lung over here, and these layers are stuck down, and I can peel it away. See how I peeled away that adhesion one layer to the next? This is not the skin of the lung.

This is the parietal pleura. This is the skin of the lung here. I haven't broken into the lung tissue at all here. We shouldn't be surprised that there would be adhesions here of the lung, the parietal layer to the visceral layer, because here, in fact, the lung tissue itself has been broken. We saw it on the chest wall. It was stuck, so that the skin of the lung actually was torn away, stuck to the ribcage, because the skin of the lung was adhered to this, and this was adhered to that, and the three of them all stuck to each other, and then taking it apart yielded a rip. That shouldn't happen. It should be a smooth point of contact.

But again, there was massive chest surgery. We can see how the lung bounces back. It's very elastic. It's an elastic structure. It should be elastic. This is good. Also, when you press down, you're pressing air out.

When you let go, and it's intruded like this, the air fills in again. I create a vacuum, and it fills in again. So the lung should be elastic and responsive to pressure, like the pressure on the chest or something. So this is good. At the same time, we see a lot of black. The blackness on the tissue represents the patterning of the lymphatic vessels filled with carbon deposition.

So here we have some remnants of the parietal layer of the pleura, and then this layer here, this is the visceral layer. This is the skin of the lung. When I lift up this layer, then I'm actually exposing little alveoli and things like that. So this is the visceral layer, just to prove there is one. This is the visceral pleura.

In case you didn't believe me. The visceral pleura, but it doesn't come off in a sheet. Oh, wow, look at that. So there I have the visceral layer of the pleura, as opposed to the parietal layer. The parietal pleura.

The visceral pleura. And then the actual parenchine, the lung tissue. So now we have some sense of the textures, qualities, and relationships of the endothoracic fascia approached first from the outside in and then viewed interiorly. We've encountered the parietal pleura from the outside in. We've encountered it where it adheres to the diaphragm, and when differentiated away from the endothoracic fascia inside the ribcage.

Then we've encountered the visceral pleura, understood as the skin of the lung, from the rear, as well as from the front, and up close.