Human Circulatory System

Low Red Blood Cell Count Causes

The Human Body Diagram
Teeth chop food into small pieces, which are moistened by saliva before the tongue and other muscles push the food into the pharynx. Lymph may pick up bacteria and bring them to lymph nodes, where they are destroyed. It was ingenious, but it was also beautiful. Eosinophils are attracted to cells coated with complement C3B, where they release major basic protein MBP , cationic protein, perforins, and oxygen metabolites, all of which work together to burn holes in cells and helminths worms. We call it the CSF. Mucus serves as a protective barrier and lubricant inside of the GI tract.

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Digestive System

This diagram shows the body's lymphatic system, which has evolved to meet this need. It's a second parallel network of vessels that extends throughout the body. It takes up proteins and other waste from the spaces between the cells, it collects them, and then dumps them into the blood so they can be disposed of.

But if you look really closely at this diagram, you'll see something that doesn't make a lot of sense. So if we were to zoom into this guy's head, one of the things that you would see there is that there are no lymphatic vessels in the brain. But that doesn't make a lot of sense, does it?

I mean, the brain is this intensely active organ that produces a correspondingly large amount of waste that must be efficiently cleared. And yet, it lacks lymphatic vessels, which means that the approach that the rest of the body takes to clearing away its waste won't work in the brain.

So how, then, does the brain solve its waste clearance problem? Well, that seemingly mundane question is where our group first jumped into this story, and what we found as we dove down into the brain, down among the neurons and the blood vessels, was that the brain's solution to the problem of waste clearance, it was really unexpected.

It was ingenious, but it was also beautiful. Let me tell you about what we found. So the brain has this large pool of clean, clear fluid called cerebrospinal fluid. We call it the CSF.

The CSF fills the space that surrounds the brain, and wastes from inside the brain make their way out to the CSF, which gets dumped, along with the waste, into the blood. So in that way, it sounds a lot like the lymphatic system, doesn't it? But what's interesting is that the fluid and the waste from inside the brain, they don't just percolate their way randomly out to these pools of CSF. Instead, there is a specialized network of plumbing that organizes and facilitates this process.

You can see that in these videos. Here, we're again imaging into the brain of living mice. The frame on your left shows what's happening at the brain's surface, and the frame on your right shows what's happening down below the surface of the brain within the tissue itself. We've labeled the blood vessels in red, and the CSF that's surrounding the brain will be in green. Now, what was surprising to us was that the fluid on the outside of the brain, it didn't stay on the outside.

Instead, the CSF was pumped back into and through the brain along the outsides of the blood vessels, and as it flushed down into the brain along the outsides of these vessels, it was actually helping to clear away, to clean the waste from the spaces between the brain's cells. If you think about it, using the outsides of these blood vessels like this is a really clever design solution, because the brain is enclosed in a rigid skull and it's packed full of cells, so there is no extra space inside it for a whole second set of vessels like the lymphatic system.

Yet the blood vessels, they extend from the surface of the brain down to reach every single cell in the brain, which means that fluid that's traveling along the outsides of these vessels can gain easy access to the entire brain's volume, so it's actually this really clever way to repurpose one set of vessels, the blood vessels, to take over and replace the function of a second set of vessels, the lymphatic vessels, to make it so you don't need them.

And what's amazing is that no other organ takes quite this approach to clearing away the waste from between its cells. This is a solution that is entirely unique to the brain. But our most surprising finding was that all of this, everything I just told you about, with all this fluid rushing through the brain, it's only happening in the sleeping brain. Here, the video on the left shows how much of the CSF is moving through the brain of a living mouse while it's awake.

Yet in the same animal, if we wait just a little while until it's gone to sleep, what we see is that the CSF is rushing through the brain, and we discovered that at the same time when the brain goes to sleep, the brain cells themselves seem to shrink, opening up spaces in between them, allowing fluid to rush through and allowing waste to be cleared out.

So it seems that Galen may actually have been sort of on the right track when he wrote about fluid rushing through the brain when sleep came on. The human body is the most complicated machine in the world and the entire structure of a human organism, and consists of a head, neck, torso, two arms and two legs The human body is the most complicated machine in the world. We see with it, hear with it, breathe with it, walk and run with it, and sense pleasure with it. Its bones, muscles, arteries, veins and internal organs are organized with marvellous design, and when we examine this design in detail we find even more amazing facts.

The human body is the entire structure of a human organism, and consists of a head, neck, torso, two arms and two legs. By the time the human reaches adulthood, the body consists of close to 10 trillion cells, the basic unit of life. Groups of cells combine and work in tandem to form tissue, which combines to form organs, which work together to form organ systems. The organ systems of the body include the musculoskeletal system, cardiovascular system, digestive system, endocrine system, integumentary system, urinary system, lymphatic system, immune system, respiratory system, nervous system and reproductive system.

The human skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors muscles, and protects organs such as the brain, lungs and heart.

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