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11 Interesting Facts About Lymph Nodes

The human body is an amazing thing. For each one of us, it's the most intimate object we know. And yet most of us don't know enough about it: its features, functions, quirks, and mysteries. Our series The Body explores human anatomy, part by part. Think of it as a mini digital encyclopedia with a dose of wow.

The lymphatic system is a crucial part of your body's ability to fight off infection and viruses. It's a key player in the immune system that functions by circulating lymphatic fluid through a series of lymph vessels all throughout your body. This fluid gathers up anything foreign, such as viruses and bacteria from your body tissues and flushes them to your lymph nodes, where immune cells attack whatever isn't helping your body. 

Mental Floss spoke to Adriana Medina, an internal medicine doctor with a specialty in hematology and oncology at the Alvin and Lois Lapidus Cancer Institute at Sinai Hospital in Baltimore, Maryland, about these important tissues. 

1. THERE ARE HUNDREDS OF NODES.

They're about size and shape of a pea, and hundreds of them are scattered all throughout the body. In order to fight many little pathogens and clear out unhelpful debris, your body needs a lot of nodes to rally to these causes, according to Medina. 

2. LYMPH NODES ARE HOME TO IMPORTANT IMMUNE CELLS.

"The lymph nodes are in charge of harboring lymphocytes," says Medina. Your body makes two main types of these immune cells, B-lymphocytes and T-lymphocytes (or B- and T-cells), which are crucial to your body's ability to fight off infections of all kinds. There are many sub-classes of the T-cells because "they are very important to attack infection," says Medina.

3. LYMPHOCYTES ESCORT FOREIGN INVADERS OUT.

When your lymph nodes receive some sort of foreign debris they recognize isn't ours, Medina says, "the B-lymphocytes are in charge of making antibodies." These antibodies "leave with the toxic substance," and signal other immune cells to come in and attack the cells.

4. WHERE DO ALL THE TOXINS GO?

Once the lymphatic fluid has grabbed up its targets, most of it returns to your blood stream, Medina explains, which is why it's so important for lymph cells to do their job: kill what aims to harm you before it gets flushed back into your system.

5. THERE ARE MANY CAUSES OF SWOLLEN LYMPH NODES.

When your immune system senses a foreign invader, be it a virus, bacteria, vaccine, or even some medications, it preps the lymph nodes to make antibodies and lymphocytes to fight off the offender. This also increases the amount of lymphatic fluid in the node, which can make it swollen and tender. Most of the time swollen lymph nodes are not a big cause for concern.

6. A HARD, RUBBERY LYMPH NODE IS A PROBLEM.

A lymph node that is harder rather than soft and persists for several weeks is worth a doctor visit. While lymph nodes can be tender or swollen and mobile when infected, "when there is a [cancerous] malignance…they're hard, rubbery, they don't move, and they don't go away. The lymph nodes are always telling us something."

7. YOU ARE THE PUMP FOR YOUR LYMPHATIC SYSTEM.

Unlike your blood, which has the heart to pump it through your body, your lymphatic fluid doesn't have a pump. Instead, it relies upon gravity and pressure, which you create when you move around, as well as light massage.

8. WHERE YOU FIND VEINS, YOU FIND LYMPHATIC VESSELS.

The lymphatic system and the circulatory system are separate systems, but connected, running in tandem like underground networks of streams. "Lymphatic vessels are distributed along the body wherever we have arteries [or] veins," says Medina.

9. YOUR LYMPH NODES AND YOUR SPLEEN WORK TOGETHER.

"The spleen is like one big lymph node," Medina says of the organ that lives between your stomach and diaphragm. "The spleen is able to produce additional blood cells in case we need it to." Additionally, she explains, many toxic substances are filtrated through the spleen. However, if something happens to your spleen and it needs to be removed, you can live without it; you just may become more prone to infection and require more vaccinations to protect you against aggressive viruses.

10. STAGES OF CANCER ARE DETERMINED BY THE NUMBER OF AFFECTED LYMPH NODES.

The easiest cancers to treat are those that remain in the tissue where they first occur. However, in metastatic cancers, cancer cells migrate to the lymph nodes, which can cause cancer to spread. "When the cancer is detected in lymph nodes, we have to try to find out how many lymph nodes are involved," Medina says. "Lymph node involvements [determines] the prognosis of the cancer." When lymph node involvement occurs, "the treatment has to be more aggressive," she says, often adding radiation to a regime of chemotherapy and other drugs.

11. RESEARCHERS ARE TURNING THE BODY'S OWN LYMPHOCYTES INTO CANCER FIGHTING TREATMENTS.

Breakthroughs in immunotherapy known as Car T-cell therapy turn the body's own immune system into a weapon against cancer by engineering patients' own immune cells to recognize and attack their tumors, according to the National Cancer Institute. "What's happening—it's just beautiful—is that [researchers] are using B-lymphocytes to fight not only breast cancer, but leukemia and lymphomas," Medina explains. "The results are so good and encouraging, changing chances of survival."

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What's Really Happening When We See 'Stars' After Rubbing Our Eyes?
Photo illustration by Mental Floss. Images: iStock.
Photo illustration by Mental Floss. Images: iStock.

It's likely happened to you before: You start rubbing your eyes and almost immediately begin seeing colors, specks, and swirls from behind your closed lids. So what's happening when you see these 2001-esque "stars"? Do they only occur upon rubbing? Does everyone experience them?

Before we can get to what causes the lights, we need to understand a bit about how the eyes work. Angie Wen, a cornea surgeon at New York Eye and Ear Infirmary of Mount Sinai, tells Mental Floss that the retina—the innermost layer of the eye—consists of millions of cells, or photoreceptors. These cells, she says, "are responsible for receiving information from the outside world and converting them to electrical impulses that are transmitted to the brain by the optic nerve. Then, the brain interprets them as images representing the world around us."

However, what we see doesn't just stop there. Sometimes "we see light that actually comes from inside our eyes or from electric stimulation of the brain rather than from the outside world," Wen says. "These bursts of seemingly random intense and colorful lights are called phosphenes, and appear due to electrical discharges from the cells inside our eyes that are a normal part of cellular function."

People have been writing and theorizing about phosphenes for thousands of years. Greek philosophers thought the bursts of light were the result of fire inside our heads: "The eye obviously has fire within it, for when the eye is struck fire flashes out," wrote Alcmaeon of Croton (6th–5th century BCE), a philosopher and early neuroscientist, of the swirls and specks someone sees after getting a blow to the head. A century later, Plato—who believed that a "visual current" [PDF] streamed out of the eye—wrote that "Such fire as has the property, not of burning, but of yielding a gentle light they [the Gods] contrived should become the proper body of each day."

Plato's take was still the dominant one through the Middle Ages. Eventually, Newton (1642–1727) theorized a concept that's more in line with what's believed today about these strange sparkly visions: The phenomenon is due to light that's produced and observed when pressure and motion is placed on the eyes.

Eleonora Lad, an associate professor of ophthalmology at Duke University Medical Center who has a background in neuroscience, explains exactly why eye rubbing generates these visions: "Most vision researchers believe that phosphenes result from the normal activity of the visual system after stimulation of one of its parts from some stimulus other than light," including putting external pressure on the eyes. (Interestingly, due to retinal damage, blind people can't see phosphenes caused by pressure, but they can see them when their visual cortex is electrically stimulated. In hopes of turning this phenomenon into improved vision for the blind, scientists have developed a cortical visual prosthesis, implanted in the visual cortex, that generates patterns of phosphenes. The device has been approved by the FDA for clinical trial.)

As Alcmaeon rightly pointed out, there are causes for the bursts of light beyond just rubbing your eyes: Getting hit in the eye can produce this phenomenon—as can a sneeze, a surprisingly powerful event that tends to clamp our eyes shut, Wen says.

Receiving an MRI or EEG may also trigger it. MRIs, for example, produce a changing magnetic field which can stimulate the visual cortex, making a person see these flashing lights. When it comes to an EEG, depending on the brain stimulation frequency band (Hz) used, some patients experience the phenomenon when closing their eyes, which is believed to come from retinal stimulation during the process.

And the activity doesn't only happen on Earth; astronauts in space have also been known to experience them. As reported in 2006 in the journal Vision Research, "over 80 percent of astronauts serving in today's NASA or ESA (European Space Agency) programs have perceived phosphenes at least in some missions and often over several orbits." They're mainly attributed to interactions between the eye and cosmic ray particles in space, outside the Earth's protective magnetic field.

No matter the cause, the bursts of light are perfectly normal—but that doesn't mean you should engage in excessive eye rubbing. Wen says ophthalmologists advise against rubbing your eyes or applying vigorous pressure; according to Lad, too much rubbing may be damaging to the cornea and lens or "result in a loss of fatty tissue around the eyes, causing the eyes to look deep-set."

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Why Your Knuckles Make That Satisfying Cracking Sound, According to Science
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Scientific curiosity is not always burdened by matters of great consequence. Over the years, considerable money and time has been applied to matters involving facial recognition between sheep, whether the flow of urine is impeded by someone watching you pee, and whether humans can capably swim in a pool full of syrup. (They can, almost as well as water.)

Now, researchers from Stanford University and Ecole Polytechnique in France have turned the roving eye of science to the phenomenon of knuckle-cracking. According to Gizmodo, a computer simulation was created to confirm an earlier theory that the audible noise that comes from the human hand after putting pressure on the knuckle was the result of gas bubbles popping inside the finger joint.

Conclusion: Probably true.

The study, published in Scientific Reports, demonstrated that microscopic bubbles inside the lubricating synovial fluid of the joint collapse when a knuckle-cracking session commences. To use an imperfect analogy, the cavitation bubbles are like the body’s Bubble Wrap. Popping them produces an audible—and for many, a very pleasing—sound.

To compile data, researchers took geometric representations of the joint's movements during a cracking session and turned them into mathematical equations. (Imaging has not been shown to be very productive in this field, as the crack takes only about 300 milliseconds and is not easily visualized.) The software models demonstrated that pressure shifts in the joint fluid increase pressure on the gas bubbles. Unlike packing material, however, the gas bubbles don't really perforate—they experience a partial collapse but remain suspended in the joint.

So does this solve the mystery surrounding cracked knuckles? Not entirely. Because it was a simulation, there's a possibility of mathematical error. Proponents of alternative theories—that it's not bubbles collapsing but bubbles being created that produce the noise—feel there's more work to be done. We can only hope a complete understanding will come in our lifetime. Fingers crossed. And cracking.

[h/t Gizmodo]

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