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What does the outside of the fish and inside of our guts have in common

Pranay Lal talks about how mucus may look repulsive but it can cleanse, moisten, protect and maintain peace, all at once. See what mucus can do, and how you can make artificial mucus, too


November 14, 2021 6:05:11 am
MucusMucus keeps delicate tissues from being infected, lubricates our eyes, protects our stomach lining (Source: Getty Images)

Pranay Lal

If you’ve had a cold, mucus is hard to miss. We call it snot, phlegm, nosie, leak, phtooey (for MAD comics fans), gunk, grey matter, and the like. There is a word for it in every language, and the Sanskrit word for it is muncati which morphed into Latin meug — for slimy, or emungere, to sneeze out, from which the English term mucus was derived. Our bodies produce more than a litre of mucus every day in our mouth, nose, lungs, throat, stomach, intestines and the rectum. They are excreted from the outer cell lining of these organs that are collectively called mucous membranes.

Mucus may be repulsive to look at, it may give us a blocked nose and a heavy head, but although it may often seem like it, its sole role is not to make you miserable! This sticky jelly performs several vital functions that allow our organs to keep working efficiently. It keeps delicate tissues from drying out and cracking, and, more importantly, it protects these tissues from being infected by the billions of microbes that we encounter, ingest and inhale every day. It is mucus that lubricates our eyes and allows us to blink. It is mucus that protects our stomach lining from dissolving by acid, which the lining itself produces. In addition, mucus is also home to trillions of beneficial microbial inhabitants, which includes viruses. We all contain our personal menagerie of microbes, and the scientific term for it is microbiome. Mucus is nearly 90 per cent water. It is rather simple to make mucus-like substance using ingredients found in your kitchen.

Here’s how you do it: You will need about 200 ml of water in a pan; a cup or a small measure; cooking gelatin or clear jelly; corn syrup or corn starch; a teaspoon and a fork for whisking the contents in the pan. First, put about half a cup of water to boil. After it simmers, add three teaspoons of gelatin until it softens, and stir it with a fork. Add about 80 gm or half a cup of corn syrup, and again whisk with a fork. Notice that thick viscous stringy bits begin to form. Reduce the flame of the stove and continue stirring, adding small amounts of water. Soon, your snot will be ready. To make it look real, add a drop of green food colour. Consider using it as layer for tarts, puddings or glazed cakes for next year’s Halloween. Students of pathology can have some fun with it in their parties!

What is so special about mucus that allows it to be so versatile and perform such a variety of functions? The secret ingredient in mucus is a set of proteins called mucins. Mucins are what biochemists term as glycoproteins (glyco-sugar), which are long-chained sugars with a protein backbone. This enables mucins to form a mesh-like polymer which acts as a barrier against pathogens and other invaders. Only a few beneficial microbes, ones that have co-evolved with the mucous membrane, are permitted to pass. Although they may look quite alike, chemically, mucus in each organ has a slightly different composition. This conveyor belt of slime cleans up our guts, lungs, noses and throats, so that they function properly. The next time you clear your throat, remember it is the mucus that you are displacing.

This is how mucus works. At the first signs of an infection, the organ sends a signal to all cells to ramp up its mucus production and to flush out the intruder. Remember, mucus contains trillions of beneficial microbes that include bacteria and viruses. Local bacterial residents put up a fight to displace the aggressor, and some viruses play the role of messengers to tell neighbouring cells to prepare for a fight. Our immune cells get alerted and if the invader gets more aggressive, our white blood cells (WBCs) and specific cells called immunoglobulins get summoned. When you develop a common cold, the throat and nose get instigated to cough or sneeze out the pathogen as much as they can. Next, the infection triggers the production of clear, thin mucus in the nose and back of the throat. This is because of an enzyme (called myeloperoxidase) found in WBCs kicks in and it successively helps cells to release two powerful oxidants — hydrogen peroxide and hypochlorous acid. The yellow-green snot you enclose in your kerchief is the battle between the coalition of your body’s cells and the invader. This concerted strategy of working for a healthy microbiome, warding off invaders, and keeping a fine balance of the numbers and types of residents, is a complicated arrangement — a bit like the governance of the UN or the North Atlantic Treaty Organization. They may look repulsive but there are few other bodily substances that cleanse, moisten, protect, and maintain peace, all at once.

Interestingly, fish have a mucus layer on the outside of their bodies that protects them from getting infected by the multitude of microbes that live in water. Fish, the oldest vertebrates to have evolved, were the first to develop mucus, and it has been passed down from the fish to every back-boned creature that has every lived since. Our guts, too, face an assault of bacteria and viruses, and it is mucus that hosts the good bacteria and viruses that repel pathogens, help in digestion and improve immune function. The sugar chain in mucin attaches to water molecules and helps the mucus to absorb, dissolve and transport food across the gut barrier. So, the next time you go aa-tishoo and see snot, remember to thank both your fish ancestors from whom you have inherited it, and also the multitude of microbes in your mucus who are looking out for you.
All hail mucus!

Pranay Lal is a Delhi-based biochemist, artist, and author. He has written two books, Indica: A Deep Natural History of the Indian Subcontinent, and Invisible Empire: The Natural History of the Viruses

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