We eat, sleep, and go to the bathroom. Yet, we never think about how all these physical needs are processed in the systems of our body when they are functioning normally.

Yes, our bodies are created with perfect systems by which our all kinds of needs are met. The digestive system is one of them. Our intestines are key elements of this system, so much so that asking someone “How are your intestines?” would be as comprehensive as asking “How are you?”

Digestive system

Food is critical to life. A human being can bear hunger for one month at most and can only endure a few days of drought. Thus, eating and drinking is crucial.

Foods as we eat them are not convenient for use by the cells. Food must be broken down into smaller pieces. This process begins in the mouth and ends at the anus, and it is called digestion.

The main task of our stomach and intestines is digestion. The teeth, salivary glands, the tongue, and the gullet – as well as swallowing – are essential secondary elements. Additionally, if the pancreas or liver fall ill, it can paralyze the whole system. While also working with the circulatory system, kidneys have the task of reabsorbing useful substances like glucose, amino acids, and water.

Our digestive system works together with the urinary system and the digestive organs like a factory. How these parts work together is still not fully understood, but more detailed research has been performed and revealed more secrets of the digestive system. By means of every discovery, it is realized that this perfect creation has a more intricate structure than is known.

The brain in the intestine

There are more neurons in our intestines than in our spinal cord and the intestines are created in a way that can move independently from the central nervous system. They have their own nervous system, known as enteric nervous system (ENS), which is also called the “second brain. “Within those yards of tubing lies a complex web of microcircuitry driven by more neurotransmitters and neuromodulators than can be found anywhere else in the peripheral nervous system. These allow the ENS to perform many of its tasks in the absence of central nervous system (CNS) control…” [1]. Thus, “… isolated segments of intestine can independently coordinate propulsive movements and propel content without any neural connections to the brain or spinal cord [2].

The intestines take action when food comes into the stomach. This movement is known as colonic migrating motor complexes (CMMC), and it moves the substances that cannot be digested, like bone and fiber. According to neurophysiologist Nick Spencer et al, “The gut wall contains a complete network of intrinsic nerves capable of propelling contents along the bowel, without any requirement of nerves originating in the brain or spinal cord” [3].

Eat different types of food

70% of our immune system cells are in our intestines. A big part of the approximately 38 trillion bacteria in our body are in our intestines, and they are useful; they have a big role in digesting food. Different groups of bacteria feed on different types of food; so for intestinal flora it is very important to have a variety of food on our table. For the ideal day on a plate Dr. Megan Rossi recommends people should “aim for at least 30 different plant species per week.” “The reason for this is that each plant contains different types of fibres and phytochemicals (the super healthy components of plants) that feed different good bacteria. The more plant variety, the more variety of gut bacteria – which is associated with health and happiness” [4].

Pets in our body

For Dr. Megan Rossi, “microbes are like our pets, so you have to take care of them and feed them” [5].

Of course, germ flora in our body is not just limited to the ones in the intestines. Bacteria, viruses, and fungi in our body are nearly scattered throughout the whole body. These living things produce pellicle on our head skin, irritate the gaps between our toes, live on our skin, are on duty among our teeth, and have ecosystems and assigned positions convenient to them. According to the situation, they keep their living spaces healthy or unhealthy. Although they number 50 trillion, they are approximately 200 grams of our body weight.  

Useful microbes

An average size human adult houses about 10¹² bacteria on the skin, 10¹⁰ in the mouth, and 10¹⁴ in the gastrointestinal tract [6].

These microorganisms are useful microbes with duties in our body. The harmless flora of microbes is generally present on the skin, mouth, teeth, nose, throat, and bowel and genital areas. There isn’t normal flora in internal organs except the large bowel. Internal organs have no microbes. If we look closely, flora is inserted in every part of our body which is dirty and has contact with the outer environment. If it was not for the useful flora, microorganisms causing illness would settle instead. Only intestinal bacteria are permanent microbes which are useful. For example, vitamin K plays a part in a crucial event like blood clotting and is produced in the intestine.

Control your stress

Research has revealed that mental and psychological stress affects the health of the intestines. Serotonin is produced automatically in case of need, and 85% of it is produced in the digestive tract. Stress suppresses the level of serotonin produced. Psychological illnesses are associated with low levels of serotonin.

Studies have shown that relaxing practices like meditation for 15-20 minutes can be good for health and reduce stress. At this point, daily prayers are a kind of therapy. Other ways to stay healthy include: avoiding things like alcohol and caffeine, and sleeping well.

Our body has ways of telling us when it’s not healthy. For instance, we can learn the digestive tract isn’t healthy if we have to use the toilet more than three times a day and fewer than three times a week.

References

1. Gershon, Michael D. “The Enteric Nervous System: A Second Brain.” Pdfs.semanticscholar.org.
2. Spencer et al. 2018. “Identification of a Rhythmic Firing Pattern in the Enteric Nervous System That Generates Rhythmic Electrical Activity in Smooth Muscle.” http://www.jneurosci.org/content/38/24/5507
3. http://www.flinders.edu.au/neuroscience/lab_visceral.html
4. https://www.dailymail.co.uk/femail/article-5543159/Doctor-debunks-myths-surrounding-gut-health-say-surprise-you.html
5. https://navva.org/brazil/health/why-the-bowel-is-considered-our-39-2nd-brain-39-and-other-5-amazing-facts-about-the-organ-news/
6. http://www.textbookofbacteriology.net/normalflora_3.html

Digestion in grain-eating birds

The digestive system of the chicken, which is a representative of the world of birds, is comprised of organs lined up in straight line succession: a beak, mouth, gullet, craw, front stomach (with gland), gizzard, small intestine, caecum, large intestine, cloacae and anus. In addition, enzymes secreted from the pancreas, liver and gallbladder also have digestive duties. Ending in a sharp point, the beak was created especially to be able to pick up single pieces of feed. Chickens do not have assisting organs like the palate, cheek, tongue or teeth that are normally found in the mouth, the first door of digestion in most animals. Ruminating animals like cows, sheep, goats and camels use the tongue instead of a beak for taking food into their mouths, and then their teeth are used to begin the breakdown of food. In chickens, however, this breakdown is initiated with the bottom and top beak. In ruminants there are taste buds in different shapes on the tip, sides and middle of their tongues which also function as the organ for the sense of taste. Since such taste buds are not found in chickens, there is also no perception of taste like that experienced in ruminating animals.

The structure and function of the gullet, or food pipe, has similar characteristics in chickens and other animals. However, just as in all birds that eat single seeds and grains, there is another digestive organ in chickens in the shape of a bag opposite to where the gullet expands. Called a craw, this tiny pouch is a place for the storage, wetting and softening of feed, and it serves the purpose of bringing food to the consistency needed for further digestion; consequently, it lightens the burden of the stomach (just like when we leave food that is difficult to cook, like chick peas or beans, standing in water overnight before we cook it).

A chicken’s stomach is composed of two different sections, the front stomach and the gizzard. The feed the chicken eats passes from the gullet and the craw to the front stomach, where digestive secretions are made. The food is stored here briefly and mixed with the special fluids of the stomach. Found in this secretion are both the pepsin enzyme, which starts the digestion of proteins, and hydrochloric acid, which is secreted to generate the pH level that makes this enzyme effective (and which also helps in the dissolution of minerals). These two important secretions are produced by different glands in the stomach. Like the craw, the gizzard, which comes after the front stomach, is the place where mechanical digestion, which is particular to all birds that eat grains, takes place. The gizzard is called the stomach with muscles because it is comprised of a pair of thick and strong muscle layers. As a result of these muscles constricting strongly, feed is broken down mechanically and ground up. While gathering feed, the chicken usually also swallows small pieces of sand, stone and limestone as if it knows how its digestive system works. Although many of us think that chickens swallow stones because they cannot distinguish them from feed, it is obvious that there is a purpose why they are doing it. If these stones, which are like “mill stones” for the digestive tract, are not found in the gizzard, the feed is not fully ground; consequently, it will pass to the small intestine in a form that will not be fully beneficial to the body.

Depending on its characteristics, the feed eaten can stay in the gizzard for a few minutes or several hours. The small intestine, which comes after the stomach, is comprised of the duodenum (twelve-finger intestine), the jejunum and the ileum. The small intestine is similar in grain-eating birds to those of other animals. The duodenum empties the secretions coming from the pancreas and the bile coming from the gall bladder. The digestion and absorption of the feed actually takes place in the small intestine due to these secretions. Final digestion and the absorption of carbohydrates and protein are effected by bacteria found at the point where the small intestine ends, in the 10-15 centimeter-long, V-shaped caecum.

The large intestine and the cloacae are found in the advanced sections of the digestive system. The role of the large intestine, which is twice as large in diameter as the small intestine, is to temporarily store the waste from the digested food and to maintain the balance of water in the body. The cloacae is a small orifice with a structure formed by the widening of the large intestine towards the anus and where the digestive, defecation and reproduction tracts open up.

While giving grain-eating birds the above mechanisms in order to nourish them, God equipped ruminating animals with different oral, dental, gastric and intestinal structures as well as different digestive strategies.

Digestion in ruminating mammals

While secreting saliva is essential for ruminating animals, it is not necessary for chickens because of differences in their digestive system. As a result of the secretion of saliva the fodder of ruminants is softened and dryness of mouth is prevented. Ptyalin (or alpha amylase), which is found in saliva, has antibacterial properties that protect animals from infections in addition to playing a role in digestion. The mother cows constantly licking their newborn calves is both an expression of compassion and also of wisdom in protecting the newborn from probable infections (Similarly, animals like dogs and cats licking their wounds and thus speeding up healing is no coincidence, but a sign of universal wisdom and mercy). This wisdom shows that saliva, of which cows secrete 90-180 liters and sheep 5-8 liters per day, is not a waste.

The stomachs of ruminants are comprised of four sections; the first three are the rumen, the reticulum and the omasum. These three sections are called the front stomach. The section that does the real work is called the abomasum. Because the nutritional value of grass is very low in comparison with meat, it is obvious that a large bodied ruminant will need a lot of grass. Consequently, the capacity of rumen being 150 liters is a wise and fitting design. In addition, the cellulase enzyme that digests the cellulose walls in plant cells is not produced in the tissues of any mammals. The possessor of infinite knowledge and power, God placed high concentrations of bacteria, protozoa, yeast and fungus-all of which can produce the cellulase enzyme needed to break down cellulose-in the rumen of ruminating mammals. The rumen acts as a fermentation factory because of these microorganisms. Breaking down the cellulose-rich food consumed by ruminants, these microorganisms both fulfill their own nutritional needs and help to meet the host’s energy, protein and vitamin (especially B12) needs within a symbiotic relationship. I wonder where the microorganisms in the rumen learned about this synthesis and assistance mechanisms!

What a magnificent engineering wonder is the “sulcus esophagus,” a semi-duct structure in the shape of a canoe that extends from the end of the food pipe in newborn ruminants to the abomasum where the essential stage of digestion takes place. Due to this structure, milk drunk reaches the last stage of the stomach without passing through the rumen, for there is no matter like cellulose in the content of milk that needs to be broken down. Consequently, there is no need for the milk to go to the rumen. If it were not like this, the milk would go directly to the rumen where it would be ruined by microorganisms, lose its nutritional quality and be like a bribe given in vain to the microorganisms in the rumen.

I hang between your stomach and your duodenum under it, attached to the intestinal mesenteries. I have two different identities in terms of my structure and function. I carry out two very different duties as a compound gland made up of both exocrine and endocrine tissues. So, I am granted a very special structure and chemical abilities to function well. One of my duties is related to the physiology of digestion: I break up the food passing from the stomach to the duodenum by pouring on it the four types of digestive enzymes I have been enabled to produce. These juices are carried through a tiny pipe to your duodenum. Two of them are used for breaking up proteins, one for carbohydrates, and one for fats. You don’t even realize it! As the food you take in passes from the stomach to the duodenum, my enzymes begin flowing faster. This is a very fine balance: while food is being digested, neither the enzymes should be wasted, nor should your intestinal walls be harmed. I don’t control the release of the enzymes. That duty is given to two hormones produced in your intestinal mucosa by the stimulus of the vagus nerve. When those hormones reach me by the bloodstream, my cells are stimulated and they secrete water, bicarbonate, and the digestive enzymes I mentioned and they flow into your duodenum through my duct.

My second job is the production of insulin and glucagon hormones, as the endocrinal pancreas. My cell clusters, which are also known as islets of Langerhans, have different types as separate groups, which you call alpha and beta. The insulin, which is produced by my beta cells, is used for regulating the glucose level in your blood. The duty of insulin is to stimulate your body cells to take the glucose in your blood and use it.

After you have a meal, the carbohydrates in it are broken down into glucose molecules, pass into the blood, and increase your blood sugar. For your body to function in a healthy way, the amount of glucose should be around 100mg/ml (it varies from 80–120). When the level is above the normal value, I secrete insulin. In this way, the sugar is carried to your cells and burned to produce energy, and its increase in your blood is brought back under control. Also, insulin helps you to store sugar in fat tissues and to turn them into fatty acids, and it slows the breaking down of fatty acids. Moreover, insulin helps you to make protein in your body by holding amino acids within your muscle tissues and storing glucose in your liver and turning it into glycogen.

The failure of my beta cells to secrete insulin is a serious problem; the consequence is “diabetus mellitus,” or what we commonly know as diabetes. A person with this disorder must abstain from various delicious foods and drinks. In cases where a strict diet does not solve the problem, patients may have to take insulin shots every day. Diabetes can cause many complications by damaging your nerves and blood vessels; I won’t go into types of diabetes so I don’t get sidetracked too much. I just wished to make a point: even a substance produced by a tiny cluster of cells can upset the functioning of many of your mechanisms. After having a meal, put your hand to the left of your abdomen below the stomach and remember what a blessing I am!

As for the glucagon hormone I secrete from my alpha cells, it does just the opposite of insulin and causes the sugar stored in your cells to be released into your bloodstream. When your blood sugar decreases-due to hunger, overwork, exercise, and so on-it causes the glycogen in your liver to be used in order to increase the level of your blood sugar. As adrenalin secreted by the adrenal glands helps glycogen to be broken down and to be released into the blood as glucose, they function as an integrated system. Glucagon also slows down the synthesis of glycogen, and it accelerates the break-up of proteins and fat metabolism. I think now you get it, Peter. Insulin and glycagon are parts of a biological feedback mechanism controlling one another. People discovered all these facts after years of lab research; now do you see how ridiculous it is to see me as a work of blind chance?

Like any other organ, I can also contract various diseases. The most common ones are acute or chronic inflammation, tumors, and cysts. I am easily troubled with inflammation in people with alcohol habits. Since enzyme secretions-and therefore digestive processes-are then not carried out properly, some undigested fats and fibers with proteins are excreted with the feces. A problem can arise with the intestines due to digestive deficiency. And if I completely fail to fulfill my duty owing to a chronic inflammation or tumor, then doctors take me out and you become dependent on insulin and a special liquid obtained from the pancreas.

It is sad to say that my cancer is not quickly recognized. It develops very fast and I try to keep up my duty as long as possible. Therefore, it is usually too late when diagnosed. There is nothing much modern medicine can do after it spreads. Although it is not definite yet, I suspect cigarettes play a role in my cancer.

As for diabetes, even though a promising method of treatment has been discovered, certain problems haven’t been overcome yet. The transplant of beta cells from the pancreas of someone who has just died-with as much tissue compatibility as possible-has had partial success. As with every other organ transplant, tissue rejection is a challenge. If the human genome project succeeds and the genetic code of the human body is thoroughly solved, it may be possible to cure diabetes by genetic engineering techniques. This is only at research level for now, but if scientists do their best, it is possible to find a way, since there is a treatment for every disease except for old age and death. You see Peter, as the vicegerents on earth, you humans are supposed to explore the secrets of the universe and appreciate the beauties you discover. I think I have said enough now. Thanks for listening, Peter!

Irfan Yilmaz is a professor of biology at Dokuz Eylul University, Izmir, Turkey.