AGEs You Know?

Do You Know Your AGE?

How and Why to
Prevent AGE Damage
Advanced glycation endproducts (AGEs) may be a
fact of life, but fighting them may extend your life.
By Will Block

f we may be so bold, which would you rather have and hold—GOLD or MOLD? OK, it’s a trick question (please don’t scold), because if truth be told, you wouldn’t want either—they’d leave you cold if you knew they were both about . . . old.

Old people, you see, are the victims of AGE—Advanced Glycation Endproducts, of which GOLD and MOLD are two prominent examples. The acronyms stand for glyoxallysine dimer and methylglyoxallysine dimer, respectively, but don’t worry—there won’t be a quiz on that. It would be wise, however, for you to become better informed about AGE (or AGEs, as they’re often called), because these chemical compounds are a key factor in the aging process.

As you will see, AGEs are formed inside your body through normal metabolism and aging, and outside your body during the preparation of some foods you eat. They’re implicated in the development or exacerbation of numerous degenerative diseases associated with aging, notably type 2 diabetes, atherosclerosis, cardiovascular disease, Alzheimer’s and other dementias, cataracts, retinal dysfunction, kidney failure, nerve damage, arthritis, and cancer.

Supplements Can Slow AGEing

It’s impossible, alas, to avoid AGEs altogether—their formation begins during early embryonic development and continues steadily for the rest of our lives. The body’s mechanisms for removing unwanted substances cannot keep up, because the AGEs are resistant to this process. Therefore, even if every other factor in the aging process could be magically eliminated, it would still be impossible to avoid aging. The good news, however, is that the “AGEing” process can be slowed down—and so, therefore, can the aging process. There are two ways to do this. Ideally, we should do both.

One way to slow AGEing involves the use of certain supplements that have been shown—in laboratory experiments, animal studies, or human clinical trials—to inhibit the formation of AGEs. Notable in this regard are: benfotiamine, a fat-soluble form of thiamine (vitamin B1); the amino acid histidine; the dipeptidecarnosine, which consists of linked histidine and beta-alanine; alpha-lipoic acid, a saturated fatty acid renowned for its potent and versatile antioxidant actions; and rutin, a flavonoid found in many plants, notably buckwheat, black tea, and apple skins.*

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*Some of the evidence for these compounds was discussed in “Reducing Glycation Reactions for Better Health and Longer Life” in the February 2008 issue.

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No! Nooo!

The other way to slow AGEing is to (are you sitting down?) avoid, as much as possible, browning the foods that you cook. Just as the colors red, orange, yellow, blue, and purple are usually signs of exceptional healthfulness in fruits and vegetables (these colors come mostly from flavonoids), the color brown should be considered a “red flag” warning ofunhealthfulness in the crusts of bakery products and in meats or vegetables that have been baked, roasted, broiled, grilled, fried, sautéed, etc. It’s better for your health to steam, boil, or stew the meats and veggies.1

I can hear you now: “No! Nooo!” I know, I knooow. Forgoing the most delicious preparation methods seems almost insane—like giving up sweets.† But it does have its rewards: better health and longer life.

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†For some good news on the sweets front, see the article on page 11 of this issue. That article and this one share an emphasis on the importance of glycemic control for maintaining good health.

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A Prediction Ignored, Then Verified

Louis Camille Maillard (1878–1936)

To understand AGEs (about which there is much confusion in the popular literature), we need to go back a century, to prewar Paris. In 1912, a young French physician and chemist named Louis Camille Maillard (Mah·YAHR) began investigating the chemical reactions between nutrient sugars (such as glucose and fructose) and amino acids, the building blocks of proteins.

When Maillard heated aqueous solutions of sugars and amino acids for a few hours, they turned a yellow-brown color, the result of a series of reactions that yielded a witches’ brew of products. Significantly, the same phenomenon occurred, albeit much more slowly, when he simply allowed the solutions to sit for a few weeks under physiological conditions (37ºC, pH 7.4).

Maillard had discovered a series of complex and important chemical reactions that now bear his name:Maillard reactions. He predicted that they would occur in the human body, especially in diabetic patients because of their chronically high glucose (blood sugar) levels. This prophetic insight went unnoticed for half a century, however, and he did not live to see it realized.

In 1971, scientists investigating the blood of diabetic patients discovered that some of the hemoglobin wasglycated. Glycation—the first step in the Maillard reactions—is the chemical attachment of a sugar molecule (either free or bound in a polysaccharide, such as starch) to an amino acid (either free or bound in a protein, such as hemoglobin). As the ensuing reactions advance through numerous complex stages, they can lead to a great variety of endproducts, most of which are harmful to us. These are the “advanced glycation endproducts” we now call AGEs.

AGEs Make Diabetes a Kind of Accelerated Aging

The sugar of greatest importance to us is glucose, because it’s the principal product of carbohydrate digestion, and it’s our principal fuel for energy metabolism. Glucose is among the least reactive of the nutrient sugars in the Maillard reactions. This may have led, through natural selection, to its being the evolutionarily favored sugar in mammalian species.2,3

The glycation reactivity of fructose (fruit sugar), on the other hand, is about ten times higher than that of glucose. Fructose is found in honey and many fruits, and it’s also one-half of the sucrose (table sugar) molecule, the other half being glucose. The exceptional propensity of fructose to produce AGEs is another reason why we (diabetics especially) should minimize our intake of sucrose and high-fructose corn syrup.

Because diabetics tend to have higher glucose levels than nondiabetics, they also have higher AGE levels at any given age, compared with nondiabetic individuals. And because AGEs form earlier in life and more rapidly in these patients, diabetes can be thought of as an accelerated form of aging. Much evidence suggests that AGEs are involved in almost all the complications of diabetes, which arise from damage to blood vessels throughout the body.4

AGEs—A Haphazard Process

Unlike most biologically important reactions, which are catalyzed by enzymes, glycation is not catalyzed. It’s a nonenzymatic version of a common and necessary biochemical process calledglycosylation, which is tightly controlled as to the time, place, and extent of its occurrence. The lack of enzymatic control over the glycation process means that this reaction can occur haphazardly—anytime, anywhere, to an extent limited only by the availability of the reactants—and it does, with generally harmful results that tend to accumulate over time.

Now you get the picture: there’s nothing to restrain glucose from reacting with amino acids and proteins, which are everywhere in the body. Since we can’t live without glucose, we can’t avoid AGEs—but we can slow down their formation. Another bit of good news is that not all glucose will react similarly with all proteins (of which there are about 25,000 different kinds in humans)—the extent of the reaction depends on a myriad of factors that can vary greatly throughout the body. But, as we saw above, the list of “hot spots” is large, and the long-term consequences are horrendous.

Most AGEs Are Incredibly Yummy

So much for the AGEs that form in our bodies as a result of normal metabolism. What about the ones we ingest with our food? Isn’t it adding insult to injury to eat the very kinds of compounds we’re trying to minimize the formation of in our bodies? Of course it is, but if you’re the kind of person who likes food, you probably love dietary AGEs (which should be called DAGEs), because they happen to be among the tastiest compounds known. (This is another of Ma Nature’s cruel jokes at our expense.)

It’s no accident that many AGEs are found in commercial food flavorings designed to make all kinds of foods taste even better, as though they’d been browned. (The Maillard reactions are, in fact, the basis of the flavoring industry.) Nor is it an accident that the bits of browned stuff left over in the frying or roasting pan, which celebrity chef Emeril Lagasse calls “yum-yums,” are yummy because of the Maillard browning, which is the principal source of DAGEs.

Oh, What a Tangled Web Maillard Wove

Over 1000 DAGEs are currently known, and there are probably many more. They’re the products of Maillard reactions occurring under dry conditions at temperatures above about 120ºC (248ºF). The tangled web of chemical reactions is so complex that many chemists have spent their whole lives trying to unravel it. The caramelization (browning) of sugar, by the way, may appear to be a Maillard-type process, but it’s not—the chemistry is entirely different.

In books on the chemistry of cooking, the Maillard reactions are portrayed in a good light because of the gustatory wonders they produce. Chefs love them, naturally, and they’re not about to commit professional suicide by shunning them just because some scientists recommend it. In any case, the books claim that the Maillard reactions occur only with high, dry heat, not at the lower temperatures involved in cooking with water, where the maximum is 100ºC (212ºF). That may be true in the kitchen, where time scales are usually very short, but in real life, as Maillard himself showed, the process does occur—very slowly—even under cool, wet conditions.

You Are So Cool (and Wet)

Not to get too personal, but your body, compared with an oven or barbeque, is rather cool and wet, and the Maillard reactions will proceed, slowly but surely, for all the days of your life. You could, however, resist this slow tide by taking antiglycating supplements every day.

And given a choice between eating browned foods that are high in Maillard products, or water-cooked foods that have virtually none . . . well, that too is a choice that only you can make. (Let’s hope the federal health police don’t someday try to make it for you.)

AGEs Large and Small There are hundreds of known, naturally occurring AGEs produced by the Maillard reactions in our bodies. Some of these are very large molecules produced by the chemical cross-linking—induced by sugars—of proteins that were never intended to be linked. This produces a kind of cellular “gunk,” which in principle is not unlike the crud that builds up in your car’s engine over time. In both cases, performance is impaired, and the system can be brought to a premature halt if suitable measures are not taken. One example of the slow damage due to cross-linking is the gradual stiffening of the protein collagen, which is the principal component of our connective tissue and cartilage. The resulting loss of tissue elasticity can occur in the heart, blood vessels, skin, eyes, kidneys, joints, etc., with results that older people know all too well. Many other AGEs are relatively small degradation products of the Maillard reactions, and some of these contain a reactive chemical group called the carbonyl group, R2C=O. [The carbonyl is the C=O part; the two Rs can be almost anything but hydrogen atoms, as, e.g., in acetone, (CH3)2C=O, which contains two methyl groups.] Carbonyl compounds are common in organic chemistry, and many of them instigate harmful chemical reactions in living organisms. In fact, the glycation reaction that begins the Maillard process involves a carbonyl group on the sugar molecule reacting with the amino group of an amino acid. The spectrum of damage caused by carbonyl compounds is calledcarbonyl stress. It’s analogous to the oxidative stress caused by reactive oxygen species, including free radicals. AGEs of a sort can also be formed, by the way, by the reactions of sugars or other reactive carbonyl compounds with two other important types of biological molecules: lipids (fats) and nucleic acids (DNA and RNA). These AGEs too are deleterious to our health.

References

1. Harding A. How food is prepared important to health: study. Reuters Health, May 7, 2007.
2. Ahmed N. Advanced glycation endproducts—role in pathology of diabetic complications. Diabetes Res Clin Pract 2005;67:3-21.
3. Ulrich P, Cerami A. Protein glycation, diabetes, and aging. Recent Prog Horm Res 2001;56:1-21.
4. Peppa M, Uribarri J, Vlassara H. Glucose, advanced glycation end products, and diabetes complications: what is new and what works. Clin Diabetes 2003;21(4):186-7.

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Will Block is the publisher and editorial director of Life Enhancement magazine.

Digestive Intelligence: A Holistic View of Your Second Brain

Each Human has two brains, one in the skull the second brain is in your digestion gut system. 



Digestive Intelligence tells the fascinating story of how our digestive systems are the centre of our bodies’ second brain and how we think and live our emotions via our stomachs.

Not impossible when you consider there is something equivalent to the size of a village football pitch hiding inside our bellies – that’s the incredible magnitude of our digestive systems. They contain an extensive network of nerve cells, called neurons, which carry information to the brain and thus have a profound effect upon our intellectual, emotional and immune processes.

Dr Matveikova answers the obvious questions: “How?” and “Why can this be so?” by explaining, in straight forward layman’s language, that the digestive system contains more than one million neurones, identical to those in the brain and is responsible for producing 90% of the body’s hormone, serotonin, the all-important hormone which makes us feel happy and full of wellbeing. It follows, that if our stomachs are “out of sorts” we can feel irritable, in a bad mood, lacking in energy and those feelings will block our intellectual productivity, tend to disorientate us and completely change our thought patterns and physical processes.

Click Here to See Inside and read the book . 

Page 13 : Preface

The other day my bank branch manager (who also happens to be an obedient patient of mine) : "I could never have been a doctor! You have too much responsibility for the health and life of others: I would feel dreadful. In the bank I can do something wrong, make an error, and nothing happens that I can't put right, but with the health of a human you can't make too many mistakes." 

Modern society demands much of a doctor. We want to have the brilliant Dr. House as our GP and to stay in good health with a minimum visits to the doctor's office, without taking pills and without suffering discomfort or pain. 

Working in a bank you comply with financial regulations and the orders you are given, which leaves little room for any doubts; you do what you are asked to do, day after day. A visit to the doctor, however, is optional, not obligatory: you can postpone your checkups and ignore your problems if you want, and you can find fault with your practitioner and not follow your doctor's instructions. 

Society doesn't force you to take care of yourself and to stay in good health. The most it does is to suggest and advise, but nobody make sure  that you are fit and well. It's not like that with bills and bank statements. To your bank manager, you are transparent and the diagnostic is always clear. To your doctor, you are a tired and secretive person with a series of problems that not even the doctor knows how to begin to deal with. Are you going to listen to the doctor and carry out the doctor's orders?

To stay in good health and prevent the development or advance of disease is your prerogative, but if you don't choose this course, society won't cast your out. On the contrary, it will look after you as best as it can -- even if you think the care you are given is  not sufficient. In Europe and most other western countries, when you fall ill, medical attention and hospital treatment will be provided. Your bank, on the other hand, will  throw you out and close your account. At a medical center, though, that is not our way; we are there to help you. 

When you go to your bank, your are prepared and are already informed about the subject in hand. There is no reason why you cannot do the same when you come in for a medical consultation. Experts say that 80 percent of the care that a chronically ill person needs can be provided  by himself, if he is a given adequate preparation and training. They also estimate that 90 percent of the illnesses and the problems that cause people to visit doctors could be prevented by following a healthy diet, doing a minimum of         activity, and observing basic hygiene. 

  For  doctors to be precise in their work and able to help their patients, they need enough space in their busy schedule for those 10 percent of cases that really need serious assistance. If the remaining 90 percent could be educated about health and personal care, imagine how helpful that would be. 

  Complaining about doctors, the current health system and long waiting lists for tests only leads to anxiety and frustration, and in the short term will not improve things. So why not take another approach and get to know yourself?


Our Second Brain and Digestive Intelligence
by Irina Matveikova.

Remarkable as it may sound to you - our digestive system has a very sophisticated design, complexity and intelligence! It acts independently and so specifically in every single person that we professionals, are regularly surprised by its behaviour. The digestive tract has always been overlooked and almost ‘discriminated’ against; treated as some less important part of the body because it appeared to be very primitive and basic in its functions. The gut was frequently considered be totally unattractive, dirty and an object of shame.

The general public used to ignore the digestive system and treat it as ‘must function’ in spite of everything thrown its way - from a bad diet and lifestyle, to abuse of alcohol, medications, smoking and drugs; until the stomach would protest and manifest extreme symptoms of pain, bloating, diarrhoea and many other problems.

So then it had to be ‘shut down’ with symptomatic treatments. People did not pay much attention to digestive discomfort; removing this temporary upset was sufficient and they never looked more deeply into the reasons behind their own digestive rebellions. Hopefully, and thanks to the last 20 years of medical research, we have changed our vision and our knowledge about digestive functions. This precious system was finally plucked from obscurity and is now positioned in its rightful place and attracts a lot of attention from scientists.

We have a true second brain in our guts; its neuronal function is very similar to the brain in our heads. Inside our belly is an extensive network of neurons located between the two muscular layers of the walls of the digestive system. Moreover, the structure of these digestive neurons is identical to that of the neurons in the brain; both produce similar chemical molecules, neurotransmitters and hormones, which are mostly necessary for our intercellular communications and the correct functioning of the entire body. In medical science our second, digestive, brain has a name: the Enteric Nervous System (ENS).

According to new data, the total number of neurons (brain cells) found in our ENS is more than one hundred million. This figure represents a considerably higher number of neurons than in the spinal cord, for example. The brain in our gut is the main production line and storage centre for many neurotransmitters. These substances regulate our moods and our emotions, physical and our psychological well-being.

The presence of such a wide variety of neurotransmitters in our intestines is a clear indication of the complexity of the rich digestive language that is spoken from our gut and of its ability to carry out neuronal functions and express its own emotions.
In 1999 it was revealed that 90 percent of serotonin (the famous ‘happiness’ hormone) is produced and stored in the intestinal walls! Only the remaining 10 percent of the body’s serotonin is synthesized in the neurons of the central nervous system - the cerebral brain - or our ‘higher brain’.

The minimal amount of serotonin in the higher brain is, nevertheless, of vital importance to human beings. It performs various functions including regulating our ‘good’ moods (that calm, relaxed sensation and feeling of wellbeing), sleep, and muscular contractions. It also intervenes in cognitive functions such as memory and learning. Serotonin is the ‘messenger of happiness’, and we do, indeed, have a sea of this substance stored in our digestive system. If we could just learn how to utilize and to mobilize the tremendous neurological and hormonal potential of our gut!

So, how can we take advantage of this valuable resource and make the best use of it for our mental and digestive health?
This is a truly challenging task for researchers.  That is why scientists and the pharmaceutical industry are currently devoting so much of their research and testing to Neurogastroenterology - a new branch of medicine that studies our Second Brain and its role in health and diseases.

Each of us from time to time has a ‘gut feeling’, a warning that comes from deep inside and can often appear in intense or extreme emotional situations. This is our second brain talking to us. It said that our second brain is more authentic, more sincere and more connected to our true inner feelings than the cerebral brain; and, furthermore, is the more rebellious one of the two. It evades any social influences, logic and our even own mental powers. If our gut nervous centre suffers neurosis, then it’s clear we should definitely not ignore it and, indeed, we cannot afford to do so because it sends us signals about our true state of health and mind.

Additionally, it is the centre of our intuition, premonition, control, fear, hidden obsessions, etc. Our digestive neurological language can present itself as a whole range of sensations: from a pleasurable thrill to a nervous knot, a hollow feeling, or a pain. So we had better stop for a while, to analyze its message and to correct the problem. The digestive system has great plasticity and capacity for recuperation and would be truly thankful - in only two-three days - for a more careful diet, good sleep, relaxation and a basic balancing of your lifestyle. We can afford this short break and self-care, can’t we?



In my book, Digestive Intelligence, you will find many tips about how to detoxify your gut and liver, how to organize your detox diet, to nourish your systems and even how to breathe correctly. I do encourage you to learn to interpret your gut signals and to understand the origin and mechanisms of your stomachs upsets and try to correct and to control them in a preventive and holistic way.
Although Western medicine has only recognized the ‘second brain’ recently, in Eastern medicine the belly has long been viewed as the vital centre of the human organism. Traditional Chinese medicine recognizes the gut as ‘the centre of energy, the sea of qi’. Qi is the vital energy, force, or impulse. In contrast to the energy controlled by willpower or ‘doing’, the qi in the belly is felt and allowed to come. Ideally, we should be in contact with this centre (the gut itself) and concentrate on its energy.
In Japanese martial arts, the hara represents the belly, man’s centre of being, the sea of qi.  To be hara-centered is equivalent to an optimal state of health and integration of all the bodily systems, longevity, and wellbeing. It leads to a general state of serenity and profound calm, awareness, reason, personal power, and balanced action.
Those with weak hara have fragile health, get angry and lose their temper easily and, when faced with adversity, they quickly lose their self-control. The expression ‘to be centered’, or in contact with our internal energy, has a lot to do with having a balanced and healthy digestive system, in the language of Western medicine.

Once again I would like to emphasize that there is a direct connection between the psyche and the stomach. Many intestinal problems can be explained by the malfunctioning of the intestinal brain, or by interferences in its communication with the higher brain. The gut brain is where fear, anxiety, or phobias originate, along with excessive control or obsessions, and also premonition, apprehension, and intuition. Scientists consider that the abdominal brain can also memorize certain emotions, childhood traumas, experience stress, and suffer its own psychoneurosis.
Nowadays we know that there is constant communication between the two brains: the one inside our skull and its brother down there in our gut and the influence travels in both directions.  I can assure you that the relationship between the two brains, which involves hormonal, metabolic, and emotional levels, is very complex—we could even call it intellectual; it is also normally quite democratic and mutually respectful.
And now we are about to discover even more secrets about our digestive world. 
New and astonishing scientific news reveals how our intestinal microbiota (the universe of bugs that lives inside our belly) influences all the functions of our entire body.

So much so that Digestive Intelligence can now be interpreted as a gut-brain-microbiota axis!

Mounting evidence is suggesting that particular aspects of human health and disease may be attributed to the trillions of microbes that inhabit our gastrointestinal tract, collectively referred to as the gut microbiota. We have more microbes in our body than the amount of our own cells. Or, put another way, we could even consider ourselves more bacteria that human! Our dependence on our ecology and the universe of bugs that cover us from inside and outside is vital.
So the microbiota associated with the human body are now being intensively studied in both aspects: as a risk factor for disease and a modulator of health and ageing. The organisms that live inside our innards contribute not only to each others function and survival but humans have evolved to depend on the extensive physiology and metabolism that microbiota provides. The power of the gut bacteria in regulating human health cannot be overestimated.

Consider this: the number of unique genes contributed by our gut inhabitants is greater by 150-fold than that encoded within the human genome. The human body uses the sequences of bacterial genomes for its own metabolic, regenerative, immune and nutritive needs. We cannot live a healthy, or a long life without the help of our bacterial universe. Mapping of the bacterial genome of each person can give us information about their health risk of different diseases, body weight and longevity tendencies and even character.  Pretty soon we will have our own bacterial identification code, which is going to be a unique digital signature. And medical genetic engineering will begin to use the extended genome of our gut microbiota for future treatments, which will bring about a quantum revolution in modern medicine.

However, digestive pathology is already growing at such an incredible speed in our Western world that currently every second adult suffers from digestive troubles. How we can stop this fast-track growth? What do we need to learn, in order to put the brakes on this rapidly spreading epidemic? It is already becoming clear to many of us that stress, tension, never-ending work and responsibilities exhaust the body and the mind and cause the systems of the body to start to fail; beginning primarily with the digestive and psychological functions.
So what realistically can we do? To stop the world and change our lives seems impossible. Medications don’t appear to be the solution to everything, either. Current studies and research in biotechnology and modern neuroscience are very important and hold great promise for the medicines of the future but it is early days yet, in terms of their practical application.
In my professional opinion, the future is in education and prevention. Each of us has to discover own health potential, learn how we function and question what is causing our health problems.  Let’s be curious about how to care and prevent and how to do things in a very practical and positive way.
No unified formula of diet, exercise or magic pill exists. Instead, we have to be self-aware and regularly perform a technical inspection of our ‘life vehicle’ (our body) by doing the detoxing and nourishment programme that I write about in my books. There, you can learn how your gut directly influences your character, behaviour and even your immune defence system. You’ll also be able to recognize the complexity of your relationship with food and discover more about the different types of intolerances and sensitivities.
You’ll know more about the connection between gut health and allergies, mental disorders, obesity, depression and, even, cancer.  We have the internal mechanisms we need for recovery and cure. Our body talks to us and warns us. If we could just decode its signals and take notice of them, then we would be much stronger and healthier.

Welcome, to your own new world of Digestive Intelligence!

how your digestive system works

How long does it take to digest food — from the time you eat it to the time you excrete it? 
The digestion process takes between 24 and 72 hours, Elimination of undigested residue food  usually begins after 24 hours. Complete elimination from the body may take several days. 

Answers from Michael F. Picco, M.D.
Digestion time varies between individuals and between men and women. After you eat, it takes about six to eight hours for food to pass through your stomach and small intestine. Food then enters your large intestine (colon) for further digestion, absorption of water and, finally, elimination of undigested food.

In the 1980s, Mayo Clinic researchers measured digestion time in 21 healthy people. Total transit time, from eating to elimination in stool, averaged 53 hours (although that figure is a little overstated, because the markers used by the researchers passed more slowly through the stomach than actual food). The average transit time through just the large intestine (colon) was 40 hours, with significant difference between men and women: 33 hours for men, 47 hours for women.

Two British doctors studied digestion time in children. They fed 35 children juice containing a red marker and asked the children's mothers to note when the stool first turned red. The mean time of transit from mouth to anus for the group was 33 hours (meaning half the children had digestion times slower than this and half had digestion times greater than this).

With Regards,
Michael F. Picco, M.D.




Your digestive system gears up
A fresh-baked apple pie has just come out of the oven. Just the sight and smell of it are enough to make you start salivating. So even before you take a bite, your digestive system has swung into action.

After the first morsel enters your mouth, the many organs of your digestive tract kick into high gear. Here's a look at how your digestive system works, from top to bottom.



Mouth and salivary glands
After you take your first bite of pie, your salivary glands produce saliva — a mixture of secretions that help lubricate and break down food. Besides the salivary glands in the lining of your mouth, you have three pairs of larger salivary glands — the parotid, sublingual and submandibular glands. You typically produce about 2 pints (about 1 liter) of saliva a day.

Not all of the work is chemical, though. As you savor the bite of pie, your teeth work to break down the pie while your tongue mixes it with saliva. This action transforms it into a soft, moist, rounded mass (bolus) suitable for swallowing.



Esophagus
As you swallow the bite of pie, muscles in your mouth and throat propel it to your upper esophagus, the tube that connects your throat to your stomach. Muscles in the wall of your esophagus create synchronized waves — one after another — that propel the pie into your stomach. In this process, called peristalsis, muscles behind the bolus of pie contract, squeezing it forward, while muscles ahead of it relax, allowing it to advance without resistance.

When the bolus reaches the lower end of your esophagus, pressure from the food signals a muscular valve — the lower esophageal sphincter — to relax and let the food enter your stomach.



Stomach
After entering your stomach, the pie is broken down further. With its powerful muscles, the stomach begins churning and mixing the food into smaller and smaller pieces. Your digestive glands in your stomach lining produce stomach acid and enzymes, which mix with the food to form a murky semifluid or paste called chyme.

Once the chyme is well-mixed, waves of muscle contractions propel it through a valve called the pylorus and into the first section of your small intestine (duodenum). The pylorus might release about an eighth of an ounce (about 4 milliliters) of chyme at a time. The rest is held back for more mixing.



Pancreas, liver and gallbladder
In your duodenum, digestion continues as chyme from the stomach mixes with a variety of digestive juices from your pancreas, liver and gallbladder:

Pancreas. The pancreas produces digestive enzymes that help break down proteins, carbohydrates and fats.

Liver. The liver produces bile, a solution that helps you digest fats.

Gallbladder. The gallbladder stores bile. As fatty food enters the upper portion of your small intestine (the duodenum), the gallbladder squeezes bile into the small intestine through the bile ducts.



Small intestine
As bile and pancreatic digestive juices mix with other juices secreted by the wall of your small intestine, digestion continues. What was once apple pie is propelled into the second portion of your small intestine, the jejunum. Here it's further broken down into smaller molecules of nutrients that can be absorbed. Then it moves into the final and longest portion of your small intestine — the ileum — where virtually all of the remaining nutrients are absorbed through the lining of the ileum's wall.

What remains of the food when it reaches the end of the ileum is a combination of water, electrolytes — such as sodium and chloride — and waste products, such as plant fiber and dead cells shed from the lining of your digestive tract.



Large intestine
As this residue passes through the colon, nearly all of the water is absorbed, leaving a usually soft but formed substance called stool. Muscles in the wall of your colon separate the waste into small segments that are pushed into your lower colon and rectum. As the rectal walls are stretched, they signal the need for a bowel movement.

When the sphincter muscles in your anus relax, the rectal walls contract to increase pressure. These coordinated muscle contractions expel the stool.

The End of Slide Show. 

Maintaining Life: Necessary Life Functions

Necessary Life Functions

We’ll take a look at what human body actually does.

Like all complex animals, humans must maintain a core set of necessary life functions to survive. These include maintaining boundaries, movement, responsiveness, digestion, metabolism, excretion, reproduction, and grow. In order to survive, humans also need nutrients, oxygen, water and an appropriate atmosphere. We’ll discuss these topics in depth below.

Maintaining boundaries

All organisms must be able to maintain boundaries and separate their internal environment from the external one. For example, each cell in the human body is enclosed by a selectively permeable membrane which allows it to take in substances and excrete waste, all while blocking potentially harmful substances. Additionally, the body itself is protected by the integumentary system, or skin. The layer of skin around our bodies protects our internal environment from the external world.

Movement
The muscular system propels our bodies and allows us to move from one place to another. The skeletal system provides the bony framework our muscles need to pull on as they work to produce movement. Without these features, humans wouldn’t be able to perform necessary life functions to survive.




Responsiveness
Responsiveness is defined as the ability to sense changes in the environment and then respond to them (also called excitability). Responsiveness is an extremely important necessary life function. For instance, if you cut your hand open on a razor blade, your body produces a reflex and you involuntarily pull your hand away from the razor. You don’t have to think about it, your body just naturally pulls your hand away. Many systems within the human body act in this exact same manner.

Digestion
In order for nutrients and minerals to be absorbed into blood , food we eat must be broken down into smaller molecules. The digestive system breaks down ingested food and liquid into smaller molecules our body can absorb. In turn, the nutrient-rich blood is then distributed throughout the body by the cardiovascular system.

Metabolism
Metabolism is a term that includes all chemical reactions that occur within the body. Metabolism is regulated by hormones secreted from (glands) the endocrine system.

Excretion
If the human body is to operate correctly, it must be able to get rid of waste and nonessential items. Several organ systems participate in the excretion of waste products. For instance, the urinary system disposes nitrogenous waste while the digestive system rids the body of indigestible food as feces.

Reproduction
In order to survive, all living organisms must reproduce. The reproductive system is responsible for producing offspring and is directly regulated by hormones of the endocrine system.

Growth
Humans must grow to survive. The scientific term for growth means “constructive activities must occur at a faster rate than destructive ones”.

Survival Needs

Survival needs include nutrients (food), oxygen, water and an appropriate atmosphere.

Nutrients
Nutrients contained in food and liquids contain chemical substances used for energy and cell building. Carbohydrates, vitamins, minerals, proteins, and fats are all vital in maintaining a healthy body. For instance, calcium helps make bones hard and vitamin D is needed in order to produce sufficient amounts of calcium.

Oxygen
Human cells can only survive for a few minutes without oxygen. Chemical reactions that release energy from foods are oxidative reactions and require oxygen. In fact, oxygen is so vital to the human body that it would only last a few minutes without it. The respiratory and cardiovascular systems work in conjunction to make oxygen available throughout the body.



Water
The human body is 60-80% water. Water is the most abundant chemical substance in the body and provides the environment necessary for life. We obtain water through food and liquids and loose it through bodily excretions and evaporation (from the skin).

Appropriate atmospheric pressure
Breathing and gas exchange in the lungs depend on the right type of atmospheric pressure. For instance, on top of Mount Everest (at high altitude), gas exchange can be inadequate for the human body to survive.

Digestive System

The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus.

The major organs of the human gastrointestinal system.

The major organs of the human gastrointestinal system are identified in this drawing. The upper gastrointestinal tract consists of the esophagus, stomach, and duodenum. The lower gastrointestinal tract includes most of the small intestine and all of the large intestine. According to some sources, it also includes the anus.

Upper Gastrointestinal Tract

The upper gastrointestinal tract consists of the esophagus, stomach, and duodenum. The exact demarcation between upper and lower can vary. Upon gross dissection, the duodenum may appear to be a unified organ, but it is often divided into two parts based upon function, arterial supply, or embryology.

The upper gastrointestinal tract includes the:

Esophagus, the fibromuscular tube that food passes through—aided by peristaltic contractions—the pharynx to the stomach.

Stomach, which secretes protein-digesting enzymes called proteases and strong acids to aid in food digestion, before sending the partially digested food to the small intestines.

Duodenum, the first section of the small intestine that may be the principal site for iron absorption.

Lower Gastrointestinal Tract

The lower gastrointestinal tract includes most of the small intestine and all of the large intestine. According to some sources, it also includes the anus.




The small intestine has three parts:

Duodenum: Here the digestive juices from the pancreas (digestive enzymes) and the gallbladder (bile) mix together. The digestive enzymes break down proteins and bile and emulsify fats into micelles. The duodenum contains Brunner's glands that produce bicarbonate, and pancreatic juice that contains bicarbonate to neutralize hydrochloric acid in the stomach.

Jejunum: This is the midsection of the intestine, connecting the duodenum to the ileum. It contains the plicae circulares and villi to increase the surface area of that part of the GI tract.

Ileum: This has villi, where all soluble molecules are absorbed into the blood ( through the capillaries and lacteals).

The large intestine has four parts:

1.Cecum, the vermiform appendix that is attached to the cecum.

2.Colon, which includes the ascending colon, transverse colon, descending colon, and sigmoid flexure. The main function of the colon is to absorb water, but it also contains bacteria that produce beneficial vitamins like vitamin K.

3.Rectum.

4.Anus.

The ligament of Treitz is sometimes used to divide the upper and lower GI tracts.




Processes and Functions of the Digestive System

Digestion is necessary for absorbing nutrients from food and occurs through two processes: mechanical and chemical digestion.

The Digestive System

The proper functioning of the gastrointestinal (GI) tract is imperative for our well being and life-long health. A non-functioning or poorly-functioning GI tract can be the source of many chronic health problems that can interfere with your quality of life. 

Here is a look at the importance of two main functions of the digestive system: digestion and absorption.

Digestion

The gastrointestinal tract is responsible for the breakdown and absorption of the various foods and liquids needed to sustain life. Many different organs have essential roles in the digestion of food, from the mechanical breakdown of food by the teeth to the creation of bile (an emulsifier) by the liver. 

Bile production plays a important role in digestion: it is stored and concentrated in the gallbladder during fasting stages, and discharged to the small intestine. Pancreatic juices are excreted into the digestive system to break down complex molecules such as proteins and fats. 

Absorption

Absorption occurs in the small intestines, where nutrients directly enter the bloodstream.

Each component of the digestive system plays a special role in these complimentary processes. The structure of each component highlights the function of that particular organ, providing a seamless anatomy to keep our body fueled and healthy.

Components of the Digestive System

The digestive system is comprised of the alimentary canal, or the digestive tract, and other accessory organs that play a part in digestion—such as the liver, the gallbladder, and the pancreas. The alimentary canal and the GI tract are terms that are sometimes used interchangeably. 

The alimentary canal is the long tube that runs from the mouth (where the food enters) to the anus (where indigestible waste leaves). The organs in the alimentary canal include the mouth (the site of mastication), the esophagus, the stomach, the small and large intestines, the rectum, and the anus. From mouth to anus, the average adult digestive tract is about thirty feet (30') long.

Processes of Digestion

Food is the body's source of fuel. The nutrients in food give the body's cells the energy they need to operate. Before food can be used it has to be mechanically broken down into tiny pieces, then chemically broken down so nutrients can be absorbed. 

In humans, proteins need to be broken down into amino acids, starches into sugars, and fats into fatty acids and glycerol. This mechanical and chemical breakdown encompasses the process of digestion.

To recap these twin processes:

Mechanical digestion: Larger pieces of food get broken down into smaller pieces while being prepared for chemical digestion; this process starts in the mouth and continues into the stomach. 

Chemical digestion: Several different enzymes break down macromolecules into smaller molecules that can be absorbed. The process starts in the mouth and continues into the intestines. 

Moistening and Breakdown of Food

Digestion begins in the mouth. A brain reflex triggers the flow of saliva when we see or even think about food. Enzymes in saliva then begin the chemical breakdown of food; teeth aid in the mechanical breakdown of larger food particles.

Saliva moistens the food, while the teeth masticate the food and make it easier to swallow. To accomplish this moistening goal, the salivary glands produce an estimated three liters of saliva per day. 

Amylase, the digestive enzyme found in saliva, starts to break down starch into simple sugars before the food even leaves the mouth. The nervous pathway involved in salivary excretion requires stimulation of receptors in the mouth, sensory impulses to the brain stem, and parasympathetic impulses to salivary glands. Once food is moistened and rolled and ready to swallow, it is known as a bolus.

Swallowing and the Movement of Food

For swallowing to happen correctly a combination of 25 muscles must all work together at the same time. Swallowing occurs when the muscles in your tongue and mouth move the bolus into your pharynx. Bolus (from Latin bolus, ball)is a small rounded mass of a substance, especially of chewed food at the moment of swallowing.
"mucin holds the particles of food together in a ball or bolus" Mucin is a glycoprotein constituent of mucus.
"mucin is secreted by the salivary glands"

The pharynx, which is the passageway for food and air, is about five inches (5") long—a remarkably small space. A small flap of skin called the epiglottis closes over the pharynx to prevent food from entering the trachea, which would cause choking. Instead, food is pushed into the muscular tube called the esophagus. Waves of muscle movement, called peristalsis, move the bolus down to the stomach.

While in the digestive tract, the food is really passing through the body rather than being in the body. The smooth muscles of the tubular digestive organs move the food efficiently along as it is broken down into easily absorbed ions and molecules.

Large-scale Breakdown in the Stomach

Once the bolus reaches the stomach, gastric juices mix with the partially digested food and continue the breakdown process. The bolus is converted into a slimy material called chyme. 



Major digestive hormones

There are at least five major digestive hormones in the gut of mammals that help process food through chemical digestion in the gall bladder, duodenum, stomach, and pancrease. These hormones are cholecystokinin, gastric inhibitory polypeptide, motilin, secretin, and gastrin.

This (see above) is a drawing of the digestive system. This shows the five major digestive hormones in the gut of mammals that help process food through chemical digestion in the gall bladder, duodenum, stomach, and pancrease. These hormones are cholecystokinin, gastric inhibitory polypeptide, motilin, secretin, and gastrin.

The stomach is a muscular bag that maneuvers food particles, mixing highly acidic gastric juice and powerful digestive enzymes with the chyme to prepare for nutrient absorption in the small intestine. Stimulatory hormones such as gastrin and motilin help the stomach pump gastric juice and move chyme. The complex network of hormones eventually prepares chyme for entry into the duodenum, the first segment of the small intestine.

Absorption in the Small Intestine

During absorption, the nutrients that come from food (such as proteins, fats, carbohydrates, vitamins, and minerals) pass through the wall of the small intestine and into the bloodstream. In this way nutrients can be distributed throughout the rest of the body. The small intestine increases surface area for absorption through tiny interior projections, like small fingers, called villi.

Waste Compaction in the Large Intestine

In the large intestine there is resorption of water and absorption of certain minerals as feces are formed. Feces are the waste parts of the food that the body passes out through the anus.

Organs of the Digestive System

The organs of the digestive system can be divided into upper and lower digestive tracts. The upper digestive tract consists of the esophagus, stomach, and the small intestine; the lower tract includes all of the large intestine, the rectum, and anus.

The human body uses a variety of mental and physiological cues to initiate the process of digestion. Throughout our gastrointestinal (GI) tract, each organ serves a specific purpose to bring our food from the plate to a digestible substance from which nutrients can be extracted.

The Digestive Tube

Our digestive system is like a long tube, with different segments doing different jobs. The major organs within our digestive system can be split into two major segments of this tube: the upper gastrointestinal tract, and the lower gastrointestinal tract.

The Upper Gastrointestinal Tract

The upper gastrointestinal, or GI, tract is made up of three main parts: 

The esophagus.

The stomach.

The small intestine. 



The Lower Gastrointestinal Tract

The lower GI tract contains the remainder of the system: 

The large intestine.

The rectum.

The anus. 

The exact dividing line between upper and lower tracts can vary, depending on which medical specialist is examining the GI tract.

Food Breakdown and Absorption: The Upper GI Tract

When we take a bite of food, the food material gets chewed up and processed in the mouth, where saliva begins the process of chemical and mechanical breakdown. The chewing process is also known as mastication. 

When we mix up food with saliva, the resulting mushy wad is called a bolus. The bolus gets swallowed, and begins its journey through the upper gastrointestinal tract.

The Esophagus

The upper GI tract begins with the esophagus, the long muscular tube that carries food to the stomach. The throat cavity in which our esophagus originates is known as the pharynx. As we swallow, the bolus moves down our esophagus, from the pharynx to the stomach, through waves of muscle movement known as peristalsis. Next the bolus reaches the stomach itself. 

The Stomach

The stomach is a muscular, hollow bag that is an important part of the upper GI tract. Many organisms have a variety of stomach types, with many segments or even multiple stomachs. As humans, we have only one stomach. 

Here our bolus gets mixed with digestive acids, furthering breakdown of the bolus, and turning the bolus material into a slimy mess called chyme. The chyme moves on into the small intestine, where nutrients are absorbed.

The Small Intestine

The small intestine is an impressive digestive tube, spanning an average of 20 feet in length. The twists and turns of the small intestine, along with tiny interior projections known as villi, help to increase the surface area for nutrient absorption. 

This snaking tube is made up of three parts, in order from the stomach: 

The duodenum.

The jejunum. 

The ileum. 

As the chyme makes its way through each segment of the small intestine, pancreatic juices from the pancreas start to break down proteins. Soapy bile from the liver, stored in the gallbladder, gets squirted into the small intestine to help emulsify—or break apart—fats. 

Now thoroughly digested, with its nutrients absorbed along the path of the small intestine, what remains of our food gets passed into the lower GI tract.

Waste Compaction and Removal: The Lower Gastrointestinal Tract

The Large Intestine (Colon)

Following nutrient absorption, the food waste reaches the large intestine, or colon. The large intestine is responsible for compacting waste material, removing water, and producing feces—our solid-waste product. 

Accessory organs like the cecum and appendix, which are remnants of our evolutionary past, serve as special pockets at the beginning of the large intestine. The compacted and dried-out waste passes to the rectum, and out of the body through the anus. Healthy gut bacteria in the large intestine also help to metabolize our waste as it finishes its journey.



Enteric Nervous System

The enteric nervous system (ENS) is a subdivision of the autonomic nervous system (ANS) that directly controls the gastrointestinal system.

The gastrointestinal (GI) system has its own nervous system, the enteric nervous system (ENS). Neurogastroenterology is the study of the enteric nervous system, a subdivision of the autonomic nervous system (ANS) that directly controls the gastrointestinal system. The ENS is capable of autonomous functions such as the coordination of reflexes. 

Although it receives considerable innervation from the autonomic nervous system, it can and does operate independently of the brain and the spinal cord. The ENS consists of some 100 million neurons, one-thousandth of the number of neurons in the brain, and about one-tenth the number of neurons in the spinal cord. The enteric nervous system is embedded in the lining of the gastrointestinal system.

Ganglia of the ENS

The neurons of the ENS are collected into two types of ganglia: 

1.The myenteric (Auerbach's) plexus, located between the inner and outer layers of the muscularis externa.

2.The submucosal (Meissner's) plexus, located in the submucosa. 

The Myenteric Plexus 

The myenteric plexus is mainly organized as a longitudinal chains of neurons. When stimulated, this plexus increases the tone of the gut as well as the velocity and intensity of its contractions. This plexus is concerned with motility throughout the whole gut. Inhibition of the myenteric system helps to relax the sphincters—the muscular rings that control the flow of digested food or food waste. 

The Submucosal Plexus

The submucosal plexus is more involved with local conditions and controls local secretion and absorption, as well as local muscle movements. The mucosa and epithelial tissue associated with the submucosal plexus have sensory nerve endings that feed signals to both layers of the enteric plexus. These tissues also send information back to the sympathetic pre-vertebral ganglia, the spinal cord, and the brain stem.




Neural control of the gut.
An illustration of neural control of the gut wall by the autonomic nervous system and the enteric nervous system.


Function and Structure of the ENS

The enteric nervous system has been described as a second brain. There are several reasons for this. For instance, the enteric nervous system can operate autonomously. It normally communicates with the central nervous system (CNS) through the parasympathetic (e.g., via the vagus nerve) and sympathetic (e.g., via the prevertebral ganglia) nervous systems. However, vertebrate studies show that when the vagus nerve is severed, the enteric nervous system continues to function.

In vertebrates, the enteric nervous system includes efferent neurons, afferent neurons, and interneurons, all of which make the enteric nervous system capable of carrying reflexes and acting as an integrating center in the absence of CNS input. For instance, the sensory neurons report mechanical and chemical conditions, while the motor neurons control peristalsis and the churning of intestinal contents through the intestinal muscles. Other neurons control the secretion of enzymes. 

The enteric nervous system also makes use of more than 30 neurotransmitters, most of which are identical to the ones found in the CNS, such as acetylcholine, dopamine, and serotonin. More than 90% of the body's serotonin is in the gut, as well as about 50% of the body's dopamine, which is currently being studied to further our understanding of its utility in the brain.

The enteric nervous system has the capacity to alter its response depending on factors such as bulk and nutrient composition. In addition, the ENS contains support cells that are similar to the astroglia of the brain, as well as a diffusion barrier around the capillaries that surround the ganglia, which is similar to the blood–brain barrier of the cerebral blood vessels.

Regulation of ENS Function

The parasympathetic nervous system is able to stimulate the enteric nerves in order to increase enteric function. The parasympathetic enteric neurons function in defecation and provide a rich nerve supply to the sigmoid colon, the rectum, and the anus.

Conversely, stimulation of the enteric nerves by the sympathetic nervous system will inhibit enteric function and capabilities. Neurotransmitter secretion and direct inhibition of the enteric plexuses cause this stall in function. If the gut tract is irritated or distended, afferent nerves will send signals to the medulla of the brain for further processing.

Gastrointestinal Reflex Pathways

The digestive system functions via a system of long reflexes, short reflexes, and extrinsic reflexes from gastrointestinal (GI) peptides that work together.

Food in the Digestive System

The digestive system has a complex system of food movement and secretion regulation, which are vital for its proper function. Movement and secretion are regulated by long reflexes from the central nervous system (CNS), short reflexes from the enteric nervous system (ENS), and reflexes from the gastrointestinal system (GI) peptides that work in harmony with each other. 

In addition, there are three overarching reflexes that control the movement, digestion, and defecation of food and food waste: 

1.The enterogastric reflex.

2.The gastrocolic reflex.

3.The gastroileal reflex.

Long and Short Reflexes

Long reflexes to the digestive system involve a sensory neuron that sends information to the brain. This sensory information can come from within the digestive system, or from outside the body in the form of emotional response, danger, or a reaction to food. 

These alternative sensory responses from outside the digestive system are also known as feedforward reflexes. Emotional responses can also trigger GI responses, such as the butterflies in the stomach feeling when nervous. 

Control of the digestive system is also maintained by enteric nervous system (ENS), which can be thought of as a digestive brain that helps to regulate motility, secretion, and growth. The enteric nervous system can act as a fast, internal response to digestive stimuli. When this occurs, it is called a short reflex. 

Three Main Types of Gastrointestinal Reflex

1.The enterogastric reflex is stimulated by the presence of acid levels in the duodenum at a pH of 3–4 or in the stomach at a pH of 1.5. When this reflex is stimulated, the release of gastrin from G-cells in the antrum of the stomach is shut off. In turn, this inhibits gastric motility and the secretion of gastric acid (HCl). Enterogastric reflex activation causes decreased motility.

2.The gastrocolic reflex is the physiological reflex that controls the motility, or peristalsis, of the gastrointestinal tract. It involves an increase in motility of the colon in response to stretch in the stomach and the byproducts of digestion in the small intestine. Thus, this reflex is responsible for the urge to defecate following a meal. The small intestine also shows a similar motility response. The gastrocolic reflex also helps make room for food in the stomach.

3.The gastroileal reflex is a third type of gastrointestinal reflex. It works with the gastrocolic reflex to stimulate the urge to defecate. This urge is stimulated by the opening of the ileocecal valve and the movement of the digested contents from the ileum of the small intestine into the colon for compaction.




Peristalis
The gastrocolic reflex is one of a number of physiological reflexes that control the motility, or peristalsis, of the gastrointestinal tract.


GI Peptides that Contribute to Gastrointestinal Signals
GI peptides are signal molecules that are released into the blood by the GI cells themselves. They act on a variety of tissues that include the brain, the digestive accessory organs, and the GI tract. 

The effects range from excitatory or inhibitory effects on motility and secretion, to feelings of satiety or hunger when acting on the brain. These hormones fall into three major categories: 

1.The gastrin family.

2.The secretin family.

3.A third family that is composed of the hormones that do not fit into either of these two families.