The Healthy Digestive System
The Healthy Digestive System
(Reprinted with Permission “Renew Your Life” by Brenda Watson)
It is estimated that as much as 40% of the population suffer from some form of digestive stress. You may be unconcerned with the details of the digestive process or just want to know how to be or become healthy. If that is your goal, then the journey to achieving that goal begins with a clear understanding of a healthy digestive system.
What is Digestion?
Digestion encompasses the chemical and motor (physical motion) activities that separate food into its most basic components so that they can be absorbed through the lining of the small intestine. Digestion is the process of converting food into chemical substances that can be absorbed and assimilated. It begins in the mouth and ends in the large intestine or colon.
What does the Digestive System Do?
The digestive system has two broad functions: The first and best known is the digestion and absorption of food. The second function is the excretion of wastes. Both of these occur primarily in the small and large intestines; hence the phrase by Gloria Gilbere, ND (Naturopathic Doctor), “The road to health is paved with good intestines.”
What Organs Make Up the Digestive System?
The digestive tract is a tube (about 30 feet long) that begins with the mouth and ends with the anus. The digestive system (or gastrointestinal tract) is made up of the mouth, the oesophagus, stomach, small intestine, large intestine and anus. Along this tube are accessory organs like the teeth, tongue, salivary glands, gallbladder, liver and pancreas.
What are the Functions of the Digestive System?
The digestive tract has three primary functions:
• Motor – assisting food movement
• Secretory – preparing food for absorption by producing digestive enzymes
• Absorptive – breaking food down and converting it into substances that can be absorbed through digestion.
The Digestive Process
Digestion begins in the mouth where the teeth chew food into smaller particles. Then saliva coats and softens those food particles with enzymes (ptyalin and amylase) that break down carbohydrates (starches and sugars). Saliva also contains enzymes, such as lysozyme, that attack bacteria and their protein coats directly.
This is the body’s first line of defence against parasites and foreign invaders. Once chewing is completed (and sometimes even when it is not), food is swallowed and transferred down the oesophagus to the stomach.
The Oesophagus
The oesophagus is a 10-inch long muscular tube, lined with mucus-producing cells, which lubricates the food so that it passes through with ease. The oesophagus transports food to the stomach through the action of its wave-like muscular contractions (peristalsis). It is coated with a protective mucous lining. The muscular valve at the bottom of the oesophagus is known as the lower oesophageal sphincter. This valve remains tightly closed when food is not being eaten so that stomach acid cannot back into the oesophagus and cause heartburn. It opens and closes quickly to allow food to pass into the stomach.
The Stomach
Many people are surprised to find that very little absorption actually occurs in the stomach. The mucous cells of the stomach can absorb some water, short-chain fatty acids and certain drugs, such as alcohol and aspirin, but the stomach is essentially a holding and mixing tank for food. Its main functions are storage and preliminary digestion. The stomach functions like a big blender, churning and liquefying food. The properly functioning stomach secretes five important substances:
(1) mucus,
(2) hydrochloric acid (HCl)
(3) a precursor of the protein-digesting enzyme pepsin
(4) gastrin, a hormone to regulate acid production, and
(5) gastric lipase, which assists in the digestion of fat.
A mucous lining coats the cells of the stomach to protect them from the HCl and enzymes that must be present for proper digestion. This alkaline mucous lining can be damaged by dehydration, over-consumption of food or aspirin, or by the bacterium Helicobacter pylori (H.pylori). This damage can often lead to gastritis (irritation of the stomach lining) or to a stomach ulcer.
Contrary to popular belief many Americans who suffer from heartburn produce too little Hydrochloric Acid (HCl), not too much. Without enough HCl you may not be able to sufficiently break down proteins. This can lead to bloating, gas and heartburn. Low HCl production can also result in problems with bacterial infections or parasites.
Hydrochloric acid (HCl) is produced by parietal cells (tiny pumps) in the lining of the stomach. This acid is needed to ensure the proper functioning of the stomach. HCl has two primary functions: It provides the acidic environment necessary for the enzyme pepsin to break down proteins; and it helps prevent infection by destroying most parasites and bacteria.
At the end of the stomach is the pyloric sphincter, which controls the opening between the end of the stomach and the duodenum, the first section of the small intestine.
The Duodenum
When food leaves the stomach, it enters the first section of the small intestine known as the duodenum. It is no called chyme, a mixture of food, HCl and mucus, which is approximately the consistency of split pea soup. As the duodenum fills, hormones released from the duodenal lining (1) delay gastric emptying, (2) promote bile flow from the liver and gallbladder and (3) promote secretion of water, bicarbonate and potent digestive enzymes from the pancreas. The surface of the duodenum is smooth for the first few inches, but quickly changes to a surface with many folds and small finger-like projections called villi or microvilli (very small projections). These projections swerve to increase the surface area and absorption capabilities of the duodenum. Properly functioning accessory organs (liver, gallbladder and pancreas) are crucial during this first stage of digestion.
The Pancreas
The pancreas is a 6-inch long accessory organ that has three main functions important to digestion:
1. Neutralizes stomach acid
2. Regulates blood sugar levels
3. Produces digestive enzymes
Digestive enzymes digest proteins, carbohydrates and fats. The proteolytic (protein-digesting pancreatic) enzymes are secreted in an inactive form and are only activated once they reach the duodenum. The other pancreatic enzymes are secreted in an active form but require ions (electrically charged molecules) or bile to be present for optimal activity. Bicarbonates are alkaline and serve to neutralize stomach acid and activate digestive enzymes. These secretions (pancreatic enzymes and bicarbonates) are delivered directly into the duodenum, the upper portion of the small intestine. The pancreas also secretes hormones, which help manage blood sugar levels, directly into the bloodstream. These hormones are insulin (sugar lowering) and glucagon (sugar raising).
The Liver and Gallbladder
The liver has several important functions, many of which are related to digestion. It produces about half the body’s cholesterol (the rest comes from food). About 80% of the cholesterol produced by the liver is used to make bile. Bile is composed of bile salts, hormones and toxins. It acts to emulsify and distribute fat, cholesterol and fat-soluble vitamins throughout the intestines. Bile is an alkaline substance that neutralizes stomach acid. Between meals, it is stored in the gallbladder, a pear-shaped organ located just below the liver. When food (chyme) enters the duodenum, a signal is sent to the gallbladder to contract, thereby releasing bile into the small intestine.
The Small Intestine
Ninety percent of all nutrients are absorbed in the small intestine, the body’s major digestive organ. The small intestine resembles a coiled hose and is approximately 20 feet long. It is here that most food is completely digested and absorbed. The small intestine contains cells that serve many functions: Some produce mucus, some make enzymes, some absorb nutrients and others are capable of killing bacteria. The cells are arranged in folds upon folds, which force the chyme to move slower so it can be broken down completely and absorbed. These folds also increase the surface area of the mucosa, the thin mucous membrane lining the walls of the small intestine.
The small intestine consists of three sections – the duodenum, the jejunum and the ileum. The duodenum (first foot of the small intestine) connects to the jejunum, which in turn connects to the ileum. The duodenum primarily absorbs minerals. The jejunum absorbs water-soluble vitamins, carbohydrates and proteins. The ileum absorbs fat-soluble vitamins, fat, cholesterol and bile salts. The walls of the small intestine secrete alkaline digestive enzymes, which continue the separation of foods – proteins into amino acids, fats into fatty acids and glycerin and carbohydrates into simple sugars.
The Colon or Large Intestine
The last organ through which food residue passes is the colon or large intestine. The three major segments are the ascending (right side of the ascending colon through the ileocecal valve (ICV), a one-way valve that connects the small and large intestines and regulates the flow of chyme entering the large intestines. The ICV is designed to let waste pass into the colon and prevent it from backing into the small intestine. When chyme passes through the ICV, then into the very lowest portion of the ascending colon, known as the caecum, it is still in a liquid state. The caecum is the first section of the five feet of colon.
Food waste travels up the ascending colon (through rhythmic waves of contraction or peristalsis), across the transverse and down the descending portion of the organ. As it moves across the transverse colon, liquid is extracted. It is the job of the colon to absorb water and nutrients from the chyme and to form faeces. The faecal matter is in a semi-solid state, gradually becoming firmer, as it approaches the descending colon. About two-thirds of stool is water, undigested fibre and food products; one-third is living and dead bacteria (bacteria naturally live in the colon). The lowest portion of the descending colon is the sigmoid. The sigmoid colon empties into the rectum. In this area, three valves regulate the faecal matter. They are called the valves of Houston. This area is normally empty unless defecation is in process.
Final stages of digestion occur in the colon with the absorption of water and nutrients not absorbed by the small intestine. The liquid and nutrients are absorbed through the intestinal wall, collected by the blood vessels in the wall lining and carried to the liver through the portal vein for filtration.
The large intestine also:
1. Secretes bicarbonate to neutralize acid end products
2. Stores waste products, bacteria and intestinal gas
3. Excretes poisons and waste products from the body
The rectum is the chamber at the end of the large intestine. Faecal matter passes into the rectum, creating the urge to defecate. The anus is the opening at the far end of the digestive tract. The anus allows faecal matter to pass out of the body. The anal sphincters keep the anus closed.
The Mucous Membrane
The walls of both the small and large intestines consist of four layers. The innermost layer of the small intestine is called the mucosa. The mucosa has two very important functions: first, it is designed to allow nutrients of the proper size to pass through it and into the bloodstream. Second, the mucosa blocks the passage of undigested food particles, parasites, bacteria and toxins into the bloodstream.
Therefore, the mucosa or mucosal lining is a vital part of the body’s immune system because it limits the volume of potential invaders. The mucosa is lined with villi and microvilli. The villi are moving absorptive cells that “suck up” small particles of digested food. On each of the villi are thousands of tiny projections of the membrane of the cell called microvilli. These little brush-like fuzzy structures (called the “brush border”) further amplify the surface area of the small intestines. Stretched end to end with all its folds, the small intestine has the approximate surface area of tennis court.
On the surface of this mucosal lining is a thick mucous layer whose surface (the glycocalyx) is highly viscous (slippery). Much of the mucus consists of the amino sugar N-acetyl-glucosamine (NAG). The body makes NAG from the amino acid L-glutamine.
L-glutamine exists in virtually all cells, and it is one of the most prevalent amino acids in the body. Humans must have L-glutamine in order to produce NAG and have a healthy mucosal lining. The mucosal lining in a healthy person sheds and then is rebuilt every three to five days. Studies have shown that individuals suffering from any inflammatory bowel disease shed this mucosal layer at a much higher rate. This may be due to an inability to convert L-glutamine into NAG.
The Digestive Environment
It is difficult to fully understand the digestive system without realizing the importance of the bacteria and microbes that live in the intestinal tract. A newborn baby has essentially no digestive bacteria. Within a few hours, the bacteria and microbes begin to colonize the digestive tract. It has been observed that breast-fed babies develop a larger colony of friendly strains of bifidobacteria than those who are bottle-fed.
Ideally, pregnant women should supplement with the friendly bacteria known as Lactobacillus (L.)acidophilus, and bifidobacteria during the third trimester of pregnancy. Friendly bacteria, also known as probiotics, discussed in chapter 8, are important for babies at the time of birth. L.acidophilus in the vagina inoculates the newborn as he/she passes through the birth canal, and it provides protection from other bacteria as well as assisting with digestion and the production of vitamins. The bifidobacteria ingested by the mother is concentrated in the breast milk and is passed on intact to the nursing baby.
These two events establish the friendly bacteria in the newborn and greatly decrease the possibility of serious infections that can occur during infancy. The mother can provide friendly bacteria for her baby by ingesting a supplement containing L.acidophilus and bifidobacteria, or by eating yogurt or kefir with liver cultures of these bacteria. It may be best to do both, since it is necessary to provide ample amounts of the probiotics on a regular basis.
These microbes exist throughout the digestive system from the mouth to the anus, but most of the bacteria liver in the large intestine. (the stomach is so acidic that almost no bacteria can liver thee.) The large intestine can contain as many as four pounds of the microbial creatures at any one time. Approximately 500 different species of microbes live in the digestive system, but only 30 to 40 species constitute 99% of the microbes in the intestinal tract. In terms of how these microbes affect the body, they can be placed into one of three categories:
1. Good (or symbiotic)
2. Neutral
3. Bad
In a healthy person, there is a ratio of approximately 80-85% combined good and neutral bacteria to 15-20% bad. In many people today, this ratio is reversed. Faulty digestion can contribute to this imbalance.
The good bacteria are sometimes called “flora” or “probiotics.” These good bacteria are beneficial because they:
1. Produce enzymes that help digest foods (e.g. lactase enzyme digests milk)
2. Produce the vitamins B, A and K
3. Produce lactic acid, which helps acidify the colon
4. Crowd bad bacteria and keep them from becoming too numerous
5. Produce organic acids that may help with fecal elimination by peristalsis
6. Produce short-chain fatty acids (butyric acid), which supply energy to intestinal cells
The two most important types of good bacteria are Lactobacillus and Bifidobacteria.
Bad bacteria produce substances that are harmful to the body. They irritate the lining of the intestines (causing gas) and can be absorbed into the bloodstream (causing disease). They cannot always be prevented from entering the body, but if the number of good and neutral bacteria stays high, then, theoretically, the bad bacteria will be kept to a minimum. Examples of bad bacteria are salmonella and H. pylori, the bacterium associated with ulcers.
The neutral bacteria are the most prevalent bacteria in the in the digestive tract. Neutral microbes have neither a positive nor negative impact.
The levels of these three types of organisms remain relatively constant throughout childhood and mid to late adult years. As we age, the levels of bad bacteria often increase and the good bacteria decrease.
The Signs of Good Digestion and Elimination
At minimum, one should have one good bowel movement per day, but two to three are ideal. A “good” bowel movement is one that is walnut brown in colour, with a consistency similar to toothpaste, about the length of a banana. The stool should be free of odour, leave the body easily, settle in the toilet water and gently submerge. The transit time for food – the elapsed time it takes for a meal to enter the mouth and then exit the rectum – should ideally be less than 24 hours. Transit time is related to exercise and the consumption of fibre and water.
The Seven Channels of Elimination:
- Colon
- Lungs
- Liver
- Skin
- Kidneys
- Blood
- Lymph
The first 5 of these channels (column 1) are all organs. The processes of the colon have been explained in this chapter. The liver, the body’s primary filtering organ, will be presented in chapter 5. The blood that flows through the vessels of the vascular (blood circulatory) system carries oxygen and nutrients to the cells of the body and removes harmful wastes. No so familiar to many is the other circulatory system, the lymphatic system, through which lymph flows.
The Lymph
The lymphatic system and the vascular system serve to eliminate poisons from cells. The lymphatic system consists of a network of vessels that extends throughout the body, following the path of the veins. The lymphatic capillaries contain a clear fluid, lymph, which carries lymphocytes (immune cells). The lymphatic system is an important part of the immune system. In fact, organs of the immune system are known as ‘lymphoid organs’. They include the following:
• Bone marrow – where lymphocytes originate.
• Spleen – a filter for the lymphatic system and a storage site for lymphocytes.
• Liver – major detoxification organ.
• Lymph nodes – small bean-shaped structures that connect with lymphatic capillaries (they are concentrated on the groin, armpits, neck and abdomen; they filter lymph and produce lymphocytes).
• Thymus gland – home of the T cells, which mobilise the body’s defence system when it is immune challenged
All these lymphoid organs are concerned with the growth, development and deployment of white blood cells (lymphocytes), whose function it is to defend the body against antigens (substances the body perceives as foreign and threatening, such as viruses, fungi, bacteria, parasites and pollen).
Kidneys
The kidneys are two bean shaped organs located just under the diaphragm in the back. The liver sends water-soluble wastes to the kidneys via the blood where this waste is eliminated through the bladder. Although small enough to fit in the palm of a hand and weighing no more than an orange, the kidneys are considered the ‘great purifiers’ of the body. Each kidney contains a million individual filter units (globules), and, according to Dr. Henry Bieler, “can filter 1700 quarts of viscous fluid (in which 50 different chemicals are dissolved) in 24 hours.” The kidneys determine which of these 50 chemicals are needed by the body, absorb them and filter out the rest. Of the blood filtered by the kidneys, 0.1% becomes urine. The kidneys have the additional function of maintaining water balance.
Lungs
The lungs, another secondary elimination organ, expel toxins from the body. One of the most common toxins is carbon dioxide. The action of deep breathing helps to move lymph and blood through the body, and with it, toxins. The lungs are lined with mucus and cilia (hair-like projections) to help protect against and remove inhaled toxins.
Skin
The skin is the body’s largest organ. It serves as a protective barrier to prevent toxins from entering the body. Because of its size, the skin can eliminate more cellular waste than the colon and kidneys combined. It eliminates wastes through its sweat glands and mucous secretions and is considered a secondary elimination organ. The skin protects our inner parts and gauges temperature needs. New skin is made every 24 hours. This skin will be as clean as the blood that flows below it, for the condition of the skin reflects the condition of all that lies beneath it.
There are three layers of skin: the outer, inner and middle layers. The outer skin is the visible layer or ‘hide’. The inner skin is called the mucous membrane. The middle skin (or serous membrane) lines the walls of the lungs, heart, abdomen and pelvic cavities, as well as this of the head and joints.
Summary
Digestion of carbohydrates starts in the mouth through the secretion of the enzymes ptyalin and amylase from the salivary glands. Food travels then through the oesophagus into the stomach. The stomach’s churning and secretion of digestive juices converts the food to chyme. Pepsin and HCl from the stomach break down protein. Chyme then enters the duodenum, where bicarbonates and digestive enzymes from the pancreas neutralise stomach acid and break down food into its component parts. Bile is secreted from the gall bladder into the duodenum to emulsify fat and decompose it for distribution. Food residue passes next into the small intestine, where 90% of absorption takes place. It then enters the large intestine through the ileocecal valve, travelling up the ascending colon, across the transverse, down the descending colon, through the rectum and out the anus. Liquid and nutrients pass through the wall of the large intestine into the bloodstream, them on to the liver for processing and filtration.
The colon houses three types of bacteria: good, neutral and bad. A balance of approximately 80% good/neutral to 20% bad is desirable for health maintenance. This balance will assist the body in normal elimination of solid waste, a minimum of one daily bowel movement (preferably two to three).
