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Food processing

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Food processing—the organs involved
Digestion, Absorption, Elimination

The human digestive system

The mouth
The oesophagus
The Stomach
The Small intestine—jejunum, ileum
The large intestine—Cecum, Appendix, ascending Colon, Transverse colon, Descending colon, Sigmoid colon
The Rectum and Anus

The journey of Food from the mouth to the Anus can be completed in a few hours or it may take several days to be completed.
The processing and movement of food down the alimentary canal depends on many factors. The journey and journey time can be influenced by:

What we eat
How much we eat
How often we eat
How active we are
How relaxed or stressed our mind is—lifestyle
How anxious we are about life
How we try to relax when evacuating
What medication we take
What medical conditions we suffer from

Mouth

The mucosa of the mouth is composed mostly of non-keratinized squamous epithelium. This mucosa continues through to the oesophagus.
Three salivary glands on each side and buccal glands in the mucosa provide the fluid known as saliva. Saliva contains water, salts, mucin, serous fluid, lysozyme, Immunoglobulin A, growth factors and the enzyme Amylase which begins the digestive process of starch in the diet.

Food is chewed or masticated in the mouth in order to make it easier to swallow. The process of digestion starts here and contact with digestive enzymes in the saliva helps convert simple starches into sugars.
This process helps create the flavour and taste in the mouth and allows us to savour the food before swallowing. Food should be chewed sufficiently enough to create a soft bolus that can be easily swallowed.
The process of chewing increases the flow of saliva to facilitate the digestive function. In addition, a growth factor protein is secreted into the salivary juice. This growth factor induces the lining of the gastrointestinal tract to renew itself and plays an important role in the healing of damaged and inflamed lining of the intestines. Thus, the more times you chew your food, the more growth factor is available for this very important function.

Oesophagus
The oesophagus is about 25cm long and is lined with non-keratinized squamous epithelium. The upper third of the oesophagus is made up of skeletal muscle, the middle is a mix with smooth muscle and the last third is made up of smooth muscle.
The function of the oesophagus is to transport food from the mouth to the stomach. Oesophageal glands located in the submucosa produce mucus for lubrication.

Once a soft bolus is formed, food is rapidly propelled down the Oesophagus by muscular contractions known as PERISTALSIS and arrives into the stomach via the lower oesophageal sphincter, which is a muscle that separates the oesophagus from the stomach. This valve is normally kept tightly closed to prevent the acidic contents of the stomach from entering the oesophagus. The muscle that makes up the lower oesophageal sphincter valve relaxes when we swallow. This opens the valve to create a passage for food to enter the stomach.

Difficulty in swallowing liquids or solids, regurgitation, chest pain and heartburn may be symptoms of motility disorders associated with the oesophagus. Dysphagia (ineffective swallowing), Achalasia (complete paralysis within the oesophagus) and Oesophageal reflux disease (heartburn and irritation of the lining of the oesophagus due to splashing upwards of acidic stomach contents into the oesophagus due to a malfunction in the lower oesophageal sphincter ). The sphincter muscle may be weakened by a Hiatus hernia.

Stomach

The body of the stomach is made up of three layers of muscle. An oblique layer, a longitudinal and a transverse layer. The three layers produce a churning and liquefying effect on the chyme in the stomach.

The main function of the stomach is to grind food into smaller particles and mix it with acid and digestive juices so that it can be further processed and absorbed when it reaches the small intestine.

The food matter that arrives into the stomach is held in place by closure of the PYLORIC SPHINCTER, a valve that controls the outlet of the stomach into the Duodenum.
Food is mechanically broken down further by a churning action of the stomach. This exposes the now softer food particles to stomach acid and juices containing digestive enzymes so that the chemical conversion of the food particles can commence.
VitaminB12 and Iron is absorbed here.

The stomach empties its contents into the intestine at a controlled rate and is highly dependent on the type of food present and its volume.
Motility is controlled by parasympathetic nervous system and secretion of Hormones (e.g. Gastrin and secretin)

Food can remain in the Stomach for up to three hours and occasionally up to six hours, depending on the type of food consumed. Fatty foods usually slow down the movement of food out of the stomach.

During periods of fasting when all digestible food has left the stomach, there are occasional bursts of very strong, synchronized contractions that are accompanied by opening of the pyloric sphincter muscle which is the gateway from the stomach into the duodenum.
These strong contractions create waves of movement that sweeps any indigestible material out of the stomach. This is the migrating motor complex and is sometimes described as “housekeeper waves”.

Stomach motility dysfunction can cause delayed gastric emptying (gastroparesis), rapid gastric emptying (dumping syndrome) and dyspepsia.

 

Small Intestine

The function of the small intestine is to complete the digestive process that started in the stomach and absorb the nutrients released.
Duodenum

The duodenum is the first 25cm of the small intestine and is the site of most digestive enzyme release. Secretions from the pancreas, intestinal mucosal cells, liver and gallbladder enter into the duodenum to begin the real process of digestion.

The presence of fatty and protein rich chyme in the duodenum causes the release of Cholecystokinin (CCK) into the bloodstream from duodenal endocrine cells. The major function of CCK is to stimulate release of bile and pancreatic juice.


Once processing of food is completed in the stomach, the PYLORIC sphincter relaxes and allows the passage of food into the small intestine. This semi solid food matter is called CHYME.
The contents of the small intestine are propelled by muscular contractions which generate contraction waves called “peristaltic contraction waves” or “peristalsis”.

The first segment of the small intestine is the Duodenum where bile from the liver via the gall bladder is secreted to help digest Fats. Juices from the pancreas help digest carbohydrate and proteins. The absorption of nutrients released by the digestive processes takes place through the many meters of small intestinal surface, which is enhanced by the huge surface area available.

During and after a meal, the intestine shows irregular contractions that move the content back and forth and mix it with the digestive juices and enzymes that are secreted into the lumen. These contractions promote digestion and absorption of the digested food by exposing it to a large surface area while slowly moving the contents forward towards the large intestine.
The first part of a meal can take from 90 to 120 minutes to arrive into the large intestine and the last portion eaten may not reach the large intestine for up-to five hours.

Abnormal motility in the small intestine can lead to symptoms of intestinal obstruction. Bloating, pain, nausea and vomiting may be experienced due to this blockage. These symptoms are due to either weak or disorganized muscular contractions which can be due to abnormalities in the muscle that makes up the gastrointestinal tube or damage to nerves that coordinate the muscular contractions.

Intestinal bacterial overgrowth

Abnormal motility due to weak and disorganized muscle contractions in the small intestine cause the housekeeper waves (migrating motor complex)  to fail the function of sweeping bacteria out of the intestine. This can result in overgrowth of bacteria in the intestine, resulting in symptoms such as bloating, pain and diarrhoea that can occur immediately after a meal because the bacteria start fermenting the food content before it can be absorbed. The fermentation process leads to production of hydrogen and other gases which cause the bloating and diarrhoea.

The Large intestine

The Colon

The large intestine begins at the Cecum and is much shorter in length while larger in diameter than the small intestine. The longitudinal muscle of the colon is arranged into three distinct bands.

Contraction of the taenia coli cause the colon to buckle producing the pouches called Haustra which increase the surface area of the colon for absorption of water and electrolytes.
The colon has deep clefts which also increases its surface area.

The main function of the large intestine is to store and process the contents arriving here so that very little water and electrolytes remain.
The Water and electrolytes that the body secretes into the lumen as digestive juice is crucial for the digestive process, but has to be recovered if dehydration of the body is to be prevented. Most of this water is reabsorbed before the contents arrive into the Cecum; however a lot still remains to be recovered. When most or all of the water has been re-absorbed by the COLON, we are left with a dried out SOLID or SEMI-SOLID faecal mass we call STOOL.

Normal faeces are roughly 75% water and 25% solids. Most of the faecal solids are made up of bacteria, undigested food, exfoliated cells, mucus and fibre.
The brown colour of faeces is due to bile acids called stercobilin and urobilin which are produced by bacterial degradation of bilirubin.
The smell of faeces originates from the gases Skatole, Mercaptans and Hydrogen Sulphide which are produced by bacterial metabolism.

This faecal mass needs to be passed on average once a day out of the body. This may depend on how many large meals one consumes per day.

Cecum

The Cecum is the first part of the colon and is a cavernous blind pouch attached to the small intestine via the Ileocecal sphincter or valve through which content from the ileum pours in. The pursed lips of the Ileocecal valve protrude into the Cecum to help prevent backflow of chyme under pressure. This valve relaxes only when a peristaltic wave arrives from the ileum.

When all food mater has been chemically processed by the action of Enzymes secreted into the intestinal lumen, what is left is usually indigestible matter.

This matter arrives into the ILEUM, which is the end portion of the small intestine and is then poured into the Cecum, which marks the beginning of the large intestine, via the Ileocecal valve.
This is a one way valve and does not permit the contents of the Cecum to re-enter the Ileum under normal conditions.

Food matter that cannot be further processed by Human digestive enzymes can arrive into the CECUM as early as fifteen minutes after a meal and most of the processed food from a meal would have passed into the Cecum within four hours of consuming it.

Appendix

This is a wormlike organ attached to the Cecum. It has a concentration of lymph tissue and is filled with lymphocytes and may be involved in the early training of the immune system.

However, the removal of the appendix has not proven to have any deleterious effects on the functioning of the immune system.

Ascending colon, Transverse colon, Descending colon, Sigmoid colon

The Cecum leads in sequence to the ascending colon, then the transverse colon, the descending colon, and the sigmoid colon before entering the rectum. The rectum possesses skeletal muscle which functions during the defecation reflex.

The purpose of Motility in the colon is to mix, store temporarily and propel the semisolid food content to a solid consistency very slowly.

Unlike the nearly constant propulsion of content in the small intestine, material moves at intervals by mass peristalsis or movement.
In between the intervals segmentation, called haustral churning, stirs the contents so that water can be absorbed more efficiently and bacteria mixed in with the content to form faeces.
The main role of the ascending colon is to receive and store mostly liquid contents discharged through the Ileocecal valve into the cavernous Cecum.

The role of the left side of the colon is to store residue for periodic expulsion into the rectum.

Muscle movements in the colon consist of

1. Minor peristaltic waves

2. Haustral churning. This is produced by segmentation contractions which serve to mix the contents and enhance absorption.

3. Mass movements or peristalsis which consists of large movements which occur at intervals associated with meals.

These movements are often initiated by the Gastrocolic reflex which stimulates the colon in response to the presence of food in the stomach.
This reflex is active after fasting and when the food is hot or cold. It causes mass peristalsis in about 15 minutes and may continue for up to 30 minutes after initiation.
These movements cause the chyme to move in large steps through the colon, stopping at each step to be further concentrated and converted into compact faeces. The process takes about 12 hours.
The faecal material, which may be about one third bacteria, one third exfoliated cells and one third indigestible material is also called stool. The exact composition is determined by diet and motility.


Propulsion of Faecal mass in the large intestine occurs by means of strong contraction waves called “mass movements” and occur up to six times a day.
These waves are usually triggered by the entry of undigested food matter from the small intestine into the Cecum.

The bodily functions of Eating, Sleeping and Movement or Exercise play an important part in this regular cycle of “mass waves” generation.

The act of getting out of bed in the morning (the ORTHOCOLIC REFLEX) is one of the most predictable triggers for a mass movement and explains why most of humanity opens their bowels first thing in the morning.
You may expect this cycle of contractions to be disturbed if any of the factors influencing them is altered in any way.

Changing ones Diet suddenly, Long distance Travel, Shift work, Lack of movement or Exercise, Changing your sleep pattern all have an effect on the mass movements and therefore the timing and ability of opening the bowel.

Content of the large intestine is propelled further towards the Rectum and Anus by the action of these mass movements.
The contents are propelled from the right side to the left side of the large intestine until they arrive at the SIGMOID colon.

A sufficient amount of SOFT, BULKY and FIRM faecal matter causes distention of the wall of the sigmoid colon and creates the first urge to open the bowels.
The re-absorption process is slow and takes time. The muscular contractions of the colon mix the contents back and forth but do not move them forward. This type of motility forces the residue to remain in the colon for up-to 30 hours to create faeces. In addition to indigestible material, there are a lot of Bacteria present. The amount of bacteria in the residue depends on diet and use of medication containing antibiotics. However, Bacteria can make up more than half the weight of faecal material.

A type of mass wave contraction called the high amplitude propagating contraction occurs in the colon and takes place 6 to 8 times per day. These contractions are very strong and begin in the ascending colon and sweep right down to the rectum. These contractions move the contents of the large intestine and create the urge to go and may trigger a bowel movement.

Rectum and pelvic floor muscles

The primary functions of the rectum and pelvic floor muscles are to prevent incontinence and to allow defecation to occur.

The Rectum, which is very elastic, forms the last 15cm of the large intestine and is the segment which stores the faecal mass arriving from the sigmoid colon temporarily before being expelled via the anal canal.

Our ability to hold on when an urge to open the bowels arrives at an inconvenient moment is due partly to the ability of the rectum to relax at first rather than contract when it senses the presence of faecal content. This action of “Holding” is supported by active contraction of the anal sphincters which block the passage of rectal contents.

When everything is working as it should, we can sense the presence of faeces in the Rectum and so make efforts to visit the loo for evacuation. However, this urge to defecate can be ignored and opening of the bowel can be postponed for several hours if need be until it is convenient to do so.

Ignoring the urge to go and postponing the defecation or opening of the bowel still means the  presence of faecal matter in the Rectum and this fact is often cause of the selective passage of GAS or FLATUS. This passing of GAS helps reduce the build up of pressure within the rectum and suppresses the rectal contraction waves.

When the force of the pressure within the large intestine and the rectal contraction waves exceeds the pressure created by the contracted muscles of the anal sphincters the need to evacuate becomes urgent and cannot be ignored. Time to go!

The pelvic floor, located below the rectum, is made up of many different muscles including the puborectalis muscle and the external and internal anal sphincter muscles.
The rectum is surrounded by sensory nerves that detect the filling of the rectal sac with faecal material. This sensation of rectal filling enables us to consciously or unconsciously squeeze the external anal sphincter to prevent incontinence until we can reach a toilet. These sensory nerves are also involved in reflexes that let the sphincter muscles relax during a bowel movement.

Any abnormality of the muscles that maintain continence can cause faecal incontinence

1. Weakness of the anal sphincter muscles that allow us to voluntarily ignore the urge to open the bowel.
This weakness can result from damage to the nerves leading to these muscles or direct injury to the pelvic floor muscles. Both types of injury can be sustained in women during the process of giving birth. (Vaginal delivery)

2. Loss of sensation for rectal fullness so we can decide when to squeeze the sphincter muscles.

3. Constipation, in which the rectum may fill up and overflow. This type of incontinence is common in children.

4. A stiff or spastic rectum, which causes faecal material to be forced through the rectum so fast that there is no opportunity to squeeze the anal sphincter muscles to try and maintain continence.
Inflammatory bowel disease can cause damage to the rectal lining and cause a stiff rectum.

Anus

Just before the gastrointestinal tract becomes the ANAL CANAL, the muscular tube makes a turn of around 80 to 90 degrees at the junction of the Rectum and the Anus. The angle at this ANO-RECTAL junction is called the Anorectal angle. This angle creates a “kink” that separates the rectum from the anus and is maintained by the contraction of a sling type muscle on the pubic floor called the PUBORECTALIS MUSCLE. Relaxation of this muscle releases its grip on the ano-rectal junction and can be manipulated by posture. The angle of 80 to 90 degree can be made larger to remove the kink formed by the muscle by adopting the SQUATT posture. Removal of the kink aligns the rectum and anal canal to create a passage for stool to pass into the anal canal.

The Anal Sphincters
These valves are made up of two circular or cylindrical muscles that surround the tube that makes up the anal canal.

One muscle is wrapped around the other and is about 3cm long. The circular muscle inside the anal canal is called the INTERNAL ANAL SPHINCTER and the one on the outside is called the EXTERNAL ANAL SPHINCTER. Both muscles have a continuous tone and are active at all times, even during sleep.

The way these Sphincters function is determined by the way they are connected to the nervous system. The INTERNAL Sphincter is innervated by the Autonomic nervous system and is under involuntary control and responds only to reflex signals. We are not able to contract or relax this muscle by conscious thought or effort. This muscle creates pressures which are higher than those created by the Sigmoid colon and the Rectum and is therefore very important in maintaining continence over the exit of Faeces and Gas.
The internal anal sphincter is kept contracted at all times except when faeces have arrived into the canal from the rectum.

The EXTERNAL ANAL SPHINCTER is made up of muscle that can be controlled by conscious thought. This is due to the fact that this muscle is innervated by the PUDENDAL nerve which is a sensory nerve originating from the spinal cord. A strong urge to go to the loo, laughing, sneezing or coughing can all lead to a reflex contraction of the EXTERNAL ANAL SPHINCTER. This contraction CLOSES the anal path and helps you maintain continence. Relaxation of this muscle takes place when you are ready to open your bowels. Relaxing the sphincter allows the anal canal to open widely so that faeces can be expelled without straining.
This fact explains two facts:
1.If complete relaxation of the External anal sphincter cannot be achieved or maintained for any reason while trying to open the bowel, the anal canal may remain closed and excessive STRAINING may be required in order to complete the process of defecation.
2.If one is not able to consciously contract the external anal sphincter with sufficient strength in order to keep the anal canal closed when faeces arrive into the anal canal from the rectum, this can lead to URGENCY and incontinence.
 How to heal and prevent Bowel disorders
Diet is not about what you should NOT eat, it’s about what you should include in the diet that matters.
As long as your diet includes the correct balance of plant foods containing soluble fibre, insoluble fibre and resistant starch your colon will produce the perfectly formed stool. The important next step is to evacuate this stool without straining so that the body does not suffer from the pressures created each time the bowel is emptied.
In order to heal and prevent bowel disorders you need to make lifestyle changes that last the rest of your life time.

1. Include more fluids and plant food containing soluble fibre, insoluble fibre and resistant starch in the diet so that the perfectly formed stool will be made in the colon and beneficial bacteria will flourish and eliminate disease causing bacteria and fungi.
2. Evacuate the perfectly formed stool by adopting the squat posture to eliminate the need to strain during bowel movements.

It is not possible or safe to squat on the modern raised toilet seat installed in all western homes and it is impossible to squat for any length of time if you have not done this from childhood onwards. This makes the use of any raised platforms impossible to adapt to.

The SquattLooStool is designed to allow you to adopt the squat posture while seated comfortably on your raised toilet seat.
The single best and easiest lifestyle change you will ever make, leading to a healthier body.