The digestive system is concerned with chewing, swallowing, processing and absorption of food, as well as removal of the unwanted part of the food from the body. Hence it is composed of the following parts:
The mouth contains the teeth, tongue and salivary glands. The teeth are used to break food into bits. The saliva (produced by the salivary glands) help to mould the food together so that the tongue can roll it into a bolus that can be swallowed. Some enzymes in the saliva also help to start the digestion of foods like carbohydrates.
This is a tube about 25cm long, through which the swallowed food bolus passes from the mouth into the stomach.
The stomach is a muscular sac which acts as a ‘hopper’, retaining and grinding food, then actively pushing it into the upper small intestines (bowel).
The stomach produces hydrochloric acid which helps sterilise the upper part of the intestines and activates enzymes for food digestion. It also produces a substance called intrinsic factor necessary for the absorption of vitamin B12 used in blood production.
Mucus and bicarbonate ions also produced by the stomach protects it from the effects of the acid and enzymes so that ulcers don’t develop.
The small intestine
The small intestine structurally has 3 parts: the duodenum, jejunum and ileum. However, doctors may sometimes refer to the small intestine as only the latter two. Stretching up to a length of about 6 metres (which is more than the height of 3 average men stacked up!), the small intestine is essential for digestion and absorption of food, as well as protection against ingested toxins.
The liver and gallbladder
The liver is the largest gland in the body, weighing approximately 1500g and receiving about 1500mLs of blood every minute. It is brownish in colour and wedge shaped, positioned in the right upper quarter of the abdomen.
The liver functions as a processing house for the absorbed carbohydrates, fats and amino acids (from protein breakdown). It is also involved in processing drugs and environmental toxins.
The gallbladder is a pear-shaped sac with a capacity of about 50mL lying under the right half of the liver. Its function is to concentrate and store bile (the greenish bitter fluid). About 1-2 litres of bile is produced by the liver cells daily. Bile helps in the absorption of fat.
The pancreas is a gland lying in the upper left quarter of the abdomen, just below the stomach. In shape, it resembles the upper end of a thick walking stick, lying sideways with the handle on the right and turned downwards. It has a length of about 15cm and firm in consistency with a somewhat bumpy surface.
The pancreas produces some enzymes necessary for the digestion of fat, protein and carbohydrate.
The large intestine (colon)
The colon is about 1.2 metres long, and as the name suggests, it is wider than the small intestines. It is divided into 4 parts: the ascending, transverse, descending and sigmoid colons. The colon absorbs water and electrolytes and also acts as a storage organs for the faeces pending when they will be ejected.
The rectum and anal canal
The rectum is continuous with the sigmoid colon and is about 12cm in length. The entry of faeces in the rectum triggers the urge to defecate. With relaxation of the muscles of around the anus, faeces is then passed out of the body through the anal canal anus).
Symptoms of Gastrointestinal Diseases
In normal health, there is some awareness of the functioning of the gut and this can be partly related to the body’s needs. For example, thirst and hunger are common symptoms and the latter may come with abdominal discomfort. A dry mouth can suggest the need to drink. Swallowing is normally felt, and there is some temperature sensation in the mouth, oesophagus and even sometimes in the stomach (such as when you gulp down some really cold drink). Vigorous contractions in the gut, the movement of gas and fluid in the gut, called borborygmus (that embarrassing sound your intestines make in a quiet room), and the sensation of fullness prior to defaecation or during constipation, are all aspects of normal sensation of gut activity.
However, problems with the digestive system can present with any of the following symptoms:
- Swallowing difficulty and pain during swallowing
- Excessive wind
- Alteration of bowel pattern
- Abdominal pain
- Abdominal swelling
- Weight loss
- Bloody vomitus
- Bleeding through the anus
- Black tarry stool
Swallowing difficulty and painful swallowing
In swallowing difficulty (dysphagia), there is an awareness of something sticking in the throat or at the back of the breastbone during swallowing. Dysphagia often has a significant cause which can be cancerous and almost always needs investigation. An oesophageal or upper gastric cancer usually presents with dysphagia and weight loss. Dysphagia can also be due to a neurological problem.
Odynophagia (pain during swallowing) may indicate infection of the inner lining of the oesophagus, classically due to candida associated with HIV infection.
This is due to the backflow of acid from the stomach into the oesophagus. It causes pain in the upper abdomen, at the back of the breastbone, and in the neck. It occurs particularly at night when the patient lies flat in bed, or after bending or stooping when abdominal pressure is increased. Alcohol often induces heartburn.
Reflux is a symptom which occurs without heartburn, when non-acidic fluid or bile regurgitates into the mouth, causing a bitter taste and a disagreeable sensation at the back of the breastbone.
Dyspepsia is the medical term for indigestion, a symptom which includes upper abdominal pain, heartburn, bloating, nausea or ‘an acid feeling’ occurring after eating or drinking. The symptom is subjective and frequent. In many cases, there is no obvious cause but it may be associated with peptic ulcer, acid reflux and occasionally cancer in the upper part of the gut.
Flatulence is associated with belching, bloated abdomen and farting. It usually represents a functional disturbance, some of which is due to excessively swallowed air. Sometimes, it is clearly related to certain foods such as vegetables. Rarely, it can be as a result of actual disease in the gut.
Vomiting may be triggered in the brain or by irritation in the stomach. Most nausea and vomiting of gut origin is associated with local discomfort in the abdomen.
Loss of appetite
Some people may not want to eat at all while some have the appetite to eat but feel full after just a few mouthfuls. This may indicate important digestive problem especially in the upper gut.
The frequency of bowel action varies greatly from person to person. The passage of formed stool less frequently than three times per week is usually taken to indicate an abnormality of bowel frequency.
Constipation may be caused by lack of fibre and/or fluid intake; drugs which slow down gut movement; abnormal gut structure like in cancers or inherited disorders; obstructed defaecation, anal tears and piles.
Diarrhoea is also subjective, but the regular passage of stool for more than three times per day, or the passage of a large amount of stool can certainly be called diarrhoea. It is common as a result of dietary indiscretion or from viral or bacterial infection.
When diarrhoea lasts more than one month, it could mean that the bowel is inflamed or there is a problem with absorption. There could also be passage of pale, bulky stools containing excess fats that commonly float in water and are difficult to flush away.
Abdominal pain is a common symptom which often accompanies serious conditions but frequently has no definable cause. It can be due to inflammation like in appendicitis; peptic ulcer or gut obstruction. Abdominal pain may also be due to causes that are not specifically in the abdomen such as metabolic disorders (lead poisoning) or depression.
A large abdomen has many causes, which include gas, fluid, pregnancy and solid masses like tumours.
It is as a result of reduced food intake (loss of appetite, swallowing difficulty or vomiting), improper absorption of nutrients or systemic effects of diseases such as cancer (within or outside the gut) or chronic infections such as tuberculosis (within or outside the gut).
Weight loss may occur in healthy people due to dieting, exercise, starvation or old age. Psychiatric conditions such as anorexia nervosa and depression can also cause weight loss. Alcoholics lose weight as a consequence of self-neglect and poor food intake.
This results from bleeding in the upper gut, causing the vomiting of blood. Blood that lies in gastric juice for a while turns black and may be vomited looking like ground coffee.
Bleeding through the anus
If bright red, separate from the stool or just on the toilet paper, this usually indicates a source in the lowest part of the gut, haemorrhoids (pile) being the commonest cause. If darker red and mixed with the stool, this usually indicates a source higher above in the large intestines, of which cancer is the most important cause.
If the stool is black and tarry, it is most probably due to bleeding from the small intestines or higher up. Sometimes, it can be from the first part of the large intestine too.
Jaundice is yellowish discolouration of the eyes and skin due to raised level of a substance called bilirubin in the blood. Bilirubin is gotten from the breakdown of red blood cells in the body. Jaundice implies disease of the liver or the bile system although it may also occur from excessive breakdown of red blood cells. It may also occur with itching or dark urine.