Gastrointestinal disorders

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Chapter 35 Gastrointestinal disorders

Chapter contents

Anatomy of the gastrointestinal tract 273

Microflora of the gastrointestinal tract 274

Gastrointestinal disorders 274

Anatomy of the Gastrointestinal Tract

There are five layers in the gastrointestinal wall (Figure 35.1):

• Longitudinal muscle layer: the outer layer of muscle. Combined with the inner circular muscle layer, its coordinated contraction creates peristalsis, which propels food through the gut.

• Circular muscle layer.

• Submucosa: a layer of dense irregular connective tissue with large blood vessels, an extensive lymph system and nerves branching into the external muscle and mucosal layer. This supply and drainage system becomes an important factor in the spread of secondary cancers.

• Mucosa: the innermost layer, which is in direct exposure to the lumen (i.e. the space within the tube of the tract). The composition of the mucosa varies depending on the area of the gastrointestinal tract. For example, in the stomach it has qualities that make it resistant to the effects of a low pH; in the small intestine it contains villi, which maximize absorption.

Figure 35.1 Cross-section of small intestine.

The blood flow from the small intestine is significant because it passes directly to the liver via the hepatic portal vein. Most of the water-soluble nutrients absorbed from the gut are transported to the liver in this way. Fat-soluble substances are absorbed by the intestinal lymphatic system and distributed to the blood by the thoracic duct, thus bypassing the liver.

The stomach mucosa contains many mucus-secreting cells; the mucus creates a protective layer over the lining of the stomach wall. The lining of the stomach is highly glandular and consists of four types of gland:

• Parietal cells: secrete hydrochloric acid (HCl) and intrinsic factor (see Chapter 13 ‘Vitamins and minerals’, p. 105).

• Mucous cells: secrete an alkaline mucus that protects the epithelium against damage due to shearing of the membranes and the acid environment of the stomach.

• Chief cells: secrete pepsin, a proteolytic enzyme. Its activity is low at a low pH (see Chapter 8 ‘Acids and bases’, p. 54) and the enzyme is therefore not fully active until it reaches the more basic medium of the small intestine (pH approximately 7.8).

• G cells: secrete the hormone gastrin.

Different areas of the stomach vary in their secretions.

Microflora of the Gastrointestinal Tract

The gastrointestinal tract is a complex and self-contained ecosystem of over 400 bacterial species. Anaerobic bacteria (bacteria that live in an environment where there is little or no oxygen) outnumber aerobic bacteria (those that require the presence of oxygen to function). Fungi are also present but, due to the population of the normal commensals, tend not exceed limits, except for a problem such as that caused by an overgrowth of, for example, Candida albicans.

Due to the existence of the commensals, a situation exists where host, bacteria and fungi live together without any adverse effects on one another. In many cases in the gastrointestinal tract, bacteria provide a very useful service, producing vitamins that are vital for health or taking part in chemical reactions necessary to activate compounds (see Chapter 13 ‘Vitamins and minerals’, p. 108). These bacteria are usually non-pathogenic. Most of the gut flora is found in the colon and lives in the lumen of the bowel; it does not normally penetrate the gut wall.

Ingestion of certain substances, e.g. antibiotics, can disturb the normal balance of these commensals, which is why carefully consideration of gut health after a course of antibiotics is important.

Gastrointestinal Disorders

Dyspepsia

This is a general term for a group of signs and symptoms:

• pain or discomfort in the upper abdomen

• bloating and feeling ‘full’ after eating

• nausea or vomiting.

All these symptoms are intermittent.

• Causes of Dyspepsia

• Acid reflux, oesophagitis or gastro-oesophageal reflux disease (GORD).

• Hiatus hernia.

• Functional dyspepsia: does not involve ulcer formation.

• Duodenitis: can be a precursor to an ulcer; a possible cause is NSAIDs.

• Gastritis: can be a precursor to an ulcer; a possible cause is NSAIDs.

• Duodenal and gastric ulcers.

• Conservative Treatment

• Check patient’s medication: patients who are taking NSAIDs or some other medications (e.g. some antibiotics, steroids) are required to stop medication.

• Patients must try to abstain from foods and drinks such as chocolate, coffee, alcohol, spicy foods and peppermint.

• Patients should try to stop smoking: chemicals inhaled from cigarettes are thought to relax the oesophageal sphincter.

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