Digestive System

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Questions Received:

  1. Why does spicy "hot" food cause the same physical reactions as heat, for example: sweating?

  2. What is the difference between an indirect and direct inguinal hernia?

  3. What is paralytic ileus, and what would cause it?

  4. Do we swallow when we are asleep?

  5. How can I improve a slow digestive tract, when toleration of fiber is poor, after use of laxatives?

  6. How are the nutrients carbohydrates, proteins, vitamins, iron and calcium of spaghetti bolognese digested?

Responses:

Why does spicy "hot" food cause the same physical reactions as heat, for example: sweating?

Updated 24th October 1997

ChilliesSpicy foods excite the nerve endings in the skin and mucosa (lining of the mouth and digestive tract) that normally respond to high temperature or injury. The information is carried by pain fibres to the central nervous system. The brain makes a judgment based on the type and variety of stimuli being received and occasionally misinterprets the information. Thus, the stimulation produced by the chemicals in spicey foods causes the brain to perceive an extreme of heat and initiate responses such as sweating and vasodilation (visible on the person’s face as flushing).

One of the active ingredients in spicey food is capsaicin, which is found in the white ‘ribs’ inside hot chillies. Capsaicin probably evolved in plants as a protective mechanism, to discourage certain pests. Different species of chilli contain different amounts of capsaicin, conferring different degrees of "hotness". In 1912 Wilbur Scoville proposed a scale of measurement based on the apparent hotness of extracts placed on the tongue after dilution. Thus, bell peppers have a rating of less than 1 Scoville unit, jalapeno chillies 103 units, habanero chillies 105 units, and pure capsaicin 107 units.

Most people think of the 'burn' of spicy food as a form of taste. In fact, the two sensory experiences are related but are very distinct. The taste modality is restricted to the tongue (and palate, in youngsters), but the pain system that can be triggered by capsaicin is distributed throughout the body, so the apparent ‘thermal’ effects of capsaicin can be induced at many locations, and not just on the tongue.

Vanilloid Receptor 1A molecular receptor has been found in the neurons which respond to both capsaicin, high temperatures, and local tissue damage. This receptor is a protein found embedded in the cell membrane, and has been labelled vanilloid receptor type 1, or VR1 for short. (It is the vanilloid group that chemically characterises capsaicin.) Capsaicin activates this receptor and causes calcium ions to flow into the nerve ending. This initiates nerve impulses that pass to the brain where they are interpreted as a burning pain. The same receptor is activated by temperatures high enough to be damaging, and by local tissue damage caused mechanically.

Continuous exposure to capsaicin causes desensitisation - if you eat chillies regularly, your tolerance to their burning taste becomes greater. This may be due to death of the neurons involved, or possibly to changes in their internal regulatory pathways. These analgesic effects of capsaicin have been turned to advantage in the treatment of chronic pain due to rheumatoid arthritis and shingles - by rubbing ointments containing capsaicin onto the skin over painful areas, the initial burning sensation is gradually replaced by a reduced perception of pain.

Menthol acts in much the same way as capsaicin, but in this case, it stimulates the fibers that register cold temperatures, not those that respond to extreme warmth. Products containing menthol send the brain an ambiguous signal of a ‘cool burn’.

The sensations produced by menthol and capsaicin are presumably accidents of human physiology - we did not evolve receptors to react specifically to these compounds. The chemicals fool pain receptors whose real purpose is to register critical events, like damage to the skin and the inflammation that often results. The tenderness around an injury is caused in part by the response of these same nerves to chemicals released in the skin.

References

Do we swallow when we are asleep?

7th July 1998

Yes - even when asleep, the swallowing reflex can occur (Orr and Johnson, 1998). It can happen for example when saliva accumulates at the back of the mouth - remember the involuntary swallowing reaction you experience when your dentist is drilling your teeth and water from the drill sprays into your pharynx? - well, a similar reaction can occur during sleep. The pharyngeal touch receptors respond to contact with solids or liquids and send nerve impulses to the swallowing centre in the medulla and lower pons region of the brainstem. Here the swallowing reflex is co-ordinated, and motor impulses are sent out to the different muscle groups concerned via several cranial nerves. The vagus nerves (the 10th pair of cranial nerves) with help from the glossopharyngeal nerves (cranial nerves no. 9) play a central role in controlling the soft palate, pharynx, and larynx. During swallowing, the respiratory centre (situated close to the swallowing centre) is inhibited and the entrance into the larynx is closed.

When we are awake, swallowing generally begins as a voluntary action and then continues as an involuntary reflex. When the food we are chewing is ready for swallowing, the bolus is lifted up against the palate by the tongue and pushed back into the pharynx as a voluntary action, where the involuntary reflex takes over. The swallowing reflex may be absent in an unconscious patient or during general anaesthesia, and care must then be taken to prevent food or liquid being inhaled and causing choking or airway obstruction, but otherwise the reflex is present and active when we are asleep and awake.

Reference

How can I improve a slow digestive tract, when toleration of fiber is poor, after use of laxatives?

28th March 1999

It appears from your question that you have tried several approaches already, but with limited success. Clearly, the content of your diet is relevant, but as you point out there is a reason why you cannot simply increase those food components such as fibre-containing vegetable materials which are generally thought to aid movement of food through the digestive tract. The other main option relates to physical activity. It is frequently observed that people who have restricted movement through age, disability or illness are more likely to experience difficulties brought on by a slow digestive tract. This is generally manifested by discomfort, constipation, and in some cases accompanied by a feeling of confusion. Even moderate activity, such as a stroll between meals, can do a lot to maintain good digestive mobility. Of course, we do not know your circumstances and therefore we do not know whether this is helpful advice in your case.

In recent years there has been a growing realisation that the network of nerve cells within the walls of the digestive tract play a very important role in the local patterns of digestive activity. Apparently there are as many neurons in the digestive tract as there are in the spinal cord - a very substantial population. This means that although the digestive tract is controlled in a global sense by the nerve supply reaching it from the brain and spinal cord, it has a lot of local autonomy in the way it functions. Not only that, it appears that digestive behaviour is adaptable and will be influenced by our way of life. Thus, people taking up stressful occupations might find that their digestive patterns change as a result. So when there is a problem with digestive processes, sometimes the best approach is to look at lifestyle factors in case there is some way of redressing the balance. Hopefully you will be able to find a way of reducing or overcoming your problem.

How are the nutrients carbohydrates, proteins, vitamins, iron and calcium of spaghetti bolognese digested?

9th March 2000

Digestion is a two-fold process involving the physical breakdown of food aggregates followed by chemical breakdown. The movement of the spaghetti bolognese through the digestive tract is carried out by series of muscular contractions.

Physical Digestion

The delightful smell and taste of the food together with the chewing activity stimulate the production of saliva. Physical digestion begins in the mouth where the voluntary action of chewing breaks down the food to form boluses that can be readily swallowed. Once swallowing has been initiated voluntarily, involuntary peristaltic waves propel the food down the oesophagus and into stomach, where it is churned and mixed with the gastric juices. This process continues the physical separation of the food which began in the mouth, and may continue for up to up to four hours. During this process the food is changed from the swallowed boluses into a semi-liquid substance called chyme (food mixed with gastric secretions). Chyme leaves the stomach by passing through the pyloric sphincter and enters the small intestine (duodenum, jejunum and ileum). In the small intestine the chyme is further broken down mechanically into smaller masses by a process known as segmentation, and further chemical digestion takes place. Any still undigested food materials and added secretions pass on through the ileocaecal valve into the caecum, the first part of the large intestine. Here, water is absorbed and residual matter compacted into faeces ready for elimination.

Chemical Digestion

  1. Carbohydrate - the initial breakdown of carbohydrate begins in the mouth where the ingested starch is acted upon by the enzyme amylase present in saliva. The starch is converted into maltose (a disaccharide). No further breakdown of carbohydrate takes place until the food, in the form of chyme, enters the duodenum where it is acted upon by pancreatic amylase and maltase. These enzymes convert any remaining starch to maltose. Maltase is also found in the small intestine. Its action here is to convert maltose to glucose (a monosaccharide) ready for absorption. Any cane sugar contained in the bolognese will be converted into glucose and fructose by the enzyme sucrase in the intestinal juice.

  2. Protein - the digestion of proteins begins in the stomach. The enzyme precursor pepsinogen (secreted by the chief cells) is converted to the protein-splitting enzyme pepsin by the strong acidity of the gastric juice. The pepsin breaks down proteins into polypeptide fragments which are broken down further in the small intestine by the pancreatic enzymes trypsin and chymotrypsin derived from the precursors trypsinogen and chymotrypsinogen. These enzymes break the polypeptides down into peptides. The final stage in the breakdown of protein takes place by the action of peptidases secreted by cells in the small intestine. These break down the peptides into amino acids ready for absorption.

  3. Vitamins, Iron and Calcium - any vitamins, iron and calcium contained in the spaghetti bolognese will be absorbed into the blood stream through the microvilli of the small intestinal lining.

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