Functional Diseases of the Alimentary Tract

By  F. W. Broderick, M.R.C.S., L.R.C.P., L.D.S., R.C.S.

            It is necessary first of all to consider shortly the innervation of the alimentary tract, so that we may be in a position to assess the vegetative disturbance on which will depend functional upset in which disease of this system will essentially rest. The vegetative nervous system controls the whole process of digestion and the utilization of foodstuffs, not only from the moment that these are placed within the mouth until the indigestible residue is evacuated, but it is, in addition, responsible for the sensations of hunger and the desire for food. It regulates both the chemical and the mechanical processes by which digestion is brought about, and, through its branches, the parasympathetic stimulating and the sympathetic inhibiting these prosesses, is responsible for the digestion and assimilation of food molecules which are the ultimate source of all bodily energy.

Anabolic Processes

As these processes are essentially anabolic, associated with the conservation of energy, it will be seen that the dominant portion of the vegetative nervous system in alimentary function is the para sympathetic. Through the chorda tympani and the auriculotemporal nerves (its upper part), it stimulates the salivary glands; through the vagus (its middle part) it brings about those sensations of hunger which lead to food being taken; it starts, and to some extent maintains the secretion of the digestive juices, and produces those peristaltic waves by which the contents of the visceral cavities are kept in contact with these juices and are moved on from one part of the alimentary tract to the next; and finally, through the sacral nerves (its lower part), it presides over the evacuation of the residue. The sympathetic portion, on the other hand, can definitely inhibit salivary secretion, and by its action on the various sphincters can delay and hold up the passage of the alimentary contents.

Any condition, therefore, which will tend to upset the close and intimate working of these two portions may, in some manner or another affect some portion or other of the digestive tract.

Langdon Brown quotes the work of Keith as providing a new conception of the movements of the alimentary tract:

“He divides the alimentary canal up into a number of neuromuscular segments, each section being cut off from its neighbor by a sphincter which effectually blocks the passage of contraction waves, and prevents them from spreading from one section to the next. He was likened the alimentary tract to a railroad, divided into block sections, each provided with a signalman and a telephone apparatus. The signalman of one section refuses to accept any further traffic until his section is clear; all sections are closely correlated: if one is blocked, the others, too, become automatically closed.

“He divides the sections as follows: (1) the pharyngeal section ending in a sphincter at the upper end of the oesophagus; (2) the cardiac sphincter marks the end of the oesophageal section and just beyond lies some modal tissue which acts as pace-maker for the movements of the stomach; (3) the gastric section ends at the pylorus, but the pace-maker for the duodental section is not reached until just above the entrance of the bile duct; (4) the duodeno-jejunal junction is marked by another sphincter with its special nerve supply. There are three peritonial bands lying to the right of the duodoenal-jejunal flexure, each containing a branch of the vagus and splanchnic (sympathetic) fibres, the first going to this, and the others to the next two sphincters; (5) the ileocecal valve is provided with a long sphincter immediately above it –this is supplied by the second branch; (6) there is a sphincter with the third of these special nerve supplies in that part of the transverse colon which lies below the pylorus; (7) at the junction of the pelvic colon with the rectum there is another sphincter; (8) finally, the alimentary tract is closed by the anal sphincters. This conception of the alimentary tract explains many of the observed disturbances of the mechanical side of digestion. An irritable focus in any section disturbs the onward progress of the food by causing a spasm of the sphincter immediately above, and often, indirectly, of the sphincters some segments higher up.

“We can express the motor disturbances of the alimentary tract under the heads of irregular and exaggerated contractions, tonic spasms, and atony. Irregular and exaggerated contractions are due to irritation of the parasympathetic, which in the vagal area produce colic, and when in the pelvic area, tenesmus. Tonic spasms and atony, on the other hand, are due to sympathetic irritation, which may express itself in excess of normal movements, spasms due to constrictions of the sphincters.