This section is from the book "A Text-Book Of Pharmacology, Therapeutics And Materia Medica", by T. Lauder Brunton. Also available from Amazon: A text-book of pharmacology, therapeutics and materia medica.
Digestion is greatly aided by the movements of the stomach, which assist it by breaking up the food and mixing it thoroughly with the gastric juice. When these are deficient, it is probable that they are stimulated by nux vomica, or strychnine, and also by bitters.
A number of experiments have lately been made by Schutz1 on the influence of drugs upon the movements of the stomach. These experiments are interesting as showing an analogy between the action of drugs on the stomach and other organs, such as the heart; but the doses applied were so large that the effects are not to be considered the same as those arising from medicinal doses. These experiments were made by observing the movements of the viscus, after removing it from the body and placing it in a moist chamber. Various drugs were administered to dogs; and after the symptoms of poisoning became well-marked, the animals were killed, and the movements of their stomachs in the moist chamber were compared with those of normal animals.
The movements of the isolated stomach depend upon :
(a) The muscular fibres contained in its walls.
(b) The motor nerve-endings by which the muscular fibres are excited to action.
(c) The ganglionic cells of Auerbach's plexus, by which the rhythmical movements of the organ are maintained.
1 Arch.f. exp. Path. u. Pharm., xxi., p. 341.
(d) The sensory nerves, by which those ganglia may be reflexly excited.
The occurrence of spontaneous movements in the stomach shows that both the ganglia and muscular fibres retain their functional power. This is shown also by the occurrence of reflex contractions, when the stomach is distended by inflation and by the production of extensive undulating contractions on local irritation by a weak electrical stimulus. As the stomach dies, the nervous apparatus loses its irritability before the muscles, so that spontaneous movements cease, reflex contraction no longer occurs on inflation, and the strength of electrical stimuli requires to be greatly increased in order to produce undulatory movements extending beyond the part actually stimulated.
When the excitability of the nervous apparatus is quite gone, that of the muscular fibres still remains. Electrical stimuli cause localised contractions corresponding to the bundles of muscular fibres directly excited by the current.
It is evident that this result will be nearly the same if the ganglia themselves are paralysed, or if the motor nerve-fibres, through which they act on the muscular fibres, are paralysed. At present, these actions have not been distinguished experimentally in the stomach, and therefore conclusions regarding the mode of action of some drugs are based to some extent upon analogy. Thus, ether and atropine both produce the effect mentioned above; but we know that ether tends to act on nerve-centres, such as those of the brain and spinal cord, while atropine tends to paralyse peripheral nerves ending in involuntary muscular fibre. The conclusion is that in the stomach also the effects of ether are due to its action on the ganglionic cells, while those of atropine are due to its action on motor nerves.
When the muscular fibres are paralysed as well as the nerves, electrical stimuli cause no contractions at all, or local contractions, which are more or less feeble according to the completeness of the paralysis.
Motor nerve-endings in the stomach are
The excitation by muscarine is shown by general contraction of the stomach. The symptoms of paralysis by atropine have been already discussed.
Less marked by Strychnine. Caffeine. Veratrine. Barium chloride.
Nicotine Pilocarpine in small doses.
Arsenic. Nicotine Pilocarpine in large doses.
The whole nervous mechanism of the stomach is paralysed by exposure to the vapour of
This paralysis is transient, and only lasts during exposure. The administration of chloroform or ether to animals so as to produce ordinary anaesthesia seems to have no action on the movements of the stomach. It must be borne in mind that while exposure to the vapour of ether or chloroform may paralyse the stomach, and that while this action is unimportant, as it may occur from an overdose of these substances, smaller doses probably increase the movements of the stomach and act as carminatives.
Fig. 128. - Action of tartar emetic on the stomach in producing active contraction of an antiperistaltic character. The dotted line shows the shape of the stomach at rest.
1 Cocaine at first causes greatly increased movement of the stomach, but its subsequent efforts are similar to those of atropine.
Absorption from the Stomach.
We know at present very little regarding the effect of drugs in stimulating absorption from the stomach, but it is probable that this is very greatly influenced by the condition of other organs.
All the processes which go on in the stomach - secretion, peristaltic action and absorption - are much influenced by the condition of the circulation.
All the blood which circulates in the stomach has to pass through the liver before it gets into the general circulation
Rectum And Haemorrhoidal Plexus.
Fig. 129. - Diagram of the veins forming part of the portal circulation. The pancreatic and splenic veins, although most important, have been omitted for the sake of clearness.
(Fig. 129), and thus the condition of the stomach is necessarily much modified by the condition of the liver. If there is any obstruction to the free flow of blood through the liver, the circulation in the stomach will necessarily be impeded, and absorption probably diminished.
Not only the blood from the stomach, but that from the intestines also, passes through the liver, and we may naturally expect that the liver itself will be influenced by the condition of the blood which passes to it from the intestinal canal.
In Dr. Beaumont's observations on Alexis St. Martin, in whom a gastric fistula existed, he found that after the stomach had been deranged by various articles of food, including fat pork, there was distress in the stomach, headache, costiveness, and a coated tongue. In the stomach there were numerous white and pustular-looking spots. Half a dozen calomel pills produced catharsis, removed the symptoms, and restored the mucous membrane of the stomach to its normal condition. Whether this effect was due to the action of the pills on the liver, or on the intestines, we cannot perhaps positively say, but at all events the improvement was readily evident to the observer's eye.
Absorption from the stomach is probably also much influenced by the condition of the nervous system. Bouley found that when the vagi were divided in a horse, strychnine no longer produced poisoning, the reason being that the absorption took place so slowly after a division of the nerves that the poison was excreted as fast as it was absorbed. The retarded absorption, however, he considers to be due, not to any alteration in the absorptive power of the stomach itself, but to diminished movement in its walls, so that its contents are not so quickly poured out into the intestine. Absorption normally goes on more slowly from the stomach than from the intestine, and so while the poison remains in the stomach it is not absorbed quickly enough to cause poisoning.