A Text-book of medical practice for practitioners and students / edited by William Bain.
- Date:
- 1904
Licence: In copyright
Credit: A Text-book of medical practice for practitioners and students / edited by William Bain. Source: Wellcome Collection.
Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.
70/1042 page 42
![tractions of their fibres. The (esophagus which now receives the ])oUis possesses tliick muscular walls, the fibres iu which are circularly arranged. In the ui)j)er third the fibres are striated, in the middle third they are mixed striated and smooth, and in the lower third they are entirely smooth. The food is driven along the (jesopliagus by a peristaltic contraction, i.e., the upper ring of fibres first contracts, closing the lumen above, and then the next ring of fibres innuediately below contracts, which thus drives tlie contents down- wards as the upper passage is closed. In this manner, hy a progressive contraction, the bolus is driven along the tube, rapidly in the first part where the muscular walls are striated, much more slowly in the lower part where the muscles are smooth. In man and in the horse the })eristaltic mechanism is not used in the swallowing of fluids, which are shot along the tube by the forcible contraction of the mylo-hyoid. The nervous mechanism of the peristalsis in this part of the alimentary tract is different from that elsewhere, for it is a reflex act. If the tube is cut right across leaving the nerves intact the peristaltic wave passes over from the upper to the lower segment as if the whole were inbict. The passage of a bolus along the oesophagus has been studied in intact animals by means of the Rontgen rays by giving them food containing bismuth subnitrate, which is o]ja(^ue to these rays, and its movement can therefore be followed. In this way it was shown that the main movement is effected peristaltically and is ([uick in the cervical (jesophagus and slow in the thoracic. Thus the bolus may remain in the lower end a few seconds before being passed into the stomach. The entrance into the stomach is guarded by a sphincter which is tonically contracted, thus preventing regurgitation from the stomach. The nerve supply to the oesophagus is by fibres from the vagus, which also sends inhibitory fibres to the sphincter. Movements of the Stomach.—These are for two purposes, viz. : (1) to churn up the contents, thus thoroughly mixing them with the gastric juice and favouring their sub- division ; and (2) to drive the contents onwards into the duodenum. Anatomically .and physiologically the stomach is divided into two parts, a larger jiortion with thin walls comprising the cardiac end and fundus, and a smaller part with thicker walls, the antrum or pyloric region. The movements of the stomach have been studied by direct inspection of the viscus, exposed by simply opening the abdomen, or exposed while the animal is immersed in a bath of warm saline solution, or again with the organ entirely removed from the body and enclosed in a warm chamber. By all these methods the conditions are very abnormal, and we have evidence that the movements thus observed are in many respects irregular. The movements have also been studied by the Rontgen ray method, and, as in this case the animal is in a perfectly normal state, the results obtained are certainly the most reliable. In such experiments it is found that the movements begin a few minutes after a meal is given. They consist at first of a series of constrictions which involve the antrum only, commencing, that is, near the middle of the stomach and travelling slowly to the pylorus. Each wave of constriction takes about forty seconds to travel over the antrujn, and as the waves follow one another at about ten seconds interval, four or five of them may be observed at one time travelling towards the pylorus. As digestion proceeds the constrictions become more and more marked, and follow one another at shorter intervals, though it is not until near the end of digestion that they become so powerful as to produce complete obliteration of the lumen. At first, the pylorus opens only when each eighth or tenth wave reaches it, but as digestion proceeds it opens more and more frequently, until, towards the close, it may open with each wave. The cardiac end and fundus remain quiet most of the time, only a few contractions passing over it from time to time, sufficient to supply the antrum with fresh material. The antrum is thus the part in which the churning movements take place, the general result of the waves being to drive the contents against the pylorus. Only the more liquid parts are at first allowed to pass through, larger masses being returned along the axis, and, if undigestible, only discharged towards the end of digestion. It has been shown that the opening of the pylorus is inhibited by the presence of acid in the duodenum, so that there is a mechanism by which no further dose of acid chyme can be discharged from the stomach until the previous one has been neutralised in the duodenum. As these waves of constriction are to be observed in stomachs enturely removed from the body, their co-ordination is certainly not of central origin. The conduction of the wave is probably entirely muscular. They are very easily inhibited, the course of the inhibitory fibres being from the sympathetics through the splanchnics. The vagus carries the motor fibres to the stomach, both to the fundus and to the antrum. The vagus also contains inhi1)itory fibres. Thus, in a curarised animal, stimulation of the yagu,s anises contraction of the oesophagus, cardiac sphincter and stomach, but if the animal he atro- pinised, the result is relaxation of the cardiac sphincter and cardiac end, followed, alter cessation of the stimulus, by marked contraction. The action of the vagus on the pyloric sphincter is to cause contraction, though relaxation may at tunes be observed. I no movements of the stomach may l)e inhibited by stimulation of any sensory nerve. I he sensory fibres from the stomach probably run in the sixth to ninth dorsal rootsj^. Vomiting.—If irritating substances have been admitted to the stomach or if the viscus](https://iiif.wellcomecollection.org/image/b21510167_0070.jp2/full/800%2C/0/default.jpg)
