Alimentary Tract (1938)

in hill parts of the elementary track there are always active we see directly the action of the esophagus in swallowing here we see the act of swallowing in the exposed esophagus of a goose a ring of contractions preceded by relaxation forces the food downward an apparatus of this kind is often used to study motility in the alimentary tract this rubber balloon is placed inside the organ to be studied when the organ contracts it forces the air out of the inflated balloon and raises the water level in this manometer by these means the stylus records the contractions on a moving paper the balloon has now been placed in the stomach of this man shortly after a light meal the large crests are caused by slow and gentle stomach contractions the short and rapid movements are caused by pressure changes from breathing in this anesthetized animal we actually see these same stomach movements which are characteristic of early digestive action they are peristaltic waves that progress downward over the lower half of the stomach the upper half of the stomach here concealed by the liver is quiet and serves mainly as a reservoir for the food the movements are orderly and regular although the stomach is an automatic organ it is regulated by the central nervous system stimulation of the vijaya nerves with an induction current causes a series of severe contractions of the stomach an abnormal state of the central nervous system or too little sugar in the blood or the use of some drugs will also result in strong contractions a condition known as hyper motility now while the stomach is showing normal action I stimulate the sympathetic nerves of the stomach the contractions gradually die out such a dual control by nerves acceleration and inhibition also governs the intestines inhibition of movements may also occur if adrenaline is greatly increased in the bloodstream or when there is a strong emotional stress as during anxiety anger and fear we can demonstrate this action of adrenaline by this piece of living and active intestinal muscle suspended in a normal salt solution as I add adrenaline to the salt solution the contractions stopped and the muscle relaxes as indicated by the stylus in this entire view of stomach and intestines we see severe contractions of the lower end of the stomach that moved toward the esophagus instead of toward the intestines this action does not occur in the normal stomach but may occur in vomiting vomiting is a very complicated process involving intricate coordination of many nerve impulses and muscles several hours after the last meal we again record the contractions in the stomach of this man by means of the balloon the strong contraction now taking place in the empty stomach causes pangs of hunger the same thing can be shown on the empty stomach of an anesthetized frog a contraction wave is starting at the upper end of the stomach these contractions give rise to hunger pangs as digestion in the stomach precedes the peristaltic waves of the stomach become stronger when the contents of the stomach gradually become more fluid some of the content is forced into the duodenum the junction of the stomach and the intestines does not open as each gastric contraction wave approaches the control of this Junction seems to be governed by the consistency of the food where the acid concentration in the duodenum as well as by the v-j and sympathetic nerves an alkaline state in the door Denham favors relaxation at the junction thus permitting food again to enter from the stomach local contractions of the intestinal wall occur rhythmically at places in the intestines where masses of food have accumulated as in the duodenum here at the left they divide the food mass hence the common name segmentation these movements thoroughly mix the food with new digestive juices and aid absorption by bringing the food mass into better contact with the absorbing walls when the food has been turned about for a while by these segmentation movements it is moved forward by peristaltic movements the wall of the intestines at and below the food mass is relaxed while the part of the wall behind the bolus is constricted this relaxation followed by a constriction passes forward along the intestine causing the food mass to move towards the large intestine usually such peristaltic waves progress for a few inches and then cease and segmentation movements are resumed in an adult man the small intestines are about 22 feet long and it takes a meal from 3 to 6 hours to pass through them all of the intestines as well as the stomach now show activity in the duodenum at the upper left may be seen strong peristaltic waves most of the absorption of digested food takes place in the lower portion of the small intestines if the inside lining of the small intestines is observed through a microscope it is seen to be covered by a mass of finger-like projections called villi the actual size of this view is 1/16 of an inch square we are looking down on the tips or free ends of the villi the villi are in constant motion and revealed two distinct types of actions there is first a swaying movement from side to side but we are more interested in observing the second type of motion which appears like pumping movements note that the villi are suddenly retracted and then relaxed more slowly the contractions are definitely muscular movements it is obvious that this mechanical movement of the villi may assist in absorption of food products both by the blood stream and by the lymphatic system after passing through the length of the small intestines the content containing mostly indigestible material or roughage and water enters the large intestines or the colon although the colon does not absorb much digested food still it does absorb and conserve much of the water the colon and the small intestines just like the stomach are essentially automatic organs but they have also the same dual control from the central nervous system the sacral and hypogastric nerves acting as accelerators and the sympathetic nerves acting as inhibitors the presence of solid matter or roughage in the intestines also has a tendency to stimulate motility irritating drugs caused violent movements the colon also commonly reveals another type of motion namely inter peristalsis these movements probably aid in the absorption of water by delaying the time when the material reaches the rectum parts of the normal colon ordinarily show long periods of quiescence 20 to 30 hours are normally required for the contents to pass through the colon during this time more and more of the water is absorbed in the contents therefore become firmer and firmer strong longitudinal as well as transverse contractions force the contents out of the colon as shown in this animal normally strong voluntary contractions of the abdominal muscle aid this action of the colon musculature the healthy elementary tract is a remarkable machine performing automatically and well on a variety of good foods in moderation if we don't worry