Peristalsis

PERISTALSIS (from Greek peristaltikos—encompassing), a special form of muscular contraction observed mainly in hollow organs supplied with smooth muscle. Peristaltic movement consists in the fact that rhythmic contractions leading to a reduction in the lumen of the organ spread from the place of their origin along its entire length (peristaltic waves). At the moment of the passage of a peristaltic wave over a certain section, the neighboring sections are in a state of relaxation. Consequently, the contents of the organ are squeezed in the direction of the wave's course. Peristaltic waves never run in isolation, but always follow one another with a certain rhythm and a certain speed. In the bodies of higher animals, peristaltic movement is observed only in hollow organs (digestive tract, ureter, etc.). In lower organisms, forms of body movement are also observed that are similar in type to the mechanism of P. (for example, the crawling of an earthworm). However, since peristaltic movement has the greatest practical significance in the activity of the intestine and the digestive tract in general, when speaking of P., one often means precisely the peristalsis of the intestines, which is also the most studied. Peristalsis of the intestines. Methods of investigation: 1) observation of the movements of the intestines of a whole animal with an opened abdominal cavity immersed in a warm saline solution, 2) observations of the movements of an intestinal loop brought out under the skin (the school of I. P. Pavlov), 3) observation of the movements of the intestines through a celluloid window sewn into the abdominal wall (Trän-Delenburg), 4) investigation of the movement of an isolated (cut out of the body) loop of intestines in Ringer's or Tyrode's solution (Magnus), 5) roentgenographic investigation of the movements of the intestines from photographs obtained after giving a per os contrast mass—barium salts or iodine (Cannon). The last method makes it possible to study P. of the intestines in humans. When using these methods, all types of intestinal movement are studied, among which the following are distinguished: a) pendulum-like movements (Pendelbewegungen)—rhythmic elongations and shortenings simultaneously covering the entire intestine, b) oscillations of the tone of the intestinal wall, manifesting themselves in prolonged changes in the length and mainly the lumen of certain sections of the intestine, and c) true peristaltic movements (Fig. 1). The latter are carried out by longitudinal, but mainly circular smooth muscle. Arising in the region of the duodenum or the beginning of the jejunum, peristaltic contractions are characterized by the regularity of their spread along the intestine and the sequential involvement of the underlying section of the intestine in contraction following the overlying one. Peristaltic contractions follow one another with a certain rhythm (in humans 10–12 per minute), and each individual period of P. consists of a series of following peristaltic waves. When studying P. in one section of the intestine, we will observe its rhythmic contractions, since when each wave passes to the underlying section, the overlying one is in a state of relaxation. P. is observed only in a filled intestine. The impulse causing the onset of P. is the stretching of the circular muscle of the intestine. In this case, the higher the tone of the muscle, the less stretching of the intestine (resp. the less increase in pressure) causes the appearance of a peristaltic wave. A decrease in the tonic tension of the circular muscles will accordingly cause a decrease in P., an increase in tone—an intensification. However, even with constant filling of the intestine, periods of P. are always succeeded by periods of rest. Innervation of P. The possibility of observing peristaltic movements in an isolated and denervated intestinal loop proves that nervous impulses do not participate in the occurrence of P. However, nervous influences (Fig. 2) exert distinct influences on the entire course of peristaltic movement: the sympathetic nervous system, represented almost exclusively by branches of the celiac nerve, inhibits all types of movement of the intestines, the parasympathetic (vagus nerve)—intensifies them (inverse relations take place for the sphincter ileo-caecalis). In the norm, vagal tone apparently predominates over sympathetic with respect to the activity of the intestine, since after cutting both the celiac and vagus nerves, P. is found to be slowed down. Thanks to the presence of this innervation, a whole series of impulses can cause a change in P. Peristalsis is delayed at all strong sensitive irritations (for example, during urination and defecation); when teasing an animal with the sight of food, P. is intensified. The possibility of changes in P. in the order of a conditioned reflex is beyond doubt: after the imperialist war in Germany, for example, cases of severe diarrhea in demobilized soldiers were described under the influence of irritants characteristic of a combat situation. Also, changes in the activity of the intestine during a number of psych. affects have been known for a long time. Along with this, sharp changes in P. occur in the order of a reflex from the mucous membrane of the intestine; for example, the introduction of oil into the intestine...

Fig. 2. Action of nerves on intestinal movements. In the left part of the curve—irritation of the vagus nerve; a sharp drop in tone is visible, a significant decrease in the peristaltic wave (in each wave pendulum-like movements are visible). In the right part—brief irritation of the sympathetic nerve; a sharp rise of the curve is visible.

NSL delays P. Cocainization of the mucous membrane eliminates these influences. The consistency of food influences P. in the respect that the denser the food, the stronger P. Therefore, P. is always more pronounced after food rich in fiber and reduced with meat food (Fig. 3). Local action of cold (for example, when introducing ice into the stomach) intensifies P., heat weakens it. Significant influence on P. is exerted by substances that take water from the intestinal wall—multivalent cations and anions, citrates, salts of oxalic acid, urea, concentrated sugar solution, polyatomic alcohols, etc. However, the laxative action of these substances is not necessarily connected with the intensification of P., the latter taking place only in strongly concentrated solutions. A number of alkaloids influence P. correspondingly to their influence on the vegetative nervous system (see above). Fig. 3. Influence of various types of food on peristalsis (schematic drawing from a roentgenogram in humans). On the left the shot was made after giving 400 g of meat, on the right—after giving 400 g of rice. A significant intensification of segmentation of the stomach (peristalsis) is visible after carbohydrate food. Adrenaline, exciting the sympathetic, and atropine, paralyzing the parasympathetic nervous system, inhibit P. Physostigmine, pilocarpine, and choline sharply intensify P. Choline is a product formed in the intestine itself and possibly playing a known role in the normal execution of P. Some pharmacol. influences also apparently are connected with the presence of choline; thus, the intensification of P. from fatty acids apparently depends on the formation of a highly active esterocolin. On this basis, some authors consider choline to be a "peristalsis hormone." The action of morphine and opium derivatives on P. is complex and not unambiguous in different animals (see Morphine, Opium). Castor oil significantly intensifies P. Essential oils manifest such an action only in weak concentrations. Small doses of potassium salts, when acting locally, intensify P. Calcium and magnesium salts, when administered intravenously, inhibit P. Products formed during fermentation and putrefaction (lower fatty acids and CO₂ during fermentation, indole, skatole, and CO₂ during putrefaction) significantly intensify P. Hence the significance of the intestinal flora for the motor activity of the intestine. About P. of the stomach—see Stomach, motor function. (P. of the esophagus—see Swallowing.)—II. of the ureters consists of a series of following contractions running from the renal pelvis to the urinary bladder in the form of a series of contractions. Individual periods of P. alternate with pauses. Each peristaltic wave drives small portions of urine into the bladder. Movements analogous to P. are observed in the seminal and urethral canals during the emission of semen during sexual intercourse.

K. Bykov, G. Konradi.