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THE DIGESTIVE SYSTEM OF VERTEBRATES

TOPIC: Motor activity of the digestive tract

Figure  This is a comparison of esophageal muscle variations in birds and mammals. Dashed lines represent striated muscle and solid red lines represent smooth muscle. The esophagus of some mammals, such as Perrisodactyls and Lagomorphs, terminates in distinct, muscular gastroesophageal sphincters. Although others , such as the birds, primates, felines, canines, suiformes, ruminant, and rodents can constrict the terminal segment of their esophagus, it lacks the thickened muscular sphincter. (From Sellers & Stevens 1977) 



Figure 6.1  Esophageal pressure events during bovine (A) deglutition, (B) regurgitation, and (C) eructation.. Numbers represent 1) cervical esophagus 79 cm cranial to cardia, 2) thoracic esophagus 40 cm cranial to cardia, 3) thoracic esophagus 19 cm cranial to cardia, and 4) pleural cavity. The peristaltic deglutition wave is accompanied by no changes in respiratory cycle. However, regurgitation is accompanied by a marked drop in pressure in the pleural cavity and thoracic esophagus, followed by an antiperistaltic wave of esophageal contraction. Eructation is recorded as a rise in intrathoracic pressure of low amplitude and approximately one-second duration, due to abdominal press. This is followed by a high pressure, short duration wave of  antiperistaltic esophageal contraction, often followed by a fluid- clearing wave of deglutition. (From Sellers & Stevens 1960)  < go to CD Chapter 6



Figure 6.2  Basal electrical rhythm of the human stomach. Slow waves of partial depolarization of the circular muscle is initiated by a pacemaker and passes over the distal half of the stomach. These initiate contractions when accompanied by spike potentials.  (Stevens 2001)  < go to CD Chapter 6



Figure 6.3  Diagrammatic sections of bovine reticulorumen and omasum.  Structures and compartments of major importance are numbered as follows:  1) cardia, 2) reticulo-omasal orifice, 3) reticulum, 4) cranial sac of rumen, 5) dorsal sac of rumen, 6) caudodorsal blind sac, 7) ventral sac of rumen, 8) caudoventral blind sac, 9) ruminoreticular fold, 10) cranial pillar, 11) right longitudinal pillar, 12) caudal pillar, 13) dorsal coronary pillar, 14) ventral coronary pillar, 15 ) omasum, 16) omasal canal, 17) omasal pillar, 18) omaso-abomasal orifice, 19) omasal lamina (leaf), 20) abomasum.  (From Sellers & Stevens 1966.)  < go to CD Chapter 6



Figure 6.4  A six-minute recording of reticuloruminal cycles and associated events in the esophagus and omasum.  Note the relationship between the contractions of the rumen and omasal canal, and the prolonged, acyclic contractions of the omasal body pressure during primary contraction of the dorsal rumen and omasal canal.  Upper traces show eructation as a biphasic wave occurring during secondary rumen contractions and the frequent waves of deglutition associated with the swallowing of saliva. (From Sellers & Stevens 1966.)  < go to CD Chapter 6



Figure 6.5  Movement of digesta during primary and secondary contractions of the reticuloruminal cycles. (From Stevens & Hume 1995.)  < go to CD Chapter 6 



Figure 6.6  Movement of digesta through the bovine omasum.  Closed arrows show movement of digesta and open arrows show movement of forestomach walls. Diagrammatic axial section (see Fig. 5.3) shows the cranial reticulum (1), reticulo-omasal orifice (2), omasal leaf portion of omasal body (3), omasal canal (4) and cranial abomasum (5).  A: All structures are relaxed during much of the cyclic contraction of the forestomach.  B: During the second reticular contraction, the reticulo-omasal orifice and omasal canal are pulled ventrally, producing a negative pressure in the canal and a closing and then opening of the orifice, which results in aspiration of digesta from the base of the reticulum.  C: Primary contraction of the rumen is associated with a primary contraction of the reticulo-omasal orifice and omasal canal, forcing fluid and small digesta particles between the leaves of the omasal body and into the abomasum.  These events are followed by relaxation of these structures (D), and repeated if the forestomach undergoes a secondary contraction.  E: At intervals that vary and are unrelated to the cyclic contractions of the forestomach, a wave of contraction passes over the omasal body, releasing its contents into the abomasum. (From Stevens & Hume 1995.)  < go to CD Chapter 6



Figure 6.7  Reticuloruminal cycles during rumination in cattle. Numbers 1 and 2 mark first and second reticular contractions seen with every cycle and the x marks the extra reticular cycle at the regurgitation stage (R) of rumination. The remasticated bolus is swallowed (D) just prior to the next reticulorumen cycle. The AP on the reticular tracing is a registration of abdominal press at the time of eructation (E). (From Stevens & Sellers 1968.)  < go to CD Chapter 6 



Figure 6.8  Schematic representation of the llama stomach. The esophagus (1) enters the first compartment (A), which is partially divided into cranial (3) and caudal (4) sacs by a pillar of muscle (7), and separated from the second compartment (B) by a constriction (8). Both compartments include regions of saccules (5,6,9) containing cardiac glandular mucosa. A ventricular groove (2) runs along the lesser curvature of the forestomach between the esophagus and the third compartment (C). The initial four-fifths of the third compartment is also lined with cardiac glandular mucosa (11,12). The terminal segment (13) is lined with proper gastric mucosa and separated from a duodenal ampulla (D), by a pyloric sphincter (14). (From Vallenas et al. 1971.)  < go to CD Chapter 6



Figure 6.9  Left, lateral, longitudinal section of the llama stomach showing the entrance of the esophagus (A), transverse pillar (B) between the cranial and caudal sacs of the first compartment and entrance to the second compartment (C). It also shows the openings to the glandular saccules in the first compartment.  (Modified from Vallenas et al. 1971.)  < go to CD Chapter 6



Figure 6.10 Pressure recording of cyclic contractions of llama forestomach. (From Vallenas & Stevens 1971a.)  < go to CD Chapter 6



Figure 6.11  Cyclic contraction of the first compartment of the llama  forestomach. A-D  show contractions of pillar and sacs. Cyclic eversion of caudal sac pouches during the three stages of contraction is shown in drawings on the right. (From Vallenas & Stevens 1971a.)  < go to CD Chapter 6



Figure 6.12a  Phases of migrating myoelectric complexes (MMC) during interdigestive (fasting) and feeding periods in carnivores and humans.  This diagram shows slow waves with no spike potentials during phase I, intermittent spike potentials during phase II, and consistent spike potentials during phase III. (From Hendrix 1987.)  < go to CD Chapter 6



Figure 6.12b  Phases of migrating myoelectric complexes (MMC) during interdigestive (fasting) and feeding periods in carnivores and humans.  This diagram shows the effects of interdigestive periods on the  MCC, which originate in the stomach and lower esophageal sphincter (LES) and pass through the small intestine. (From Hendrix 1987.)  < go to CD Chapter 6

 

Figure 6.12c  Phases of migrating myoelectric complexes (MMC) during interdigestive (fasting) and feeding periods in carnivores and humans.  This diagram shows the effects of feeding on the  MCC, which originate in the stomach and lower esophageal sphincter (LES) and pass through the small intestine.  Feeding interrupts the cycle and increases the duration of phase II. (From Hendrix 1987.)  < go to CD Chapter 6



Figure 6.13  Relationship between the velocity of propagation of myoelectric complexes and the length of the small intestine.  The hatched area shows the 95% confidence limits.  The median daily number of jejunal complexes is high in ruminants and low in carnivores, because of the obliterating effect of feeding in the latter species.  (From Ruckebusch 1981.)    < go to CD Chapter 6



Figure 6.14  Relationship between digesta flow and electrical slow waves and migrating spike bursts in the cat colon. Slow waves (SW) appear to originate from a pacemaker midway along the colon, spread toward the cecum, and tend to produce digesta flow in the same direction. Migrating spike bursts (MSB) begin at a variable position in the proximal colon and migrate toward the rectum. These are accompanied by contractions, which tend to move digesta in that direction. (From Christensen et al. 1974)  < go to CD Chapter 6

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