The Digestive System EFE Veterinary Science Overview of Digestive System Schematic representation of the digestive apparatus in the dog. 1, Mouth; 2, salivary glands; 3, pharynx; 4, esophagus; 5, stomach; 6, liver; 7, duodenum; 8, pancreas; 9, jejunum; 10, ileum; 11, cecum; 12, colon; 13, rectum; 14, anus. The Mouth (Dog) General view of the oral cavity of the dog. 1, Vestibule; 2, canine tooth; 2′, philtrum; 3, hard palate; 4, soft palate; 5, tongue; 6, sublingual caruncle; 7, palatoglossal arch; 8, palatine tonsil; 9, frenulum. Hard and Soft Palates Dog and Cow The hard and soft palate of the dog. 1, Philtrum; 2, incisive papilla; 3, hard palate with rugae; 4, soft palate; 5, palatoglossal arch; 6, intrapharyngeal ostium; 7, palatopharyngeal arches; 8, esophagus. The hard palate of a cow. 1, Dental pad; 2, incisive papilla; 3, rugae of hard palate; 4, palatine raphe; 5, P2; 6, buccal papillae The Tongue (Dog) The tongue of the dog. The soft palate and the esophagus are sectioned in the median plane. 1, Apex; 2, body; 3, root, forming floor of oropharynx; 4, median groove; 5, vallate papilla; 6, fungiform papillae; 7, palatoglossal arch; 8, palatine tonsil in tonsillar fossa; 9, epiglottis; 10, frenulum. Tooth Structure Figure 03-13. Schematic longitudinal section of a simple tooth. 1, Enamel; 2, dentine; 3, cement; 4, pulp; 5, apical foramen; 6, periodontal ligament; 7, socket (alveolus); 8, gum. Equine Premolars Figure 03-14. Premolar teeth exposed in the upper jaw of a horse. The part protruding above the gum is the clinical crown (1); the whole enamel-covered part is the anatomical crown or body (2) of the tooth. Deciduous (“baby”) Teeth Figure 03-15. Schematic drawings representing tooth eruption and replacement. A, Eruption of a deciduous tooth. The primordium of the permanent tooth is located on the lingual side of the deciduous tooth. B, The fully developed deciduous tooth within a bony alveolus. The crown of the permanent tooth has already formed. C, The permanent tooth is ready to break through. The root of the deciduous tooth has been resorbed; formation of the root of the permanent tooth is in progress. Permanent Dentition of the Dog Dental Formula of the dog: I3/3, C1/1, P4/4, M1/2 Permanent Dentition of the Cat Dental Formula of the Cat: I3/3, C1/1, P4/4, M1/1 Permanent Dentition of the Pig Permanent dentition of the pig, upper (A) and lower (B) jaws. 1, Lingual surface; 2, vestibular surface; 3, distal surface; 4, mesial surface. Dental Formula: I3/3, C1/1, P3/4, M4/3 Permanent Dentition of the Horse Figure 03-19. Permanent dentition of the horse, upper (A) and lower (B) jaws. 1, Wolf tooth (P1); 2, diastema. Dental Formula: I3/3, C1/1, P4/4, M3/3 Permanent Dentition of the Cow Figure 03-20. Permanent dentition of cattle, upper (A) and lower (B) jaws. Dental Formula: I0/4, C0/0, P3/3, M3/3 Muscles of Mastication Figure 03-21. The muscles of mastication of the dog, left lateral aspect (A), in section (B). 1, Temporalis; 2, masseter; 3, 3′, rostral and caudal bellies of digastricus; 4, mylohyoideus; 5, medial pterygoid; 6, origin of lateral pterygoid; 7, tongue; 8, mandible; 9, zygomatic arch; 10, level of transection (B). The Pharynx Figure 03-27. Schematic drawing of the pharynx showing its rostral connection with the nasal and oral cavities and caudal connection with the esophagus and larynx. 1, Nasal cavity; 2, oral cavity; 3, soft palate; 4, nasopharynx; 5, root of tongue; 6, larynx (protruding through pharyngeal floor); 7, laryngopharynx (piriform recess); 8, caudal end of palatopharyngeal arch; 9, esophagus; 10, lamina of cricoid cartilage; 11, trachea. Structures of the Neck Figure 03-29. Lateral view of the bovine neck. In midneck the esophagus lies on the left dorsolateral aspect of the trachea. 1, Esophagus; 2, trachea; 3, pharyngeal musculature; 4, sternocephalicus muscle; 5, nuchal ligament. Esophageal Structure Figure 03-30. Semischematic drawing of the structure of the esophagus, sectioned longitudinally and transversely. 1, Mucosa; 2, muscular layer (longitudinal and circular); 3, adventitia. Abdominal Viscera (Dog) Figure 14-05. Abdominal viscera of the dog after removal of the greater omentum. 1, Liver; 2, stomach; 3, spleen; 4, small intestine; 5, bladder. Abdominal Viscera (Dog) Figure 14-07. Visceral projections on the left (A) and right (B) canine abdominal walls. 1, Diaphragm; 2, liver; 3, stomach; 4, spleen; 5, 5′, left and right kidneys; 6, descending colon; 7, small intestine; 7′, descending duodenum; 8, pancreas; 9, rectum; 10, female urogenital tract; 11, bladder. Radiographs of the Canine Abdomen Figure 14-08. Lateral (A) and ventrodorsal (B) radiographic views of the canine abdomen. 1, Liver; 2, pyloric part of stomach; 2′, descending duodenum; 3, spleen; 4, os penis; 5, cecum; 6, fundus of stomach; 7, left kidney; 8, bladder. The Stomach (Canine) Figure 03-35. A, Visceral surface of stomach (dog). 1, cardia; 2, pylorus. Interior of the Stomach (Canine) Figure 03-35. B, Interior of stomach (dog). 1, cardiac opening; 2, fundus; 3, body; 4, pyloric antrum. Comparison: Monogastric, Hindgut Fermenter and Ruminant Figure 03-36. Gastrointestinal tracts of the dog (A), of the horse (B), and of cattle (C) laid out in one plane. 1, Stomach; 2, small intestine; 3, cecum; 4, ascending colon; 5, descending colon The Digestive Tract and Aortic Branches Figure 03-39. Distribution of the celiac artery of the dog (ventral view). 1, Aorta; 2, celiac artery; 3, hepatic artery; 4, splenic artery; 5, left gastric artery; 6, left gastroepiploic artery; 7, gastroduodenal artery; 8, right gastric artery; 9, cranial mesenteric artery; 10, pancreas; 11, spleen; 12, stomach; 13, liver. Canine Intestinal Tract Figure 03-40. Intestinal tract of the dog (schematic). 1, Stomach; 2, descending duodenum; 3, caudal flexure; 4, ascending duodenum; 5, jejunum; 6, ileum; 7, cecum; 8, ascending colon; 9, transverse colon; 10, descending colon; 11, rectal ampulla; 12, jejunal lymph nodes. Barium Radiographs (Dog) Figure 14-12. Lateral (A) and ventrodorsal (B) radiographic views of the canine abdomen after administration of a barium suspension. 1, Stomach; 2, pyloric part; 3, descending duodenum; 4, caudal flexure of duodenum; 5, jejunum. Barium Radiographs (Cat) Figure 14-14. Lateral (A) and ventrodorsal (B) radiographic views of the feline abdomen after administration of a barium suspension. 1, Liver; 1′, fat-filled falciform ligament elevating the liver; 2, gas and barium in stomach; 2′, fundus; 2″, pyloric part of stomach; 3, descending duodenum—the striking “string-of-pearls” appearance (characteristic of cats) is due to segmental peristalsis; 4, jejunum; 5, ascending colon; 6, transverse colon; 7, descending colon; 7′, gas in descending colon; 8, kidneys (superimposed). Abdominal Organs (Dog) Figure 03-41. Ventral view of the abdominal organs of the dog after removal of the greater omentum. 1, Liver; 2, stomach; 3, spleen; 4, descending duodenum; 5, jejunum; 6, bladder; 7, diaphragm. Canine Abdominal Organs Figure 14-15. The canine duodenum, cecum, and colon in situ; ventral view. 1, Liver; 2, stomach; 3, spleen; 4, pancreas; 5, descending duodenum; 6, ascending duodenum; 7, ileum; 8, cecum; 9, 10, 11, ascending, transverse, and descending colon; 12, vessels in root of mesentery; 13, duodenocolic fold; 14, bladder. Intestinal Structure Figure 03-42. Transverse section through the gut. The artery and vein reach the gut via the mesentery; the larger branches fail to reach the antimesenteric border. 1, Mucosa; 2, submucosa; 3, muscle layer; 4, serosa; 5, mesentery. Duodenal Villi (Rat) Figure 03-43. Scanning electron micrographs of rat duodenal villi (A) and of a vascular cast of the same tissue demonstrating subepithelial capillary plexuses (B). Intestinal Lymph Nodules Figure 03-44. Patch of aggregated lymph nodules in ileum (horse). Large Intestines Figure 03-45. Schematic drawing of the large intestine of the domestic mammals: carnivores (Car), the pig (su), ruminants (Ru), and the horse (eq). Cranial is to the upper right. 1, Ileum; 2, cecum; 3, ascending colon; 4, transverse colon; 5, descending colon; 6, rectum and anus; 7, aorta; 8, celiac artery; 9, 9′, cranial and caudal mesenteric arteries; 10, 10′, dorsal diaphragmatic and pelvic flexures of ascending colon; 11, 11′, proximal and distal loops of ascending colon. Mesenteric Arteries (Dog) Figure 03-49. Distribution of the cranial and caudal mesenteric arteries to the intestines of the dog (dorsal view). a, Jejunum; b, ileum; c, cecum; d, ascending colon; e, transverse colon; f, descending colon; g, rectum. 1, Aorta; 2, cranial mesenteric artery; 3, ileocolic artery; 4, middle colic artery; 5, right colic artery; 6, colic branch of ileocolic artery; 7, mesenteric ileal branch; 8, antimesenteric ileal branch; 9, jejunal arteries; 10, caudal mesenteric artery; 11, left colic artery; 12, cranial rectal artery. The Portal Vein Figure 03-50. Semischematic dorsal view of the formation of the portal vein (dog). 1, Portal vein; 2, splenic vein; 3, gastroduodenal vein; 4, cranial mesenteric vein; 5, caudal mesenteric vein; 5′, ileocolic vein; 5″, middle colic vein; 6, left gastric vein; 7, right gastroepiploic vein; 8, cranial pancreaticoduodenal vein. Liver (Comparative) Figure 03-51. Caudal surface of the liver of the dog (A), pig (B), horse (C), and cattle (D). The median planes are indicated. The liver is asymmetrical, less so in the dog, more so in the pig and horse, and most in cattle, in which the bulk of the organ is displaced to the right. Note the absence of a gallbladder from the horse liver. Canine Liver Figure 03-52. A, Visceral surface of liver (dog). 1, Gallbladder; 2, hepatic ducts. Pig Liver Hepatic Lobules (Pig) Pig Liver Figure 03-54. B, Liver (pig) (28×). 1, central v.; 2, interlobular a.; 3, hepatic lobule; 4, interlobular connective tissue; 5, centrolobular venule. Bile Drainage (Dog) Figure 03-55. The bile drainage system of the dog. 1, Gallbladder; 2, bile duct; 3, cystic duct; 4, hepatic ducts. The Pancreas (Canine) Figure 03-56. The pancreas of the dog (caudal view). 1, Esophagus; 2, stomach; 3, cranial flexure of duodenum; 4, descending duodenum; 5, left lobe of pancreas; 6, body; 7, right lobe; 8, caudal flexure of duodenum; 9, bile duct; 10, mesoduodenum. Canine Abdominal Viscera Abdominal Viscera (Horse) Figure 21-06. Visceral projections on the left abdominal wall (including the diaphragm). 1, Cut edge of diaphragm; 1′, rib 6; 2, stomach; 3, liver; 4, spleen; 5, descending colon (banded); 6, jejunum (smooth); 7, left dorsal colon; 8, left ventral colon. Abdominal Viscera (Horse) Figure 21-07. Visceral projections on the right abdominal wall (including the diaphragm). 1, Cut edge of diaphragm; 1′, rib 6; 2, liver; 3, right kidney; 4, descending duodenum; 5, body of cecum; 6, right ventral colon; 7, right dorsal colon. Equine Digestive Tract Figure 21-11. The intestinal tract seen from the right, schematic. The caudal flexure of the duodenum and the cranial mesenteric artery (17) have been displaced to the right of the animal to lie over the base of the cecum. 1, Stomach; 2, 3, descending and ascending duodenum; 4, jejunum; 5, ileum; 6, cecum; 6′, cecocolic fold; 7, right ventral colon; 8, ventral diaphragmatic flexure; 9, left ventral colon; 10, pelvic flexure; 11, left dorsal colon; 12, dorsal diaphragmatic flexure; 13, right dorsal colon; 13′, ascending mesocolon; 14, transverse colon; 15, descending (small) colon; 16, rectum; 17, cranial mesenteric artery. The Equine Stomach Figure 21-09. B, Notice the white mucosa of the fundus. The Gastrophilus larvae are an incidental finding in this part of the stomach. 4, Margo plicatus is clearly visible. The Equine Cecum Figure 21-13. The cecum in situ. 1, Base of cecum; 2, body of cecum; 3, apex of cecum; 4, right ventral colon. Bovine Abdominal Viscera Figure 28-04. Topography of the abdominal viscera. A, Relationship of abdominal viscera to the left abdominal wall. 1, Esophagus; 2, outline of spleen; 3, reticulum; 4, dorsal sac of rumen; 5, ventral sac of rumen, covered by superficial wall of greater omentum; 6, fundus of abomasum, covered by superficial wall of greater omentum. Interior of the Bovine Stomach Figure 28-04. Topography of the abdominal viscera. B, The interior of the stomach seen from the left. 3, reticulum; 4, dorsal sac of rumen; 7, reticular groove; 8, body of abomasum; 9, atrium ruminis; 10, caudodorsal blind sac; 11, caudoventral blind sac; 12, ventral sac of rumen (opened). Bovine Stomach (left) Figure 28-07. A, Bovine stomach, left side. 1, Reticulum; 2, omasum; 3, abomasum; 4, rumen. Bovine Stomach (right) Figure 28-07. B, Bovine stomach, right side. 2, omasum; 3, abomasum; 4, rumen. Rumen (papillated mucosa) Figure 28-16. A, Rumen papillated mucosa taken from a Waterbuck (left) and a lesser Kudu. Reticulum Figure 28-16. B, Reticulum: mucosal ridges outlining “cells” characteristic of the reticular mucosa (cow). Stratification of Ingesta Figure 28-17. Stratification of ingesta in the ruminoreticulum, left lateral view. 1, Gas bubble; 2, coarse forage (“floating mat”); 3, more finely ground material with higher specific gravity than 2; 4, liquid zone; 5, atrium ruminis; 6, reticulum; 7, esophagus The Omasum Figure 28-21. A, Internal surface of omasum (cow). 1, Omasal laminae The Abomasum Figure 28-21. B, Internal surface of abomasum (cow). 1, Abomasal folds. The Abomasum Figure 28-22. Opened abomasum as seen from behind, above, and slightly from the left. 1, Omasoabomasal opening through which the omasal laminae can be seen; 2, abomasal folds; 3, fundus; 4, body; 5, pyloric part; 6, torus pyloricus; 7, pylorus. Bovine Intestinal Tract Figure 28-26. Right lateral view of the bovine intestinal tract, schematic. 1, Pyloric part of abomasum; 2, duodenum; 3, jejunum; 4, ileum; 5, cecum; 6, ileocecal fold; 710, ascending colon; 7, proximal loop of ascending colon; 8, centripetal turns of spiral colon; 9, centrifugal turns of spiral colon; 10, distal loop of ascending colon; 11, transverse colon; 12, descending colon; 13, rectum; 14, jejunal lymph nodes; 15, Avian Oropharynx Figure 37-14. Oropharynx opened by the reflection of the lower jaw. 1, Median and lateral palatine ridges; 2, openings of salivary glands; 3, choana; 4, infundibular cleft; 5, body of tongue; 6, root of tongue; 7, “mechanical” papillae; 8, laryngeal mound; 9, glottis; 10, branchial cornu of hyobranchial apparatus; 11, esophagus; 12, position of trachea. The Avian Neck Figure 37-15. Ventral view of the dissected neck. B, Detail of neck with crop. 5, trachea; 7, esophagus; 8, crop. Avian Viscera Figure 37-16. Viscera after removal of ventral body wall, ventral view. 1, Esophagus; 2, trachea; 3, pectoralis, cut; 4, crop; 5, sternotrachealis; 6, coracoid bone, cut; 7, right cranial vena cava; 8, heart; 8′, common carotid artery; 8″, subclavian artery; 9, 9′, right and left lobes of liver; 10, gizzard (its caudal blind sac); 11, duodenal loop, enclosing pancreas; 12, vent; 13, one of the ceca. Avian Stomach Figure 37-17. Stomach, ventral surface (A) and opened ventrally (B). 1, Esophagus; 2, proventriculus; 3, papillae; 4, deep proventricular glands, visible on cut surface; 5, lumen of gizzard; 6, caudal blind sac; 7, cranial blind sac; 8, pyloric orifice; 9, cranioventral muscle mass; 10, duodenum. The Avian Stomach Figure 37-18. Stomach of chicken. 1, Esophagus; 2, spleen; 3, proventriculus; 4, gizzard with aponeurosis (4′); 5, duodenum. Opened Avian Stomach Figure 37-19. Opened stomach. Note grit inside gizzard (right). Avian Intestinal Tract Figure 37-20. Isolated intestinal tract with detail of ileocolic junction. 1, Pylorus; 2, 2′, dorsal and ventral lobes of pancreas; 3, duodenal loop; 4, bile and pancreatic ducts entering duodenum; 5, jejunum; 6, vitelline diverticulum; 7, ileum; 7′, ileum opened; 8, ileocecal fold; 9, ceca; 9′, cecum opened; 10, cecal tonsil; 11, colon; 11′, colon opened; 12, cloaca; 13, vent. The Avian Cloaca Figure 37-22. Median section of the cloaca, semischematic. 1, Colon; 2, coprodeum; 2′, coprourodeal fold; 3, urodeum; 3′, uroproctodeal fold; 4, proctodeum; 5, vent; 6, ureteric orifice; 7, papilla of deferent duct; 8, position of oviduct orifice (only on left side); 9, cloacal bursa; 9′, dorsal proctodeal gland; 10, skin; 11, tail feather; 12, uropygial gland; 12′, papilla of uropygial gland; 13, muscles surrounding caudal vertebrae.