Veterinary anatomy of intestine

comparative Anatomy of the domestic animals intestines

1. Veterinary A natomy O f T he I ntestine By Prof. Dr. Abdelmohaimen Mostafa Saleh Professor of Anatomy & Embryology Assiut University

2. It extends from stomach to anus. It consists of small and large intestine. The small intestine includes duodenum, jejunum and ileum, It can be divided into fixed part (duodenum) and mesenteric part (jejunum and ileum). The large intestine consists of the cecum, colon, rectum and anal canal. Canines have shortest intestine followed by equines, pig and ruminants.

3. The duodenum It extends from pylorus to duodenojejunal flexure. It consists of three parts, three flexures and three ligaments. Parts and course: -Three parts are: cranial part, descending duodenum and ascending duodenum. -Three flexures are :cranial, caudal, and duodenojejunal. = Cranial part: passes to the right on the viseral surface of the liver forming cranial flexure, which continues as descending duodenum.

4. The cranial part is attached to the liver by the hepatoduodenal ligament . It presents the major & minor duodenal papillae at which the major pancreatic duct with the bile duct & the accessory pancreatic duct open. In horse, the major duodenal papilla lies inside the ampulla hepatopancreatica . The cranial part of duodenum forms a sigmoid loop in horse & ruminants

5. = Des. Duodenum: runs caudally on right side in relation to ascending colon. It forms caudal flexure behind right kidney and base of cecum, then it turns to left and cranially to continue as ascending duodenum. = Asc.Duodenoum : runs cranially on left side in relation to descending colon , then it turns ventrally to to join jejunum at duodenojejunal flexure. ** Cranial part forms sigmoid loop in horse, ruminants and pig. It presents major and minor duodenal papillae at which pancreatic ducts with bile duct open.

6. Fixation of duodenum: 1- Mesoduodenum : short fold except dog has relatively wide one. 2-Hepatoduodenal ligament: attaches cranial part of duodenum to liver. 3-Duodenocolic ligament: attaches Asc . duodenum to des. colon

7. The jejunum It is the longest part of small intestine, extends from duodenojejunal flexure to ileum. Mesentery: - It is a wide fan-shaped peritoneal fold. - it is long and allows jejunum great range, especially in dog and horse.

8. Position : It varies according to species: In ruminants and pig: long jejunum, found mainly on right half of abdominal cavity, surrounding coiled ascending colon. In dog: jejunal loops occupy abdominal floor and is covered by greater omentum . In horse: because of great length of the mesentery, jejunal loops have great motility and are not confined to particular area but found mostly in left dorsal quadrate. As a result of mobility of jejunal coils in equines, intestinal colic may develop.

9. The ileum It is the short terminal part of the small intestine, It is suspended by the mesoileum and is attached to the cecum by the ileocecal ligament . It terminates at the cecocolic junction through the ileal orifice . In horse, the ileal orifice lies in the cecum on the ileal papilla which is encircled by a venous plexus working as ileal sphincter .3

10. The cecum Definition: - It initial blind part of large intestine. It varies in size, shape and position in different species. Vermiform appendix of cecum of man is absent in domestic animals but presents in rabbit.

11. Size: depends on species; it is shortest in cat and increasingly longer in dog, pig, ruminants and horse . Position: it lies on the right side of abdominal cavity in all animals except in pig on the left side. Communcation : i n all animals ileum joins cecum at ileocecal orifice. In addition only in horse cecum joins colon at cecocolic orifice, but in other animals it continues with colon without definite line of demarcation. Shape: Is mostly cylindrical in shape.

12. Muscular bands: present only in pig and horse. Fixation: 1-Mesocecum: between cecum and dorsal abd.wall . 2-Ileocecal ligament: between cecum and ileum. 3- Cecocolic ligament: between cecum and ascending colon (in horse).

13. Cecum in horse:- It has remarkable size and position. It occupies large part of right half of abdominal cavity, from pelvic inlet to intrathoracic part of abd . cavity. It consists of base, body and apex . The base: most dorsal part lies in right flank region. It has dorsal greater and ventral lesser curvatures. Both ileocecal and cecocolic orifices open on lesser curvature. The body: extends cranioventrally to lie between right and left ventral colon on abdominal floor. The apex: narrowest cranial end, lies in xiphoid region of abdominal cavity. The body has four bands; dorsal, ventral, lateral and medial. The dorsal band is attached to ileocecal ligament and lateral one to cecocolic ligament. The bands make four rows of sacculations .

14. Cecum of Dog : It is irregularly twisted ( screw - like ), directed caudally but its blind end points cranially. The cecum of dog lies in the right flank, related dorsally to the right kidney, ventrally to the jejunum and ileum, laterally to the descending duodenum and right lobe of pancreas, caudally it is surrounded by the caudal flexure of duodenum. Cecum of Pig : The cecum of pig is cylinderical in form, it lies against the dorsal and cranial parts of the left flank extending caudally with its apex on the abdominal floor reaching the inguinal region, It has 3 bands ( taeniae ) in addition to 3 series of saculations . The ileocaecal ligament is attached to the ventral taenia.

15. Cecum of Ruminants : The cecum of ruminants is cylindrical and is marked off from the colon only by the point of termination of ileum, It lies against the right flank separated from it by the grater omentum , It extends in a caudo-dorsal direction toward the pelvic inlet. Its caudal blind end projects freely from the opening of the supraomental recess.

16. The colon The colon is divided into ascending, transverse and descending colon. The ascending colon lies mainly the in right side, the transverse colon in the left side, and descending colon crosses the median plane from right to left side.

17. Ascending colon of dog: The simplest arrangement of colon presents in dog as in man. It passes cranially on right side, crosses median plane infront to cranial mesenteric artery as transverse colon; it then passes caudally on left side as descending colon.

18. Ascending colon of pig: The ascending colon of pig consists of only a spiral loop ( ansa spiralis ) which consists of 3 close double spiral coils in the form of a cone . These coils are formed of centripetal coils & centrifugal coils which are continuous with each other at the central loop The centripetal coils has 2 taeniae which are absent on the centrifugal ones.

19. Ascending colon of ruminants: It consists of three loops, proximal, spiral and distal. Proximal loop : “S” shape, consists of three parts; ventral, middle and dorsal. The ventral one is directed cranially , the middle part caudally and the dorsal part continues cranially by spiral loop . Spiral loop: consists of two coils; centripetal and centrifugal, which form intestinal disc. Both coils unite at central flexure. Distal loop: consists of two parts; dorsal and ventral. The dorsal one is directed caudally and the ventral one cranially and continued with transverse colon.

20. Ascending (great) colon of horse: The ascending colon of horse consists of double U-shaped loops , one dorsal to the other with the convex parts toward the diaphragm. It consists of the right ventral colon, ventral diaphragmatic flexure , left ventral colon, pelvic flexure , left dorsal colon, dorsal diaphragmatic flexure and right dorsal colon.

21. The right ventral part is attached to the cecum by the cecocolic ligament , passes cranioventrally. It reaches the diaphragm forming the ventral diaphragmatic flexure which is situated dorsal to the xiphoid cartilage. It continues on the left side as the left ventral colon . This part passes on the abdominal floor till the pelvic inlet where it curves dorsally forming the pelvic flexure and continues cranialward as the left dorsal colon . When the left dorsal colon reaches the diaphragm it forms the dorsal diaphragmatic flexure from which, the right dorsal colon passes caudally, it increases in size and is known as the Ampulla coli . It then crosses the median plane as the transverse colon. The dorsal colon is attached to the ventral colon by a very short intercolic ligament which become wide at the pelvic flexure

22. The ventral parts of ascending colon have 4 bands . The left dorsal colon and pelvic flexure have 1 band , while right dorsal colon and dorsal diaphragmatic flexure have 3 bands . The diameter varies at different parts. The widest part is right dorsal colon , followed by right and left ventral colon. The pelvic flexure and the beginning of left dorsal colon have the narrowest diameter . Fixation of ascending colon by: 1-Mesocolon. 2-Intercolic lig . 3-Cecocolic lig .

23. Transverse colon - It begins from ascending colon at right side, then passes to left side cranial to cranial mesenteric artery to continue as descending colon. - It has no bands or sacculations . Descending (small) colon It lies in the left dorsal quadrant of body cavity. It passes caudally under the dorsal abdominal wall with which it is attached by mesocolon and attached to ascending duodenum by duodenocolic ligament. It enters pelvic cavity to continue as rectum. - In ruminants, it presents sigmoid colon. - In horse, it is long, has two bands. Its coils in horse are easily distinguished from jejunal coils by their diameter, bands and sacculations .

24. Rectum The rectum is continuation of descending colon as it enters the pelvis. It has peritoneal and retroperitoneal parts, and has no bands or sacculations . Before ending at short anal canal, the rectum enlarged forming ampulla recti which is very prominent in horse, but absent in sheep and goat. The relation of rectum varies in both sexes. In males, it is related ventrally to urinary bladder and accessory genital glands, while in females it is related to uterus and vagina.

25. Anal canal - It is the short terminal portion of digestive tract. The anus is the terminal orifice. The external and internal sphincter muscles surround anus and keep opening closed. Striated external sphinter M. arises from caudal vertebrae, but internal sphinter M.is the thickened continuation of circular smooth muscle coat of rectum.

26. In Dog : It present 3 zones : cutaneous , intermediate & columnar . The cutaneous zone is continuous with the skin of the anus and present on each side a small opening for the paraanal sinus (which contains smelly secretion). . The intermediate zone is a narrow indistinct area. . The columnar zone which presents several longitudinal folds or columns.

27. There are 3 groups of glands in the anal canal : circumanal , anal & anal sac glands. The circumanal glands are found in the submucosa. The anal glands open in the intermediate zone. The anal sac glands lie in the wall of the anal sac. In pig : The anal canal resembles that of dog. In ruminants : The anal canal has no intermediate zone . In horse : The anal canal presents an anorectal line at its junction with the rectum & an anocutaneous line at its junction with the anus.

28. References: - - Nickel , Schummer (1995): The Viscera of Domestic Mammals (The Anatomy of the Domestic Animals) . - Dyce, Sack, andWensing's (2015):Textbook of Veterinary Anatomy - Klaus Dieter Budras (2011): Bovine Anatomy. - https://www.google.com.eg/imghp?hl=ar&tab=wi&ogbl