1. Digestive System

2. Digestive system is concerned directly with:
Prehension
Mastication
Digestion
Absorption
Expulsion of the undigested portion.

3. Digestive system consists of :
1.Digestive tract –consists of a muscular tube lined with mucus membrane that is continuous with the external skin at the mouth and at the anus.
2. Accessory glands-salivary glands, liver, pancreas.

4. General structure of digestive tract:
The wall of digestive tract comprises of 4 walls.
1. Tunica Mucosa-innermost layer. Closest to the lumen. It is composed of epithelium cells, connective tissues and smooth muscles.
2. Tunica submucosa-Immediately outer to T. mocosa. Made up of loose connective tissues. Blood vessels and nerves are found in this layer.

5. 3. Tunica muscularis-Next to the T. submucosa
3. Tunica muscularis-Next to the T. submucosa. Well developed layer of muscles. 4. Tunica serosa-The outermost layer. Visceral peritoneum with a thin layer of connective tissue under it.

6. Organs
Organs involved are:
Mouth
Pharynx
Esophagus
Stomach/forestomac
Small intestine
Large intestine
Accessory glands (salivary glands, liver, pancreas etc.)

7. Mouth
Used primarily for holding, grinding and mixing food. It is also used to manipulate the environment (grasping) and defensive/offensive weapon.
Structure making up the mouth is lips, teeth, tongue, cheek and cheek muscles.
Glands near the mouth:
mainly salivary glands which are of four types- parotid, mandibular and sublingual.

8. Lips-entrance into the mouth
Lips-entrance into the mouth. Appearance and mobility varies among species.
Lips are densely innervated by sensory fibers making them very sensitive tactile organ.
Lips of sheep,goats horses are soft and flexible making them the organ of prehension.
Lips in cattle and pigs are stiffer and less mobile.

9. Teeth
All mammals have four kinds of teeth- incisors, canines, premolars, and molar.
Mamals are heterodonty meaning that they have various types of teeth that are specialized for different aspects of prehension and mastication.

10. The incisors -cutting the food
The incisors -cutting the food. Ruminants lack upper incissors-has dental pad in its place.
Premolars and molars -crushing /grinding
The canines -tearing the food/flesh (poorly developed in man but are well developed in other mammals such as great cats)
Milk teeth – temporary teeth of young falls off later on replaced by Permanent teeth – last for long time

11. Tongue Mass of muscles covered with mucus membrane.
Divided into apex, body and root.
The muscles of the tongue have fibers oriented in longitudinal, perpendicular and transverse directions permitting the tongue a wide range of movement. This is particularly evident in cattle, which uses its tongue as organ on prehension.
The surface of the tongue has large numbers of projections –papillae.

12. Pharynx Common passage for the food and air.
The muscles of the walls of the pharynx are responsible for orderly directing food, air and liquid-Regulates Swallowing and breathing.
Pharyngeal dysfunction causes serious problems. It can result in food entering the lungs causing aspiratory pneumonia.
At the entrance into trachea- epiglottis that regulate the direction of food and air.

14. Oesophagus:
Muscular tube, extending from pharynx to stomach/forestomach.
At the neck it is seen towards the left side of trachea (this position is to be noted for the surgical procedure involving esophagus like choke removal)
Inside the thoracic cavity oesophagus is found dorsal to the trachea and between aorta and trachea.

15. Non-ruminants
The digestive organs of non-ruminants and ruminants are very much similar except in the stomach.
The non-ruminants are single-stomach animals-monogastric animals. e.g. pig, horse, poultry,men etc.
Located just behind the diaphragm on the left side.
Somewhat bent and pear shaped.

16. Four regions namely-
1.Oesophageal region.
2.Cardiac region-joining of esophagus to stomach, near to heart.
At the junction of esophagus and stomach are thickening of muscles- sphincter. This sphincter is well developed in horses, so they cannot vomit.

17. 3.Fundic region.
4.Pyloric region- has a sphincter called pylorus that control gastric emptying into intestine.
Except esophageal region, rest of the region has gland in their mucosa.
Cardiac region contains cardiac glands that secrets mucus.

18. Fundic region contains fundic glands (gastric gland proper) produces digestive enzymes. Most dominant glands in stomach.
Pyloric glands produces mucus.
The surface area of the stomach is increased by in-folding of the epithelial cells –gastric folds.

20. Two types of simple stomach

21. Ruminant stomach
Actually a single stomach modified by marked expansion of the esophageal region into three distinct and voluminous diverticula-rumen, reticulum and omasum.
These three are collectively known as forestomach.
Forestomach are lined with non- glandular epithelium.

22. Comprises a series of chambers where food is digested by microorganisms before passing to the glandular portion.
The glandular portion (true stomach) is abomasum which receives the digested food from forestomach.

23. Ruminants
Rumen
large muscular sac that extends from the diaphragm to the pelvis filling the left side of the abdominal cavity.
Rumen is subdivided internally into compartments by muscular pillars.
These pillars are visible as grooves on the external surface of the rumen.
At the region of cardia there are two heavy muscle folds. The two folds creates a groove called esophageal groove.

24. The act of suckling initiates a reflex that contracts the folds converting it into a tube. This tube delivers the milk directly to omasum and abomasum. So the milk bypasses rumen and reticulum and avoids souring of the ingested milk.

25. Recticulum
located immediately behind the diaphragm just behind the heart.
Most cranial compartment.
It is located immediately caudal to the diaphragm opposite to the heart.
It is also called the ‘honey comb’-Mucosa is thrown into intersecting ridges that give the appearance of “honey comb”

26. Omasum
Located to the right of the rumen and reticulum, just caudal to the liver.
spherical organ filled with muscular liminae that lie in sheet, giving the appearance of pages of a book- also called as also called “book-stomach”
Pappilae are studded with short, blunt papillae that help in grinding roughage before it enters abomasum.
Also sorts foodstuffs- smaller particles are passed to abomasum and the coarser ones are returned to reticulum.

27. Abomasum (True stomach)
The true stomach in ruminants and it is similar to the stomach of monogastric animals. And its body extends caudad on the right side of the rumen.
The glandular region are same as in the simple stomach.
Pylorus controls the flow of materials from stomach to intestine.

30. Intestine Starts from the pylorus of the stomach. Described as
Small intestine
Large intestine.

31. Small intestine
Made up of three parts- duodenum, jejunum and ileum. (based on the histological differences)
Small intestine is the chief site for absorption in all domestic animals.
On the mucous membrane it contains finger like projection called villi (vilus) that aid in absorption of digested food.  

32. Duodenum
First part of intestine.
Attached to the body wall by mesoduodenum.
Ducts from pancreas and liver opens into duodenum emptying it digestive juices from these glands i.e. bile from liver that contains bile salt and bile pigment
Secretions from pancreas contain digestive enzymes that aid is digestion.

33. Jejunum
Is the second segment of intestine and it continues with ileum.
Longest portion of small intestine (upto 28 mts in horses)
Numerous lymph nodes present in its mucosa and submucosa.
Ileum
Is the last part of on intestine and it joins with large intestine at ileo-ceco-colic junction.
Short and last part of small intestine.
Contains goblet cells- mucus producing cells.

34. Large intestine
Starts from ileo-caeco-colic junction
Consists of Caecum, Colon, rectum and anal canal.
Colon divided into descending colon, ascending colon and transverse colon
Water absorption takes place in this part of intestine.
More variations from species to species than in small intestine.

36. Digestive system of chicken
Modified form of digestive system.
Has beak without teeth in it instead of mouth.
Oesophagus has a diverticulum called crop-act as storage and soften the feed.
Pear shaped structure –proventriculus- also soften the feed.Conected with gizzard -involved in grinding the feed (bird used small pebbles to aid in grinding feed in gizzard –grit

37. Gizzard is followed by small intestine, which is divided, into duodenum, jejunum and ileum.

38. Birds have a pair of caeca (caecum) unlike animals.
Large intestine starts at ileo-caecal junction and ends at cloaca-common opening for both digestive system and urinary system.

40. Digestion in ruminants
Digestion is first done by microbes in the rumen - called microbial digestion.
Rumen maintains optimum pH and temperature for the microbial growth - plant substances are digested. This leads to microbial growth producing large quantity of microbial protein.

41. The feed along with microbes are pushed into successive compartments of forestomach and when food reaches abomasums there is sudden drop in pH.
The acidic pH kills all microbes and the protein digested and absorbed for use by animal.
Where as the carbohydrate is directly converted into volatile fatty acids that can be absorbed into circulation for utilization.

42. Digestion in non-ruminants
No microbial digestion, so there is no fore stomachs seen in ruminants.
While in animals like horse, rabbit microbial digestion takes place in well- developed functional caecum.
In first group of animals digestion is enzymatic and starts from mouth with the mixing of saliva.
There is secretion of enzymes at every stage of digestion before absorption start in small intestine.

43. Clinical Importance Mouth
Site for the examination for lesion in viral disease like foot-and-mouth disease. Lesion normally seen in the form of vesicle at lips, gum, dental pad and tongue.

44. Oesophagus
At the base of the mouth oesophagus is located dorsal to trachea and at middle third of the neck oesophagus courses on the left side of the trachea. This location is important from the surgical point of view in choke (oesophageal obstruction) management in animals.

45. Rumen
Located on the left side of animal body, at paralumber fossa. Any surgical procedures associated with rumen like Trocarisation, rumenotomy, has to be performed on the left side of the animal and not on the right side.
Even caesarian section is also done on left.

46. Reticulum
Due to its close location with the heart it may result in traumatic reticulo- pericarditis due to lodging of sharp objects like nail that may be present in commercial feed.

47. Abomasum
In pregnant animals abomasums may get displaced either to left or right side or may result in torsion. In any of these cases feed intake and production will be hampered.
Intestine
This is one of the sites where internal parasites like round worms get localized and cause harm to the animal. Apart from this, organ like liver also will be infested by parasite like live fluke

48. Accessory glands
In addition to numerous small glands located in the walls of the stomach and intestine, accessory glands include the Salivary glands, pancreas and the liver.

49. Salivary glands
In domestic farm animals there are three pairs of well defined glands and scattered lobules of salivary tissues (minor salivary glands).
The chief salivary glands are :
Parotid
Mandibular
Sublingual

52. The minor salivary glands are:
Labial
Buccal
Lingual
Palatine

53. Parotid salivary gland:
Located ventral to the ear
The duct opens into the mucus membrane of the cheek near the 3-4 maxillary cheek tooth.
Mandibular salivary gland:
Located ventral to the parotid gland.
The duct opens ventral to the tongue at the base of the mouth.
Sublingual salivary gland:
Located deep in the mucus membrane near the floor of the mouth.
Duct opens into the floor of the mouth just ventro-lateral to the tongue.

54. Secretions from salivary glands
Secretions from salivary glands can be serous, mucus or mixed.
Parotid s. gland- produces serous saliva.
Mandibular and sublingual-mixed (both serous and mucus)
Minor salivary glands-mucus saliva.

55. Pancreas
An irregularly lobulated organ that lies adjacent to the proximal duodenum.
Compound gland with both endocrine and exocrine function.
Exocrine portion produces sodium bicarbonate and digestive enzymes into the duodenum.
The endocrine portion produces insulin and glucogan.

56. Liver Largest gland in the body.
Varies in numbers of lobes and precise location from one species to another.
Located immediately caudal to the diaphragm towards right.
All domestic animals except horses has a gall bladder for stotrage of bile.
Secretion for liver, pancreas and gall bladder open through a common opening at the major doudenal papilla.

57. Comparative anatomy

58. Comparative anatomy