Veterinary Anatomy: Gastrointestinal Tract

• Gatrointestinal tract includes dental terminology, including the dental formula of the dog and numbering system, and lumbar organs of the gastrointestinal tract and the order of food passage, peristalsis.
• The digestive system can be described in terms of oral to aboral.
• Landmarks of the digestive tract include the mouth, salivary glands, pharynx, esophagus, stomach, liver, duodenum, pancreas, jejunum, ileum, cecum, colon, rectum, and anus.

Oral Cavity

• The oral cavity starts between the lips and continues into the pharynx.
• It is divided into two segments: the oral vestibule and the oral cavity proper.
• The oral vestibule is located between the teeth/margins of the jaws (internally) and the lips/cheeks (externally).
• The oral cavity proper is located inside the dental arch.
• Its ventral boundary is the nasal cavity, and the dorsal boundary is the hard and soft palate.
• Lateral boundaries are the cheeks, with the caudal boundary being the palatoglossal arch.
• Annexed organs include the tongue, salivary glands, and teeth.

The tongue

• It is a highly muscular organ that is capable of vigorous and precise movements.
• It occupies the greater part of the oral cavity, and has three segments: the base (root), body, and apex.
• The tongue is covered by many types of mucosa - filiform, fungiform, foliate, and vallate papillae.
• Cats have keatinized filiform papillae- the conical papillae.

Salivary Glands

• Salivary glands function to secrete saliva, which keeps the mouth moist, facilitates mastication, and lubricates food passage.
• There are small (minor) salivary glands located in the lips, cheeks, tongue, soft palate, pharynx, and esophagus.
• The major salivary glands include: parotid, mandibular, sublingual, and zygomatic (specific for carnivores).

Dentition

• There are two types of dentition: brachydont and hypsodont.
• Brachydont dentition is characterized by short crowns, well developed roots, and obvious division between the crown and root.
• Hypsodont denition is characterized by high crowned teeth and enamel that extends deep to the gum line.

Tooth Anatomy

• The crown is covered by enamel, terminating at the level of the neck.
• The neck is between the crown and root of the tooth.
• The root is covered by cementum and implanted in a seperate socket.

Tooth Types

• There are permanent (adult) teeth and deciduous (baby) teeth.

Dental Formula

• The dental formula can be used to represent the dentition in each quadrant of the mouth.
• I3-C1-P4-M2/I3-C1-P4-M3 = 42 means there are 42 teeth in total.
• 3-1-4-2/3-1-4-3 gives you the number of incisors, canines, premolars, and molars in each half of the mouth.

Triadan Numbering System

• Dentition can be identified using the Triadan numbering system, which divides the mouth into 4 quadrants: -The upper right quadrant begins with 100. -The upper left quadrant begins with 200. -The lower left quadrant begins with 300. -The lower right quadrant begins with 400.
• The teeth in each quadrant are numbered 01-11, starting from the incisors towards the molars.

The pharynx

• This is a funnel shaped chamber, located behind the oral cavity; it continues into the esophagus.
• It's a common segment for the respiratory and digestive systems.
• There are three parts: the oropharynx, nasopharynx, and laryngopharynx. The pharynx provides a passageway/connection between the nasal and oral cavities with the esophagus and larynx.

The Larynx

• This is a cartilaginous "voice-box" in between the pharynx and trachea; inferior to the esophagus.
• The larynx functions to protect the airway, make sound, and divert food and water into the esophagus.

The Esophagus

• The esophagus conveys food from the pharynx to the stomach.
• It has three parts: cervical, thoracic and abdominal.

The Stomach

• The stomach is the dilated segment of the digestive system that is between the esophagus and the duodenum. This is where digestion is initiated.
• The stomach has two orifices, the cardia (communication w/ esophagus) and the pyloric (communication w/ duodenum).
• The left extremity is the fundus, the right extremity is the pyloric extremity, and in between the extremities is the body/corpus of the stomach.
• The lesser curvature faces right, and the greater curvature faces left.
• Stucture of the stomach is made of three distinct layers
• The serosa is the peritoneum and covers the entire organ.
• The smooth muscle layer has three overlapping, but incomplete layers.
• The mucosa has gastric glands. In dogs and cats, the stomach is a simple, completely glandular stomach.

The Small and Large Intestines

• The order from the stomach is duodenum, pancreas, jejunum, ileum, cecum, colon, rectum, and anus.

The Small Intestine Segments

• The duodenum is short and is the most fixed part of the small intestine, suspended via mesoduodenum; connects to the jejunum.
• The jejunum is the longest segment of the small intestine, forming the coils of the small intestine and connecting to the ileum.
• The ileum is the last segment, and is short; in dogs, the ileum opens into the ascending colon (ileocolic orifice).

The Large Intestine Segments

• The cecum is short, twisted in dogs and coma-shaped in cats; it's located on the right side of the abdomen
• The cecum connects with the ascending colon - ceocolic orifice.
• The colon continues the cecum with three segments: acsending colon (lies on the right side of their abdomen, travers colon (is between ascending and descending), descending colon- lies on the left of the abdomen
• The rectum is the last part of the large intestine that continues with the anus.

The Liver

• The liver is located in the most cranial part of the abdomen, immediately behind the diaphragm muscle.
• There are six lobes of the canine liver: right lateral, right medial, left lateral, left medial, quadrate, and caudate. The surfaces are called the parietal (diaphragmatic) surface and visceral surface
• The liver is between the right medial and quadrate lobes and the gall bladder.

The Pancreas

• The pancreas is closely related to the duodenum with similar aspect, with both endocrine and exocrine functions.
• Its three segments are the body, left lob and right lob of pancreas.
• It also has two ducts: the pancreatic (inconstant in dog) and accessory pancreatic.