Digestive System (Part 1) - Digestive Tract

The module introduces the anatomy of the digestive system, divided into the digestive tract and accessory organs. It aims to help identify organs and structures within each segment. The canine digestive system is monogastric and relatively short.

The oral cavity, extending from the lips to the pharynx, is divided into the oral vestibule (space between lips/cheeks and teeth) and the oral cavity proper (space occupied by the tongue). Communication occurs via interdental spaces, including the diastema.

Details on the lips, forming rostral and lateral boundaries, with dogs having pendulous upper lips creating a large vestibule. The cheeks are small due to a large mouth-opening. The hard palate forms the dorsal roof, with palatine rugae and a median raphe. The soft palate is a continuation of the hard palate, notably long in dogs, affecting brachycephalic breeds. The incisive papilla and its connection to the vomeronasal organ are also discussed.

Teeth are specialized structures for food processing and social interaction, arranged in upper and lower dental arcades. Each tooth has a crown (visible part covered by enamel) and a root (embedded in the gum, covered by cementum). The neck is the junction. The three main substances of mammalian teeth are dentine (bulk, contains pulp), enamel (hardest part, covers crown), and cementum (bone-like layer, holds tooth in gum, found only in root in dogs).

The four surfaces of teeth are described: vestibular (faces lips/cheeks), lingual (faces tongue), contact (faces adjacent teeth, further classified as mesial or distal), and occlusal (faces opposing arch). Dog dentition is diphyodont (two sets of teeth) and heterodont (various types of teeth: incisors, canines, premolars, molars). Incisors are for nipping, canines are long and pointed, and premolars and molars (cheek teeth) are for grinding. The upper fourth premolar and first lower molar are referred to as carnassial teeth.

The dental formula for dogs is explained, detailing the notation for incisors, canines, premolars, and molars in both temporary and permanent sets. A puppy has 28 temporary teeth, which are replaced by 42 permanent teeth. Molars are only present in permanent dentition.

The tongue is divided into a free apex, a body, and a caudal root, all highly mobile due to muscular attachments. Key features include the lingual frenulum and the median sulcus on the dorsal surface. The dorsal surface is covered with papillae, categorized as mechanical (filiform, conical, marginal) or gustatory (fungiform, foliate, vallate), differing in location, structure, and presence of taste buds.