[ZOO301] Digestive System Reviewer

ULBIS, CHRISTINE MARIE HONG 3BIOLOGY-6 DIGESTIVE SYSTEM Filter Feeding – passively filtering organic matter out of the incoming respiratory stream and propelling the food particles to the rear of the pharynx for swallowing can only be employed by aquatic organisms DIGESTIVE TRACT also called “alimentary canal” a tube. Seldom straight and often tortuously coiled, that commences at the mouth and empties either into a vented cloaca or directly to the exterior via an anus functions in the digestion and absorption of foodstuffs and in elimination of undigested wastes Peristalsis – the process of propelling food from the pharynx to the vent or anus by smooth muscle tissue in the walls of the tract Major Subdivisions of the tract:  Oral Cavity and Pharynx  Esophagus  Stomach  Intestine Emptying into the tract are the ducts from accessory organs, principally pancreas, liver, and gallbladder. These organs and their ducts arise as evaginations from the embryonic digestive tract. Other evaginations known as ceca, having one function or another, are common. The digestive tract and accessory organs constitute the digestive system. Pleuroperitoneal Cavity – major component of the coelom, along with the lungs in tetrapods In mammals, birds and a few reptiles, the lungs occupy separate pleural cavities, and the digestive organs beyond the esophagus occupy an abdominal (peritoneal) cavity. The coelom arises by the delamination, or splitting, of the early lateral-plate mesoderm into two sheets, somatic and splanchnic mesoderm. The space between the two sheets becomes the coelom. Visceral Peritoneum – outer covering of the digestive tract

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continuous with the parietal peritoneum, which lines the body wall

Three Regions of Embryonic Digestive Tract:  Midgut – the part containing the yolk when present, or to which the yolk sac is attached  Hindgut – caudal to the midgut; becomes the remainder of the intestine and the cloaca  Foregut – anterior to the midgut; elongates to form part of the oral cavity, the pharynx, esophagus, stomach, and much of the small intestine MOUTH AND ORAL CAVITY Gnathosome Fishes: Mouth opens into the oropharyngeal cavity which exhibits teeth of one variety or another, and walls perforated by gill slits. It terminates at a short esophagus. Its roof is primary palate. Tetrapods: The mouth opens into an oral cavity (buccal cavity) that houses the teeth and tongue. It leads to the pharynx. Its roof is primary palate. Reptiles: Most have an incomplete secondary palate. This leaves in the roof of the oral cavity, a deep cleft, the palatal fissure, that channelizes respiratory air between the choane (internal nares of amniotes) and the pharynx. Anurans: Paired Vocal Sacs, which are reverberating chambers beneath the floor of the pharynx, open into the oral cavity near the angles of the jaws. Mammals: A trench called the oral vestibule, separates the gurns, or alveolar ridges, from the cheeks and lips. In many rodents, an opening leads from the vestibule on each side into a check pouch in which hamsters and others transport grain from the fields to the burrow for storage. Birds: Some seed- and grain-eating birds have a median sublingual seed pouch that lies upon the caudal portion of the mylohyoid muscle beneath the oral cavity and is retracted by what may be homologue of the gneioglossus muscle of mammals. When full, it hangs beneath the rea of the oral cavity in a sling composed of the mylohyoid muscle. It is emptied by shaking the head vigorously,