Digestive (Manual)

• Coelom


  Cavity associated with both the digestive and the respiratory systems and the pericardial cavity that surrounds the heart
• Coelom


  Its functional importance is that it allows the organs of the systems it encloses to move freely within and facilitates their action
• In vertebrates, the coelom is the cavity of the hypomere and is never segmented.
• Parietal peritoneum 


  The outer wall of the hypomere + inner surface of the layer of voluntary muscles
• Visceral peritoneum or serosa 


  The inner walls of the hypomeres of the two sides becoming the covering layer of the intestine and other viscera
• Mesentery 


  Above and below the intestine the two walls of the hypomere are in contact and form a double-walled membrane
• Mesentery

  Dorsal wall of the coelom + intestine: dorsal mesentery

  Ventral wall of the coelom + intestine: ventral mesentery
• Mesogaster or greater omentum


  The portion of the dorsal mesentery attached to the stomach
• Dorsal mesenteries: mesogaster, mesoduodenum, mesointestine, mesocolon, mesorectum
• Mesoduodenum 


  Mesogaster that is associated with the duodenum
• Dorsal mesenteries

  Mesointestine: supports the small intestine,

  Mesocolon: relates to the colon,

  Mesorectum: connected to the rectum.
• In mammals, the dorsal mesentery is often a site for fat deposition.
• The ventral mesentery is reduced in size and persists only as few specialized ligaments.
• Ligaments of the ventral mesentery: coronary, falciform, gastroduodenohepatic or lesser omentum, median
• Ligaments of the ventral mesentery

  Falciform ligament: attaches the anterior end of the liver to the ventral body wall

  Gastroduodenohepatic ligament or lesser omentum: connects the stomach to the liver and duodenum

  Median ligament: lies between the urinary bladder and the ventral body wall.
• In the adults of all vertebrates, the coelom is divided into at least two compartments by the formation of a partition called the transverse septum, which develops at the posterior end of the heart and cuts off the heart from all of the other viscera.
• The transverse septum thus divides the coelom into a small anterior compartment, the pericardial cavity, which contains only the heart, and a very large posterior compartment, the pleuroperitoneal cavity, which contains all of the other viscera.
• The pericardial cavity in fishes and urodeles is anterior to the pleuroperitoneal cavity, and the transverse septum in those groups passes transversely across the body.
• In the Anura and all vertebrates above Anura the pericardial cavity has descended posteriorly, so that it comes to lie ventral to the anterior part of the pleuroperitoneal cavity; the transverse septum then assumes an oblique position.
• In that portion of the pleuroperitoneal cavity that lies dorsal to the pericardial cavity, the lungs are situated. This condition of the coelom, is found in Anura and in most reptiles.
• In some reptiles, especially the Crocodilia, and in birds and mammals the pleuroperitoneal cavity is divided into anterior and posterior parts by various fusions between the transverse septum and other coelomic folds; in mammals the closure is accomplished chiefly by the pleuroperitoneal or nephric fold, which descends from the dorsal body wall and fuses with the transverse septum. The partition so formed is known as the oblique septum in birds and the diaphragm in mammals.
• The oblique septum or diaphragm forms immediately posterior to the lungs.
• That portion of the pleuroperitoneal cavity cut off anterior to the oblique septum or diaphragm consequently contains the lungs.
• That part of the pleuroperitoneal cavity cut off posterior to the oblique septum or diaphragm is called the peritoneal or abdominal cavity.
• Peritoneal cavity 


  It encloses the greater part of the digestive tract and the urogenital system.
• In birds and mammals, the coelom is divided into four compartments-the pericardial cavity, the two pleural cavities, and the peritoneal cavity. This arrangement greatly increases the efficiency of lung respiration.
• The primitive intestine or archenteron, is produced by the process of invagination in the gastrula stage of the embryo.
• It is at first a simple tube of endoderm with one opening to the exterior, the blastopore.
• The adult digestive tract consists of a thick-walled tube, composed of both endodermal and mesodermal elements, of which the latter predominates.
• The anterior and posterior ends of the digestive tube are lined by ectoderm as a result of invagination processes.
• The anterior invagination is called the stomodaeum, which eventually forms the oral cavity, and the posterior one, the proctodaeum or anal cavity.
• The oral cavity is bounded by the jaws in front and on the sides, the palate above, and the buccal floor bearing the tongue below.
• Lips and cheeks differentiate in higher forms. It is customary to distinguish the space between lips and teeth as the vestibule.
• In Lungfishes and tetrapods, the nasal cavities open into the roof of the oral cavity by the internal nares or choanae.
• Choanae are primitively anteriorly placed but tend to move backward, and in Crocodilia, birds, and mammals assume a far posterior position through the formation of the secondary palate.
• The secondary palate is imperfectly formed in birds.
• Choanae reaches its best development in mammals, where it is continued backward by a fleshy fold, the soft palate, so that the nasal passages are still further prolonged posteriorly.
• The purpose of soft palate is to separate the food and respiratory passage.
• Three parts of the nasal apparatus in tetrapods: cavum nasi proprium, vestibulum, nasopharayngeal duct
• Nasal apparatus

  Cavum nasi proprium: the major, primary, or principal nasal cavity, which is usually an enlarged chamber lined by sensory olfactory epithelium

  Anterior to former is the tubular vestibulum that leads to the external naris,

  Posterior is nasopharyngeal duct that leads to the choana.

  Projections from the lateral wall into the cavum nasi propum are termed conchae.