The Digestive System

Front 1

Most digestive system organs reside in the abdominopelvic cavity. All ventral body cavities contain slipplery serous membranes. The Peritoneum of the abdominopelvic cavity is the most extensive of these membranes. The Visceral peritoneum covers the external surfaces of the most digestive organs and is continuous with the parietal peritoneum that lines the body wall. B/w the 2 peritoneums is the peritoneal cavity a slitlike potential space containing a slippery fluid secreted by the serous membranes. the serous fluid lubricates the mobile digestive organs allowing them to glide easily across one other and along the body wall as they carry out their activities.

Back 1

A mesentery is a double layer of peritoneum a sheet of 2 serous membranes fused back to back that extends to the digestive organs from the body wall. Mesenteries provide routes for blood vessels lymphatics and nerves to reach the digestive viscera hold organs in place and store fat. in most places the mesentery is dorsal and attaches to the the posterior abdominal wall. but their is also a ventral such as the one that extends from the liver to the anterior abdominal wall.
-not all alimentary canal organs are suspended by mesentery.
-duodenum is the first part o the small intestine. and some parts of the large intestine are called retroperitoneal organs.
-digestive organs like the stomach that keep their mesentery and remain in the peritoneal cavity are called intraperitoneal and peritoneal organs.

Front 2

-peritonitis is inflammation of the peritoneum. can be from a piercing abdominal wound, a perforating ulcer that leaks stomach juices into the peritoneal cavity, or poor sterile technique during abdominal surgery. most commonly result from a burst appendix that sprays bacteria-containing feces all over the peritoneum. the peritoneal coverings tend to stick together around the infection site. this localizes the infection providing time for macrophages to prevent the inflammation from spreading. if peritonitis becomes widespread within the peritoneal cavity it is dangerous and often lethal.

Back 2

splanchnic circulation includes those arteries that branch off the abdominal aorta to serve the digestive ograns and the hepatic portal circulation. the arterial supply-the branches of the celiac trunk that serve the spleen, liver and stomach and the mesenteric arteries that serve the small and large intestines normally receive one quarter of the cardiac output. this percentage increases after a meal, the hepatic portal circulation collects nutrient rich venous blood draining from the digestive viscera and delivers it to the liver.

Front 3

From the esophagus to the anal canal, the walls of the alimentary canal have the same four basic layers, or tunics- mucosa, submucosa, muscularis external, and serosa. Each layer contains a predominant tissue type that plays a specific role in food breakdown.

Back 3

The mucosa, or mucous membrane the innermost layer is a moist epithelial membrane that lines the alimentary canal lumen from mouth to anus, its major functions are to : secrete mucous, digestive enzymes, and hormones' absorb the end products of digestion into the blood; protect against infectious dx. The mucosa in a particular region of the gi tract may perform one of these 3 fx; 1.a lining epithelium, 2. a lamina propia, 3. a muscularis mucosae

Front 4

mouth esophagus and anus are stratifies epithelium
epithelium of the mucosa is simple columnar epithelium rich in mucus secreting cells.
this mucous produce protects certain digestive organs from being digested by enzymes working within their cavities and eases food passage along the tract. Lamina propria which underlines the epithelium is loose areolar ct its capillaries nourish te epithelium and absorb digested nutrients. Its isolated lymphoid follicles part of MALT, (the mucosa associated lymphoid tissue), help defend us against bacteria and other pathogens which have access to our digestive tract. particularly large collections of lymphoid follicles occur within the pharynx as the tonsils and in the appendix. External to the lamina is the muscularis mucosae a scant layer of smooth muscle cells that produces local movements of the mucosa. in the small intestine, this muscle layer's toe throws the mucosa into a series of small folds that immensenly increase its surface area.

Back 4

The Submucosa; external to the mucosa, is areolar ct containing a rich supply of blood and lymphatic vessels lymphoid follicles and nerve fibers which supply the surrounding tissues of the GI tract wall. its abundant elastic fibers enable the stomach to regain its normal shape after termporarly storing a large meal

Front 5

The Muscularis Externa; surrounds the submucosa, it is also called muscularis, responsible for segmentation and peristalsis. has inner circular layer and outer longitudinal layer of smooth muscle cells. in several places along the tract the circular layer thickens, forming sphincters that act as valves to control food passage from one organ to the next and prevent backflow.

Back 5

The Serosa, the outermost layer of the intraperitoneal organs, is the visceral peritoneum. in most alimentary canal organs it is formed of areolar ct covered with mesothelium a single layer of squamous epithelial cells. in the esophagus which is located in the thoracic instead of the abdominopelvic cavity the serosa is replaced by an adventitia ordinary fibrous ct that binds the esophagus to surrounding structures. retroperitoneal organs have both a serosa on the side facing the peritoneal cavity and an adventitia on the side abutting the dorsal body wall

Front 6

alimentary canal has its own in house nerve supply staffed by the so called enteric neurons which communicate widely with one another to regulate digestive system activity. These semiautonomous enteric neurons constitute the bulk of the two major intrinsic nerve plexuses found in the walls of the alimentary canal; the submucosal and myenteric nerve plexuses

Back 6

The submucosal nerve plexus occupies the submucosa whereas the large myenteric nerve plexus lies b/w the circular and longitudinal muscle layers of the muscularis externa. Enteric neurons of these plexuses provide the major nerve supply to the GI tract wall and control GI tract motility or motion. Controll of the patterns of segmentation and peristalsis is largely autonomic involving pacemaker cells and local reflex arcs b/w enteric neurons in the same or different organs.

Front 7

The enteric nervous system is linked to the central nervous system by 1. afferent visceral fibers 2. sympathetic and parasympathetic branches motor fibers of the autonomic nervous system that enter the intestinal wall and synapse with neurons in the intrinsic plexuses. Hence, extrinsic controls exerted by autonomic fibers via long reflex arcs also regulate digestive activity. Parasympathetic inputs enhance digestive activities whereas sympathetic impulses inhibit them.

Back 7

The mouth is also called oral cavity, or buccal cavity, boundaries are lips anteriorly cheeks laterally, palate superiorly, and tongue inferiorly. Its anterior opening is the oral orifice. Posteriorly the oral cavity is continouos with the oropharynx. Lines of mouth are thick stratified squamous epithelium which withstands considerable friction. the epithelium on the gums, hard palate, and dorsum of the tongue is slightly keratinized or extra protection against abrasion during eating. oral mucosa responds to injury by producting antimicrobial peptides called defensins which helps to explain how the mouth a site teeming with dx causing microbes remains so remarkably healthy.

Front 8

The Lips and Cheeks; lips (labia), and cheeks which help keep food b/w the teeth when we chew are composed of a core of skeletal muscle covered externally by skin. The orbicularis oris muscle forms the fleshy lips; the cheeks are formed largely by the buccinators. The recess bounded externally by the lips and cheeks and internally by the gums and teeth is the oral vestibule. The area that lies within the teeth an gums is the oral cavity proper. The labial frenulum is a median fold that joins the internal aspect of each lip to the gum.

Back 8

The Palate, forming the roof of the mouth, has 2 distinc parts, the hard palate anteriorly and the soft palate posteriorly. The hard palate is underlain by the palatine bones and the palatine processes of the maxillae and it forms a rigid surface against which the tongue forces food during chewing. The mucosa on either side of its raphe( a midline ridge is slightly corrugated which helps create friction) The soft palate is a mobile fold formed mostly of skeletal muscle that rises reflexively to close off the nasopharynx when we swallow.
-Laterally the soft palate is anchored to the tongue by the palatoglossal arches and to the wall of the oropharynx by the more posterior palatopharyngeal arches. these 2 paired folds form the boundaries of the fauces, (throat), the arched area of the oropharynx that contains the palatine tonsils, projecting downward from the free edge of the soft palate is the fingerlike uvula.