Anatomy & Physiology

Anatomy & Physiology Study Guide which provides essential lubrication. The parietal peritoneum lines the inner surfaces of the body wall. Mesenteries Portions of the digestive tract are suspended within the peritoneal cavity by sheets of serous membrane that connect the parietal peritoneumwith the visceral peritoneum. These mesenteries are double sheets of peritoneal membrane. Mesenteries keep the organs attached and in a fix position and prevent intestines from becoming entangled during the digestive process or while the body is being contorted. The lesser omentum steadies the location of the stomach and provides an access route for blood vessels and other structures entering or leaving the liver. The falciform ligament is used to stabilize the position of the liver relative to the diaphragm and abdominal wall. The Mucosa The inner lining, or mucosa , of the digestive tract, is a mucous membrane consisting of epithelium, moistened with glandular secretions, and a lamina propria of areolar tissue. The lamina propria is composed of areolar tissue that also contains blood vessels, sensory nerve endings, lymphatic vessels, smooth muscle cells, and scattered areas of lymphoid tissue. In most areas of the digestive tract, the lamina propria contains a thin sheet of smooth muscle and elastic fibers. This sheet is called the muscularis mucosae . The Submucosa The submucosa is a layer of dense and uneven connective tissue that surrounds the muscularis mucosae. Along with its outer margin, the submucosa contains a network of natural nerve fibers and scattered neurons. This submucosal plexus (or Meissner ) lies along the inner border of the muscularis externa , a region dominated by smooth muscle cells. These layers are a vital part of the mechanical process and movement of materials along the digestive tract. The Serosa Along with most portions of the digestive tract inside the peritoneal cavity, the muscularis externa is covered by a serous membrane known as the serosa. There is no serosa covering the muscularis externa of the oral cavity, pharynx, esophagus, and rectum, where a dense network of collagen fibers firmly attaches the digestive tract to adjacent structures. This fibrous sheath is called an adventitia . 23.3 The Movement of Digestive Materials The digestive tract's muscular layers consist of visceral smooth muscle tissue. The smooth muscle along the digestive tract has rhythmic cycles of activity due to the presence of pacesetter cells . These smooth muscle cells trigger a wave of contraction that spreads throughout the entire muscular sheet. The coordinated contractions of the muscularis externa are essential in the movement of materials along the tract, through peristalsis, and in mechanical processing, through segmentation. Peristalsis The muscularis externa propels materials from one portion of the digestive tract to another by contractions known as peristalsis. Peristalsis consists of waves of muscular contractions that move a Achieve Page 315 of 368 ©2018