Anatomy of the Gastrointestinal Tract (GIT) PDF

Anatomy of the Gastrointestinal Tract (GIT) Dr Hayder Almayali Learning Objectives 1)Identify the GIT and its main divisions 2) Illustrate the structures of parts of main divisions of the GIT. 3) Recognize the anatomical relations between the various parts of the GIT  GIT Also called Digestiv...

Anatomy of the Gastrointestinal Tract (GIT) Dr Hayder Almayali Learning Objectives 1)Identify the GIT and its main divisions 2) Illustrate the structures of parts of main divisions of the GIT. 3) Recognize the anatomical relations between the various parts of the GIT  GIT Also called Digestive tract or Alimentary canal. It’s the tubular system responsible for ingesting and digesting the food needed for survival and growth. Besides, it’s also responsible for absorbing the nutrients and water into the blood stream and the excretion of the waste products. Measuring around 9 meters in length, the GIT starts in the oral cavity and ends at the anal region. It occupies the abdominal cavity (abdomen proper and pelvic cavity). Parts of the GIT: I) Main Parts: A) Upper GIT: 1) Oral Cavity 2) Pharynx 3) Esophagus 4) Stomach B) Lower GIT: 1) Small Intestine 2) Large Intestine 3) Rectum 4) Anal Region II) Associated Organs: A) Salivary glands B) The Liver C) Gall Bladder D) The Pancreas The Oral Cavity: The cavity between the lips anteriorly and the oral pharynx posteriorly. It’s roofed by the Palate and floored by the Sublingual structures (structures below the tongue): muscles, salivary glands and mucus membrane). Tongue The salivary glands pour the saliva through their ducts into the oral cavity. The salivary glands are three pairs (Rt & Lt): 1) Parotid glands 2) Submandibular glands 3) Sublingual glands  The Pharynx: The space between the nasal and oral cavities superiorly and the upper esophagus and the Larynx inferiorly. It has a very important role in swallowing, breathing and speaking. It’s made of three parts: 1) Nasal pharynx: the posterior extension of the nasal cavity. 2) Oral pharynx: the posterior extension of the oral cavity. 3) Laryngeal pharynx: the space just above the Larynx. The Esophagus: The muscular tube that connects the pharynx to the stomach (see the lecture of the thoracic cavity). The Stomach: It’s a muscular j-shaped hollow organ that stores, mixes and breaks down the food by the acids (HCl) and enzymes (Pepsin) before passing it into the small intestine. It has three parts, from above below: a) Fundus b) Body c) Pyloric antrum The Stomach It has two orifices (openings): 1) Cardiac orifice: near the fundus, through which it’s connected to the lower esophagus. 2) Pyloric orifice: at the end of the pyloric antrum, through which it’s connected to the 1st part of the small intestine. The Small Intestines: They are the longest part of the GIT (6-7 meters). It’s responsible for digesting the food and absorbing the nutrients. It’s divided into: 1) 1st part: duodenum (c-shaped, connected to the stomach, surrounds the head of the pancreas) 2) 2nd part: jejunum (around 2.5 meters, has a thicker wall, and therefore more nutrient absorption capacity) 3) 3rd part: Ileum (the terminal & longest part (3.5 meters), connected to the Cecum of the large intestines). The Large Intestines (also called Large Bowel or Colon): Around 1.5 meter in length, they are the main site for water absorption and stool (feces) formation. They are also the site for the beneficial bacteria that help in digesting the fibers and the production of vitamins K and B12. They are divided into: 1) Cecum (short segment and connected to the ileum) 2) Ascending colon (lies in the rt side of the abdomen) 3) Transverse colon (lies anterior-inferior to the stomach) 4) Descending colon (on the lt side of the abdomen) 5) Sigmoid colon (s-shaped, lies in the pelvic cavity, connects the colon to the rectum) The Rectum: it’s a pelvic structure, functions as a temporary storage for feces. Anal canal & Anus: the terminal part of the GIT. It controls the defecation by the muscular sphincters. All the tubular GIT from the esophagus down to the large intestines have three layers in their walls: 1) Inner layer: mucus membrane specialized for absorption of water & digested nutrients. 2) Middle layer: smooth muscle layers for propelling (pushing forward) the food inside them. the coordinated rhythmic contractions of the smooth muscles of the GIT walls are called “Peristalsis”. 3) Outer layer: serous membrane that covers (& protects) the tracts and helps in hanging them inside the abdominal cavity.  The Peritoneum: Like the pleura in the thorax, the abdominal cavity has its double layer membrane called “Peritoneum”. The inner visceral peritoneum wraps the stomach and intestines, and the outer parietal peritoneum lines the inside of the abdominal cavity walls. The space between the two layers is the peritoneal cavity which contains small amount of lubricating fluid. The Peritoneum sends folds of its layers in various directions inside the abdominal cavity to create certain structures that has specific functions. These structures are: 1) The Mesentery: double peritoneal layers that attaches some GIT parts to the posterior abdominal wall, like the small intestine, transverse colon and sigmoid colon. 2) The Omentum: double layers of peritoneum between the stomach-duodenum and other organs.  The Omentum It’s of two types: A) Greater Omentum: between the lower border of the stomach-duodenum on one side and the transverse colon on the other side. B) Lesser Omentum: between the upper border of the stomach-dudenum and the liver.  The Omentum The functions of the Omentum are: 1) Storing of fat as a source of energy when the body needs that. 2) Protection against microbes by having lymphoid tissue, which are part of the immune system of the body. 3) It controls any injury (perforation) or infection (peritonitis) site in the abdominal cavity by wrapping it to prevent the spread of the infection or the injury. Thank You Any Questions?