Gastrointestinal Tract (GIT)

• The Gastrointestinal Tract (GIT) is also known as the digestive tract or alimentary canal.
• The GIT tubular system ingests and digests food for survival and growth.
• The GIT absorbs nutrients and water into the bloodstream and excretes waste products.
• Measuring about 9 meters in length, the GIT starts in the oral cavity and ends at the anal region.
• The GIT occupies the abdominal and pelvic cavities.

Main Parts of the GIT:

• Upper GIT consists of the oral cavity, pharynx, esophagus, and stomach.
• Lower GIT consists of the small intestine, large intestine, rectum, and anal region.

Associated Organs of the GIT:

• Associated organs include salivary glands, liver, gall bladder and the pancreas.

The Oral Cavity:

• The oral cavity is between the lips anteriorly and the oral pharynx posteriorly.
• The oral cavity is roofed by the palate and floored by sublingual structures.
• Sublingual structures include muscles, salivary glands, and mucous membranes.
• The salivary glands pour saliva through their ducts into the oral cavity.
• There are three pairs of salivary glands: right and left.
• The salivary glands include parotid, submandibular, and sublingual glands.

The Pharynx:

• The pharynx is the space between the nasal and oral cavities superiorly, and the upper esophagus and larynx inferiorly.
• The pharynx is important in swallowing, breathing, and speaking.
• The three parts of the pharynx are the nasal pharynx, oral pharynx, and laryngeal pharynx.
• The nasal pharynx is the posterior extension of the nasal cavity.
• The oral pharynx is the posterior extension of the oral cavity.
• The laryngeal pharynx is the space just above the Larynx.

The Esophagus:

• The esophagus is a muscular tube that connects the pharynx to the stomach.

The Stomach:

• The stomach is a muscular, J-shaped hollow organ.
• Stores, mixes and breaks down food with acids (HCl) and enzymes (Pepsin).
• The stomach has three parts: fundus, body, and pyloric antrum.
• The stomach has two orifices.
• The cardiac orifice is near the fundus connecting to the lower esophagus.
• The pyloric orifice is at the end of the pyloric antrum, connecting to the first part of the small intestine.

The Small Intestines:

• The small intestines are the longest part of the GIT, measuring 6-7 meters.
• Responsible for digesting food and absorbing nutrients.
• The small intestine has three parts: duodenum, jejunum, and ileum.
• The duodenum is C-shaped, connected to the stomach, and surrounds the head of the pancreas.
• The jejunum is about 2.5 meters long, has a thicker wall, and more nutrient absorption capacity.
• lleum is the terminal and longest part (3.5 meters) and is connected to the Cecum of the the large intestines.

The Large Intestines:

• The large intestines are also called the large bowel or colon.
• The large intestines are around 1.5 meters in length, which is the main site for water absorption and stool formation.
• The large intestines contain beneficial bacteria that help in digesting fibers and producing vitamins K and B12.
• There are 5 parts to the large intestine: Cecum, Ascending colon, Transverse colon, Descending colon, and Sigmoid colon.
• The cecum is a short segment connected to the ileum.
• The ascending colon lies on the right side of the abdomen.
• The transverse colon lies anterior-inferior to the stomach.
• The descending colon lies on the left side of the abdomen.
• The sigmoid colon is S-shaped, lies in the pelvic cavity, and connects the colon to the rectum.

The Rectum:

• The rectum is a pelvic structure that functions as a temporary storage for feces.

Anal Canal and Anus:

• The anal canal and anus are the terminal part of the GIT.
• The anal canal and anus control defecation by use of muscular sphincters.

GIT three-layer walls:

• The tubular GIT from the esophagus down to the large intestines have three layers in their walls.
• The inner layer is a mucus membrane specialized for absorption of water and digested nutrients.
• The middle layer is smooth muscle layers for propelling food inside.
• Peristalsis is the term name for coordinated rhythmic contractions of the smooth muscles of the GIT walls.
• The outer layer is a serous membrane that covers and protects the tracts and helps in hanging them inside the abdominal cavity.

The Peritoneum:

• The abdominal cavity has a double-layer membrane called the peritoneum.
• The inner visceral peritoneum wraps the stomach and intestines.
• The outer parietal peritoneum lines the inside of the abdominal cavity walls.
• The peritoneal cavity is the space between the two layers that contain a small amount of lubricating fluid.

Mesentery

• The mesentery is a double peritoneal layer that attaches some GIT parts to the posterior abdominal wall, such as the small intestine, transverse colon, and sigmoid colon.

Omentum

• Omentum is a double layer of peritoneum between the stomach-duodenum and other organs.
• There are two types: the greater and lesser omentum.
• The greater omentum is between the lower border of the stomach-duodenum on one side and the transverse colon on the other side.
• The lesser omentum lies between the upper border of the stomach-dudenum and the liver.

Functions of omentum

• Serves as a store of fat for energy.
• Provides protection against microbes, due to lymphoid tissue which is part of the immune system.
• Helps to control injury or any site of infection by wrapping the site to prevent spreading.

Overview of the gastrointestinal tract (GIT), also known as the digestive tract. Review the main parts of the upper and lower GIT, including the oral cavity, pharynx, esophagus, stomach, small and large intestine. Learn about the associated organs such as salivary glands, liver, and pancreas.