Gastrointestinal Tract Anatomy and Physiology

Study Notes

Gastrointestinal Tract

The gastrointestinal tract is approximately 7 to 7.9 m (23 to 26 feet) in length, extending from the mouth to the anus.
It is associated with accessory organs such as salivary glands, liver, gallbladder, and pancreas.

Esophagus

The esophagus is a hollow muscular tube, approximately 25 cm (10 inches) in length.
It passes through the diaphragm at an opening called the diaphragmatic hiatus.

Stomach

The stomach is situated in the left upper portion of the abdomen, under the left lobe of the liver and the diaphragm, overlaying most of the pancreas.
It has a capacity of approximately 1500 mL.
The stomach stores food, secretes digestive fluids, and propels partially digested food or chyme.
It has four anatomic regions: cardia, fundus, body, and pylorus.
The pyloric sphincter is formed by circular smooth muscle in the wall of the pylorus and controls the opening between the stomach and the small intestine.

Small Intestine

The small intestine is the longest segment of the gastrointestinal tract.
It has approximately 70 m (230 feet) of surface area for secretion and absorption.
It is divided into three sections: duodenum, jejunum, and ileum.
The ileum terminates at the ileocecal valve.

Large Intestine

The large intestine has segments including ascending, transverse, and descending colon.
The sigmoid colon, rectum, and anus complete the terminal portion.
A network of striated muscle forms both the internal and external anal sphincters, regulating the anal outlet.

Blood Supply of GIT

The gastrointestinal tract receives blood from arteries that originate along the entire length of the thoracic and abdominal aorta.
Veins that return blood from the digestive organs and the spleen form the portal venous system.
The portal venous system is composed of five large veins: superior mesenteric, inferior mesenteric, gastric, splenic, and cystic veins.
The blood flow to the GI tract is about 20% of the total cardiac output and increases significantly after eating.

Innervation of GIT

The sympathetic nervous system has an inhibitory effect on the GI tract, decreasing gastric secretion and motility and causing the sphincters and blood vessels to constrict.
Parasympathetic nervous system stimulation causes peristalsis and increases secretory activities.
The sphincters relax, except for the sphincter of the upper esophagus and external anal sphincter, which are under voluntary control.

Functions of Digestive System

The digestive system performs functions such as chewing and swallowing, gastric function, small intestine function, colonic function, waste products of digestion, and gut microbiome.

Chewing and Swallowing

Approximately 1.5 L of saliva is secreted daily from the parotid gland, submaxillary gland, and sublingual gland.
Saliva contains ptyalin or salivary amylase, an enzyme that begins the digestion of starches.
Water and mucus in saliva help lubricate the food as it is chewed, facilitating swallowing.

Gastric Function

The stomach breaks down food into more absorbable components and aids in the destruction of most ingested bacteria.
Pepsin, an enzyme for protein digestion, is the end product of the conversion of pepsinogen from the chief cells.

Description

Test your knowledge on the anatomy and physiology of the gastrointestinal tract, including the esophagus, stomach, small and large intestines, rectum, and anus. Learn about the associated accessory organs such as salivary glands, liver, gallbladder, and pancreas.