Abdomen - Anatomy, Functions, and Conditions

Introduction

The abdomen is the body space from the chest to the pelvis. The diaphragm is the upper border of the abdomen, and the lower end is the level of the pelvic bone. The abdomen comprises all the organs involved in digestion, such as the stomach, small intestine, liver, pancreas, and large intestine. The abdomen also comprises other organs such as the spleen, gallbladder, and kidneys. In addition, several important blood vessels pass through the abdomen, including the inferior vena cava, aorta, and many small branches. Common conditions affecting the abdomen are peritonitis, dyspepsia, appendicitis, gastritis, and many more.

What Is the Anatomy of the Abdomen?

The anterior portion of the abdomen is lined by fascia, a thin, tough layer of tissue. The front of the fascia has abdominal muscles and skin; at the back, there are back muscles and the spine.

The different structures of the abdomen are:

The Muscles of the Abdomen: The walls of the abdomen are divided into anterolateral and posterior sections. The walls of the abdomen form a flexible boundary that encloses the viscera and helps maintain its position and prevent any injury. The anterolateral wall of the abdomen consists of four external and internal layers: skin, superficial fascia, muscles, and peritoneum. The posterior wall of the abdomen is complex anatomy consisting of a pelvic girdle, posterior abdominal muscles, lumbar vertebrae, and associated fascia. The major blood vessels, nerves, and organs are located on the inner surface of the posterior abdominal wall.

Blood Vessels of the Abdomen: The arteries which supply the abdomen are

1. Aorta.

2. The superior mesenteric artery.

3. The inferior mesenteric artery.

4. The coeliac trunk.

The venous drainage from the abdomen is done by:

1. A systemic venous system consists of the inferior vena cava as a major vessel.

2. The Portal venous system has a portal vein as the main vessel.

The Gastrointestinal Tract: It is a long passage through which the food passes and undergoes digestion. The different parts of the gastrointestinal tract are:

1. The Esophagus: It is a long fibromuscular tube that is approximately 25 centimeters long and helps transport food from the pharynx to the stomach.

2. The Stomach: It is the storage pouch for the food located between the Esophagus and duodenum. It has a 'J' shape, and the anterior and posterior surfaces are lined by peritoneal covering. The stomach is divided into four parts- cardia, fundus, body, and pylorus.

3. The Small Intestine: It is the longest organ located in the abdomen, with a length of approximately 22 feet. The process of digestion and nutrient absorption takes place mostly in the small intestine. It extends from the pylorus of the stomach, starting at the duodenum, and then extends to the ileocaecal junction. The small intestine has three parts- duodenum, jejunum, and ileum.

4. The Large Intestine: is the distal part of the gastrointestinal tract that starts from the cecum and ends at the anus. It surrounds the small intestine in a 'square question mark' pattern. It is further divided into four parts- ascending colon, transverse colon, descending colon, and sigmoid colon.

5. The Rectum: It is the last part of the gastrointestinal tract, which is followed by the anus, through which the feces are passed out of the body.

The Liver: It is a peritoneal organ that is positioned in the right upper quadrant of the abdomen. The liver is the largest gland in the body and the largest vital organ in the abdominal cavity.

• The Gallbladder: It is a pear-shaped organ located within the hypochondriac region of the abdomen. It is inferiorly surrounded by the liver and anterior abdominal wall and posteriorly by the transverse colon and duodenum.

• The Pancreas: It is an organ situated below the stomach and possesses both exocrine and endocrine functions.

• The Spleen: It is an organ resembling the size of a clenched fist that functions as a blood filter by removing old red blood cells. It also plays a role in immune responses.

• The Kidneys: These are bilateral bean-shaped organs situated in the posterior abdomen region. It is connected to other organs, such as the urinary bladder and ureters.

• The Mesentery: It is the double-folded peritoneal tissue that suspends both the intestines from the posterior abdominal wall.

What Is the Function of the Abdomen?

As the abdomen comprises so many visceral organs, its function depends on the organs' functions. Therefore, the function of each organ present in the abdomen are:

• The Esophagus: It is the food pipe that helps the transportation of food from the mouth to the stomach, where its digestion starts.

• The Stomach: It stores the food for the longest duration, about 3 to 4 hours. The stomach secretes hydrochloric acid and other gastric juices, which initiate the process of digestion.

• The Small Intestine: A large part of digestion takes place in the small intestine in the presence of bile and gastric enzymes. Gastric enzymes are fluids that help to break down complex nutrients, carbohydrates, proteins, and fats into simpler forms for absorption. The absorption of nutrients and water also takes place in the small intestine.

• The Large Intestine: After almost completing the process of digestion and absorption, the leftover food enters the large intestine, where the rest of the water is absorbed, and the feces is passed to the rectum.

• The Pancreas: It functions as an exocrine and endocrine organ as it secretes enzymes and hormones. The enzymes secreted by the pancreas are gastric enzymes, namely amylase, lipase, and peptidases which help to convert complex nutrients like carbohydrates, proteins, and fats into simpler forms. It also secretes hormones insulin and glucagon, which help to regulate blood glucose levels in the body.

• The Liver: It is the most important organ in the abdomen, which helps in both digestion and metabolism of nutrients and drugs. It secretes bile which plays an important role in the process of digestion. The glucose is converted into energy in the liver.

• The Gallbladder: It stores bile which is secreted by the liver and passed to the small intestine through the biliary duct.

• Spleen: It helps in the filtration of blood by removing old red blood cells from new ones.

• The Kidneys: Kidneys are the organs that help to excrete waste products from the body in the form of urine. It infiltrates the water present in the body and helps to excrete elements like ammonia from the body. It helps to maintain the electrolyte balance of the body.

What Are the Common Conditions Affecting the Abdomen?

• Peritonitis: Inflammation of the peritoneum covering the abdomen is known as peritonitis. It can be caused due to infection spreading from any abdominal organ. It leads to pain and abdominal wall rigidity.

• Cholecystitis: Cholecystitis is the blockage or obstruction of gallbladder leading to inflammation and accumulation of bile. This leads to severe pain in the right side of the abdomen.

• Peptic Ulcer Diseases: H.pylori infection or side effects of anti-inflammatory drugs can lead to soreness in the stomach and duodenum due to increased concentration of acid.

• Gastritis: Inflammation of the stomach which can lead to severe abdominal pain, nausea, or vomiting. It can be caused due to H. pylori infection or side effects of drugs.

• Intestinal Obstruction: Blockage in a section of the intestine or the entire intestine. This can be due to food or any other reasons. It leads to impairment of digestion and many other severe problems.

• Hepatitis: Inflammation of the liver, mainly due to viral infection, is known as hepatitis. Other causes include alcohol, drugs, or compromised immune systems.

• Abdominal Hernia: A weakening or gap in the abdominal tissue through which the intestine can protrude is known as an abdominal hernia.

• Abdominal Distension: Increased amount of gas in the intestine leads to swelling of the abdomen.

Conclusion:

The abdomen is the part of the body that comprises the visceral organs such as the liver, the stomach, the kidneys, and the intestines, which play a very important role in digestion and other body functions. The function of the abdomen is to store these organs and regulate their functions. Therefore, any condition affecting the abdomen or its organs should be treated well, as it can cause severe complications and be life-threatening.