A Complete Guide to Your Abdomen

The abdomen is the frontal body cavity between the chest and pelvis that holds vital organs like the stomach, kidneys, bladder, liver, and intestines. Informally called the belly or stomach region, the abdomen is made up of protective tissues, membranes, and muscles. Without the abdomen, your body couldn't support and protect organs needed for digestion, urination, and bowel movements.

Because the abdomen contains different organs, medical conditions that affect these organs often cause abdominal pain. Almost everyone experiences abdominal pain at some point due to stomach viruses, gas, or constipation. However, abdominal pain can also indicate health conditions like kidney stones, pancreatitis, and appendicitis. Cancer and abdominal conditions can also directly affect the abdomen's tissues and fluid.

Anatomy of the Abdomen 

The abdomen is a body cavity—a hollow, fluid-filled space that holds organs and other bodily structures. Organs inside the abdomen include:

• Digestive system organs like the stomach, small intestine, large intestine (colon), pancreas, appendix, liver, and gallbladder
• Lymphatic system organs like the spleen and lymph vessels
• Urinary system organs like the kidneys, ureters (tubes that carry urine), and bladder
• Reproductive organs like the uterus, ovaries, and fallopian tubes 
• Blood vessels (arteries and veins)
• Parasympathetic and sympathetic nerves

Structure 

As the largest body cavity, the abdomen's vertical oval shape makes up most of the body's trunk. Fluid fills the inside of the abdominal cavity to help pad and lubricate organs so they can move without friction. Membranes, tissues, and muscles cover the organs that make up the abdominal wall. Layers of the abdomen include:

• Peritoneum: This thin membrane covers the inside of the abdominal cavity (parietal peritoneum) and the organs (visceral peritoneum). Along with ligaments, a large double layer of the peritoneum (the mesentery) attaches abdominal organs together or to the rear abdominal wall. 
• Preperitoneal adipose tissue: This fatty tissue creates a pad that covers the abdominal cavity. It also fills in space that doesn't contain organs.
• Areolar tissue: This loose connective tissue made from collagen fibers and elastic tissue helps connect skin to muscles. It also gives the abdomen structure to help support the body and protect organs. 
• Transversalis fascia: This thin layer of connective tissue lines the abdominal cavity to help support organs and muscles in the abdomen.
• Transversus abdominis: As the deepest abdominal muscle layer, the transversus abdominis helps protect organs by holding them in place and stabilizing the abdomen and lower back.
• Obliques: These twin muscles are located on the right and left of the waist, surrounding the six-pack muscles. The internal and external obliques help the trunk twist left and right.  
• Superficial fascia: This stringy connective tissue surrounding organs and other structures in the abdomen flexes and stretches to help your abdominal muscles and tissue move.
• Subcutaneous tissue: This deep layer of fatty and connective tissue allows your skin to move over other tissues and muscles. It also helps absorb shock to protect your abdominal organs and muscles. 

Location

The abdomen is located on the forward-facing part of the lower torso. This cavity sits below your chest—right under your lungs—and above the top of your pelvis. A muscular division called the diaphragm separates your lungs from the abdomen. The back muscles and your spine are located behind the abdominal cavity.

The parasympathetic nervous system's main nerve, the vagus nerve, extends from the neck to the abdomen. The parasympathetic nervous system helps control body functions like digestion, immune response, and heart rate. The abdomen connects to the circulatory system via various blood vessels. The aorta carries blood from the heart to the digestive tract organs. The inferior vena cava moves blood from the abdomen to your lower extremities so it can return to your heart.

Anatomical Variations 

Birth defects can cause the abdominal wall to develop abnormally, causing openings where organs protrude out of the body. Birth defects that affect the anatomy of the abdomen include gastroschisis and omphalocele.

Gastroschisis is a defect in the abdominal wall that causes the large and small intestines to push through, usually to the right of the belly button. There is no membrane covering the exposed organs.

Omphalocele, also known as exomphalos, is when organs like the intestines, stomach, and liver push through an opening in the center of the abdominal wall—where the umbilical cord meets the abdomen. A membrane covers the opening and organs.

What Does the Abdomen Do?

As a body cavity, the abdomen's job is to hold and protect vital internal organs of the digestive, urinary, endocrine, exocrine, circulatory, and female reproductive systems. The membrane, tissue, and muscle layers work together to support these organs so they don't fall out of the cavity and also protect them from the outside world.

The abdomen aids in protecting and supporting a developing fetus, too. During pregnancy, the abdomen's muscles stretch and organs squish to the top of the cavity to help accommodate the growing uterus.

The abdomen also connects abdominal organs to the circulatory, lymphatic, and nervous system. Blood vessels branch throughout the abdomen to move blood to and from organs to help them function. Lymph vessels throughout the abdomen act like channels that drain lymph left behind after blood moves through your abdominal organs. Lymph is a clear liquid that contains white blood cells that help filter out bacteria, waste, and abnormal cells that can make you sick. 

Nerves from the sympathetic and parasympathetic nervous systems also pass through the abdomen and into organs. The sympathetic nervous system activates during stress and increases activity to control your fight-or-flight response. The nerves in the abdomen help slow digestion to reroute energy and activate liver energy stores. The parasympathetic nervous system signals your body to relax and helps signal organs in your abdomen to start digestion and urination.

Associated Conditions

Health conditions associated with the abdomen often affect specific organs or the abdominal cavity and walls. Abdominal swelling or bloating is usually a sign of gas, but it can signal a more serious condition. Abdominal pain is the most common health-related issue related to the abdomen.

Abdominal Wall and Cavity Conditions

Health conditions that directly affect the abdominal wall and cavity include: 

• Hernia: A small sac that forms when the small intestine pushes through a hole, tear, or weak area in the abdominal wall's muscle. An incisional hernia can occur after abdominal surgery. An umbilical hernia forms around the belly button when the muscle doesn't fully close after birth.
• Ascites: This fluid buildup between the abdominal lining and organs causes the abdomen to swell. Scarring of the liver (cirrhosis) usually causes ascites.
• Peritonitis: A condition where the peritoneum—the membrane that covers the abdomen and its organs—becomes inflamed or infected. Symptoms can include abdominal pain, swelling, fever, and vomiting. A hole in a digestive tract organ or bile leaking into the abdominal cavity can cause this dangerous condition.
• Abdominal adhesions: These bands of scar-like tissue inside the abdomen form between organs or between organs and the abdominal wall. Adhesions can happen after abdominal surgery and cause the intestines and other abdominal organs to twist or compress enough to cause blockages. 
• Abdominal distension: This abdominal swelling, or distention, makes your abdominal region larger than usual. Overeating, fluid buildup, or intestinal or bowel blockages can cause it.

Abdominal Cancers and Related Conditions

Cancer and related conditions that affect the abdomen include: 

• Peritoneal mesothelioma: This rare cancer affects the peritoneum lining in the abdominal cavity. Asbestos exposure—a carcinogenic fibrous mineral once used in building materials—causes this cancer.  
• Pseudomyxoma peritonei (PMP): This is a condition where cancerous growths fill the abdominal cavity with jelly-like fluid. PMP is caused by cancers in the abdomen—like stomach, colon, pancreatic, or ovarian cancer.
• Peritoneal carcinomatosis: This is cancer that has spread to the peritoneum from other cancers like those of the colon/rectum, pancreas, stomach, ovaries, and gallbladder. 
• Mesenteric panniculitis (sclerosing mesenteritis): This rare condition is often associated with cancer. It causes inflammation of the mesentery—folds of peritoneum tissue at the back of the abdomen. Over time, it can scar abdominal tissues. It can also cause abdominal swelling and chronic or intermittent abdominal pain. 

Abdominal Organ Conditions

Other conditions that cause abdominal pain and issues are related to organs inside the abdomen. Some common conditions affecting abdominal organs include:

• Appendicitis: Inflammation of the appendix causes on-and-off pain in the middle of the abdomen. The pain eventually travels to the lower right side of the abdomen, where the appendix is located. 
• Gallstones: These blockages in the gallbladder can cause colicky pain and digestive issues.
• Pancreatitis: This swelling of the pancreas can cause pain on the left side of the abdomen.
• Kidney stones: Mineral deposits from the kidneys create blockages in the urethra (the tube that lets urine release from your body), making urinating difficult and painful. 
• Intestinal colic: This is when hardened feces, food, scar tissue, tumors, polyps, or inflamed tissue create partial or complete blockage in the intestines. It causes cramp-like abdominal pain.
• Bowel obstruction: A blockage in the small or large bowel can prevent stool from passing, causing pain in the upper abdomen and near the belly button.

Diagnostic Testing

To diagnose abdominal issues, a healthcare provider will typically consider your symptom history, perform a physical examination, and run diagnostic tests. Tests that help diagnose abdomen-related health issues include:

• Blood tests: Drawing blood and testing it in a lab can identify infections or organ problems.
• Urine tests (urinalysis): This test examines a person's urine for pH level, appearance, abnormal substances, proteins, and bacteria.  
• Stool tests: Examining a stool sample with or without a microscope can help diagnose digestive tract system issues.
• Abdominal X-ray: This imaging test uses electromagnetic waves to take pictures of the inside of the abdomen and its organs. It can identify blockages or injuries.
• Transabdominal ultrasound: This imaging test uses sound waves to see inside the abdomen and look at organs and blood vessels. It can help identify tumors, organ abnormalities, and kidney stones.
• Endoscopy: This test inserts a tube with a tiny camera called an endoscope into your mouth or rectum to look inside your digestive tract. This test can help identify issues with your intestines or stomach.
• Barium enema: This special type of X-ray looks at the large intestine. Barium sulfate is inserted into the rectum during the test to help highlight specific areas of the colon.
• Computerized tomography (CT) scan: An imaging test that creates pictures of the abdomen from different angles. CT scans give a three-dimensional view of the abdomen to identify injury, fluid, tumors, infections, blood clots, and internal bleeding. 

Tips for Keeping Your Abdomen Healthy

You can keep your abdomen healthy by caring for its organs and muscles. Here are some everyday lifestyle changes that help your abdomen: 

• Drink more water: Staying hydrated allows your organs and tissues to function. Water also helps you avoid kidney stones and moves digestion along so you don't become constipated. 
• Reduce your alcohol intake: Excessive drinking can increase your risk of liver disease, digestive issues, and pancreatitis.
• Eat more fiber: Help your digestion and bowel movements by eating fruits, vegetables, and whole grains that are rich in fiber. 
• Exercise regularly and safely: Exercising can help strengthen your abdominal muscles to help prevent injury. However, lifting heavy weights with bad form can damage your abdominal wall. 
• Take note of your diet: If you notice certain dairy products or spicy foods cause abdominal pain or bloating, consider avoiding or limiting these foods to see if they are the source of discomfort. 

A Quick Review 

The abdomen is a hollow, fluid-filled space that holds organs and other bodily structures. Organs inside the abdomen include the stomach, large intestines, small intestines, spleen, liver, kidneys, and bladder. The ovaries, uterus, and fallopian tubes are also inside the abdomen. 

The abdomen's membranes, tissues, and muscle layers help protect and support these vital organs. Blood vessels, nerves, and lymph vessels in the abdomen also connect your organs to larger bodily systems to help them function.

When a health condition affects an organ in the abdomen, you'll typically experience abdominal pain, swelling, or bloating. Certain cancers and health conditions can also directly affect the abdomen's membranes, tissues, and muscle walls. 

You can keep your abdomen—and the organs it protects—healthy by practicing lifestyle choices like reducing your alcohol intake and getting regular physical activity.