Abdomen (Anatomy): Definition, Function, Muscles | Biology Dictionary (2023)

Abdomen Definition

The abdomen refers to the region between the pelvis (pelvic brim) and the thorax (thoracic diaphragm) in vertebrates, including humans. The space constituting the abdomen is termed the abdominal cavity. The borders of the abdominal cavity are comprised of the posterior peritoneal surface, the anterior abdominal wall, the inferior pelvic inlet, and the superior thoracic diaphragm. The abdomen functions to house the digestive system and provides muscles essential for posture, balance, and breathing.

Abdomen Anatomy

The abdomen is comprised primarily of the digestive tract and other accessory organs which assist in digestion, the urinary system, spleen, and the abdominal muscles (shown below). The majority of these organs are encased in a protective membrane termed the peritoneum. While the digestive organs and assessor organs are located within the peritoneum, the kidneys, ureters and urinary bladder are located outsider of the peritoneum, and thus, are considered by some scientists to be pelvic organs.

Digestive Tract

The organs of the digestive tract consist of the small and large intestines, the stomach, cecum, and the appendix. The stomach is located between the esophagus and the small intestine in the upper left region of the abdomen. The stomach is responsible for the secretion of digestive enzymes and gastric acid required to digest food products. The small intestine is situated between the stomach and large intestine and consists of the three segments (duodenum, jejunum, and ileum), each exhibiting distinct functional properties. The duodenum is situated around the top of the pancreas and receives the digested stomach contents known as gastric chyme. The duodenum functions to neutralize the acid contained in the gastric chyme, as well as break down proteins and fat via enzymes and bile. The jejunum is the middle segment of the small intestine and is responsible for the absorption of sugar, amino acids, and fatty acids into the bloodstream. The final segment of the small intestine is the ileum, which connects to the large intestine. The ileum is responsible for the absorption of vitamin B12, as well as any remaining nutrients. The large intestine consists of the cecum, colon, rectum, and anus and stretches the entire width of the abdominal cavity. The primary function of the large intestine is to absorb water and store the remaining food material as feces until it can be excreted from the body via defecation.

Accessory Digestive Organs

The organs which assist in digestion consist of the pancreas, liver, and gallbladder. These organs secrete various hormones (i.e., insulin), enzymes, and bile via specialized ducts to aid in digestion. In particular, the pancreas functions as an endocrine organ which secretes a variety of digestive enzymes as well as hormones which aid in the digestion of food passing through the digestive tract. The pancreas is located behind the stomach. The liver is located in the upper right quadrant of the abdomen and functions to produce bile, which is responsible for breaking down fats. The liver also functions to produce hormones, regulate the storage of glycogen, and detoxification of the blood. The gallbladder is responsible for the storage of bile produced by the liver until it is released into the small intestine. The gallbladder is situated in the abdomen just under the right lobe of the liver.

Spleen

The spleen functions as a secondary lymphoid organ and is responsible for the removal of red blood cells via active filtration. The spleen also acts as a reservoir of red blood cells and metabolizes hemoglobin obtained from old red blood cells. The spleen is located in the upper left quadrant of the abdomen.

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Urinary System

The urinary system consists of the kidneys, ureters, and urinary bladder, which are responsible for the filtration and excretion of waste in the form of urine from the body. Since these organs are located outside of the peritoneum, they can also be considered pelvic organs by some researchers. In particular, the kidneys function to filter the blood of waste products, regulate blood pressure, and control the blood pH. The ureters are connected to the kidneys and are used to drain urine into the urinary bladder. The urinary bladder serves as to store the accumulated urine until it can be excreted via urination.

Abdomen Function

The primary functions of the abdomen consist of digestion, breathing, posture and balance, as well as movement. The major organs located in the abdomen are associated with digestion, for which the functions are described above. The abdomen is also required for breathing via the accessory muscles of respiration. Such muscles are also involved in postural support, movement, balance, coughing, urination, vomiting, singing, childbirth, and defecation.

Respiration

Although the diaphragm controls respiration under steady-state conditions, the accessory muscles of respiration assist in respiration when greater effort is required. These muscles include the scalene and sternocleidomastoid muscles which serve to raise the ribcage. When these muscles are engaged, it is typically a sign of respiratory distress, such as that observed during an asthma attack.

Movement and Posture

Abdominal muscles are also required for the maintenance of posture and balance, as well as movement. The transverse abdominis muscle and internal obliques affect posture by providing spinal support during rotation and lateral flexion, and stabilize the spine when standing. Both of these muscles are situated deep within the abdomen. The external obliques also function to support the lateral flexion and stabilize the spine when standing. Finally, the rectus abdominis functions to bend the spine forward.

Abdominal Muscles

The abdominal muscles consist of three distinct layers residing within the abdominal wall and extend to the pubis, iliac crest, lower ribs, and vertebral column. The muscle fibers merge at the midline, surround the rectus abdominus, and join on the other side at a point known as the linea alba. The abdominal muscle fibers criss-cross each other for added strength, with the transverse abdominal muscle extending horizontally forward, and the internal and external obliques running upward and downward, respectively towards the front (shown below).

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Rectus Abdominis

The muscles comprising the rectus abdominis are long and flat, with three tendinous intersections crossing over the muscle. As described above, the three muscles forming the lateral abdominal wall enclose the rectus abdominis in a sheath. The rectus abdominal muscles begin at the pubis bone, line the sides of the linea alba and attach to the lower ribs. The inguinal canal passes through the lower layers of the rectus abdominis muscles in the groin accommodate the attachment of the uterus in females and the dissention of the testes from the abdominal wall in males.

Transverse Abdominal Muscle

The transverse abdominal muscle is a flat, triangular muscle composed of horizontal fibers that is situated between the internal oblique and transverse fascia. The transverse abdominal muscle attaches at the inner lip of the ilium, the lumbar fascia, and the inner surface of cartilage on the six lower ribs. The transverse abdominal muscle passes behind the rectus abdominis to meet the linea alba.

Pyramidalis Muscle

The pyramidalis muscle is a small, triangular-shaped muscle situated in front of the rectus abdominis in the lower portion of the abdomen. The pyramidalis muscle stretches from the pubic bone to the linea alba, joining before the umbilicus. The pyramidalis muscle functions to contract the linea alba (shown below).

Quiz

1. Which of the following statements is NOT true regarding the pancreas?
A. The pancreas is situated behind the stomach.
B. The pancreas secretes insulin.
C. The pancreas is an endocrine gland.
D. The pancreas is a secondary lymphoid organ.

Answer to Question #1

D is correct. The pancreas is an endocrine gland situated behind the stomach and is responsible for the secretion of insulin, digestive enzymes, and other factors that aid in digestion. The spleen and lymph nodes are secondary lymphoid organs.

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2. A primary function of the spleen is:
A. Regulation of blood pressure.
B. The production of digestive enzymes.
C. Secondary lymphoid organ.
D. All of the above are primary functions of the spleen.

Answer to Question #2

C is correct. The spleen functions to remove red blood cells from circulation, serve as a secondary lymphoid organ, and acts as a reservoir of red blood cells. The kidneys regulate blood pressure and digestive enzymes are produced primarily by the pancreas, stomach, and liver.

3. The major muscles providing spinal support required for posture in humans are:
A. Rectus abdominus
B. Transverse abdominus
C. Linea alba
D. Pyramidalis

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Answer to Question #3

B is correct. The transverse abdominus muscle and internal obliques affect posture by providing spinal support during rotation and lateral flexion, and stabilize the spine when standing. The rectus abdominus functions to bend the spine forward. The linea alba is the fibrous structure that forms the midline of the abdomen and provides a site of muscle attachment for the abdominal muscles. The pyramidalis muscle is a small triangular-spaced muscle located in the lower abdomen and functions to contract the linea alba.

4. Which of the following abdominal organs is NOT required for digestion?
A. Liver
B. Gallbladder
C. Spleen
D. Pancreas

Answer to Question #4

C is correct. The spleen functions to remove old and senescent red blood cells from circulation and acts as a secondary lymphoid organ, but does not aid in digestion. The liver aids digestion via the production of bile and digestive enzymes. The pancreas secretes insulin, and digestive enzymes, and the gallbladder stores the bile produced by the liver until it is required during the digestion of food products.

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References

  • Bilal M, Voin V, Topale N, Iwanaga J, Loukas M, and Tubbs RS. (2017). The Clinical anatomy of the physical examination of the abdomen: A comprehensive review. Clin Anat. 30(3):352-356.
  • Stensby JD, Baker JC, and Fox MG. (2016). Athletic injuries of the lateral abdominal wall: review of anatomy and MR imaging appearance. Skeletal Radiol. 45(2):155-62.

FAQs

What is abdomen and its function? ›

The abdomen ultimately serves as a cavity to house vital organs of the digestive, urinary, endocrine, exocrine, circulatory, and parts of the reproductive system. The anterior wall of the abdomen has nine layers.

What does abdomen mean in anatomy? ›

(ab-DAH-mih-nul) Having to do with the abdomen, which is the part of the body between the chest and the hips that contains the pancreas, stomach, intestines, liver, gallbladder, and other organs.

What are the 2 muscles of the abdomen? ›

Structure and Function
  • 2 vertical muscles located on the midline (bisected by linea alba): Rectus abdominis; and pyramidalis.
  • 3 flat muscles on the anterolateral side arranged from superficial to deep; external abdominal oblique, internal abdominal oblique, transversus abdominis.

What is function abdominal pain? ›

Functional abdominal pain, also known as intractable abdominal pain, is persistent stomach pain that does not resolve with usual therapeutic treatment. The pain may be constant or may come and go. Approximately 10 to 15 percent of school-age children have functional abdominal pain at some point.

Which term means abdomen? ›

The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. The area occupied by the abdomen is called the abdominal cavity.

What is the abdomen muscle called? ›

Rectus abdominis: This pair of muscles goes down the middle of your abdomen from your ribs to the front of your pelvis. The muscles hold your internal organs in place and keep your body stable during movement.

What are the muscles of the abdomen? ›

The abdominal muscles consist of three flat muscles (two obliques and the transversus) and two vertical muscles (the rectus abdominis and pyramidalis). Together, they form the abdominal wall between the bony ribs and the pelvis. They provide structure and strength to the front and sides of your abdomen.

What are the 7 core muscles? ›

The major muscles of your core include your transverse abdominis, multifidus, internal and external obliques, erector spinae, diaphragm, pelvic floor muscles, and (of course) your abs, the rectus abdominis.

Where is the abdomen in the body? ›

The abdomen is the largest space (cavity) in the body. It lies between the chest and the pelvis, holding many of the body's organs. These include the liver, stomach, and intestines.

What is abdomen in a sentence? ›

Word forms: abdomens

Your abdomen is the part of your body below your chest where your stomach and intestines are. He went into the hospital to undergo tests for a pain in his abdomen.

Why is it called abdomen? ›

Borrowed from Middle French abdomen, from Latin abdomen, possibly from abdō (“conceal”), from ab (“away”) + *dĕre (“to put, place”).

What are the three main abdominal muscles? ›

abdominal muscle, any of the muscles of the anterolateral walls of the abdominal cavity, composed of three flat muscular sheets, from without inward: external oblique, internal oblique, and transverse abdominis, supplemented in front on each side of the midline by rectus abdominis.

How many abdominal muscles? ›

But in actuality there are 4 separate muscles that contribute to your overall abdominal development. The 4 distinct muscles that make up your abs. Each of these 4 muscles has a different, yet important, role to play – so you want to make sure that your workouts train all of them effectively.

What are the 5 layers of abdomen? ›

Classically the anterolateral abdominal wall has been described as separate layers from superficial to deep as follows:
  • Skin.
  • Subcutaneous tissues (further divided into the more superficial Camper's fascia and the deeper Scarpa's fascia)
  • External oblique muscle.
  • Internal oblique muscle.
  • Transversus abdominis muscle.
Jul 25, 2022

How is functional abdominal pain treated? ›

The main objective of treatment for functional abdominal pain is to restore normal daily function. Medical intervention is combined with cognitive behavioral therapy (CBT) to help manage symptoms. Dietary changes can also help. Fortunately, functional abdominal pain causes no serious long-term health problems.

What is functional abdominal pain in adults? ›

Definition. FAPS represents a pain syndrome attributed to the abdomen that is poorly related to gut function, is associated with some loss of daily activities, and has been present for at least 6 months. The pain is constant, nearly constant, or at least frequently recurring.

How do I get rid of functional abdominal pain? ›

How Is Functional Abdominal Pain Treated?
  1. diet changes such as avoiding foods that cause gas (like broccoli and cauliflower), fried foods, carbonated drinks (like soda), and spicy foods.
  2. medicines that help with cramping or lower the amount of acid in the stomach.
  3. pain medicine.
  4. counseling or relaxation techniques.

What is abdominal pain called? ›

Other terms used to describe abdominal pain are stomachache, tummy ache, gut ache and bellyache.

What causes abdominal pain? ›

Less serious causes of abdominal pain include constipation, irritable bowel syndrome, food allergies, lactose intolerance, food poisoning, and a stomach virus. Other, more serious, causes include appendicitis, an abdominal aortic aneurysm, a bowel blockage, cancer, and gastroesophageal reflux.

What word is short for abdominal muscle? ›

The rectus abdominis muscle, (Latin: straight abdominal) also known as the "abdominal muscle" or simply the "abs", is a paired straight muscle.

What is a function of the abdominal muscles quizlet? ›

It's the "bearing down" movement used for bowel movements, urination, childbirth, coughing, vomiting, etc.

What causes weak abdominal muscles? ›

Muscle weakness or decreased control of these muscles can be a result of surgery, injury or inactivity. Common signs of weakness or decreased control of your core muscles can lead to dysfunction in your movement and, ultimately, affect your quality of life.

What is the most important core muscle? ›

The deepest layer of abdominal muscles, and arguably the most important, is your transverse abdominis (sometimes called the "corset" or "Spanx" of the core), which stabilizes your spine and pelvis.

What is the function of the abdominal muscles? ›

They keep the body straight, therefore, we correct the posture. Not only in our daily life, but also when we exercise. This will help us prevent back pain and possible injuries. They help us to compensate the body: the lower back pain we mentioned before, in most cases due to the lack of abdominal muscle tone.

What is difference between abdomen and stomach? ›

Abdomen and Stomach are two major body parts for animals. The stomach is a part of the abdomen and together they help to absorb and digest the food taken. Apart from the stomach, the abdomen also contains other organs such as small intestine, colon and Liver.

Is abdomen and stomach the same? ›

The area of the body that contains the pancreas, stomach, intestines, liver, gallbladder, and other organs.

How many abdomen are there? ›

There are nine regions of the abdomen that house various organs. These regions are broken into three areas: the upper, middle, and lower abdomen. In the upper abdomen, the right hypochondriac, epigastric, and left hypochondriac regions reside.

What is the meaning of lower abdomen? ›

/ˈæb.də.mən/ the lower part of a person's or animal's body, containing the stomach, bowels, and other organs, or the end of an insect's body. The human torso. -bellied.

What is the function of stomach in one sentence? ›

Your stomach's purpose is to digest food and send it to your small intestine. It has three functions: Temporarily store food. Contract and relax to mix and break down food.

Why is the abdomen divided? ›

The human abdomen is divided into quadrants and regions by anatomists and physicians for the purposes of study, diagnosis, and treatment. The division into four quadrants allows the localisation of pain and tenderness, scars, lumps, and other items of interest, narrowing in on which organs and tissues may be involved.

What is the most important organ in the abdomen? ›

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.

Where exactly is your abdomen? ›

The abdomen is the largest space (cavity) in the body. It lies between the chest and the pelvis, holding many of the body's organs. These include the liver, stomach, and intestines.

What causes abdomen pain? ›

Less serious causes of abdominal pain include constipation, irritable bowel syndrome, food allergies, lactose intolerance, food poisoning, and a stomach virus. Other, more serious, causes include appendicitis, an abdominal aortic aneurysm, a bowel blockage, cancer, and gastroesophageal reflux.

What are the three functions of abdomen? ›

Abdomen Function

The primary functions of the abdomen consist of digestion, breathing, posture and balance, as well as movement. The major organs located in the abdomen are associated with digestion, for which the functions are described above.

What is the 2nd most important organ? ›

While your heart is a vital organ, the brain (and the nervous system that attaches to the brain) make up the most critical organ system in the human body. The human nervous system is responsible for coordinating every movement and action your body makes.

Does the abdomen have bones? ›

The main bones in the abdominal region are the ribs. The rib cage protects vital internal organs. There are 12 pairs of ribs and they attach to the spine. There are seven upper ribs, known as “true” ribs, which attach to the sternum (breastbone) in the front of body.

Where does the abdomen start and end? ›

The abdomen (commonly called the belly) is the body space between the thorax (chest) and pelvis. The diaphragm forms the upper surface of the abdomen. At the level of the pelvic bones, the abdomen ends and the pelvis begins.

What is the lower abdomen called? ›

The hypogastric, or below the stomach, region.

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