The abdomen (colloquially called the gut, belly, tummy, midriff, tucky, or stomach[ Abdomen. Dictionary.com. The American Heritage Dictionary of the English Language, 4th Edition. Retrieved 22 October 2007]
In humans, the abdomen stretches from the thorax at the thoracic diaphragm to the pelvis at the pelvic brim. The pelvic brim stretches from the lumbosacral joint (the intervertebral disc between Lumbar vertebrae and S1) to the pubic symphysis and is the edge of the pelvic inlet. The space above this inlet and under the thoracic diaphragm is termed the abdominal cavity. The boundary of the abdominal cavity is the abdominal wall in the front and the peritoneal surface at the rear.
In vertebrates, the abdomen is a large body cavity enclosed by the abdominal muscles, at the front and to the sides, and by part of the vertebral column at the back. Lower ribs can also enclose ventral and lateral walls. The abdominal cavity is continuous with, and above, the pelvic cavity. It is attached to the thoracic cavity by the diaphragm. Structures such as the aorta, inferior vena cava and esophagus pass through the diaphragm. Both the abdominal and pelvic cavities are lined by a serous membrane known as the parietal peritoneum. This membrane is continuous with the visceral peritoneum lining the organs.[ Peritoneum. The Veterinary Dictionary. Elsevier, 2007. Retrieved 22 October 2007] The abdomen in vertebrates contains a number of organs belonging to, for instance, the digestive system, urinary system, and muscular system.
Contents
The
abdominal cavity contains most organs of the
digestive system, including the
stomach, the
small intestine, and the colon with its attached appendix. Other digestive organs are known as the accessory digestive organs and include the
liver, its attached
gallbladder, and the
pancreas, and these communicate with the rest of the system via various ducts. The
spleen, and organs of the
urinary system including the
, and
also lie within the abdomen, along with many blood vessels including the
aorta and
venae cavae. The
urinary bladder,
uterus,
, and
ovary may be seen as either abdominal organs or as pelvic organs. Finally, the abdomen contains an extensive membrane called the
peritoneum. A fold of peritoneum may completely cover certain organs, whereas it may cover only one side of organs that usually lie closer to the abdominal wall. This is called the
retroperitoneum, and the kidneys and ureters are known as
retroperitoneal organs.
Muscles
There are three layers of muscles in the
abdominal wall. They are, from the outside to the inside:
external oblique,
internal oblique, and transverse abdominal.
The first three layers extend between the
vertebral column, the lower ribs, the
iliac crest and pubis of the
hip. All of their fibers merge towards the midline and surround the
rectus abdominis in a sheath before joining up on the opposite side at the linea alba. Strength is gained by the criss-crossing of fibers, such that the
external oblique runs downward and forward, the
internal oblique upward and forward, and the transverse abdominal horizontally forward.
The transverse abdominal muscle is flat and triangular, with its fibers running horizontally. It lies between the internal oblique and the underlying transverse fascia. It originates from the inguinal ligament, costal cartilages 7–12, the iliac crest and thoracolumbar fascia. Inserts into the conjoint tendon, xiphoid process, linea alba and the pubic crest.
The rectus abdominis muscles are long and flat. The muscle is crossed by three fibrous bands called the tendinous intersections. The rectus abdominis is enclosed in a thick sheath, formed as described above, by fibers from each of the three muscles of the lateral abdominal wall. They originate at the pubis bone, run up the abdomen on either side of the linea alba, and insert into the cartilages of the fifth, sixth, and seventh ribs. In the region of the groin, the inguinal canal, is a passage through the layers. This gap is where the testes can drop through the wall and where the fibrous cord from the uterus in the female runs. This is also where weakness can form, and cause .
The pyramidalis muscle is small and triangular. It is located in the lower abdomen in front of the rectus abdominis. It originates at the pubic bone and is inserted into the linea alba halfway up to the navel.
Function
Functionally, the human abdomen is where most of the digestive tract is placed and so most of the absorption and digestion of food occurs here. The alimentary tract in the abdomen consists of the lower
esophagus, the
stomach, the
duodenum, the
jejunum,
ileum, the
cecum and the appendix, the
ascending colon,
transverse colon and
, the
sigmoid colon and the
rectum. Other vital organs inside the abdomen include the
liver, the
kidneys, the
pancreas and the
spleen.
The abdominal wall is split into the posterior (back), lateral (sides), and anterior (front) walls.
Movement, breathing and other functions
The abdominal muscles have different important functions. They assist as muscles of exhalation in the breathing process during
Exhalation. Moreover, these muscles serve as protection for the inner organs. Furthermore, together with the back muscles they provide postural support and are important in defining the form. When the
glottis is closed and the
thorax and
pelvis are fixed, they are integral in the
cough,
urination,
defecation,
childbirth,
vomit, and singing functions.
When the pelvis is fixed, they can initiate the movement of the trunk in a forward motion. They also prevent
hyperextension. When the thorax is fixed, they can pull up the pelvis and finally, they can bend the vertebral column sideways and assist in the trunk's rotation.
Posture
The transverse abdominis muscle is the deepest muscle; therefore, it cannot be touched from the outside. It can greatly affect the body's posture. The internal obliques are also deep and also affect body posture. Both of them are involved in rotation and lateral flexion of the
Vertebral column and are used to bend and support the spine from the front. The external obliques are more superficial and are also involved in rotation and lateral flexion of the spine. They also stabilize the spine when upright. The rectus abdominis muscle is not the most superficial abdominal muscle. The tendonous sheath extending from the external obliques cover the rectus abdominis. The rectus abdominis is the muscle that very fit people develop into "six-pack" abs, though there are five vertical sections on each side. The two bottom sections are just above the pubic bone and usually not visible. The rectus abdominals' function is to bend one's back forward (flexion). The main work of the abdominal muscles is to bend the spine forward when contracting concentrically.
Society and culture
Social and cultural perceptions of the outward appearance of the abdomen has varying significance around the world. Depending on the type of society,
obesity can be perceived as an indicator of wealth and prestige due to excess food, or as a sign of poor health due to lack of exercise. In many cultures, bare abdomens are distinctly sexualized and perceived similarly to breast cleavage.
Exercise
Being key elements of spinal support, and contributors to good posture, it is important to properly exercise the abdominal muscles together with the back muscles because when these are weak or overly tight they can suffer painful spasms and
injuries. When properly exercised, abdominal muscles contribute to improved posture and balance, reduce the likelihood of
back pain episodes, reduce the severity of back pain,
protect against injury,
help avoid some back surgeries, and help with the healing of back problems, or after spine surgery. When strengthened, the abdominal muscles provide flexibility as well. The abdominal muscles can be worked by strength and fitness exercises, and through practicing disciplines of general body strength such as
Pilates,
yoga,
, and
jogging.
Clinical significance
Abdominal obesity is a condition where
abdominal fat or visceral fat, has built up excessively between the abdominal organs. This is associated with a higher risk of
heart disease,
asthma and type 2 diabetes.
Abdominal trauma is an injury to the abdomen and can involve damage to the abdominal organs. There is an associated risk of Exsanguination and infection.
A scaphoid abdomen is when the abdomen is sucked inwards.
Disease
Many gastrointestinal diseases affect the abdominal organs. These include
stomach disease,
liver disease, pancreatic disease,
gallbladder and
bile duct disease; intestinal diseases include
enteritis,
coeliac disease,
diverticulitis, and irritable bowel syndrome.
Examination
Different medical procedures can be used to examine the organs of the gastrointestinal tract. These include
endoscopy,
colonoscopy,
sigmoidoscopy,
enteroscopy, oesophagogastroduodenoscopy and virtual colonoscopy. There are also a number of
medical imaging techniques that can be used. Surface landmarks are important in the examination of the abdomen.
Surface landmarks
In the mid-line, a slight furrow extends from the
xiphoid process above to the
pubic symphysis below, representing the linea alba in the abdominal wall. At about its midpoint sits the umbilicus or
navel. The
rectus abdominis on each side of the linea alba stands out in muscular people. The outline of these muscles is interrupted by three or more transverse depressions indicating the tendinous intersections. There is usually one about the xiphoid process, one at the navel, and one in between. It is the combination of the linea alba and the tendinous intersections which form the abdominal "six-pack" sought after by many people.
The upper lateral limit of the abdomen is the subcostal margin (at or near the subcostal plane) formed by the cartilages of the (8, 9, 10) joining one another. The lower lateral limit is the anterior crest of the ilium and Poupart's ligament, which runs from the anterior superior spine of the ilium to the spine of the pubis. These lower limits are marked by visible grooves. Just above the pubic spines on either side are the external abdominal rings, which are openings in the muscular wall of the abdomen through which the spermatic cord emerges in the male, and through which an inguinal hernia may rupture.
One method by which the location of the abdominal contents can be appreciated is to draw three horizontal and two vertical lines.
Horizontal lines
-
The highest of the former is the transpyloric line of C. Addison, which is situated halfway between the suprasternal notch and the top of the pubic symphysis, and often cuts the pyloric opening of the stomach an inch to the right of the mid-line. The hilum of each kidney is a little below it, while its left end approximately touches the lower limit of the spleen. It corresponds to the first lumbar vertebra behind.
-
The second line is the subcostal line, drawn from the lowest point of the subcostal arch (tenth rib). It corresponds to the upper part of the third lumbar vertebra, and it is an inch or so above the umbilicus. It indicates roughly the transverse colon, the lower ends of the kidneys, and the upper limit of the transverse (3rd) part of the duodenum.
-
The third line is called the intertubercular line, and runs across between the two rough tubercles, which can be felt on the outer lip of the crest of the ilium about from the anterior superior spine. This line corresponds to the body of the fifth lumbar vertebra, and passes through or just above the ileo-caecal valve, where the small intestine joins the large intestine.
Vertical lines
The two vertical or mid-Poupart lines are drawn from the point midway between the anterior superior spine and the pubic symphysis on each side, vertically upward to the costal margin.
-
The right one is the most valuable, as the ileo-caecal valve is situated where it cuts the intertubercular line. The orifice of the appendix lies an inch lower, at McBurney's point. In its upper part, the vertical line meets the transpyloric line at the lower margin of the ribs, usually the ninth, and here the gallbladder is situated.
-
The left mid-Poupart line corresponds in its upper three-quarters to the inner edge of the descending colon.
The right subcostal margin corresponds to the lower limit of the liver, while the right nipple is about half an inch above its upper limit.
Quadrants and regions
The abdomen can be divided into quadrants or regions to describe the location of an organ or structure. Classically, quadrants are described as the left upper, left lower, right upper, and right lower. Quadrants are also often used in describing the site of an abdominal pain.
The abdomen can also be divided into nine regions.
|
| left hypochondriac/hypochondrium |
| left lumbar/flank/latus/lateral |
| left inguinal/iliac |
These terms stem from "hypo" meaning "below" and "epi" means "above", while "chondron" means "cartilage" (in this case, the cartilage of the rib) and "gaster" means stomach. The reversal of "left" and "right" is intentional, because the anatomical designations reflect the patient's own right and left.)
The "right iliac fossa" (RIF) is a common site of pain and tenderness in patients who have appendicitis. The fossa is named for the underlying iliac fossa of the hip bone, and thus is somewhat imprecise. Most of the anatomical structures that will produce pain and tenderness in this region are not in fact in the concavity of the ileum. However, the term is in common usage.
Across animal phyla and classes
Chordata
Mammals
Abdominal organs can be highly specialized in some mammals. For example, the stomach of
, (a
suborder of mammals that includes
cattle and
sheep), is divided into four chambers –
rumen, reticulum,
omasum and
abomasum.
[" Ruminant." The Veterinary Dictionary. Elsevier, 2007. Retrieved 22 October 2007]
Arthropoda
In
, the abdomen is built up of a series of upper plates known as
and lower plates known as
, the whole being held together by a tough yet stretchable membrane.
Insects
In
, the abdomen contains the insect's digestive tract and reproductive organs. It consists of eleven segments in most orders of insects, though the eleventh segment is absent in the adult of most higher orders. The number of these segments does vary from species to species with the number of segments visible reduced to only seven in the common
honey bee. In the
Collembola (springtails), the abdomen has only six segments.
The abdomen is sometimes highly modified. In Apocrita (bees, ants and wasps), the first segment of the abdomen is fused to the thorax and is called the propodeum. In , the second segment forms the narrow petiole. Some ants have an additional postpetiole segment, and the remaining segments form the bulbous gaster.
Unlike other arthropods, insects possess no legs on the abdomen in adult form, though the Protura do have rudimentary leg-like appendages on the first three abdominal segments, and Archaeognatha possess small, articulated "styli" which are sometimes considered to be rudimentary appendages. Many larval insects including the Lepidoptera and the Symphyta (sawflies) have fleshy appendages called on their abdominal segments (as well as their more familiar thoracic legs), which allow them to grip onto the edges of plant leaves as they walk around.
Arachnida
In
arachnids (spiders, scorpions and relatives), the term "abdomen" is used interchangeably with "
opisthosoma" ("hind body"), which is the body section posterior to that bearing the legs and head (the prosoma or
cephalothorax).
See also
External links
