Abdomen
Encyclopedia
In vertebrate
s such as mammal
s the abdomen (belly) constitutes the part of the body between the thorax
(chest) and pelvis
. The region enclosed by the abdomen is termed the abdominal cavity
. In arthropod
s it is the most distal section of the body which lies behind the thorax or cephalothorax
.
The human abdomen (also called the belly) is the part of the body between the pelvis
and the thorax
. Anatomically, the abdomen stretches from the thorax at the thoracic diaphragm
to the pelvis at the pelvic brim
. The pelvic brim stretches from the lumbosacral angle (the intervertebral disk between L5 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.
, the stomach
, the duodenum
, the jejunum
, ileum
, the cecum
and the appendix
, the ascending
, transverse
and descending colon
s, 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 anterioriet (front) walls.
The transversus abdominis muscle is flat and triangular, with its fibers running horizontally. It lies between the inner oblique and the underlying transversalis fascia. It originates from Poupart's ligament, the inner lip of the ilium, the lumbar fascia and the inner surface of the cartilage
s of the six lower ribs. It inserts into the linea alba behind the rectus abdominis.
The rectus abdominis muscle
s are long and flat. The muscle is crossed by three tendinous
intersections called the linae transversae. 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.
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 half way up to the umbilicus
.
and assist in the breathing process. 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.
The transverse abdominus muscle is the deepest muscle, therefore, it cannot be touched from the outside. It can greatly affect the body posture. The internal obliques are also deep and also affect body posture. Both of them are involved in rotation and lateral flexion of the spine
and are used to bend and support the spine from the front. The external obliques are more superficial and they are also involved in rotation and lateral flexion of the spine. Also they stabilize the spine when upright. The rectus abdominus muscle is not the most superficial abdominal muscle. The tendonous sheath extending from the external obliques cover the rectus abdominus. The Rectus abdominus is the muscle that very fit people develop into the 6-pack ab look. Although, it should really be an 8 pack as there are 4 vertical sections on each side. The 2 bottom sections are just above the pubic bone and usually not visible, hence, the 6 pack abs. 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 coencentrically.
episodes, reduce the severity of back pain, protect against injury by responding efficiently to stresses, help avoid some back surgeries, and help healing from a back problem or after spine surgery. Also, when strengthened, the abdominal muscles provide flexibility as well.
The abdominal muscles can be worked out by practicing disciplines of general body strength such as Pilates
, yoga
, T'ai chi, and jogging
among others. There are also specific routines to target each of these muscles.
The abdomen contains most of the tubelike organs of the digestive tract, as well as several solid organs. Hollow abdominal organs include the stomach
, the small intestine
, and the colon
with its attached appendix
. Organs such as the liver
, its attached gallbladder
, and the pancreas
function in close association with the digestive tract and communicate with it via ducts. The spleen
, kidney
s, and adrenal gland
s also lie within the abdomen, along with many blood vessels including the aorta
and inferior vena cava
. Anatomists may consider the urinary bladder
, uterus
, fallopian tube
s, and ovaries
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. Anatomists call the latter type of organs retroperitoneal.
above to the pubic symphysis
below, representing the linea alba in the abdominal wall. At about its midpoint sits the umbilicus or navel. On each side of it the broad recti muscles stand out in muscular people. The outline of these muscles is interrupted by three or more transverse depressions indicating the lineae transversae. There is usually one about the ensiform cartilage, one at the umbilicus, and one between. It is the combination of the linea alba and the linea transversae which form the abdominal "six-pack" sought after by many people.
The upper lateral limit of the abdomen is the subcostal margin formed by the cartilages of the false ribs (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.
The right subcostal margin corresponds to the lower limit of the liver
, while the right nipple is about half an inch above the upper limit of this viscus
.
These three horizontal and two vertical lines divide the abdomen into nine "regions." (Note that "hypo" means "below" and "epi" means "above", while "chond" means "cartilage" (in this case, the cartilage of the rib) and "gast" means stomach. The reversal of "left" and "right" is intentional, because the anatomical designations reflect the position on the patient. )
.
, and by the vertebral column
dorsally. Lower ribs can also enclose ventral and lateral walls. The abdominal cavity is continuous with the pelvic cavity. It is separated from 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. The abdomen in vertebrates contains a number of organs
belonging, for instance, to the digestive tract and urinary system
.
Abdominal organs can be highly specialized in some animals. For example the stomach of ruminant
s (a suborder of mammals) is divided into four chambers - rumen
, reticulum
, omasum
and abomasum
.
The invertebrate abdomen is built up of a series of upper plates known as tergites and lower plates known as sternites, the whole being held together by a tough yet stretchable membrane.
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 honeybee. 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 ant
s the second segment forms the narrow petiole
. Some ants have an additional postpetiole segment, and the remaining segments form the bulbous gaster
. The petiole and gaster (abdominal segments 2 and onward) are collectively called the metasoma
.
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 proleg
s 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.
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s such as mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s the abdomen (belly) constitutes the part of the body between the thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
(chest) and pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
. The region enclosed by the abdomen is termed the abdominal cavity
Abdominal cavity
The abdominal cavity is the body cavity of the human body that holds the bulk of the viscera. It is located below the thoracic cavity, and above the pelvic cavity. Its dome-shaped roof is the thoracic diaphragm , and its oblique floor is the pelvic inlet...
. In arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s it is the most distal section of the body which lies behind the thorax or cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...
.
The human abdomen (also called the belly) is the part of the body between the pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
and the thorax
Chest
The chest is a part of the anatomy of humans and various other animals. It is sometimes referred to as the thorax or the bosom.-Chest anatomy - Humans and other hominids:...
. Anatomically, the abdomen stretches from the thorax at the thoracic diaphragm
Thoracic diaphragm
In the anatomy of mammals, the thoracic diaphragm, or simply the diaphragm , is a sheet of internal skeletal muscle that extends across the bottom of the rib cage. The diaphragm separates the thoracic cavity from the abdominal cavity and performs an important function in respiration...
to the pelvis at the pelvic brim
Pelvic brim
The pelvic brim is the edge of the pelvic inlet. It is an approximately apple-shaped line passing through the prominence of the sacrum, the arcuate and pectineal lines, and the upper margin of the pubic symphysis....
. The pelvic brim stretches from the lumbosacral angle (the intervertebral disk between L5 and S1) to the pubic symphysis
Pubic symphysis
The pubic symphysis or symphysis pubis is the midline cartilaginous joint uniting the superior rami of the left and right pubic bones. It is located anterior to the urinary bladder and superior to the external genitalia; for females it is above the vulva and for males it is above the penis...
and is the edge of the pelvic inlet
Pelvic inlet
The pelvic inlet or superior aperture of the pelvis is a planar surface which is typically used to define the boundary between the pelvic cavity and the abdominal cavity .Its position and orientation relative to the skeleton of the pelvis is anatomically defined by its...
. The space above this inlet and under the thoracic diaphragm is termed the abdominal cavity
Abdominal cavity
The abdominal cavity is the body cavity of the human body that holds the bulk of the viscera. It is located below the thoracic cavity, and above the pelvic cavity. Its dome-shaped roof is the thoracic diaphragm , and its oblique floor is the pelvic inlet...
. The boundary of the abdominal cavity is the abdominal wall in the front and the peritoneal surface at the rear.
Human abdomen
Functionally, the human abdomen is where most of the alimentary 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 esophagusEsophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
, the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
, the duodenum
Duodenum
The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum...
, the jejunum
Jejunum
The jejunum is the middle section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms middle intestine or mid-gut may be used instead of jejunum.The jejunum lies between the duodenum...
, ileum
Ileum
The ileum is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may be used instead of ileum.The ileum follows the duodenum...
, the cecum
Cecum
The cecum or caecum is a pouch, connecting the ileum with the ascending colon of the large intestine. It is separated from the ileum by the ileocecal valve or Bauhin's valve, and is considered to be the beginning of the large intestine. It is also separated from the colon by the cecocolic...
and the appendix
Vermiform appendix
The appendix is a blind-ended tube connected to the cecum , from which it develops embryologically. The cecum is a pouchlike structure of the colon...
, the ascending
Ascending colon
The ascending colon is smaller in caliber than the cecum.It passes upward, from its commencement at the cecum, opposite the colic valve, to the under surface of the right lobe of the liver, on the right of the gall-bladder, where it is lodged in a shallow depression, the colic impression; here it...
, transverse
Transverse colon
The transverse colon, the longest and most movable part of the colon, passes with a downward convexity from the right hypochondrium region across the abdomen, opposite the confines of the epigastric and umbilical zones, into the left hypochondrium region, where it curves sharply on itself beneath...
and descending colon
Descending colon
The descending colon of humans passes downward through the left hypochondrium and lumbar regions, along the lateral border of the left kidney....
s, the sigmoid colon
Sigmoid colon
The sigmoid colon is the part of the large intestine that is closest to the rectum and anus. It forms a loop that averages about 40 cm...
and the rectum
Rectum
The rectum is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. The human rectum is about 12 cm long...
. Other vital organs inside the abdomen include the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
, the kidneys, the pancreas
Pancreas
The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...
and the spleen
Spleen
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...
.
The abdominal wall is split into the posterior (back), lateral (sides), and anterioriet (front) walls.
Muscles
The transversus abdominis muscle is flat and triangular, with its fibers running horizontally. It lies between the inner oblique and the underlying transversalis fascia. It originates from Poupart's ligament, the inner lip of the ilium, the lumbar fascia and the inner surface of the cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
s of the six lower ribs. It inserts into the linea alba behind the rectus abdominis.
The rectus abdominis muscle
Rectus abdominis muscle
The rectus abdominis muscle, also known as the "six pack", is a paired muscle running vertically on each side of the anterior wall of the human abdomen . There are two parallel muscles, separated by a midline band of connective tissue called the linea alba...
s are long and flat. The muscle is crossed by three tendinous
Tendon
A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...
intersections called the linae transversae. 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.
The pyramidalis muscle
Pyramidalis muscle
The pyramidalis is a small and triangular muscle, anterior to the Rectus abdominis, and contained in the rectus sheath.-Attachments and actions:...
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 half way up to the umbilicus
Navel
The navel is a scar on the abdomen caused when the umbilical cord is removed from a newborn baby...
.
Functions
The abdominal muscles have different important functions. They provide movement and support to the trunkTorso
Trunk or torso is an anatomical term for the central part of the many animal bodies from which extend the neck and limbs. The trunk includes the thorax and abdomen.-Major organs:...
and assist in the breathing process. 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.
The transverse abdominus muscle is the deepest muscle, therefore, it cannot be touched from the outside. It can greatly affect the body posture. The internal obliques are also deep and also affect body posture. Both of them are involved in rotation and lateral flexion of the spine
Vertebral column
In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...
and are used to bend and support the spine from the front. The external obliques are more superficial and they are also involved in rotation and lateral flexion of the spine. Also they stabilize the spine when upright. The rectus abdominus muscle is not the most superficial abdominal muscle. The tendonous sheath extending from the external obliques cover the rectus abdominus. The Rectus abdominus is the muscle that very fit people develop into the 6-pack ab look. Although, it should really be an 8 pack as there are 4 vertical sections on each side. The 2 bottom sections are just above the pubic bone and usually not visible, hence, the 6 pack abs. 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 coencentrically.
Exercise
Being a key element to support the spine and contribute to a good posture, it is important to properly exercise the abdominal muscles together with the back muscles as when weak or overly tight they can suffer painful spasms as well as injuries. When properly exercised, these muscles contribute to improve posture and balance, reduce the likelihood of back painBack pain
Back pain is pain felt in the back that usually originates from the muscles, nerves, bones, joints or other structures in the spine.The pain can often be divided into neck pain, upper back pain, lower back pain or tailbone pain...
episodes, reduce the severity of back pain, protect against injury by responding efficiently to stresses, help avoid some back surgeries, and help healing from a back problem or after spine surgery. Also, when strengthened, the abdominal muscles provide flexibility as well.
The abdominal muscles can be worked out by practicing disciplines of general body strength such as Pilates
Pilates
Pilates is a physical fitness system developed in the early 20th century by Joseph Pilates in Germany, the UK and the USA. As of 2005, there were 11 million people practicing the discipline regularly and 14,000 instructors in the United States....
, yoga
Yoga
Yoga is a physical, mental, and spiritual discipline, originating in ancient India. The goal of yoga, or of the person practicing yoga, is the attainment of a state of perfect spiritual insight and tranquility while meditating on Supersoul...
, T'ai chi, and jogging
Jogging
Jogging is a form of trotting or running at a slow or leisurely pace. The main intention is to increase fitness with less stress on the body than from faster running.-Definition:...
among others. There are also specific routines to target each of these muscles.
Organs
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
, the small intestine
Small intestine
The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
, and the colon
Colon (anatomy)
The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...
with its attached appendix
Vermiform appendix
The appendix is a blind-ended tube connected to the cecum , from which it develops embryologically. The cecum is a pouchlike structure of the colon...
. Organs such as the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
, its attached gallbladder
Gallbladder
In vertebrates the gallbladder is a small organ that aids mainly in fat digestion and concentrates bile produced by the liver. In humans the loss of the gallbladder is usually easily tolerated....
, and the pancreas
Pancreas
The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...
function in close association with the digestive tract and communicate with it via ducts. The spleen
Spleen
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...
, kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
s, and adrenal gland
Adrenal gland
In mammals, the adrenal glands are endocrine glands that sit atop the kidneys; in humans, the right suprarenal gland is triangular shaped, while the left suprarenal gland is semilunar shaped...
s also lie within the abdomen, along with many blood vessels including the aorta
Aorta
The aorta is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it branches off into two smaller arteries...
and inferior vena cava
Venae cavae
The superior and inferior vena cava are collectively called the venae cavae. They are the veins that return deoxygenated blood from the body into the heart. They both empty into the right atrium....
. Anatomists may consider the urinary bladder
Urinary bladder
The urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. A hollow muscular, and distensible organ, the bladder sits on the pelvic floor...
, uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
, fallopian tube
Fallopian tube
The Fallopian tubes, also known as oviducts, uterine tubes, and salpinges are two very fine tubes lined with ciliated epithelia, leading from the ovaries of female mammals into the uterus, via the utero-tubal junction...
s, and ovaries
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
as either abdominal organs or as pelvic organs. Finally, the abdomen contains an extensive membrane called the peritoneum
Peritoneum
The peritoneum is the serous membrane that forms the lining of the abdominal cavity or the coelom — it covers most of the intra-abdominal organs — in amniotes and some invertebrates...
. 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. Anatomists call the latter type of organs retroperitoneal.
Surface landmarks
In the mid-line a slight furrow extends from the ensiform cartilage/xiphoid processXiphoid process
The xiphoid process, or xiphisternum or metasternum, is a small cartilaginous process of the lower part of the sternum which is usually ossified in the adult human. By age 15 to 29, the xiphoid usually fuses to the body of the sternum with a fibrous joint. Unlike the synovial articulation of major...
above to the pubic symphysis
Pubic symphysis
The pubic symphysis or symphysis pubis is the midline cartilaginous joint uniting the superior rami of the left and right pubic bones. It is located anterior to the urinary bladder and superior to the external genitalia; for females it is above the vulva and for males it is above the penis...
below, representing the linea alba in the abdominal wall. At about its midpoint sits the umbilicus or navel. On each side of it the broad recti muscles stand out in muscular people. The outline of these muscles is interrupted by three or more transverse depressions indicating the lineae transversae. There is usually one about the ensiform cartilage, one at the umbilicus, and one between. It is the combination of the linea alba and the linea transversae which form the abdominal "six-pack" sought after by many people.
The upper lateral limit of the abdomen is the subcostal margin formed by the cartilages of the false ribs (8, 9, 10) joining one another. The lower lateral limit is the anterior crest of the ilium
Ilium (bone)
The ilium is the uppermost and largest bone of the pelvis, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bone which is considered to be an ilium.The name comes from the Latin ,...
and Poupart's ligament, which runs from the anterior superior spine of the ilium to the spine of the pubis
Pubis (bone)
In vertebrates, the pubic bone is the ventral and anterior of the three principal bones composing either half of the pelvis.It is covered by a layer of fat, which is covered by the mons 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
Spermatic cord
The spermatic cord is the name given to the cord-like structure in males formed by the ductus deferens and surrounding tissue that run from the abdomen down to each testicle.-Contents of spermatic cord:...
emerges in the male, and through which an inguinal hernia
Inguinal hernia
An inguinal hernia is a protrusion of abdominal-cavity contents through the inguinal canal. They are very common , and their repair is one of the most frequently performed surgical operations....
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 half-way between the suprasternal notchSuprasternal notchThe suprasternal notch , also known as the jugular notch, is part of human anatomy. It is a large, visible dip.-Anatomical location:...
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 hilumHilum of kidneyThe renal hilum or renal pedicle of the kidney is the recessed central fissure. The medial border of the kidney is concave in the center and convex toward either extremity; it is directed forward and a little downward. Its central part presents a deep longitudinal fissure, bounded by prominent...
of each kidneyKidneyThe kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
is a little below it, while its left end approximately touches the lower limit of the spleenSpleenThe spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...
. 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 colonTransverse colonThe transverse colon, the longest and most movable part of the colon, passes with a downward convexity from the right hypochondrium region across the abdomen, opposite the confines of the epigastric and umbilical zones, into the left hypochondrium region, where it curves sharply on itself beneath...
, the lower ends of the kidneys, and the upper limit of the transverse (3rd) part of the duodenumDuodenumThe duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of 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 two and a half inches (60 mm) 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 intestineSmall intestineThe small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
joins the largeLarge intestineThe large intestine is the third-to-last part of the digestive system — — in vertebrate animals. Its function is to absorb water from the remaining indigestible food matter, and then to pass useless waste material from the body...
.
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 vermiform appendixVermiform appendixThe appendix is a blind-ended tube connected to the cecum , from which it develops embryologically. The cecum is a pouchlike structure of the colon...
lies an inch lower, at McBurney's pointMcBurney's pointMcBurney's point is the name given to the point over the right side of the abdomen that is one-third of the distance from the anterior superior iliac spine to the navel...
. In its upper part, the vertical line meets the transpyloric line at the lower margin of the ribs, usually the ninth, and here the gallbladderGallbladderIn vertebrates the gallbladder is a small organ that aids mainly in fat digestion and concentrates bile produced by the liver. In humans the loss of the gallbladder is usually easily tolerated....
is situated. - The left mid-Poupart line corresponds in its upper three-quarters to the inner edge of the descending colonDescending colonThe descending colon of humans passes downward through the left hypochondrium and lumbar regions, along the lateral border of the left kidney....
.
The right subcostal margin corresponds to the lower limit of the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
, while the right nipple is about half an inch above the upper limit of this viscus
Viscus
In anatomy, a viscus is an internal organ, and viscera is the plural form. The viscera, when removed from a butchered animal, are known collectively as offal...
.
9-region scheme
| right hypochondriac/hypochondrium Hypochondrium The hypochondrium is the upper part of the abdomen dorsal to the lowest ribs of the thorax. The word derives from the Greek term ὑποχονδρος hupochondros, meaning abdomen, or literally under cartilage.The liver is found in the right hypochondrium.... |
epigastric/epigastrium Epigastrium The epigastrium is the upper central region of the abdomen. It is located between the costal margins and the subcostal plane.... |
left hypochondriac/hypochondrium |
| right lumbar Lumbar In tetrapod anatomy, lumbar is an adjective that means of or pertaining to the abdominal segment of the torso, between the diaphragm and the sacrum ... /flank Flank Flank may refer to:* Flank, the side of either a horse or a military unit*Flanking maneuver in military tactics* Flank , the waveform edge formed when a signal goes high or low... /latus Latus (anatomy) The latus is a region of the abdomen between the hypochondrium and inguinal region.In some contexts, it is sometimes called the flank or lumbar region.... /lateral |
umbilical Umbilical region The umbilical region, in the anatomists' abdominal pelvic nine-region scheme, is the area surrounding the umbilicus . This region of the abdomen contains part of the stomach, the head of the pancreas, the duodenum, a section of the transverse colon and the lower aspects of the left and right kidney... |
left lumbar/flank/lateral |
| right inguinal Inguinal In human anatomy, the inguinal region refers to either the groin or the lower lateral regions of the abdomen. It may also refer to:* Conjoint tendon, previously known as the inguinal aponeurotic falx, a structure formed from the transversus abdominis insertion into the pecten pubis* Granuloma... /iliac Iliac Iliac can refer to one of the following:* Iliac artery* Ilium * Iliac vein* Iliac fossa... |
hypogastric Hypogastrium The hypogastrium is an area of the human abdomen located below the navel. The pubis bone constitutes its lower limit.... /suprapubic |
left inguinal/iliac |
4-region scheme
Another way of dividing the abdomen is by using 4 quadrants:| right upper quadrant (RUQ) | left upper quadrant Left upper quadrant (abdomen) thumb|right|A Graphic showing Contents of Left upper quadrantThe Left upper quadrant of the human abdomen, often abbreviated as LUQ, is used to refer to a portion of the abdomen that allows doctors to localise pain and tenderness, scars, lumps and other items of interest... (LUQ) |
| right lower quadrant Right lower quadrant (abdomen) thumb|right|A Graphic showing Contents of The Right lower quadrant of the human abdomen, often abbreviated as RLQ, is used to refer to a portion of the abdomen that allows doctors to localise pain and tenderness, scars, lumps and other items of interest... (RLQ) |
left lower quadrant Left lower quadrant (abdomen) thumb|right|A Graphic showing Contents of The left lower quadrant of the human abdomen is the area left of the midline and below the umbilicus. The abdomen is divided into quadrants by doctors to localise pain and tenderness, scars, lumps and other items of interest... (LLQ) |
Terminology
A scaphoid abdomen is when the abdomen is sucked inwards. In a newborn it may represent a diaphragmatic herniaDiaphragmatic hernia
Diaphragmatic hernia is a defect or hole in the diaphragm that allows the abdominal contents to move into the chest cavity. Treatment is usually surgical.The following types of diaphragmatic hernia exist:* Congenital diaphragmatic hernia** Morgagni's hernia...
.
Vertebrates
In vertebrates, the abdomen is a large cavity enclosed by the abdominal muscles, ventrally and laterallyAnatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
, and by the vertebral column
Vertebral column
In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...
dorsally. Lower ribs can also enclose ventral and lateral walls. The abdominal cavity is continuous with the pelvic cavity. It is separated from the thoracic cavity
Thoracic cavity
The thoracic cavity is the chamber of the human body that is protected by the thoracic wall ....
by the diaphragm
Thoracic diaphragm
In the anatomy of mammals, the thoracic diaphragm, or simply the diaphragm , is a sheet of internal skeletal muscle that extends across the bottom of the rib cage. The diaphragm separates the thoracic cavity from the abdominal cavity and performs an important function in respiration...
. Structures such as the aorta
Aorta
The aorta is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it branches off into two smaller arteries...
, inferior vena cava and esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
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. The abdomen in vertebrates contains a number of organs
Organ (anatomy)
In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...
belonging, for instance, to the digestive tract and urinary system
Urinary system
The urinary system is the organ system that produces, stores, and eliminates urine. In humans it includes two kidneys, two ureters, the bladder and the urethra.-Kidney:...
.
Abdominal organs
- Digestive tract: StomachStomachThe stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
, small intestineSmall intestineThe small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
, large intestineLarge intestineThe large intestine is the third-to-last part of the digestive system — — in vertebrate animals. Its function is to absorb water from the remaining indigestible food matter, and then to pass useless waste material from the body...
with cecumCecumThe cecum or caecum is a pouch, connecting the ileum with the ascending colon of the large intestine. It is separated from the ileum by the ileocecal valve or Bauhin's valve, and is considered to be the beginning of the large intestine. It is also separated from the colon by the cecocolic...
and appendix - Accessory organs of the digestive tract: LiverLiverThe liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
, gallbladderGallbladderIn vertebrates the gallbladder is a small organ that aids mainly in fat digestion and concentrates bile produced by the liver. In humans the loss of the gallbladder is usually easily tolerated....
and pancreasPancreasThe pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist... - Urinary system: KidneyKidneyThe kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
s and ureters - but technically located in retroperitoneumRetroperitoneumThe retroperitoneal space is the anatomical space in the abdominal cavity behind the peritoneum. It has no specific delineating anatomical structures...
- outside peritoneal membrane - Other organs: SpleenSpleenThe spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...
Abdominal organs can be highly specialized in some animals. For example the stomach of ruminant
Ruminant
A ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first compartment of the stomach, principally through bacterial actions, then regurgitating the semi-digested mass, now known as cud, and chewing it again...
s (a suborder of mammals) is divided into four chambers - rumen
Rumen
The rumen, also known as a paunch, forms the larger part of the reticulorumen, which is the first chamber in the alimentary canal of ruminant animals. It serves as the primary site for microbial fermentation of ingested feed...
, reticulum
Reticulum
Reticulum is a small, faint constellation in the southern sky. Its name is Latin for a small net, or reticle—a net of crosshairs at the focus of a telescope eyepiece that is used to measure star positions...
, omasum
Omasum
The omasum, also known as the bible, the fardel, the manyplies and the psalterium, is the third compartment of the stomach in ruminants...
and abomasum
Abomasum
The abomasum, also known as the maw, and the rennet-bag, and the read, is the fourth and final stomach compartment in ruminants. It secretes rennin - the artificial form of which is called rennet, and is used in cheese creation....
.
Invertebrates
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 honeybee. In the Collembola (Springtails) the abdomen has only six segments.
The abdomen is sometimes highly modified. In Apocrita
Apocrita
Apocrita is a suborder of insects in the order Hymenoptera.Apocrita includes wasps, bees and ants, and consists of many families. It includes the most advanced hymenopterans and is distinguished from Symphyta by the narrow "waist" formed between the first two segments of the actual abdomen; the...
(bees, ants and wasps), the first segment of the abdomen is fused to the thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
and is called the propodeum
Propodeum
The propodeum is the first abdominal segment in Apocrita Hymenoptera . It is fused with the thorax to form the mesosoma. It is a single large sclerite, not subdivided, and bears a pair of spiracles. It is strongly constricted posteriorly to form the articulation of the petiole, and gives apocritans...
. In ant
Ant
Ants are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. More than...
s the second segment forms the narrow petiole
Petiole (insect)
In entomology, the term petiole is most commonly used to refer to the constricted first metasomal segment of members of the Hymenopteran suborder Apocrita; it may be used to refer to other insects with similar body shapes, where the metasomal base is constricted...
. Some ants have an additional postpetiole segment, and the remaining segments form the bulbous gaster
Gaster
The gaster is the bulbous posterior portion of the metasoma found in Apocrita Hymenoptera . This begins with abdominal segment III on most ants, but some make a postpetiole out of segment III, in which case the gaster begins with abdominal segment IV....
. The petiole and gaster (abdominal segments 2 and onward) are collectively called the metasoma
Metasoma
The metasoma is the posterior part of the body, or tagma, of arthropods whose body is composed of three parts, the other two being the prosoma and the mesosoma. In insects, it contains most of the digestive tract, respiratory system, and circulatory system, and the apical segments are typically...
.
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
Archaeognatha
Archaeognatha is an order of wingless insects, also known as jumping bristletails. They are among the least evolutionarily changed insects, appearing in the Devonian period along with the arachnids. The name Archaeognatha is derived from Greek Archaeos meaning "ancient" and gnatha meaning "jaw"...
possess small, articulated "styli" which are sometimes considered to be rudimentary appendages. Many larval insects including the Lepidoptera
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...
and the Symphyta (Sawflies) have fleshy appendages called proleg
Proleg
A Proleg is the small fleshy, stub structure found on the ventral surface of the abdomen of most larval forms of insects of the order Lepidoptera, though they can also be found on other larval insects such as sawflies and a few types of flies....
s 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.