• ABDOMINAL WALL
  • abdominal wall
    • anterior abdominal wall
      • Rectus sheath
      • Muscles
    • posterior abdominal wall
      • Muscles
    • side of abdomen
• ABDOMINAL CAVITY
  • Regiones abdominales (Abdominal regions)
  • regio hypochondriaca (hypochondrium)
  • epigastrium
  • umbilical region
  • peritoneum
    • Special regions
      • Supracolic compartment or subphrenic space
      • Infracolic compartment
      • Paracolic gutter
      • Peritoneal Fossa ( recess )
  • QUADRANTS
    • UPPER RIGHT
      • LIVER
      • RIGHT KIDNEY
    • UPPER LEFT
      • Stomach
      • left kidney
    • LOWER
      • FEMALE GENITAL SYSTEM
      • LOWER RIGHT
        • ileum
        • Appendix
        • Caecum
      • LOWER LEFT
        • sigmoid colon
        • rectum

• Middle lower trunk
  • Hinder-part; ‖ the direct Muscles: or transverse Bones.
    • LOIN, Chine.
    • RIB.
  • Side-part; ‖ more general: or more specially the lower part of it.
    • SIDE, Lateral, collateral.
    • FLANK, Rand.
  • Fore-part; more general: or more specially the concave middle part of it.
    • BELLY, Paunch, Pannel, Peritenaeum.
    • NAVEL, Vmbilical.

The abdomen (colloquially called the belly, tummy, midriff 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 trunk. The area occupied by the abdomen is called the abdominal cavity. In arthropods it is the posterior tagma of the body; it follows the thorax or cephalothorax.

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 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.

In vertebrates, the abdomen is a large body cavity enclosed by the abdominal muscles, at 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.[3] The abdomen in vertebrates contains a number of organs belonging to, for instance, the digestive system, urinary system, and muscular system.

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.[5] 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.[5]

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 Poupart's ligament, the inner lip of the ilium, the lumbar fascia and the inner surface of the cartilages of the six lower ribs. It inserts into the linea alba behind the rectus abdominis.

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 inguinal hernias.

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.

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 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.

Terminology

• Angles - costal angle , renal angle , subcostal angle
• Spine - posterior superior iliac spine , anterior superior iliac spine
• Line - Linea alba , Linea semilunaris

• 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 two and a half inches (64 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 intestine joins the large intestine.

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.

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. The quadrants are referred to as the left lower quadrant, left upper quadrant, right upper quadrant and right lower quadrant. These terms are not used in comparative anatomy, since most other animals do not stand erect.

The left lower quadrant includes the left iliac fossa and half of the flank. The equivalent in other animals is left posterior quadrant. The left upper quadrant extends from the umbilical plane to the left ribcage. This is the left anterior quadrant in other animals. The right upper quadrant extends from umbilical plane to the right ribcage. The equivalent in other animals is right anterior quadrant. The right lower quadrant extends from the umbilical plane to the right inguinal ligament. This in other animals is the right posterior quadrant.

The nine regions offer more detailed anatomy and are delineated by two vertical and two horizontal lines.

QUADRANTS

The left lower quadrant (LLQ) of the human abdomen is the area left of the midline and below the umbilicus. The LLQ includes the left iliac fossa and half of the left flank region. The equivalent term for animals is left posterior quadrant. Important organs here are:

• the descending colon and sigmoid colon
• the left ovary and fallopian tube
• the left ureter

The left upper quadrant (LUQ) extends from the median plane to the left of the patient, and from the umbilical plane to the left ribcage. The equivalent term for animals is left anterior quadrant. Important organs here are:

• Stomach
• Spleen
• Left lobe of liver
• Body of pancreas
• Left kidney and adrenal gland
• Splenic flexure of colon
• Parts of transverse and descending colon

The right upper quadrant (RUQ) extends from the median plane to the right of the patient, and from the umbilical plane to the right ribcage. The equivalent term for animals is right anterior quadrant. Important organs here are:

• Liver
• Gall bladder with biliary tree
• Duodenum
• Head of pancreas
• Right kidney and adrenal gland
• Hepatic flexure of colon

The right lower quadrant (RLQ) extends from the median plane to the right of the patient, and from the umbilical plane to the right inguinal ligament. The equivalent term for animals is right posterior quadrant. Important organs here are:

• Cecum
• Appendix
• Ascending colon
• Right ovary and Fallopian tube
• Right ureter

REGIONS

Nine regions of the abdomen can be marked using two horizontal and two vertical dividing lines. The vertical lines are the mid-clavicular lines taken from the mid-point of each clavicle. The upper horizontal line is the subcostal line taken from the inferior parts of the lowest costal cartilages. The lower horizontal line is the intertubercular line connecting the tubercles of the pelvis.[3][4]

The three main centrally positioned regions are the epigastric region, the umbilical region, and the hypogastric region also known as the pubic region.

On the sides of the abdomen the other six regions are the left and right hypochondriac regions, on either side of the epigastrium; the left and right lumbar flank regions, on either side of the umbilical region, and the left and right iliac or inguinal regions on either side of the hypogastrium.[3][4]

(Hypo- means below; epi- means above; 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.)