Conceptual overview
General description
The abdomen is a roughly cylindrical chamber extending from the inferior margin of the thorax to the
superior margin of the pelvis and the lower limb. The inferior thoracic aperture forms the superior
opening to the abdomen and is closed by the diaphragm. Inferiorly, the deep abdominal wall is
continuous with the pelvic wall at the pelvic inlet. Superficially, the inferior margin of the abdominal
wall is the superior margin of the lower limb.
Figure 4.1. Boundaries of the abdomen.
The chamber enclosed by the abdominal wall (abdominal cavity) contains a single large peritoneal
cavity, which freely communicates with the pelvic cavity.
Abdominal viscera are either suspended in the peritoneal cavity by mesenteries or positioned
between the cavity and the musculoskeletal wall.
1
,Figure 4.2. Arrangement of abdominal contents (inferior view).
Abdominal viscera include:
• major elements of the gastrointestinal system—the distal end of the esophagus, stomach,
small and large intestines, liver, pancreas, and gallbladder
• the spleen
• components of the urinary system—kidneys and ureters
• the suprarenal glands
• major neurovascular structures
Functions
Houses and protects major viscera
The abdomen contains major elements of the gastrointestinal system, the spleen, and parts of the
urinary system.
Viscera under the domes of the diaphragm (these domes project superiorly above the costal margin
of the thoracic wall) are much of the liver, gallbladder, stomach, spleen and parts of the colon, and as
a result these abdominal viscera are protected by the thoracic wall. The superior poles of the kidneys
are deep to the lower ribs.
Viscera not under the domes of the diaphragm are supported and protected predominantly by the
muscular walls of the abdomen.
2
, Figure 4.3. The abdomen contains and protects the abdominal viscera.
Breathing
One of the most important roles of the abdominal wall is to assist in breathing:
• During inspiration, it relaxes to accommodate expansion of the thoracic cavity and the
inferior displacement of abdominal viscera during contraction of the diaphragm.
• During expiration, it contracts to assist in elevating the domes of the diaphragm, thus
reducing thoracic volume.
Material can be expelled from the airway by forced expiration using the abdominal muscles, as in
coughing or sneezing.
3
General description
The abdomen is a roughly cylindrical chamber extending from the inferior margin of the thorax to the
superior margin of the pelvis and the lower limb. The inferior thoracic aperture forms the superior
opening to the abdomen and is closed by the diaphragm. Inferiorly, the deep abdominal wall is
continuous with the pelvic wall at the pelvic inlet. Superficially, the inferior margin of the abdominal
wall is the superior margin of the lower limb.
Figure 4.1. Boundaries of the abdomen.
The chamber enclosed by the abdominal wall (abdominal cavity) contains a single large peritoneal
cavity, which freely communicates with the pelvic cavity.
Abdominal viscera are either suspended in the peritoneal cavity by mesenteries or positioned
between the cavity and the musculoskeletal wall.
1
,Figure 4.2. Arrangement of abdominal contents (inferior view).
Abdominal viscera include:
• major elements of the gastrointestinal system—the distal end of the esophagus, stomach,
small and large intestines, liver, pancreas, and gallbladder
• the spleen
• components of the urinary system—kidneys and ureters
• the suprarenal glands
• major neurovascular structures
Functions
Houses and protects major viscera
The abdomen contains major elements of the gastrointestinal system, the spleen, and parts of the
urinary system.
Viscera under the domes of the diaphragm (these domes project superiorly above the costal margin
of the thoracic wall) are much of the liver, gallbladder, stomach, spleen and parts of the colon, and as
a result these abdominal viscera are protected by the thoracic wall. The superior poles of the kidneys
are deep to the lower ribs.
Viscera not under the domes of the diaphragm are supported and protected predominantly by the
muscular walls of the abdomen.
2
, Figure 4.3. The abdomen contains and protects the abdominal viscera.
Breathing
One of the most important roles of the abdominal wall is to assist in breathing:
• During inspiration, it relaxes to accommodate expansion of the thoracic cavity and the
inferior displacement of abdominal viscera during contraction of the diaphragm.
• During expiration, it contracts to assist in elevating the domes of the diaphragm, thus
reducing thoracic volume.
Material can be expelled from the airway by forced expiration using the abdominal muscles, as in
coughing or sneezing.
3
