Everything about Abdomen totally explained
In
vertebrates such as
mammals 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
arthropods it's the most distal section of the body which lies behind the thorax or
cephalothorax.
Vertebrates
In vertebrates the abdomen is a large cavity enclosed by the abdominal muscles
ventraly and
lateraly and by
vertebral column dorsally. Lower ribs can also enclose ventral and lateral walls. Abdominal cavity is continuous with pelvic cavity. It is separated from
thoracic cavity by
diaphragm. Structures such as the
aorta, inferior
vena cava and
esophagus pass through the diaphragm. Both abdominal cavity and pelvic cavity are lined by a serous membrane known as
parietal peritoneum. This membrane is continuous with
visceral peritoneum lining the organs. Abdomen in vertebrates contains a number of
organs belonging for instance to
digestive tract and
urinary system.
Abdominal organs
Invertebrates
The invertebrate abdomen is built up of a series of concave upper plates known as
tergites and convex 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
ants, the first segment of the abdomen is fused to the
thorax and called the
propodeum. The second segment forms the narrow
petiole. Some ants have an additional
postpetiole segment, and the remaining segments form the bulbous
gaster.
(External Link
) 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
prolegs 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.
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