DEV2022 – LECTURE 12
Functions of abdominal wall muscles:
The abdominal pressure can be increased or decreased. The abdominal muscles
also bring stability to the vertebral column via the attachment to the roots. When
they contract or relax have an action upon the structures to which they are
attached – the trunk and the pelvis. Via the agency of the diaphragm, forms the
top of the container of the abdominal cavity is essential in breathing.
Raising intra-abdom pressure:
If you increase abdominal pressure, structures inside are influenced.
Segmental cutaneous innervation:
The skin overlying the trunk and particularly the abdominal cavity is innervated
in a dermatome type pattern.
Major features of the abdomen:
The abdominal cavity is not really a ‘cavity’ as there are no empty spaces. The
cavity is filled with organs. However, the space between organs is a cavity, where
that cavity is filled with fluid.
Extends superiorly to the diaphragm. It merges with the pelvic cavity. This cavity
is completely closed in males from the external environment. In females, it is
open to the external environment. The cavity is a sac, which is lined by a
membrane. A serous sac is a membrane that secretes a serous or watery fluid.
The cavity is lined by a serous membrane (simple, squamous epithelium with
supporting connective tissue, which secretes fluid). This is why an organ inside
the abdom cavity is called a viscous (wet and sticky). They are kept wet and
sticky by the serous membrane.
Parietal covering walls
Visceral covering all the organs inside the enclosed space.
Visceral peritoneum covering over the organs.
Visceral nerves and vessels coming from a origin – spinal cord, autonomic nerves,
aorta, etc. and they transit from their origin to the viscera.
Parietal layer receives it nerves and vascular supply from the body wall, so they
have somatic nerve supply (motor and sensory).
The visceral layer is not innervated by somatic nerves, but the nerves supply to
the viscera, which is the autonomic nervous sytem. Hence pain associated with
something wrong with the viscera is not highly localized to a dermatome
because there are not dermatomes. It is diffuse and wide spread because it's a
member of the autonomic nervous system.
As it’s developed during embryogenesis, it is invaginating into the body cavity,
and its taking its parietal and visceral membranes with it to produce an
attachment. 2 sheets of surround membrane equal a mesentery. This allows structures to reach the viscera and in converse, structures from the viscera
return to the body wall – nerve, veins, arteries, lymphatics.
The mesenteries, in addition to providing a supply line of structures – vessels,
nerves and lymphatics – also allow mobility of the gut. The mesentery is thin and
delicate, like a rubber band where they can stretch and return to its original state.
Mobility in some organs in the abdominal cavity is important for grinding food
and processing food into packets, where we eventually expel as faeces.
Vessels and nerves:
Mesentery is a thin sheet, double layered serous membrane.
Intraperitoneal viscera of GI tract:
If they are intraperitoneal, these organs are suspended by mesenteries in the
cavity. If something is being suspended, they will have mobility.
Other organs are behind the peritoneal cavity where we call them posterior
peritoneal organs. They include the kidneys, adrenals and ureters. They do not
have a mesentery, as they are not free to move – they are fixed.
Their mesentery during embryogenesis has fused with the parietal peritoneum.
So they are no longer suspended in any way. The net result in this is that the
organs in the retroperitoneal cavity are fixed, while some are mobile. Those,
which are mobile, can expand (stomach). Mesenteries are not only the supply
chain but they also allow the gut that they suspend to be mobile, and also allow
expansion and contraction.
The gut and associated organs:
The gut tract is a tube from the mouth to anus. Derived from endoderm.
The digestive tube is different as it has glands that are derived from that
primitive gut tube (liver, pan