Summary
Summary NEPHROLOGY 1- USMLE RX BRICKS
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A SUMMARY OF THE IMPORTANT TOPICS IN NEPHROLOGY FOR THE STEP 1 USMLE EXAMS
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Anatomy of thePosterior Abdominal
Wall
By ScholarRx
Updated May 6, 2022
access_time13 min
Learning Objectives (2)
After completing this brick, you will be able to:
● Describe the relationship of the kidneys in the retroperitoneal space
as it relates to posterior abdominal wall anatomy.
● 1
● Describe the structure and relationships of the posterior abdominal
wall, including the aorta (including collateral channels), inferior
vena cava (including collateral tributaries), lymphatics, muscles
(psoas major, quadratus lumborum), sympathetic chain, and lumbar
plexus.
● 2
cableCASE CONNECTION
CT is a 22-year-old woman you are seeing in the emergency
department because she has a fever and back pain. Two weeks ago,
she was treated for a kidney infection. “I thought I was all better,” she
says. “But now I have a different type of bad back pain. I get pain in
my back when I bring my knee up to my chest in one of my stretching
exercises. I think I have a fever, too.” CT reports no urinary
,symptoms. On exam, CT’s temperature is 100.5°F, and her pain is
reproduced when you flex her hip.
What could be the cause of CT’s new back pain? Why does her pain
get worse when she flexes her hip? Consider your answers as you
read, and we’ll revisit at the end of the brick
GO TO CONCLUSION arrow_downward
What Is the Posterior Abdominal
Wall?
It might not be the flashiest anatomical structure, but if you want to
stand upright, and keep your retroperitoneal organs (like your
kidneys) in place, the posterior abdominal wall is pretty important.
Located at the back of the body, bounded by the lateral abdominal
walls and the posterior parietal peritoneum, the posterior abdominal
wall is a complex combination of muscles, bones, nerves, and vessels
that provides structural support for the body and for the organs of the
retroperitoneal space.
What Forms the “Bed” of the
Posterior Abdominal Wall?
The posterior abdominal wall extends from the 12th rib to the sacrum
and iliac crests. Its deepest levels act as a bed that supports the rest of
the abdominal wall and also the organs in the retroperitoneum.
,The retroperitoneum is the region of the abdominal cavity that lies
underneath the peritoneum. It’s sometimes called a “potential” space,
because it isn’t a nice big open space filled with fluid; it contains
organs like the adrenals and kidneys, but there isn’t much space
around them because the parietal peritoneum is tightly adherent to
these organs.
The bed of the posterior abdominal wall consists of the spinal column
and two main muscles (Figure 1):
● The psoas major is the most medial posterior abdominal wall
muscle and is immediately adjacent to the lumbar vertebrae (L1-
L4). Its main action is flexion and lateral rotation at the hip, so it
plays a major role in walking.
● The quadratus lumborum is lateral to the psoas major. Its
main function is to fix and stabilize the 12th rib and diaphragm
during inspiration.
What Forms the “Roof” of the
Posterior Abdominal Wall?
The diaphragm is a muscle and the most superior part of the posterior
abdominal wall: it forms a “roof” over the abdominal wall. When we
inhale, the diaphragm contracts and is drawn inferiorly into the
abdominal cavity. It is innervated by the phrenic nerve (C3-C5) as
well as the intercostal nerves.
What Are the Tributaries of the
Aorta?
, There are many vessels that pass through or posterior to the
diaphragm in the posterior abdominal wall. One of these vessels is the
aorta, which passes posterior to the diaphragm at T12 and then
branches into many collateral channels. The easiest way to remember
all of the branches of the aorta is to separate out the unpaired vs the
paired arteries (Figure 2).
The unpaired arteries mostly supply the GI viscera and arise from the
anterior portion of the aorta. Let’s look at these arteries in a cranial to
caudal fashion (ie, “head to tail”). The celiac trunk supplies
embryonic foregut derivatives, which include the esophagus all the
way down to the proximal duodenum. There are also accessory organs
supplied by the celiac trunk, which include the gallbladder, liver,
pancreas, and spleen.
● The superior mesenteric artery (SMA) supplies midgut
derivatives, which include the distal duodenum to the proximal
two-thirds transverse portion of the colon.
● The inferior mesenteric artery (IMA) supplies hindgut
derivatives, which include the distal third of the transverse colon
to upper portion of the rectum.
The paired arteries mostly arise from the posterolateral portion of the
aorta. From cranial to caudal, these include the following:
● Inferior phrenic arteries
● Suprarenal arteries
● Renal arteries
● Lumbar arteries (usually four of them)
The testicular/ovarian arteries are paired; however, they rise anteriorly
from the aorta. The median sacral artery is unpaired and is the most
caudal branch of the aorta.
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