Posterior Abdominal Wall & Diaphragm Flashcards
What are the bones of the posterior abdomen?
LV1-LV5 + their intervertebral discs, ribs 11-12, the sacrum, and the ala (wing) of the sacrum
What are the lumbar vertebrae like?
Large vertebral bodies, with short, stocky pedicles, long transverse processes, and large spinous processes. Their articular facets interlock.
How does the ilium articulate with the sacrum?
At the sacro-iliac joint. The upper part of each ilium articulates with the ala - the wing-like transverse process of the sacral vertebrae.
What is the anterior edge of S1 called?
It projects forward and is called the promontory
Where are the floating ribs located in relation to the kidneys?
Rib 11 is posterior to the superior part of the left kidney
Rib 12 is posterior to the superior part of the right and left kidney
What are the muscles of the posterior abdominal wall?
3 (sometimes 4) paired Iliacus Quadratus lumborum Psoas major Sometimes: psoas minor (50%, sometimes only 1 side too)
1 unpaired
Diaphragm
What are the origin, insertion, action, and innervation of psoas major?
Origin: Bodies, discs, and transverse processes of T12 and L1-L5
Insertion: Lesser trochanter of femur
Innervation: Lumbar plexus (L1-L3)
Action:
With iliacus on one side: flexes the thigh.
Acting alone: Flexes trunk laterally
Acting with opposite psoas + iliacus: Flexes trunk
What is the course of the psoas major muscle?
T12-L5 vertebral column, goes inferolaterally and its tendon runs posterior to the inguinal ligament and anterior to the hip joint to reach femur
What are the origin, insertion, action, and innervation of psoas minor?
Short belly and long tendon like palmaris longus. Lies anterior to psoas major
Origin: T12-L1 vertebrae
Insertion: Iliopubic eminence on pelvic rim
Innervation: L1
Action: Helps psoas major flex the pelvis and lumbar region of vertebral column
What are the origin, insertion, action, and innervation of iliacus muscle?
Lateral and inferior to p. major. Fibers cross sacroiliac joint
Origin: Superior 2/3 of iliac fossa
Insertion: Lesser trochanter of femur, fibers join tendon of psoas major muscle
Innervation: Femoral nerve L2-L4
Action: Flexes thigh, stabilizes hip joint with p. major
What is the iliopsoas muscle?
The name for the psoas major and iliacus muscles together. They are referred to together because they share a common tendon and are the chief flexors of the thigh, helping to maintain erect posture at the sacroiliac joint.
They have extensive relations to the kidneys, ureters, cecum, appendix, sigmoid colon, pancreas, lymph nodes, lumbar plexus, etc
What is a psoas abscess?
An abscess resulting from tuberculosis in the lumbar region which could spread through the fascia enclosing the p. major muscle and pass inferiorly over the pelvic brim into the femoral triangle.
What are the origin, insertion, action, and innervation of quadratus lumborum?
Square muscle which forms a sheet in abdominal wall.
Origin: Transverse processes of L1-L5, medial half of inferior border of 12th rib
Insertion: Iliolumbar ligament and internal lip of iliac crest
Innervation: T12, L1-L4
Action: Extends and laterally flexes the vertebral column, fixes 12th rib during inspiration
What is the iliolumbar ligament?
Strong triangular ligament that connects the tips of LV5 to the iliac crest
What parts of the diaphragm move during inspiration?
Only its dome because the peripheral parts are attached to the inferior margin of the osteocartilagenous thoracic cage and superior lumbar vertebrae.
It moves down during inspiration -> contraction. Forms the floor of the thoracic cavity and roof of abdominal cavity
What are the three parts of the muscular part of the diaphragm? Where do they collectively attach?
- Sternal
- Costal
- Lumbar
They all attach to the central tendon
What is the sternal part of the diaphragm and what hypothetical space is found here?
Two muscular slips attaching to posterior aspect of xiphoid process. They converge on the central tendon, and lateral to each slip is a gap known as the sternocostal hiatus - contains superior epigastric artery
What is the costal part of the diaphgram and what is the vertebrocostal triangle?
Fibers making a dome which originate from the inferior six ribs and their costal cartilages on each side. Ribs 11/12 is separated from lumbar part by the vertebrocostal triangle, which is normally filled by loose connective tissue
What forms the lumbar part of the diaphragm and what vertebral levels are the major landmarks?
Two musculotendinous crura (legs) which form aortic hiatus
Disc between TV12 and LV1 = median arcuate ligament, from which originate the left and right crura
Right crus - extends down to LV3
Left crus - extends down to LV2
What is median vs medial vs lateral arcuate ligaments?
Median - origin of left and right crus, around aortic hiatus
Medial - Thickening of psoas fascia over the superior part of p. major. The muscle fibers radiate towards central tendon
Lateral - thickening of thoracolumbar fascia over superior quadratus lumborum, extending towards central tendon
What is the central tendon of the diaphragm fused with, and what does it resemble?
Central tendon is fused with inferior surface of fibrous pericardium. It resembles a clover leaf from the three areas of thickened fascia
Where is the diaphragm prone to herniation, and what is the most common spot? When does this happen?
Prone to herniation wherever muscles fuse, since it is formed by the fusion of various muscles. This happens when there is increased thoracic or abdominal pressure often during car accident.
Common spot: Vertebrocostal triangle, since it is where muscle fibers of costal and lumbar diaphragm fuse.
Where do congenital hernias most often happen and what structures can enter into the thorax?
Esophageal opening or stenocostal hiatus
-stomach, intestines, and spleen can herniate through
What are the three diaphragmatic aperatures through which things pass, and what vertebral levels are they at?
- Vena caval foramen - TV8
- Esophageal hiatus - TV10
- Aortic hiatus - TV12
What is the vena caval foramen and how is it affected during inspiration?
It is at TV8 where the IVC descends into the abdomen. Since the IVCC is adherent to the margin of the caval opening, inspiration widens the foramen, dilating the IVC
What structure forms the esophageal hiatus and why is this relevant to function?
The right crus does, at the TV10 level. It also forms the esophageal sphincter, which constricts the distal end of the esophagus during inspiration so gastric contents do not reflux into the esophagus
What structures pass through the esophageal hiatus?
Esophagus, anterior and posterior vagal trunks
What structures does the aortic hiatus transmit and why is the aorta unaffected by inspiration?
Transmits thoracic duct, azygos vein, and aorta. It is unaffected by contractions of the diaphragm because it is posterior to the median arcuate ligament, and thus does not technically pass through the muscular part of the diaphragm.
What is the sternocostal hiatus and what vessels pass through?
The small gap between the sternal and costal parts of the diaphragm, usually superior epigastric vessels pass through
How do the greater + lesser splanchnic nerves + hemiazygos vein pass through the diaphragm?
Pierce the crura, all typically the left crura
How do the subcostal nerves and vessels pass through the diaphragm?
Posterior to the lateral arcuate ligaments
How do the sympathetic trunks pass through the diaphragm?
Posterior to the medial arcuate ligaments
What arteries supply the superior part of the diaphragm?
- Superior phrenic branch - from thoracic aorta
- Musculophrenic - from ITA
- Pericardiacophrenic - from ITA
What artery supplies the inferior part of the diaphragm?
Inferior phrenic artery - from abdominal aorta
What nerve carries pain + proprioception to the diaphragm in the middle?
The phrenic nerve. It is also the motor innervation of the diaphragm
What nerves carry sensory innervation to the peripheral diaphragm?
6th + 7th intercostal nerves on both sides, + subcostal nerve.
What is the referred pain of the diaphragm which is not phrenic?
Pain in costal margin of abdomen is due to sensory impulses travelling with the intercostal nerves
How is the diaphragm involved in blood flow?
Contraction will dilate IVC, allowing return of venous blood to heart
How is the diaphragm involved in abdominal strianing?
Assists the anterior abdominal muscles in raising intra-abdominal pressure when it contracts. This is important in micturition, defecation, and childbirth
What is the fascial lining of the posterior abdominal wall continuous with? How is it named?
The tranversalis fascia of the anterior abdominal abdominal wall. It is named for each muscle it encloses
What is the iliac fascia? What does it form superiorly? What is it continuous with laterally?
It is the fascia that encloses the psoas and iliacus muscles. Superiorly it is thickened to form the medial arcuate ligament, and forms the anterior layer of thoracolumbar fascia
As with all of these, it is continuous with the tranversalis fascia laterally
What are the lateral attachments of the thoracolumbar fascia? What is the lumbar part?
The fascia of the internal oblique and transversus abdominis muscles.
Lumbar part: Fascia extending between 12th rib and iliac crest
The thoracolumbar fascia splits into three layers medially. What muscles lie between each layer?
Between anterior and middle: Quadratus lumborum
Between middle and posterior: Deep back muscles
Remember, the P. major muscle is anterior to the transverse processes and medial to the vertebral body
What is the lumbar plexus?
A network of nerves formed within the substance of the psoas major muscle, by the ventral rami of L1-L4
What nerves pass lateral to the psoas major muscle from superior to inferior? What spinal cord level gives them?
- Iliohypogastric (L1)
- Ilioinguinal (L1)
- Lateral femoral cutaneous (L2, L3)
- Femoral (L2, L3, L4) - huge, like musculocutaneous
What nerve passes anterior to the psoas major muscle and what spinal cord level gives it?
Genitofemoral nerve - L1, L2
What nerves pass medial to the psoas major muscle and what spinal cord levels give them?
Obturater - L2, L3, L4 - also pretty big
Lumbosacral trunk - L4-L5
What is the course of the iliohypogastric nerve?
Nerve from L1, often in common trunk with ilioinguinal. Travels anterior to fascia of quadratus lumborum and near ASIS, piercing transversus abdominus before dividing into its two branches
What are the two branches of the iliohypogastric and what do they supply?
Lateral branch - pierces internal and external oblique to supply skin of lateral side of gluteal region
Anterior branch - runs between internal and external obliques before piercing external aponeurosis and supplying suprapubic region
Where does the ilioinguinal nerve run and what does it supply?
From L1, pierces the transversus abdominis, runs medially in inguinal canal and exits through superficial ring. Supplies anterior side of thigh, and skin over anterior scrotum / labia majora
What does the lateral femoral cutaneous nerve supply?
From L2 and L3, enters thigh below inguinal ligament, divides into two branches to supply anterior and lateral skin of thigh
What does the femoral nerve do and what is its terminal branch called?
It is the largest branch of lumbar plexus, descending between the p. major and iliacus muscles and goes into thigh posterior to inguinal ligament.
Motor: to extensors
Sensory: to thigh and foot anteriorly and medially
Terminal branch: Saphenous nerve
What are the two branches of the genitofemoral nerve and what are their actions?
From L1/L2
Genital: Enters inguinal canal thru deep ring, supplies motor to cremasteric in males, and sensory in that region
Femoral - Enters femoral sheath and supplies skin of femoral triangle
What is the function of the obturator?
Passes medially to p. major, enters medial thigh through obturator foramen.
Motor: Three adductor muscles + gracilis
Sensory: Medial side of thigh + hip joint
What is the function of the lumbosacral trunk?
Formed by L4 + L5, helps form sacral plexus, does not participate in lumbar plexus
What does the abdominal aorta become, and at what level?
Becomes two common iliac arteries at LV4
At what levels are the three unpaired visceral branches of the abdominal aorta. What is the terminal branch of the last one?
- Celiac trunk - TV12
- Superior mesenteric artery - LV1
- Inferior mesenteric artery - LV3. Terminal branch is superior rectal artery supplying upper rectum
What are the paired visceral branches of the abdominal aorta?
- Middle suprarenal artery - Supply adrenal glands
- Renal arteries - inferior to SMA, supply kidneys
- Gonadal - inferior to renal arteries, run inferior on p. major muscle. Right one will pass over IVC. Supply gonads
What are the two types of gonadal arteries and where would they run?
- Testicular artery - passes thru deep ring and enters inguinal canal to become part of spermatic cord
- Ovarian artery - similar course, but crosses the proximal ends of the external iliac vessels to enter the pelvis where it supplies ovary and uterine tube
What is the unpaired parietal branch of the abdominal aorta (to body wall)?
Median sacral - artery arises from posterior side of aorta just proximal to its bifurcation and descends in midline anterior to vertebral bodies
What are the paired parietal branches of the abdominal aorta?
- Inferior phrenic arteries - to inferior diaphragm, coming from near celiac trunk
- Lumbar arteries - 4 pairs which have anterior and posterior branches to supply body wall
What is the largest vein of the body and does it have valves? What forms it?
Inferior vena cava, and no valves except for a variable non-functional one at its orifice.
Formed by union of common iliac veins anterior to LV5.
What is the course of the IVC?
Originates at LV5 to the right of median plane, inferior to aorta bifurcation. Ascends on right p. major muscle, passes through caval opening at TV8
Where do lumbar veins typically drain?
They can drain directly into inferior vena cava, or the ascending lumbar vein which lies posterior to the p. major and enters the thorax posterior to the medial arcuate ligament
What do the right and left ascending lumbar veins become?
Right - joins right subcostal vein to form azygos vein
Left - joints left subcostal vein to form hemiazygos vein
Why are the ascending lumbar veins important in IVC blockage?
Can receive blood from thorax and lower limb to enter the azygos vein and bring blood to the right atrium through the SVC.
What are the main lymph nodes of the posterior abdominal wall?
Lumbar lymph nodes, which lie on both sides of aorta / IVC. They also receive lymph from viscera and common iliac lymph nodes
What is cisterna chyli? Where is it?
Sac-like expansion at inferior end of thoracic duct which is sometimes absent. It lies on right side of L1 / L2, posterior to right crus of diaphragm.
It receives lymph from lumbar lymph nodes and passes it to thorax via thoracic duct.
