Dissector Answers - Abdominal Wall

Learning Objectives:

Upon completion of this session, the student will be able to:

  1. Recall the basic terminology used to define the surface representations of the regions of the abdomen.
  2. Identify the major skeletal landmarks of the abdominopelvic cavity.
  3. Define the innervation, blood supply, and lymphatic drainage of the anterior abdominal wall.
  4. Describe the formation of the rectus sheath.
  5. Describe the layers of the anterolateral abdominal wall.

Learning Objectives and Explanations:

1. Recall the basic terminology used to define the surface representations of the regions of the abdomen. (W&B 417, N 260, TG , 5-01B, 5-01C)

Depending on the context or clinical situation, there are two different ways that the abdomen can be divided:

The "quick and dirty" way is to draw two lines, one down the midline and the other horizontal through the umbilicus. The result is four quadrants: the right upper quadrant, left upper quadrant, right lower quadrant, and left lower quadrant. The contents are as follows:

Right Upper Quadrant rt. lobe of liver, gallbladder, pylorus, the first three parts of the duodenum, head of the pancreas, rt. suprarenal (adrenal) gland, rt. kidney, rt. colic (hepatic) flexure, sup. part of ascending colon, rt. half of transverse colon
Left Upper Quadrant lt. lobe of liver, spleen, most of stomach, jejunum and proximal ileum, body and tail of pancreas, lt. suprarenal (adrenal) gland, lt. kidney, lt. colic (splenic) flexure, sup. part of descending colon, lt. half of transverse colon
Right Lower Quadrant cecum, appendix, most of ileum, inf. part of ascending colon, rt. ovary, rt. uterine tube, rt. ureter, rt. spermatic cord
Left Lower Quadrant sigmoid colon, inf. part of descending colon, lt. ovary, lt. uterine tube, lt. ureter, lt. spermatic cord

The other way is to draw four lines. Two are horizontal, one at the lower rib margins and the other passing through the iliac tubercles. The other two are vertical, passing through the middle of each clavicle. The result is nine regions: the right hypochondriac region, epigastric region, left hypochondriac region, right lumbar region, umbilical region, left lumbar region, right inguinal region, hypogastric region, and the left inguinal region. Do not worry about knowing the exact contents of each specific region, although a general idea, along with some clinical information, is given in #7 below. (In Greek, chondros = cartilage, so hypochondriac = under cartilage. Epigastric is "upon the stomach", while hypogastric is "under the stomach". In Latin, inguinalis = groin.)

This illustration offers a different view of the ones above:

Images from "Anatomy of the Human Body" by Henry Gray are provided by:

2. Identify the major skeletal landmarks of the abdominopelvic cavity. (W&B 417, N 150, 178, 240, 260, 468, TG 6-4) 3. Define the innervation, blood supply, and lymphatic drainage of the anterior abdominal wall. (W&B 419-421, 429-431, N 177, 184, 247, 249, 250, 252, 258, 259, 479, 480, TG 5-02, 5-05, 6-33, 6-34)

4. Describe the formation of the rectus sheath. (W&B 421, 425-427, N 244, 247, TG 5-05, 5-06, 5-06)

The rectus sheath is formed by the interweaving of the aponeuroses of the external oblique, internal oblique, and transversus abdominis muscles. It encloses the rectus abdominis and pyramidalis muscles (only present 80% of the time - see below). It is divided into two parts, superior and inferior, by the arcuate line, which is halfway between the pubic crest and the umbilicus.

The superior part of the sheath completely surrounds the rectus abdominis muscles. The anterior layer (lamina) is made of contributions from the external abdominal oblique and the internal abdominal oblique aponeuroses. The posterior layer (lamina) is composed of fibers from the transversus abdominis aponeurosis and the internal abdominal oblique aponeurosis. (Thine eyes doth not deceive thee - the internal abdominal oblique aponeurosis splits into two parts, one contributing to the anterior and the other contributing to the posterior layers of the sheath.)

The inferior part is deficient posteriorly because all three aponeuroses contribute to the anterior layer of the sheath. The only thing left on the posterior aspect of the rectus abdominis muscle, then, is the thin transversalis fascia.

The fibers all meet in the middle and interweave at the linea alba.

For more than you ever wanted to know about anatomical variation, the University of Iowa has a great site, an "Illustrated Encyclopedia of Human Anatomic Variation". Here is a quick and dirty link to the section on muscles of the abdominal wall, (including the pyramidalis).
5. Describe the layers of the anterolateral abdominal wall. (W&B 421-428, N 241, 242, 243, 244, 247, 253, TG 5-04, 5-05)

The anterior portion and the lateral portion of the abdominal wall are often considered together (anterolateral) because the muscles are functionally similar, and are functionally different than those of the posterior aspect.

Lateral: from superficial to deep: skin, fatty layer of superficial fascia (Camper's fascia), membranous layer of superficial fascia (Scarpa's fascia), deep fascia, external abdominal oblique muscle, deep fascia, internal abdominal oblique muscle, deep fascia, tranversus abdominis muscle, transversalis fascia, extraperitoneal fat, parietal peritoneum

Anterior (superior to arcuate line): from superficial to deep: skin, fatty layer of superficial fascia, membranous layer of superficial fascia, deep fascia, external abdominal oblique aponeurosis*, anterior layer of internal abdominal oblique aponeurosis*, rectus abdominis, posterior layer of internal abdominal oblique aponeurosis*, transversus abdominis aponeurosis*, transversalis fascia, extraperitoneal fat, parietal peritoneum

Anterior (inferior to arcuate line): from superficial to deep: skin, fatty layer of superficial fascia, membranous layer of superficial fascia, deep fascia, external abdominal oblique aponeurosis*, internal abdominal oblique aponeurosis*, transversus abdominis aponeurosis*, rectus abdominis, transversalis fascia, extraperitoneal fat, parietal peritoneum

* rectus sheath

Cultural enrichment: Check out these sections from the 1918 version of Gray's Anatomy of the Human Body! Some of the terms are (of course) out-of-date, but the illustrations are timeless.

The Muscles and Fasciae of the Abdomen - The Abdominal Aorta - The Lymphatics of the Abdomen and Pelvis - The Abdominal Portion of the Sympathetic System - Surface Anatomy of the Abdomen - Surface Markings of the Abdomen

Questions and Answers:

6. Name the four quadrants of the anterior abdominal wall, and list the important structures and organs found there. (N 268, TG 5-01B)
See Objective 1 above.
7. Name and define the nine regions of the anterior abdominal wall, list the importance of each. (N 268, TG 5-01C)
8. In the thigh, observe the large superficial inguinal lymph nodes, with afferent and efferent channels, below the plane of the inguinal ligament. What regions do they drain? (N 258, 528, TG 6-33, 6-34)
They drain everything below the umbilicus including:
9. Distinguish between the fatty layer and the membranous layer of the subcutaneous tissue. (N 249, TG 5-02)

The fatty layer is the superficial layer, also known as Camper's fascia, lies just below the skin. This is a big depot for fat (spare tire, beer belly). The membranous layer, also known as Scarpa's fascia, is deeper. It is well-defined below the umbilicus.

10. What is the extent of the membranous layer of the subcutaneous tissue? (N 249, 380, TG 5-02)
This layer continues inferiorly as the superficial perineal fascia (Colles fascia) in the scrotum and labia majora, and also extends to the posterior border of the urogenital triangle (a line drawn between the two ischial tuberosities). It is attached to the iliac crest, the fascia lata of the thigh, and the pubic symphysis. The layer ends 1-2 cm into the thigh, below the inguinal region.
11. What are the characteristics of the subcutaneous tissue that continues into the scrotum as the tunica dartos scroti? (N 387, 388, TG 6-31)
This superficial fascia of the scrotum and penis is entirely fat-free and contains smooth muscle to wrinkle the scrotum and elevate the testes, usually in response to actions like jumping into Lake Michigan in January, or even July.
12. Locate exemplary anterior and lateral cutaneous branches of one of the segmental nerves to the abdominal wall. What is their source? Which segmental nerves supply the abdominal wall? Do they run horizontally or follow the slope of the ribs? (N 257, 258, TG 5-02)
See #3 for full description.
Source: ventral primary rami of spinal nerves
Segmental nerves: intercostal nerves (T7-T11) and the subcostal nerve (T12)
Course: they follow the slope of the ribs, curving slightly downwards as you move lateral to medial
13. Define the superficial inguinal ring and locate it on the anterior abdominal wall using anatomical landmarks. (N 259, 263, TG 5-08A, 5-09A)

The superficial inguinal ring is a passageway through the abdominal wall, formed by a gap in the external abdominal oblique muscle. It is located just superior and lateral to the pubic tubercle. Its components are as follows:

14. Consider the sources and extent of distribution of the ilioinguinal nerve. (N 257, 258, 497, 498, TG 5-02, 5-38)
15. What does the superficial inguinal ring transmit in the female? In the male? (TG 5-08A, 5-09A)
16. How do you differentiate the external abdominal oblique from the internal abdominal oblique? (N 249, 250, TG 5-04)
The fibers of the external abdominal oblique originate on the lower ribs, running inferomedially towards the linea alba (like hands in your pockets). This is the same direction as the external intercostal muscles. The fibers of the internal abdominal oblique originate more laterally, on the iliac crest and thoracolumbar fascia, and run superomedially, like the internal intercostals.
17. Where do the iliohypogastric and ilioinguinal nerves pierce the internal and external abdominal oblique muscles? To where do they distribute? (N 267, TG 5-02, 5-38)
Both nerves begin their journey between the internal abdominal oblique and transversus abdominis muscles, but at the anterior superior iliac spine they jump out a layer and lie between the external abdominal oblique aponeurosis and the internal abdominal oblique muscle. Both nerves supply the skin and muscles of the anterior abdominal wall. Think about their names to determine distribution. Iliohypogastric gets the hypogastric regions of the abdomen. Ilioinguinal goes through the inguinal canal to become the anterior scrotal or anterior labial nerve as it passes through the superficial ring.
18. Where does the cremaster muscle lie in relation to the external spermatic fascia? (N 387, 388, TG 5-08, 5-10)
In the male, the cremaster muscle lies just deep to the external spermatic fascia. It is the middle covering of the spermatic cord and an extension of the internal abdominal oblique m. In the female, it is very small and does not pass through the superficial ring.
19. Note also that the segmental nerves and vessels are in the "plane of separation", between the internal abdominal oblique muscle and the transversus abdominis muscle, that you are now attempting to open. How do the iliohypogastric and ilioinguinal nerves differ in this respect? (N 257, 258, TG 5-02, 5-38)
See question 17 above.
20. Find the segmental vessels and nerves on the surface of the transversus abdominis muscle and consider their level, origin, areas of distribution, oblique orientation, and the manner in which they enter the rectus sheath. (N 257, 258, TG 4-08)
See the discussion of anterior and lateral cutaneous nerves above. They are oblique because they roughly follow the oblique curves of the ribs. They penetrate the posterior lateral portion of the rectus sheath, passing behind the rectus abdominis, then they penetrate the rectus and the anterior layer to the sheath to end in the skin and subcutaneous tissue.
21. Locate superior and inferior epigastric arteries. What are their sources? Do they anastomose? (N 190, 255, 262, TG 5-05)
The superior epigastric artery comes from internal thoracic artery (the other branch of the internal thoracic is the musculophrenic artery). The inferior epigastric artery comes from external iliac artery. They run inside the rectus sheath, and yes, they anastomose.
22. At what level (relative to the umbilicus) do you find the arcuate line? Is it distinct? (N 255, TG 5-05, 5-07)
The arcuate line is a transverse line halfway between umbilicus and pubic symphysis. It is usually distinct, but occasionally it is a gradual transition.
23. What tissue is left on the posterior side of the rectus muscle caudal to this line? (N 252, TG 5-05, 5-07)
Only the transversalis fascia, extraperitoneal connective tissue and peritoneum are left.
24. Note how each muscle layer contributes to the rectus sheath. What muscles contribute aponeurotic fibers to the posterior wall of the sheath at each level? (N 252, TG 5-05, 5-06, 5-06)
see #4 and #5 above.