The abdomenThe abdominal wall

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The abdomen is the region of the body that is located between the diaphragm above and the pelvic inlet below.

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Abdominal regions. The abdomen can be divided to 9 regions by

four imaginary lines.The Rt. And Lt. vertical lines extending from

the midclavicular point superiorly to midinguinal point inferiorly.

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Two transverse lines1. The lower plain intertubercular plain extends

between the Rt. And Lt. iliac tubercles2. The upper subcostal plain extends between

the lowest point of the costal edge. Or transpyloric plane that pass through L1 or

the midway between the jugular notch and the pubic symphysis.

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We may also divide the abdomen to four regions (quadrants )by two crossing line

The vertical midline. Transverse line passing through the umbilicus.

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The structures of the abdominal wall from out side to inside.

1. Skin.2. Superficial fascia.3. Deep fascial.4. Muscles.5. Extraperitoneal fascial.6. Parietal peritoneum.

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Skin is loosely attached to the underlining structures except ate the umbilicus.

The lines of cleavage runs downward and forward horizontally around the trunk.

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Superficial fascia.1. Superficial fatty layer (Camper’s fascia).It’s continuous with superficial fat over the rest

of the body. In the scrotum is modified as a thin smooth

muscular layer called dartos muscle.

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2. Deep membranous layer.(Scarpa’s fascia).Its thin and fades out superiorly and laterally

where it becomes continuous with the superficial fascia of the back and the thorax.

Inferiorly passes on to the front of the thigh and fuses with the deep fascia of the thigh about 2.5 cm bellow the inguinal ligament.

In the midline inferiorly. It form a tubular sheath for the penis (or clitoris) so it doesn’t attach to the pubis.

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Bellow the perineum it inters the wall of the scrotum. From here it passes to be attached on each side to the pubic arch and there its referred as Colles fascia.

Posteriorly it fuses with the perineal body and the posterior margin of the perineal membrane.

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Deep fascia. Is a thin layer of connective tissue covering

the muscles, it lies immediately deep to the membranous layer of superficial fascia.

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Muscles of the anterior abdominal wall.It connects the thoracic cage to the hip bones as

a three large flat sheets and a wide vertical muscle.

1. External oblique.2. Internal oblique.3. Transversus abdominal. 4. Rectus abdominis.

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Other anterior abdominal wall muscles.1. Pyramidalis muscle.2. Cremasteric muscle.

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External Oblique The external oblique muscle is a broad, thin,

muscular sheet that arises from the outer surfaces of the lower eight ribs and

fans out to be inserted into1. The xiphoid process.2. The linea alba.3. The pubic crest. 4. The pubic tubercle.5. The anterior half of the iliac crest.

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Most of the fibers are inserted by means of a broad aponeurosis.

the most posterior fibers passing down to the iliac crest form a posterior free border.

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superficial inguinal ring is a triangular-shaped defect in the external oblique aponeurosis lies immediately above and medial to the pubic tubercle.

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The spermatic cord (or round ligament of the uterus) passes through this opening and carries the external spermatic fascia (or the external covering of the round ligament of the uterus) from the margins of the ring

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Between the anterior superior iliac spine and the pubic tubercle, the lower border of the aponeurosis is folded backward on itself, forming the inguinal ligament.

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From the medial end of the ligament, the lacunar ligament extends backward and upward to the pectineal line on the superior ramus of the pubis . Its sharp, free crescentic edge forms the medial margin of the femoral ring

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The lateral part of the posterior edge of the inguinal ligament gives origin to

1. part of the internal oblique 2. transversus abdominis muscles. To the inferior rounded border of the inguinal

ligament is attached the deep fascia of the thigh, the fascia lata

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Internal Oblique The internal oblique muscle is also a broad,

thin, muscular sheet that lies deep to the external oblique; most of its fibers run at right angles to those of the external oblique.

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It arises from 1. the lumbar fascia,2. the anterior two thirds of the iliac crest,3. and the lateral two thirds of the inguinal

ligament. The muscle fibers radiate as they pass upward

and forward.

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It inserts into1. the lower borders of the lower three ribs and their

costal cartilages.2. the xiphoid process.3. the linea alba.4. and the symphysis pubis.

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The internal oblique has a lower free border that arches over the spermatic cord (or round ligament of the uterus) and then descends behind it to be attached to the pubic crest and the pectineal line.

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Near their insertion, the lowest tendinous fibers are joined by similar fibers from the transversus abdominis to form the conjoint tendon.

The conjoint tendon is attached medially to the linea alba.

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As the spermatic cord (or round ligament of

the uterus) passes under the lower border of the internal oblique, it carries with it some of the muscle fibers that are called the cremaster muscle.

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The transversus muscle is a thin sheet of muscle that lies deep to the

internal oblique, and its fibers run horizontally forward

It arises from the 1. deep surface of the lower six costal cartilages

(interdigitating with the diaphragm),2. the lumbar fascia, 3. the anterior two thirds of the iliac crest,4. and the lateral third of the inguinal ligament.

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The posterior border of the external oblique muscle is free,

whereas the posterior borders of the internal oblique and transversus muscles are attached to the lumbar vertebrae by the lumbar fascia

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Rectus Abdominis The rectus abdominis is a long strap muscle

that extends along the whole length of the anterior abdominal wall.

It is broader above and lies close to the midline, being separated from its fellow by the linea alba.

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It arises by two heads1. from the front of the symphysis pubis.2. from the pubic crest. It inserts1. into the fifth, sixth, and seventh costal cartilages

and2. the xiphoid process . When it contracts, its lateral margin forms a

curved ridge that can be palpated and often seen and is termed the linea semilunaris, this extends from the tip of the ninth costal cartilage to the pubic tubercle.

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The rectus abdominis muscle is divided into distinct segments by three transverse tendinous intersections: at the level of the

1. xiphoid process.2. umbilicus.3. halfway between these two. These intersections are strongly attached to the

anterior wall of the rectus sheath.

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The rectus abdominis is enclosed between the aponeuroses of the external oblique, internal oblique, and transversus muscles which form the rectus sheath

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Pyramidalis The pyramidalis muscle is often absent. It arises by its base from the anterior surface

of the pubis. it inserts into the linea alba. It lies in front of

the lower part of the rectus abdominis.

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Rectus Sheath The rectus sheath is a long fibrous sheath that

encloses the rectus abdominis muscle and pyramidalis muscle (if present)

and contains1. rectus abdominis muscle and pyramidalis

muscle (if present)2. the anterior rami of the lower six thoracic

nerves and3. the superior and inferior epigastric vessels4. and lymph vessels.

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It is formed mainly by the aponeuroses of the three lateral abdominal muscles

For ease of description the rectus sheath is considered at three levels

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1. Above the costal margin, the anterior wall is formed by the aponeurosis of the external oblique. The posterior

wall is formed by the thoracic wall—that is, the fifth, sixth, and seventh costal cartilages and the intercostal spaces.

2. Between the costal margin and the level of the anterior superior iliac spine, the aponeurosis of the internal oblique splits to enclose the rectus muscle; the external oblique aponeurosis is directed in front of the muscle, and the transversus aponeurosis is directed behind the muscle.

3. Between the level of the anterosuperior iliac spine and the pubis, the aponeuroses of all three muscles form the

anterior wall. The posterior wall is absent, and the rectus muscle lies in contact with the fascia transversalis.

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At the site where the aponeuroses forming the posterior wall pass in front of the rectus at the level of the anterior superior iliac spine, the posterior wall has a free, curved lower border called the arcuate line

At this site, the inferior epigastric vessels enter the rectus sheath and pass upward to anastomose with the superior epigastric vessels.

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The rectus sheath is separated from its fellow on the opposite side by a fibrous band called the linea alba. This extends from the xiphoid process down to the symphysis pubis and is formed by the fusion of the aponeuroses of the lateral muscles of the two sides.

Wider above the umbilicus, it narrows down below the umbilicus to be attached to the symphysis pubis.

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The posterior wall of the rectus sheath is not attached to the rectus abdominis muscle.

The anterior wall is firmly attached to it by the muscle's tendinous intersections.

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Function of the Anterior Abdominal Wall Muscles

The oblique muscles laterally flex and rotate the trunk.

The rectus abdominis flexes the trunk and stabilizes the pelvis.

and the pyramidalis keeps the linea alba taut during the process.

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The muscles of the anterior and lateral abdominal walls assist the diaphragm during inspiration by relaxing as the diaphragm descends so that the abdominal viscera can be accommodated.

The muscles assist in the act of forced expiration that occurs during coughing and sneezing by pulling down the ribs and sternum.

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Their tone plays an important part in supporting and protecting the abdominal viscera.

By contracting simultaneously with the diaphragm, with the glottis of the larynx closed, they increase the intra-abdominal pressure and help in micturition, defecation, vomiting, and parturition

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Nerve Supply of Anterior Abdominal Wall Muscles

The oblique and transversus abdominis muscles are supplied by the lower six thoracic nerves and the iliohypogastric and ilioinguinal nerves (L1).

The rectus muscle is supplied by the lower six thoracic nerves.

The pyramidalis is supplied by the 12th thoracic nerve.

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The nerves of the anterior abdominal wall are the anterior rami of the lower six thoracic and the first lumbar nerves.

They pass forward in the interval between the internal oblique and the transversus muscles.

The thoracic nerves are the lower five intercostal nerves and the subcostal nerves

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and the first lumbar nerve is represented by the iliohypogastric and ilioinguinal nerves, branches of the lumbar plexus.

They supply the skin of the anterior abdominal wall, the muscles, and the parietal peritoneum.

The lower six thoracic nerves pierce the posterior wall of the rectus sheath to supply the rectus muscle and the pyramidalis (T12 only).

They terminate by piercing the anterior wall of the sheath and supplying the skin.

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The first lumbar nerve has a similar course, but it does not enter the rectus sheath.

It is represented by the iliohypogastric nerve, which pierces the external oblique aponeurosis above the superficial inguinal ring,

and by the ilioinguinal nerve, which emerges through the ring.

They end by supplying the skin just above the inguinal ligament and symphysis pubis.

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Dermatomes of the abdominal wall. The xiphoid process: T7 The umbilicus: T10 The pubis: L1

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The fascia transversalis is a thin layer of fascia that lines the

transversus abdominis muscle and is continuous with a similar layer lining the diaphragm and the iliacus muscle

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Extraperitoneal Fat The extraperitoneal fat is a thin layer of

connective tissue that contains a variable amount of fat and lies between the fascia transversalis and the parietal peritoneum.

Parietal Peritoneum The walls of the abdomen are lined with

parietal peritoneum. This is a thin serous membrane and is continuous below with the parietal peritoneum lining the pelvis.

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