Abdomin

Anatomy

The Abdomen
The abdomen :
The region between diaphragm and pelvic inlet.
The abdominal wall :
Surface anatomy :
Umbilicus : It is a consolidated scar representing the site of attachment of the umbilical cord in fetus, it is situated in the midline . lies at the level between L3 , L4 vertebrae .
Vertical lines: each vertical line (Rt & Lt) passes through the midpoint between the anterior superior iliac spine and symphysis pubis.
Subcostal plane :The horizontal subcostal plane joins the lowest point of the costal margin on each side (that is the 10 th costal cartilage). This plane lies at the level of L3 .
Intertubercular plane :
It joins the tubercle on the iliac crests and lies at the level of L5 .

For localization of pain or swelling or for location of deep structures , the abdomen is divided by the 2 vertical lines + subcostal plane + intertubercular plane into 9 regions : epigastric + Rt & Lt hypochonderial + umbilical +Rt & Lt lumbar (flank) + hypogastric + Rt & Lt iliac (inguinal , groin) regions .

Superficial fascia :

It is divided into 2 layers :
Superficial fatty layer (Camper's fascia)
Deep membranous layer (Scarpa's fascia)
The superficial fatty layer is continuous with the superficial fat over the rest of the body, while the membranous layer is confined to the abdominal region and it is attached to fascia lata of the thigh, thus retention of fluid in the abdominal wall will not descend into the thigh.
MUSCLES OF ABDOMINAL WALL
Muscles of the anterolateral abdominal wall :
In the anterolateral abdominal wall we have three broad muscular sheets , that are aponeurotic in front , and these muscles from exterior to interior are:
1-External oblique. 2-Internal oblique. 3- Transversus abdominis.
Cremaster muscle (around spermatic cord) which is derived from the lower fibers of the internal oblique .
Muscles in the anterior abdominal wall : there are 2 vertical muscles
1-Rectus abdominis . 2-Pyramidalis .
Muscles of the posterior abdominal wall are:
1. quadrates lumborum. 2. psoas muscles ( major & minor ).
Anterolateral muscles
External oblique muscle:
Arises from the outer surfaces of the lower eight ribs , the muscle fibers are directed downward , forward and medially to be inserted by its aponeurosis into the linea alba (a midline vertical fibrous band , extends from the xiphoid process down to the symphysis pubis), xiphoid process , pubic bone.
The most posterior muscle fibers descend vertical & inserted into the anterior half of the iliac crest .
The external oblique aponeurosis will give the following derivatives :
Inguinal ligament :
It is formed by the thickening & backward folding of the lower border of ext. oblique aponeurosis on itself , between the anterior Superior iliac spine & pubic tubercle .
Lacunar ligament :
It is a horizontal & backward extension of the medial end of inguinal ligament ( ing. lig.) on the pectineal line of the superior ramus of the pubis.
Pectineal ligament :
It is the lateralward continuation of the lacunar ligament along the pectineal line .
The crura ( med. & lat. Crura ) of the superficial inguinal ring :
The superficial inguinal ring is a triangular shaped cleft in the external oblique aponeurosis , it lies immediately above & lateral to the pubic tubercle . the ring is bordered on either side by strong fibrous bands which are the medial & lateral crura which are derived from the external oblique aponeurosis .(spermatic cord or round ligament of uterus pass through the superficial inguinal ring)
Intercrural fibers :
These fibers extend from the inguinal ligament crossing the crura ,giving them strength .
External spermatic fascia :
It is the continuation of the intercrural fibers along the spermatic cord .
The external oblique aponeurosis shares in the formation of the anterior wall of rectus sheath .


Internal oblique muscle :
It arises from the lumbar fascia , iliac crest , inguinal ligament & iliacus fascia. The muscle fibers will radiate and most of them will directed upward ,forward & medially running at right angles to those of external oblique muscle. The muscle is inserted into the linea alba ,xiphoid process, pubic symphysis by its aponeurosis & to the lower borders of the lower three ribs & their costal cartilages.
Note: During descending of testes, as the spermatic cord or round ligament of uterus passes under the lower border of the internal oblique , it carries with some muscle fibers that are called cremaster muscle.
Internal oblique shares in the formation of the anterior & posterior walls of rectus sheath.

Transversus abdominis muscle :

The inner most layer , it arises from the inner surface of the lower six costal cartilages, lumbar fascia , iliac crest & inguinal ligament .
The fibers runs horizontally , forward & medially to be inserted through its aponeurosis to the linea alba , xiphoid process & symphsis pubis.
This muscle also share in the formation of the posterior wall of rectus sheath.
Conjoint tendon ( falx inguinalis )
It is the lowest tendinous fibers of the internal oblique & the transversus abdominis muscles that joined each other. It is attached medially to the linea alba & fixed to pubic crest & pectineal line .
Action of external & internal oblique muscles :
Support abdominal contents.
Compress abdominal contents.
Flexion & rotation of the trunk.
Assist in expiration , micturition ,defecation ,parturition & vomiting.
Action of transverssus abdominis muscle: compresses abdominal contents.

The multi-direction arrangement of muscle fibers of anterolateral muscle is helpful point in surgery ,because the surgeon will make a small muscle-splitting incision.
Anterior muscles
Rectus abdominis muscle :
It is a vertical muscle along the anterior abdominal wall lying on either side of linea alba. It is broad & thin above , while narrow & thick below. The muscle arises from the superior ramus of pubis & symphysis pubis. It inserts into 5th , 6th and 7th costal cartilages & xiphoid process. Its lateral border form a curved ridge called linea semilunaris (it extends from the tip of the 9th costal cartilage to the pubic tubercle) .
The rectus abdominis muscle is divided into segments by three transverse tendinous intersections , one at the level of xiphoid process, one at the level of umbilicus & one half way between these two.
Pyramidalis muscle :
It is a small triangular muscle, often absent.
Rectus sheath :
It is a fibrous sheath that encloses the rectus abdominis & the pyramidalis muscles. This sheath contains in addition to these 2 muscles , the anterior rami of the lower six thoracic nerves & the superior & inferior epigastric arteries. The sheath is formed mainly by the aponeuroses of the three anterolateral abdominal muscles.
Formation of the rectus sheath :
In the upper 3/4 of the abdominal wall ( between the costal margin & the level of the anterior superior iliac spine ) , the aponeurosis of the internal oblique splits at the lateral border the rectus abdominis muscle into ant. and post. layers to enclose the rectus abdominis, the external oblique aponeurosis is directed in front of the ant. layer of internal oblique aponeurosis, while the transversus abdominis aponeurosis is directed behind the post. layer of internal oblique aponeurosis.
(thus the anterior wall = aponeuroses of internal & external oblique ms.
& the posterior wall = aponeuroses of internal &transverses abdominis ms)
In the lower 1/4 of the abdominal wall (between the level of the anterior superior iliac spine & the pubis ) , the aponeuroses of the three muscles ( int.& ext. & trans. ms.) form the anterior wall, while the posterior wall is absent from apponeurosis & the rectus muscle lies in contact with transverslis fascia (form posterior wall) .
The line of shifting in the arrangement of these aponeuroses is called arcuate line. At this site the inferior epigastric vessels enter the rectus sheath.
The posterior wall of the rectus sheath is not attached to rectus abdominis muscle, while the anterior wall is firmly attached to the muscle by tendinous intersections.


Posterior abdominal wall muscles
Quadratus lumborum :
Arises from the posterior part of iliac crest & ascends upward to be inserted into last rib. It bends the trunk toward the same side. It is supplied by T12 & upper 3 lumbar nerves.
Psoas muscle :
Arise from the sides & bodies & transverse processes of lumbar vertebrae & also from 12th thoracic vertebra to be inserted into the lesser trochanter of femur with iliacus muscle. It flexes the thigh at the hip joint.
( nerve supply is through upper 4 lumbar nerves )