Lecture 1--Anterior Abdominal Wall NGM Module

Learning Objectives At the end of the session the students should be able to: A. Enumerate layers of anterior abdominal wall. B. Discuss structure of anterior abdominal wall. C. Identify blood supply, lymphatic drainage and nerve supply of anterior abdominal wall. Suggested reading: Clinical Anatomy by Region 9th Edition, PAGE 112 – 131.

Layers of the Anterior Abdominal Wall ABDOMINAL WALL : Bounded superiorly by the xiphoid process and costal margins, posteriorly by the vertebral column, and inferiorly by the upper parts of the pelvic bones. Its layers consist of: – Skin – Superficial fascia; fatty and membranous layers – Muscles – Extra-peritoneal fascia – Peritoneum (parietal)

Skin It is loosely attached to the underlying structures except at the umbilicus. The lines of cleavage in the skin are constant, run downward and forward almost horizontally around the trunk. The umbilicus is a scar representing the site of attachment of the umbilical cord in the fetus.

Superficial Fascia It is divided into: Superficial fatty layer (fascia of Camper): – Continuous with the superficial fat over the rest of the body and may be extremely thick in obese persons. Deep membranous layer (Scarpa's fascia): – A thin layer that blends with the deep fascia of thigh, extends into the penis and scrotum (or labia majora), and into the perineum as Colle’s fascia.

Muscles of the anterior abdominal wall Lateral muscles: – External oblique muscle – Internal oblique muscle – Transversus abdominus muscle They are clinically important in making up of the rectus sheath and the inguinal canal, and also because they must be divided in making lateral abdominal incisions. Rectus abdominus muscle

Lateral muscles External oblique muscle – Arises from outer surfaces of lower eight ribs – Fans out to be inserted into the xiphoid, linea alba, the pubic crest, pubic tubercle and ant ½ of iliac crest. – From pubic tubercle to ant superior iliac spine its lower border forms the inguinal Ligament. Internal oblique muscle – Arises from the lumbar fascia, ant. 2/3 of iliac crest and lateral 2/3 of the inguinal ligament. – Inserted into lowest six costal cartilages, linea alba, and pubic crest.

Contd Transversus abdominus muscle – Arises from lowest six costal cartilages, lumbar fascia, ant. 2/3 of iliac crest and lateral 1/3 of inguinal ligament; – Inserted into the lineal alba and pubic crest. Points to note: The direction of the fibres of Ext oblique is downwards and forwards, the internal oblique upwards and forwards and the transversus abdominus transversely. Ext oblique has its posterior border free but internal and transversus arise from lumbar fascia posteriorly.

Contd Rectus abdominus muscle – Vertically arranged on both sides of the linea alba. – Arises on a 3 inch horizontal line from 5-7 th costal cartilages. – Inserted into the pubic crest for a length of 1 inch. – Lies in a sheath which is formed by the aponeurotic expansions of the lateral muscles.

Actions of abdominal muscles Four main roles: – To move the trunk – To depress the ribs (expiration) – To compress the abdomen (evacuation, expiration and heavy lifting) – To support the viscera (intestines only)

Nerve Supply The rectus abdominus and external oblique muscles, both are supplied by T7-T12 nerves. The internal oblique and transversus abdominus muscles are also supplied by the same nerves (T7-T12) but with the addition of L1.

Blood Supply – Superior epigastric Art(branch of int thoracic Art) – Inferior epigastric Art(branch of external iliac Art) – Post intercostal, subcostal and – Lumbar arteries (branches from the aorta) – Deep circumflex Art(branch of external iliac Art)

Lymphatic drainage Superficial part of wall: – Above the umbilicus → axillary lymph nodes (pectoral group) – Below the umbilicus → superficial inguinal lymph nodes Deep part of wall: – Above the umbilicus → mediastinal lymph nodes – Below the umbilicus → external iliac and para- aortic lymph nodes

Clinical Correlates Membranous layer of superficial fascia and extravasation of urine. Muscle rigidity Surgical incisions