Fares Jaber Anatomy Lecture 25 May 1st 2012

Abdominal Wall

Anterior : Has four muscles set into three layers.

Outermost Layer: External Oblique muscle Its fibers run downwards forwards and medially, which means it originates from above, namely the lower eight ribs. It inserts into an acute angle made up of a vertical line called the and a horizontal line made up of the Pubic Tubercle, the Ligament and the Iliac Crest.

Linea Alba (vertical line): is a fibrous structure that runs down the midline of the from Xiphoid process to Pubic Symphysis. The name means white line and the Linea Alba is indeed white, being composed mostly of collagen .

Horizontal Line: to understand the horizontal line we have to take a look at the hip bone. It is made up of three main parts.

1) Lower anterior part, called the , has a tubercle on its upper part, called the Pubic Tubercle 2) Upper part, called the Ilium. The upper border of the Ilium is a bit wide, and thus called the Iliac Crest 3) Lower posterior part: called the Ischium

Between the Pubic Tubercle and the Iliac Crest there is free space, in which the fibers of the External Oblique rolls upon itself to form a ligament, called the .

To sum up, External Oblique inserts into the horizontal line starting medially at the Pubic Tubercle, then laterally it rolls upon itself in the space between the Pubic Tubercle and the Iliac

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Fares Jaber Anatomy Lecture 25 May 1st 2012

Crest to form the Inguinal Ligament, and most laterally inserts into the Iliac Crest. It also inserts into the vertical line in the Linea Alba.

Notes  The Inguinal Ligament separates the abdomen above from the lower limb below.  In the lower fibers of the External Oblique, just above the Pubic Tubercle, there is an opening called the Superficial Inguinal Ring.

Middle Layer: Internal Oblique muscle Its fibers run upwards forwards and medially, which means it originates from below, namely the Inguinal Ligament, and the Iliac Crest. It inserts into an acute angle made up of the Symphasis Pubis, the Linea Alba and the lower three ribs.

Its lower fibers participate in forming an arch tendon called the Conjoint tendon.

Inner Layer: Transversus Abdominis muscle It is called Transversus because it runs horizontally medially and forwards till it inserts into the Linea Alba. It shares its origin with both the External and Internal Obliques, to be originating below from [medial to lateral: the Inguinal Ligament and the Iliac Crest] as well as from the lower six ribs above.

Its lower fibers participate in forming an arch tendon called the Conjoint tendon. Facia Transversalis is a thin layer of facia that lines the Transversus Abdominis muscle.

The Linea Alba is a common insertion site for the last three muscles.

Rectus Abdominis muscle: It originates inferiorly from the Pubic Tubercle(front of the Symphysis Pubis and from the Pubic Crest according to the book) and runs upwards straight till it inserts into the 5th, 6th and 7th costal cartilage. While the External Oblique, the Internal Oblique and the Transversus Abdominis run medially to be inserted on the Linea Alba, they get crossed in the center by the Rectus Abdominis. At the crossing point, the fibrous tendon of the Internal Oblique get divided into two, and the insertion of the three muscles makes two layers, one anterior to the , and one posterior to the Rectus Abdominis muscle. This fibrous sheath surrounds the Rectus Abdominis completely, forming a structure called the .

Rectus Sheath: It encloses the Rectus Abdominis muscle completely and contains the superior and inferior epigastric vessels and lymph vessels. It is formed mainly by the of the External Oblique, the Internal Oblique and the Transversus Abdominis muscles.

Nerve Supply: All the above muscles are supplied by the lower five intercostal nerves and the subcostal nerves sensory and motor.

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Fares Jaber Anatomy Lecture 25 May 1st 2012

Blood Supply: Superior Epigastric artery branching from the Internal Thoracic Artery, and the Inferior Epigastric artery

The veins have corresponding names to the arteries

Lymphatic Drainage: Above the umbilicus level, the lymph drains into the Axilla. Below the umbilicus level, the lymph drains into the Inguinal lymph nodes.

Action: 1) Supports abdominal contents (muscle tone* holds viscera** in position) 2) When contracted they push the diaphragm above, which in turn compresses the lungs, aiding in expiration 3) When contracted while keeping the diaphragm fixed, they increase the intra- abdominal pressure, which helps in vomiting, defecation and parturition (giving birth) 4) Being oblique in direction, they assist in flexing and rotating the trunk (lateral rotation of the vertebral column)

*: muscle tone is the continuous and passive partial contraction of the muscles, or the muscle’s resistance to passive stretch during resting state **: viscera refers to the soft internal organs of the body, especially those contained within the abdominal and thoracic cavities

The : The Facia Transversalis has an opening near the Inguinal region called the Deep Inguinal Ring. The Inguinal Canal is an oblique passage through the lower part of the anterior abdominal wall. It is formed by the Deep Inguinal Ring of the Facia Transversalis, the Superficial Inguinal Ring of the External Oblique, and roofed by the arch Conjoint tendon of the Internal Oblique and the Transversus Abdominis.

Function of the Inguinal Canal (Advantage): In males, it provides passageway for the Spermatic cord to pass into the abdomen. In females, it permits the passage of the round ligament of the uterus. It is more important and big in males, and is rudimentary in females.

Inguinal Hernia: If the intra-abdominal pressure increases, viscera of the abdominal cavity can be displaced and moved to the Inguinal Canal causing an . The risk of Inguinal hernia is bigger in males than females, because the Inguinal Canal is relatively small in females.

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Fares Jaber Anatomy Lecture 25 May 1st 2012

Diaphragm (Superior "wall") It is a partition that separates the thoracic cavity from the abdominal cavity. It is dome shaped and consists of a peripheral muscular part and central fibrous part, thus it's musculofibrous.

Origin: It originates from the margins of the thoracic openings and the vertebral column. Its origin can be divided into three main parts:

1. Anteriorly it originates from the posterior aspect of the Xiphoid process of the sternum 2. Laterally it originates from the inner aspect of the lower six ribs and their costal cartilages 3. Posteriorly it originates from the vertebral column as two origins, each called a crus. The right crus is larger and originates from the upper three lumbar vertebrae, while the left crus is smaller and originates from the upper two lumbar vertebrae

Insertion: All the origins of the diaphragm fan out and gather in the central part forming the central tendon, which is the most superior point in the diaphragm. The central tendon is made up of fibrous tissue, in contrast to the fleshy origins of the diaphragm along the circumflex of the thorax.

Nerve Supply: The Phrenic nerve with the roots C3, C4, C5. It is considered the most important nerve in the body because if it gets injured, the diaphragm will go into paralysis. Since the diaphragm is the chief respiratory muscle, the body is unable to breathe when it's paralyzed.

Action: When the diaphragm contracts it descends downwards, increasing the vertical diameter of the thoracic cavity, starting the inhaling stage of breathing. That's why the diaphragm is the chief muscle of respiration.

Openings of the diaphragm:

Aortic Opening: It transmits the Aorta. It lies exactly in the midline, opposite to the lower border of T12(it lies anterior to the body of T12 according to the book), behind the diaphragm between the two crura. Why behind the diaphragm? As long as we're breathing, the diaphragm keeps contracting, so if the aorta passed through the diaphragm, it would be constricted continuously by the diaphragm disturbing the supply of blood to the lower half of the body.

Esophageal Opening: It transmits the Esophagus. It is a muscular opening that lies one inch towards the left side, opposite to T10 vertebra. It passes through the diaphragm through the right crus in its fanning part. When we breath the diaphragm descends downwards pressing the stomach, which in turn

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Fares Jaber Anatomy Lecture 25 May 1st 2012 pushes the food inside it through any opening including the Esophagus; but, the right crus acts as a sphincter which contracts along with the diaphragm and closes the Esophagus, preventing retardation of food.

Caval Opening: It transmits the Inferior Vena Cava. It lies one inch towards the right side in relation to the midline. It is the most superior opening opposite to T8. It passes through the fibrous partition, the central tendon. Because the central tendon is made up of fibrous tissue which doesn't contract, the vein stays open through the contraction of the diaphragm.

I advise you to read the book to gain a better understanding of the whole deal. For instance the part about the Rectus Sheath is really only touched upon through the lecture and this sheet. Good luck. -Fares Jaber

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