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The anterior abdominal wall
Branches of the internal thoracic artery
(1) The superior epigastric artery enters the rec-tus sheath, deep to the seventh costal cartilage.
It lies deep to the rectus abdominis, supplies that muscle, and sends branches through it to the over-lying skin. It anastomoses with the inferior epigas-tric artery.
(2) The musculophrenic artery runs along the up-per surface of the costal origin of the diaphragm to the eighth intercostal space. It gives branches to the diaphragm and anterior abdominal wall.
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Arteries of the anterior abdominal wall
See Clinical Applications 8.1 and 8.2 for the prac-tical implications of the anatomy in this chapter.
the abdominal wall deep to the internal oblique muscle.
CLINICAL APPLICATION 8.1 Hernias The presence of the femoral and inguinal canals at the
lowest part of the abdomen means that there is con-tinuous pressure on these canals from the weight of the abdominal contents. Hernias tend to occur where struc-tures enter or leave the abdominal or pelvic cavities and the wall is either intrinsically weak or has been weakened by surgery. Hernias can also occur more easily when the abdominal wall is stretched by excessive accumulation of fat in the abdomen or following repeated pregnancies.
The presence of chronic cough, lifting of heavy weights, or straining to pass urine through a partially obstructed urethra may also cause or aggravate a hernia.
In a femoral hernia, the peritoneum overlying the abdominal end of the femoral canal is forced through it into the proximal part of the thigh. This outpocket of peritoneum forms the hernial sac. The hernial sac passes through the femoral ring, formed by the inguinal liga-ment anteriorly, the lacunar ligaliga-ment medially, and the pectineal ligament posteriorly. The pressure of this ring on the herniating bowel may obstruct the loop of the small intestine in the sac or even cut off its blood supply so that it becomes gangrenous. Relieving the pressure on the femoral ring is usually achieved by dividing the lacunar ligament, a procedure which requires caution so as not to injure an abnormal obturator artery which may lie on it.
Protrusion of an abdominal viscus through the abdominal wall of the inguinal region is an inguinal hernia. An indirect inguinal hernia arises lateral to the inferior epigastric artery and traverses the inguinal canal.
It may be predisposed to by the persistence of the processus vaginalis. The processus vaginalis is the tube of peritoneum which extends from the abdomen into the scrotum, along which the testis descends [Chapter 9].
Under normal circumstances, the cavity of the processus is obliterated shortly after birth, leaving only a small part of it around the testis patent. If the processus persists, it forms a ready-made hernial sac, along which a loop of intestine may pass. This is one type of indirect inguinal hernia. The other type occurs when a secondary hernial sac passes through the inguinal canal from deep to su-perficial inguinal rings. A direct inguinal hernia usually occurs from the weakening of the conjoint tendon. The hernial sac pushes through the weakened conjoint ten-don and distending the superficial inguinal ring. Direct inguinal hernias arise medial to the inferior epigastric artery.
An umbilical hernia usually occurs as a result of ab-dominal distension, e.g. by repeated pregnancies. The umbilical scar in the linea alba tends to stretch and thin.
Unlike the muscular parts of the abdominal wall, it does not return to its normal thickness once the distending force is removed and it may subsequently bulge out-wards, forming a hernial sac. In utero, there is a physi-ological extension of the peritoneal cavity into the root of the umbilical cord. If this persists, a congenital umbilical hernia is present at birth. The presence of a peritoneal dimple at the umbilicus, as at the deep ingui-nal ring, following obliteration of the peritoneal exten-sion, may also facilitate a hernia at these points.
CLINICAL APPLICATION 8.2 Superficial reflexes
Abdominal reflexes
Superficial reflexes are reflexes that have evolved to protect the viscera from external danger. The ab-dominal reflex consists of contraction of abab-dominal muscles in response to sensory abdominal stimula-tion (in an effort to protect the abdominal viscera). To elicit the reflex, the subject is made to lie down
com-fortably, with the anterior abdominal wall exposed.
Using a blunt object, the abdominal skin is gently stroked from lateral to medial. A normal positive re-sponse is the contraction of the underlying abdominal muscles, with the umbilicus moving to the side of the stimulus. The test is done on all four quadrants of the abdomen.
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The anterior abdominal wall
Study question 1: what cutaneous nerves supply the anterior abdominal wall? (Answer: ventral rami of T. 7–T. 12.)
Study question 2: which of these nerves are likely to be affected in a patient who has an absent abdominal reflex in the right lower quadrant? (Answer: from the informa-tion given, it is clear that the reflex is normal on the left, so the nerves on the left side are unaffected. The reflex is also normal in the right upper quadrant. As the skin around the umbilicus is supplied by the ventral ramus of T. 10, it is likely that the lower thoracic nerves (T. 10–T. 12) of the right side are affected.)
Cremasteric reflex
Contraction of the cremaster muscle pulls the testis up towards the superficial inguinal ring (in an effort to pro-tect the testis from injury). To elicit the reflex, the skin on the medial side of the upper thigh is lightly stroked.
The upward movement of the testis on the same side indicates a positive test.
Study question 1: what is the sensory nerve supply to the medial side of the upper thigh? (Answer: the ilio-inguinal nerve (L. 1)).
Study question 2: what is the nerve supply of the cremaster muscle? (Answer: the genital branch of the genitofemoral nerve (L. 1, L. 2)).
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contracts, it decreases the surface area of the scro-tum and helps to decrease the heat loss through the thin, fat-free skin. The dartos also forms an in-complete septum between the testes. Each testis is covered by three fascial sheaths—the external spermatic fascia, the cremasteric fascia and muscle, and the internal spermatic fascia. In the scrotum, these layers are fused together and are difficult to differentiate, except by the presence of loops of the cremaster muscle in the middle layer. The testis is The male external genitalia includes the penis,
the scrotum, and its contents—the testes and spermatic cords.