Anterior Abdominal Wall Anatomy and Layers

• Study notes on the anterior abdominal wall

Pelvic Bone Anatomy

• Pubic symphysis is the fibro-cartilaginous joint where the two pubic bones meet.
• Pubis is the medial anterior part of the pelvis.
• Ischium refers to the lower posterior parts of the pelvis.
• Ilium makes up the upper portion of the pelvis.
• Pubic tubercle serves as the attachment for the inguinal ligament.
• Pubic crest is the origin of the rectus abdominis muscle.
• Anterior superior iliac spine (ASIS) is another attachment point for the inguinal ligament and creates a noticeable bump.
• Iliac crest refers to the upper margin of the iliac bones.
• The three main sections of the pelvic bone are the ilium, pubis, and ischium.

Abdominal Wall Layers

• The layers of the abdominal wall, from superficial to deep, are:
  • Skin
  • Camper's fascia (fatty)
  • Scarpa's fascia (membranous)
  • External oblique (with deep fascia)
  • Internal oblique (with deep fascia)
  • Transversus abdominus (with deep fascia)
  • Transversalis fascia
  • Extraperitoneal fat
  • Parietal peritoneum

Abdominal Wall Muscles

• Lateral abdominal wall consists of three muscle groups: external oblique, internal oblique, and transversus abdominus.
• Rectus abdominis makes up the anterior abdominal wall.
• External oblique muscle attaches from ribs 5-12 to the iliac crest, ASIS to pubic tubercle, and the rectus sheath.
• Internal oblique muscle attaches to the lower ribs, costal cartilages, iliac crest, thoracolumbar fascia, inguinal ligament, pubic bone, and rectus sheath.
• Transversus abdominus muscle attaches to lower ribs, costal cartilages, iliac crest, inguinal ligament, pubic bone, and rectus sheath.
• Inguinal ligament extends from the pubic bone to the anterior superior iliac spine.
• Rectus abdominis is the "abs" muscle.
• Tendinous intersections are three transverse bands of collagen fibers dividing the rectus abdominis.
• Linea alba is a midline tendinous seam joining the abdominal muscles.
• Rectus abdominis muscle attaches to costal cartilages 5-7, xiphoid process, pubic crest, and pubic symphysis.
• Aponeurosis is a flat fibrous sheet of connective tissue that attaches muscle to bone or other tissue, possibly acting as fascia.
• External oblique, internal oblique, and transversus abdominus muscles form the rectus sheath through aponeurosis.

Rectus Sheath Aponeurosis

• Above the arcuate line:
  • Anterior layer of the rectus sheath is formed by the external and internal oblique aponeuroses.
  • Posterior layer is formed by the internal oblique and transversus abdominus aponeuroses.
• Below the arcuate line:
  • Anterior layer is formed by the external oblique, internal oblique, and transversus abdominus aponeuroses.
  • There is no posterior layer below the arcuate line.

Abdominal Muscle Actions

• Abdominal muscles work synergistically and antagonistically.
• Trunk flexion involves the synergistic action of external obliques, internal obliques, and rectus abdominis.
• Trunk rotation involves the synergistic action of contralateral external and internal obliques.
• Abdominal compression involves the synergistic action of the external oblique, internal oblique, rectus abdominis, and transversus abdominal muscles.

Nerve Supply

• Abdominal muscles are innervated by:
  • Thoracoabdominal nerves (T6-T11)
  • Subcostal nerves (T12)
  • Ilioinguinal/iliohypogastric nerves (L1)
• Intercostal nerves continue as thoracoabdominal nerves.
• Lateral cutaneous branch stems from the intercostal nerves to innervate the skin of the lateral chest wall.
• Anterior cutaneous branch stems from the intercostal nerves to innervate the skin of the anterior chest wall.

Arteries

• Internal thoracic artery is a branch of the subclavian artery that supplies the pericardium and anterior chest wall.
• Musculophrenic artery is a terminal branch of the internal thoracic artery.
• Superior epigastric artery is a continuation of the internal thoracic artery.
• Intercostal and subcostal arteries are small paired arteries branching from the posterior thoracic aorta.
• Inferior epigastric artery is a branch of the external iliac artery.
• External iliac artery supplies the lower limbs.

Inguinal Region

• The inguinal region extends from the ASIS to the pubic bone.
• The inguinal canal contains:
  • Spermatic cord (male) + vasculature
  • Round ligament of uterus (female)
  • Ilioinguinal nerve (L1)
  • Genital branch of genitofemoral nerve (L1-L2)
• The inguinal canal begins at the deep inguinal ring and ends at the superficial inguinal ring.
• Superficial inguinal ring is a triangular opening in the external oblique aponeurosis.
• Deep inguinal ring is an opening in the transversalis fascia.
• The inguinal ligament forms the inferior border of the inguinal canal.
• Cremasteric muscle, an extension of the internal oblique, descends to the testis and raises/lowers it in response to stimuli.
• The inguinal canal forms in response to the development of reproductive organs.
• Gubernaculum pulls the testes through the inguinal canal, or becomes the round ligament of the uterus.

Scrotum

• Transversalis fascia becomes the internal spermatic fascia in the scrotum.
• Internal oblique muscle becomes the cremaster spermatic fascia in the scrotum.
• External oblique aponeurosis becomes the external spermatic fascia in the scrotum.
• Dartos muscle wrinkles the scrotal skin and pulls the scrotum close to the body.
• Tunica vaginalis covers the testis and epididymis.
• Testis is the male reproductive organ that produces sperm and hormones.
• Spermatic cord extends upward from the epididymis and attaches to each testicle.
• Medial crus is the medial margin of the superficial inguinal ring.
• Genitofemoral nerve (L1-L2) innervates male/female genitalia and the male cremaster muscle.

Inguinal Hernias

• Inguinal hernias are protrusions of abdominal viscera into the inguinal canal.
• Two types of inguinal hernias: direct (acquired) and indirect (congenital).
• Direct hernia: Weakening of the abdominal wall leads to the intestine running parallel to the spermatic cord.
• Indirect hernia: Intestine passes through the deep ring and travels with the spermatic cord.

Concise study notes on the anterior abdominal wall. Covers pelvic bone anatomy, including the ilium, pubis, ischium, and key landmarks like the ASIS and pubic tubercle. Also details abdominal wall layers from superficial skin to the deep transversus abdominis.