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Overview of GI tract and Abdominal Wall BY NADI AHMEDWhat we will cover today: 1 2 3 4 contents of the 9 contents of the 4 anatomicalhe microscopic blueprint abdominal regions abdominal quadrants arrangement of the of the wall of the anterolateral gastrointestinal tract inguinal ligamentdThe 9 regions of the abdomen• Transpyloric plane cuts through the pylorus of the stomach (also called subcostal plane) • Intertubercular plane cuts through the iliac tubercles of the pelvis • All abdominal contents are found in these 9 zones1) Right hypochondrium 2) Epigastrium 3) Left hypochondrium 4) Right Lumbar 5) Umbilical 6) Left Lumbar 7) Right inguinal 8) Suprapubic 9) Left groin The contents of the 9 regionsThe Abdominal QuadrantsA. Right upper quadrant (RUQ) B. Left upper quadrant (LUQ) C. Right lower quadrant (RLQ) D. Left lower quadrant (LLQ)Content of each quadrantThe Superficial Fascia The superficial fascia is connective tissue. The composition of this layer dependson its location: •Above the umbilicus – a single sheet of connective tissue. It is •Below the umbilicus – divided into two layers; the fatty superficial layer (Camper’s fascia) and the membranous deep layer (Scarpa’s fascia). • The superficial vesselsand nervesrun between these two layers offascia.Muscles of the abdominal wall • The muscles of the anterolateral abdominal wall can be divided into two main groups: • Flat muscles – three flat muscles, situated laterally on either side of the abdomen. • Vertical muscles – two vertical muscles, situated near the mid-line of the body.Flat Muscles Attachments (Origin → Muscle Insertion) Actions Innervation Ribs 5-12 → Iliac crest, Contralateral rotation of the Thoracoabdominal nerves External Oblique (T7-T11), Subcostal nerve pubic tubercle torso (T12) Inguinal ligament, iliac Bilateral: Compresses Thoracoabdominal nerves (T7-T11), Subcostal nerve Internal Oblique crest, lumbodorsal fascia → abdomen; Unilateral: (T12), Branches of lumbar Ribs 10-12 Ipsilateral rotation of torso plexus Inguinal ligament, costal cartilages 7-12, iliac crest, Thoracoabdominal nerves thoracolumbar fascia → Compression of abdominal (T7-T11), Subcostal nerve Transversus Abdominis Conjoint tendon, xiphoid contents (T12), Branches of lumbar process, linea alba, pubic plexus crestVertical Muscles Muscle Attachments (Origin → Actions Innervation Insertion) Pubic crest → Xiphoid Compresses abdominal Rectus Abdominis process, costal cartilage ofviscera, stabilizes pelvis Thoracoabdominal nerves during walking, (T7-T11) ribs 5-7 depresses ribs Pyramidalis Pubic crest, pubic Tenses the linea alba Subcostal nerve (T12) symphysis → Linea alba• A - internal oblique • B - external oblique • C - rectus abdominis • D - transversus abdominis Rectus Sheath • Rectus Sheath: Formed by the aponeuroses of the three flat muscles; encloses the rectus abdominis and pyramidalis. Anterior Wall: • Formed by the external oblique aponeurosis and half of the internal oblique aponeurosis. Posterior Wall: • Formed by half of the internal oblique aponeurosis and the transversus abdominis aponeurosis. Arcuate Line: Located midway between the umbilicus and pubic symphysis. • Below this point, all aponeuroses move to the anterior wall, leaving no posterior wall. Transverse section of rectus sheath A. Parietal peritoneum B. Transversalis fasica C. Transversus abdominis D. Internal oblique E. External oblique F. Linear alba G. Rectus abdominis Dermatomes of the anterior abdominal wall A - epigastric region T5-T9, B – umbilical region T10-T11 C – hypogastric region T12- L1 Blood vessels that supply the anterior abdominal wall • The 2 main vessels which supply the anterior abdominal wall are the superior and inferior epigastric arteries, which run in the rectus sheath posterior to the rectus abdominis muscle - The superior epigastric artery arises from the internal thoracic - The inferior epigastric artery arises from the external iliac • The abdominal wall also receives blood from the: - Musculophrenic - internal thoracic - Subcostal - thoracic aorta - Superficial epigastric - femoral - Superficial circumflex iliac - femoral - Deep circumflex iliac - external iliacInguinal Canal • Short passage that extends inferiorly and medially, through the inferior part of the abdominal wall • It is superior and parallel to the inguinal ligament • It acts as a pathway by which structures can pass from the abdominal wall to the external genitalia • It also has clinical importance: acts as a potential weakness in the abdominal wall and so is a common site of herniation Deep (internal) Ring of inguinal canal • Above the midpoint of the inguinal ligament - lateral to the inferior epigastric vessels • Midway between the anterior superior iliac spine and the pubic symphasis • Created by the transversalis fascia - invaginates to form a covering of the contents of the inguinal canal - Forms the internal spermatic fascia of the spermatic cord in men and the round ligament in women • Forms the beginning of the inguinal canal Superficial Ring of inguinal canal • Marks end of inguinal canal - lies just superior to the pubic tubercle • Formed by the evagination of the external oblique, which forms another covering of the inguinal canal contents • Triangle shaped opening - Apex points superolaterally - Base is formed by the pubic crest - Medial crus are attached to the pubic symphasis - Lateral crus are attached to the pubic tubercle • At the apex opening, the 2 crura are held together by intercrural (crossing) fibres, which run perpendicular to the aponeurosis of the external oblique and prevent the ring form widening • This continuation of tissue is the external spermatic fascia Histology of the GI Tract INSIDE OUTSIDEHistology of GI Tract Summary of layers of GI Tract •Mucosa (Innermost Layer) •Epithelium: •Stratified squamous (oral cavity, pharynx, esophagus) → withstands mechanical stress. •Simple columnar (rest of GI tract) → secretion & absorption. •Enteroendocrine cells secrete hormones to regulate digestion.Lamina propria: •Areolar tissue containing blood vessels, nerves, lymphatics, smooth muscle, and mucous gland cells. •Muscularis mucosae: •Thin smooth muscle layer (inner circular & outer longitudinal). •Contractions alter lumen shape & move epithelial folds. •Submucosa •Dense irregular connective tissue with blood vessels, lymphatics, and Meissner’s plexus (sensory & autonomic neurons). •May contain exocrine glands that secrete buffers & enzymes. •Muscularis Externa •Smooth muscle: Inner circular layer & outer longitudinal layer. •Myenteric plexus (between muscle layers): •Parasympathetic (PSNS) → increases muscle tone & activity. •Sympathetic → inhibits contraction (relaxation). •Adventitia/Serosa (Outer Layer) •Serosa (mesothelial covering) in most of the GI tract. •Adventitia (fibrous connective tissue) in oral cavity, pharynx, esophagus, rectum → firmly attaches structures.