Gastrointestinal System Lecture 01 PDF

Gastrointestinal system Lecture 01 Kumudu Nisansala BSc (Hons) in Human Biology (USJ) Visiting Lecturer, Faculty of Allied Health Sciences, University of Ruhuna Learning outcomes Basic structure of the G...

Gastrointestinal system Lecture 01 Kumudu Nisansala BSc (Hons) in Human Biology (USJ) Visiting Lecturer, Faculty of Allied Health Sciences, University of Ruhuna Learning outcomes Basic structure of the GI system Structure of the anterior abdominal wall Anatomy of the gastrointestinal system Blood supply to the gastrointestinal system Hepato-billiary system Embryological basis for developmental abnormalities of the GI tract  Gastrointestinal system = Digestive system Gastrointestinal tract (GI tract) & its accessory organs Specialized for Ingestion Propulsion Digestion Absorption Elimination of waste products GI tract – long tube extend from mouth to anus Parts of the GI tract Mouth Pharynx Esophagus Stomach Small intestine Large intestine Anus Accessory organs 3 pairs of salivary gland Pancreas Liver & biliary tract Anterior abdominal wall Forms the front boundary of the abdominal cavity Consist of layers arranged from superficial to deep The wall extends from xiphoid process to pubic symphysis Costal margin – superior lateral margins Iliac crest – lower lateral boundary Layers of the anterior abdominal wall 1. Skin 2. Superficial fascia 3. Muscles 4. Transversalis fascia 5. Extraperitoneal fat 6. Parietal peritoneum 1. Skin Outermost layer Thin & elastic Allow enormous stretching Eg: pregnancy & with accumulation of fat, fluid Umbilicus A normal scar in the anterior abdominal wall Remnant of the umbilical cord 2. Superficial fascia Lies beneath the skin Below the level of the umbilicus divided into 2 layers Superficial fatty layer – Fascia of Camper Deep membranous layer – Fascia of Scarpa Fascia of Camper Contain variable amount of fat Continuous with the superficial fascia of the adjoining part of the body In the penis it is devoid of fat & in the scrotum it is replaced by the dartos fascia Fascia of Scarpa Lies deep to the fatty layer Continuous below with the superficial fascia of the perineum (Colles’ fascia), dartos fascia of the penis & fascia lata of the thigh 3. Muscles & aponeuroses Four large muscles – on either side of the midline Flat muscles – External oblique Internal oblique Transversus abdominis Vertical muscle – Rectus abdominis Each flat muscle have an aponeurosis Converge at the midline to form linea alba Forms the rectus sheath around the rectus abdominis muscle External oblique muscle Arises by 8 digitations from the outer surface of the middle shafts of the lower ribs Muscle fibres run inferomedially (hand in pocket direction) The aponeurosis extends medially from the muscle & contributes to Anterior wall of the rectus sheath The formation of the inguinal ligament Internal oblique muscle Lies deep to the external oblique Arises from Lateral two third of the inguinal ligament Anterior two third of the intermediate area of the iliac crest Thoracolumbar fascia Muscle fibres run superomedially  Its aponeurosis splits to 2 layers to enclose the rectus abdominis muscle above the arcuate line Anterior layer – forms the anterior wall of the rectus sheath with external oblique aponeurosis Posterior layer – forms the posterior wall of the rectus sheath with transversus abdominis aponeurosis Transversus abdominis muscle Arises from Lateral one third of the inguinal ligament Anterior two third of the iliac crest Thoracolumbar fascia Inner surfaces of the lower 6 costal cartilages Muscle fibres are directed horizontally forwards (transversely) Its aponeurosis contributes to the posterior wall of the rectus sheath above the arcuate line Below the arcuate line it forms the anterior wall Rectus abdominis muscle Paired vertical muscles running from the pubic symphysis to the xiphoid process & costal cartilages Muscle fibres arise from 2 tendinous heads Lateral head arise from the lateral part of the pubic crest Medial head arise from the medial part of the pubic crest & anterior pubic ligament Muscle fibres run vertically upwards & insert superiorly into the xiphoid process & 5th, 6th & 7th costal cartilages The muscle is enclosed within the rectus sheath Divided into segments by tendinous intersections Rectus sheath An aponeurotic sheath covering the rectus abdominis muscle Formed by aponeuroses of the 3 flat muscles Has 2 walls ; anterior & posterior Anterior wall is complete Posterior wall is incomplete. Deficient below the arcuate line  Laterally the sheath extends till linea semilunaris Curved tendinous landmark on each side Represents the lateral boundary of the rectus muscle Extends from 9th costal cartilage to the pubic tubercle  Above the costal margin Anterior wall – external oblique aponeurosis Posterior – deficient. Rectus muscle rests directly on the 5th, 6th & 7th costal cartilages Between the costal margin & the arcuate line Anterior wall – external oblique aponeurosis & anterior layer of the internal oblique aponeurosis Posterior wall – posterior layer of internal oblique aponeurosis & transversus abdominis aponeurosis Below the arcuate line Anterior wall – aponeuroses of all 3 flat muscles The aponeuroses of the transversus abdominis & internal oblique are fused but external oblique aponeurosis remains separate Posterior wall – deficient The rectus muscle rests on the fascia transversalis 4. Transversalis fascia Inner surface of the abdominal muscles is lined by fascia Separates the abdominal muscles from the peritoneum The part of the fascia which lines the inner surface of the transversus abdominis – transversalis fascia Anteriorly – adherent to the linea alba above the umbilicus Posteriorly – merges with the thoracolumbar fascia & continuous with the renal fascia Inferiorly – attached to the iliac crest, inguinal ligament & continuous with fascia iliaca Medially attached to the pubic tubercle, pubic crest & pectineal line Prolonged into the thigh as anterior wall of the femoral sheath 5. Extraperitoneal fat A layer of connective tissue with variable amounts of fat Lies between the transversalis fascia & the parietal peritoneum 6. Parietal peritoneum The innermost layer A serous membrane lining the abdominal cavity Inguinal ligament Formed by lower border of the external oblique aponeurosis – thickened & folded backwards on itself Extends from the anterior superior iliac spine to the pubic tubercle Lies beneath the fold of the groin Fascia lata is attached to the lower border of the ligament Upper surface gives origin to internal oblique & transversus abdominis Forms the floor of the inguinal canal Inguinal canal An oblique intermuscular passage in the lower part of the anterior abdominal wall 4 cm long Extends from deep inguinal ring to the superficial inguinal ring Deep inguinal ring An oval opening in the transversalis fascia Situated 1.2 cm above the midpoint of the inguinal ligament From the margins of this opening the fascia is projected along the canal Superficial inguinal ring Triangular gap in the external oblique aponeurosis Base – pubic crest Two sides – lateral & medial margins of the opening (crura) Boundaries of the inguinal canal Anterior wall – external oblique aponeurosis & internal oblique muscle Posterior wall – transversalis fascia & conjoint tendon Roof – arching fibres of internal oblique & transversus abdominis muscle Floor – inguinal ligament & lacunar ligament Structures pass through the inguinal canal Spermatic cord in males or round ligament of the uterus in females Ilioinguinal nerve  Inguinal canal – weak point in the anterior abdominal wall Vulnerable to inguinal herniation Inguinal triangle (Hesselbach's triangle) ??? find Blood supply to the anterior abdominal wall Superior epigastric artery – runs in the rectus sheath & supplies the upper portion Inferior epigastric artery – arise from external iliac artery. Enters the rectus sheath anastomoses with superior epigastric. Supplies the lower portion Deep circumflex iliac artery – arise from external iliac artery & supplies inferior & lateral parts Superficial epigastric & superficial circumflex iliac artery – branches of the femoral artery. Supplies the inferior part Small branches of the intercostal & subcostal artery supplies lateral part Lymphatic drainage Superficial lymphatics above the umbilicus drain into the axillary nodes Below the umbilicus – to superficial inguinal lymph nodes Deep lymphatics drainage follow the arteries Lymph along superior epigastric artery drain into – parasternal nodes Along inferior epigastric & circumflex iliac artery – into external iliac nodes Along intercostal arteries – into intercostal nodes Nerve supply T7 –T11 intercostal nerves Subcostal nerve (T12) Ilioinguinal nerve (L1) Iliohypogastric nerve (L2) References BD Chaurasia’s Human Anatomy – volume 2 Grays Clinical anatomy