USMLE First Aid Organ Systems GI – Flashcards
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Primitive GI begins to form around which week in embryological development?
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4th week
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In the 4th week, the endoderm gives rise to
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intestinal epithelium and glands
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In the 4th week, mesoderm gives rise to
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connective tissue, muscle, and wall of intestine
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5th Week of Embryological Development
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intestine elongates and midgut loop herniates through umbilicus.
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Names of limbs of midgut loop and what each limb gives rise to
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cranial limb becomes distal duodenum and proximal ileum caudal limb becomes distal ileum to proximal 2/3rds of transverse colon
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What is a key event in the 10th week of development?
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midgut loop returns to abdominal cavity in its final fixed position after rotating a total of 270 degrees counterclockwise around axis of the superior mesenteric artery
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Omphalocele
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Failure of bowel to return to the abdomen following herniation of abdominal contents into base of umbilical cord during 5th week of embryonic life. Herniated intestine is covered by peritoneal membrane. Most commonly affects children of mothers of extremes of reproductive age.
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Presentation of Omphalocele
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2nd trimester ultrasound (95% of cases) or herniated sac found at birth
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Associated anomalies of Omphalocele
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Beckwith-Wiedemann syndrome: Gigantis, macroglossia, umbilical defect, and hypoclycemia Pentalogy of Cantrell: Omphalocele, diaphragmatic hernia, cleft sternum, absent pericardium, and intracardiac defects
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Diagnosis of Omphalocele
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alpha-Fetoprotein (AFP) serum values are elevated in 70% of cases
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Gastroschisis
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Full-thickness abdominal wall defect caused by vascular injury during development allowing small or large bowel to escape abdominal cavity. No protective peritoneal membrane covers herniated intestine. Most common in children born to women younger than 20.
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Presentation of Gastroschisis
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Similar to omphalocele. Extruded abdominal contents are usually right of the abdominal midline
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Treatment of Gastroschisis
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Artificial covering may be used to minimize heatfluid loss and assist with temperature regulation (exposed bowel causes increased heat loss)
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Ladd's Bands
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Aberrant peritoneal attachments that causes partial or complete obstruction of the duodenum due to malrotation during development
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Midgut Volvulus
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Malrotated intestine twists on axis of SMA, compromising intestinal blood flow
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Presentation of Midgut Volvulus
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May occur at any time during 1st year of life and presents with sudden onset of severe bilious emesis, abdominal pain and distention, and rectal bleeding
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Bilious Emesis
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presumed to be midgut volvulus until proven otherwise
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Treatment of Malrotation
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Ladd's procedure
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Duodenal Atresia
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In weeks 6 and 7 of development, duodenum becomes completely obstructed by proliferating endoderm. Failure of duodenum to recanalize by week 10 results in duodenal atresia.
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Presentation of Duodenal Atresia
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Newborn may be small for gestational age. Vomiting (often bilious) and abdominal distention within 48 hours after birth.
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Pyloric Stenosis
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Idiopathic congenital elongation and thickening of pylorus, resulting in obstruction of gastric outlet.
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Presentation of Pyloric Stenosis
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Nonbiliious projectile vomiting at 3-6 weeks but notable absence of other signs of illness (fever, diarrhea)
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Diagnosis of Pyloric Stenosis
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Palpable mass size of an olive in epigastric region
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Margins of Abdomen
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Diaphragm superiorly, inlet of pelvis inferiorly
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Linea Alba
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Vertical fibrous band that extends from symphysis pubis to xiphoid process and lies in midline. Formed by fusion of aponeuroses of muscles of anterior abdominal wall that is represented by a median groove.
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Linea Seminlunaris
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Lateral edge of rectus abdominis muscle and crosses costal margin at tip of 9th costal cartilage
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Inguinal Groove
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Formed by rolled-under margin of aponeurosis of external oblique muscle
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Transpyloric Plane
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Cuts through pylorus horizontally and passes through tips of 9th costal cartilages on each side. Lies at L1.
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What does the transpyloric plane identify?
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Pylorus of stomach, duodenojejunal junction, neck of pancreas, and hila of kidneys
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Subcostal Plane
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Horizontal plane joining lowest point of costal margin on each side. Lies at level L3.
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Intertubercular Plane
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Horizontal plane joining tubercles on iliac crests. Lies at level L5.
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McBurney's Point
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RLQ at 2/3rds distance from umbilicus to anterior superior iliac spine. Pain in this location indicates appendicitis.
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Right Hypochondriac Region
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Liver and gallbladder (Kidney) and suprarenal gland Colon, hepatic flexure
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Epigastric Region
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Liver (Transverse colon) Abdominal aorta and vena cava Pylorus and duodenum (first part)
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Left Hypochondriac Region
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Stomach Spleen (Kidney) and suprarenal gland Colon, splenic flexure
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Right Lumbar Region
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Kidney Colon, ascending Small intestine Duodenum (first part)
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Umbilical Region
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(Transverse colon) Duodenum and pancreas Abdominal aorta and vena cava Small intestine Iliac vessels
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Left Lumbar Region
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Kidney Colon, descending Pancreas Small intestine (jejunum)
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Right Iliac region
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Cecum Appendix Small intestine (ileum)
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Hypocastric Region
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Distensible organs of pelvis (bladder/uterus) Small intestine Iliac vessels Spermatic cords
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Left Iliac Region
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Sigmoid colon Small intestine
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Layers of Anterolateral Abdominal Wall
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Skin Superficial fascia (fatty Camper's and membraneous Scarpa's) Deep fascia Aponeurosis External oblique muscle - lateral wall Internal oblique muscle - lateral wall Transversus abdominis muscle - lateral wall Transversalis fascia Extraperitoneal fat Parietal peritoneum
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Inguinal Canal
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Site of inguinal hernias
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Boundaries of inguinal canal
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Deep inguinal ring Superficial inguinal ring Anterior wall Posterior wall Roof Floor
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Patent communication between abdominal cavity and scrotal sac
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Failure of processus vaginalis to obliterate
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Boundaries of Femoral Triangle
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Superiorly: Inguinal ligament Laterally: Sartorius muscle Medially: Adductor longus muscle
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Third Spacing
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Non-intravascular space where fluid and edema can accumulate
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Common causes of ascites
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Liver failure, right heart failure, ovarian cancer
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Pneumoperitoneum
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air or other gas in peritoneal cavity (intestinal/stomach perforation, or intentional insufflation for laparoscopy)
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Parietal Peritoneum
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Outer membranes that lines deep surface of abdominal walls and inferior surface of diaphragm
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Nerve Supply of Parietal Peritoneum
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Nerves of surrounding abdominal muscles and skin Intercostal and phrenic nerves in abdominal region Obturator nerve in pelvic region
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Visceral Peritoneum
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Membrane that directly covers abdominal organs. No somatic nerve supply.
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Intraperitoneal Viscera
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Stomach First part of duodenum Jejunum, ileum, cecum, and appendix Transverse and sigmoid colon Proximal rectum Liver and gallbladder Tail of pancreas Spleen
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Extraperitoneal Viscera
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Parts 2, 3, and 4 of duodenum Ascending and descending colon Distal rectum Head, neck, and body of pancreas Abdominal aorta Inferior vena cava Kidneys, ureters, and adrenal glands
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Lesser Sac (Omental Bursa) of Peritoneal Cavity
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Posterior to stomach, liver, and lesser omentum
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Epiploic Foramen (Winslow's Foramen)
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Enables communication between greater and lesser sac of peritoneal cavity
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Greater Sac
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Subdivided by transverse mesocolon into supracolic compartment and infracolic/pelvic compartments below mesocolon
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Supracolic Compartment
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Divided by falciform ligament
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Subphrenic Recess
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Area to right of falciform ligament between liver and kidney
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Mesentary
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Double layer of peritoneum that wraps around abdominal organs, includes blood vessels, and attaches organ to its major blood supply
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Gradual occlusion of abdominal aorta can result in
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Claudication and impotence
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3 Main Branches of Celiac Trunk
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Supply structures derived from foregut: Left gastric Splenic Common hepatic
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Superior Mesenteric Artery
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Supplies derivatives of midgut
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Inferior Mesenteric Artery
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Supplies hindgut derivatives, distal 3rd of transverse colon, descending colon, sigmoid colon, superior portion of rectum
