TLDR;
This video provides a comprehensive review of abdominal and pelvic anatomy, focusing on key structures, their relationships, and clinical correlations. It covers the posterior abdominal wall, diaphragm development, anterior abdominal wall, inguinal canal, fetal circulation, stomach, duodenum, pancreas, spleen, and liver. The lecture emphasizes important points for exams, including muscle origins, nerve pathways, arterial branches, and potential clinical scenarios.
- Posterior abdominal wall muscles and lumbar plexus
- Development and clinical significance of the diaphragm
- Anterior abdominal wall layers and inguinal canal anatomy
- Fetal circulation and postnatal changes
- Detailed anatomy and relations of the stomach, duodenum, pancreas, spleen, and liver
Posterior Abdominal Wall [1:15]
The posterior abdominal wall is formed by the psoas major, quadratus lumborum, and transversus abdominis muscles. The lumbar plexus, which gives rise to several nerves, is located on this wall. Key nerves include the iliohypogastric, ilioinguinal, lateral cutaneous nerve of the thigh (which can be compressed, causing meralgia paresthetica), genitofemoral (with genital and femoral branches), and femoral nerve. The femoral nerve passes through the iliopsoas groove, originating from L2-L4 nerve roots. The medial and lateral arcuate ligaments and the crura of the diaphragm also contribute to the posterior abdominal wall. The abdominal aorta bifurcates at the L4 vertebral level into the common iliac arteries, while the inferior vena cava (IVC) forms at L5.
Abdominal Aorta Branches [7:38]
The abdominal aorta has several branches, categorized as terminal, ventral, lateral, and dorsal. The terminal branches are the common iliac arteries. The ventral branches include the celiac trunk (supplying the foregut at T12), superior mesenteric artery (supplying the midgut at L1), and inferior mesenteric artery (supplying the hindgut at L3). Lateral branches supply paired organs: inferior phrenic, middle suprarenal, renal, and gonadal arteries. Dorsal branches include four pairs of lumbar arteries and the median sacral artery.
Diaphragm Development [12:47]
The diaphragm develops from four main components: the septum transversum (forming the central tendon), the dorsal mesentery of the esophagus (forming the crura), the body wall (forming the peripheral parts), and the pleuroperitoneal membranes (forming the posterior part of the central tendon). Failure of the pleuroperitoneal membranes to fuse can result in a Bochdalek hernia, where abdominal organs, most commonly the kidney, herniate into the thoracic cavity.
Anterior Abdominal Wall and Inguinal Canal [16:24]
The layers of the anterior abdominal wall include skin, superficial fascia, external oblique aponeurosis, internal oblique, transversus abdominis, fascia transversalis, extraperitoneal fat, and peritoneum. The inguinal canal's anterior wall is formed by the external oblique aponeurosis (entire extent) and the internal oblique (lateral part). The roof is formed by the conjoint tendon (internal oblique and transversus abdominis), the posterior wall by the fascia transversalis (entire extent) and conjoint tendon (medial part), and the floor by the external oblique and inguinal ligament.
Inguinal Canal Openings and Contents [20:39]
The superficial inguinal ring is a defect in the external oblique aponeurosis, while the deep inguinal ring is a defect in the fascia transversalis. The contents of the inguinal canal in males include the spermatic cord and ilioinguinal nerve; in females, they include the round ligament of the uterus and ilioinguinal nerve. The ilioinguinal nerve is considered a partial content. The spermatic cord contains the vas deferens, artery to the vas, cremasteric artery, testicular artery, pampiniform plexus of veins, genital branch of the genitofemoral nerve, and lymphatics from the testes.
Testes Coverings and Hasselbach's Triangle [23:24]
The coverings of the testes, from outside in, are the external spermatic fascia (from external oblique aponeurosis), cremasteric fascia (from internal oblique), internal spermatic fascia (from fascia transversalis), tunica vaginalis (parietal and visceral layers, from peritoneum), tunica albuginea, and tunica vasculosa. Hasselbach's triangle is bounded by the rectus abdominis, inferior epigastric artery, and inguinal ligament. Direct inguinal hernias occur through Hasselbach's triangle, while indirect inguinal hernias pass through the deep inguinal ring and exit through the superficial ring. The obliterated umbilical artery (medial umbilical ligament) divides Hasselbach's triangle into medial and lateral parts.
Fetal Circulation [30:35]
The umbilical cord contains two umbilical arteries and one umbilical vein. The left umbilical vein carries oxygenated blood from the placenta and joins the left branch of the portal vein. The ductus venosus connects the left branch of the portal vein to the IVC, bypassing the liver. Blood flows from the IVC to the right atrium, then to the left atrium via the foramen ovale. If blood enters the right ventricle, it goes to the pulmonary trunk, bypassing the lungs via the ductus arteriosus (derived from the sixth aortic arch) to the aorta.
Postnatal Changes in Fetal Circulation [37:41]
After birth, the left umbilical vein becomes the ligamentum teres in the falciform ligament, the ductus venosus becomes the ligamentum venosum, and the foramen ovale becomes the fossa ovalis. The part of the umbilical artery between the bladder and umbilicus obliterates to form the medial umbilical ligament, while the non-obliterated part becomes the superior vesical artery. The urachus, connecting the bladder to the umbilicus in fetal life, obliterates to form the median umbilical ligament. Failure of the urachus to obliterate can result in a urinary fistula or weeping umbilicus.
Stomach Anatomy and Relations [42:50]
The stomach's posterior relations form the stomach bed, including the left kidney, left suprarenal gland, splenic artery, pancreas, spleen, left crus of the diaphragm, and transverse colon. These structures are separated from the stomach by the lesser sac. The greater sac is the space between the anterior abdominal wall and the stomach. Fluid can pass from the greater sac to the lesser sac through the epiploic foramen (of Winslow). The epiploic foramen is bounded anteriorly by the lesser omentum (containing the hepatic artery, portal vein, and bile duct), posteriorly by the IVC, superiorly by the caudate lobe of the liver, and inferiorly by the first part of the duodenum.
Duodenum Anatomy and Relations [48:02]
The duodenum is 25 cm long and divided into four parts. The entire duodenum is retroperitoneal except for parts of the first and fourth segments. The first part is 5 cm long; its anterior relations include the neck of the gallbladder, and its posterior relations include the portal vein, bile duct, and gastroduodenal artery. Ulcers on the posterior wall of the first part can erode the gastroduodenal artery. The second part is 7.5 cm long, crossed anteriorly by the transverse colon and mesocolon, and lies on the right kidney posteriorly. The third part is 10 cm long, crossed anteriorly by the root of the mesentery and superior mesenteric vessels, and lies on the right psoas major, right ureter, aorta, and IVC posteriorly. The fourth part is 2.5 cm long, with the inferior mesenteric vein as its posterior relation, related to the paraduodenal fossa. The superior pancreaticoduodenal artery supplies the duodenum above the bile duct opening, while the inferior pancreaticoduodenal artery supplies below.
Pancreas Anatomy and Relations [58:57]
The pancreas consists of the head, neck, body, tail, and uncinate process. The head is related to the first part of the duodenum superiorly, the third part inferiorly, and the second part on the right side. Anterior relations include the first part of the duodenum and transverse colon/mesocolon. Posterior relations include the IVC, right renal vein, right crus of the diaphragm, and bile duct. The neck's anterior relation is the pylorus of the stomach, and posterior relations include the portal vein and superior mesenteric vein. The body's superior border is related to the splenic artery, and anterior relations include the stomach and transverse colon. Posterior relations, from right to left, include the aorta with the origin of the superior mesenteric artery, left renal vein, left crus of the diaphragm, left kidney, left suprarenal gland, and splenic vein. The tail lies in the splenorenal ligament.
Pancreas Tail and Uncinate Process [1:11:14]
The tail of the pancreas enters the hilum of the spleen and lies within the lienorenal ligament. The tail contains a high concentration of islets of Langerhans. The uncinate process is related anteriorly to the superior mesenteric vessels and posteriorly to the abdominal aorta.
Spleen Anatomy [1:13:46]
The spleen's dimensions are approximately 1 x 3 x 5 inches, weighs about 7 ounces, and lies between the 9th and 11th ribs. The long axis of the spleen is directed along the 10th rib, making a 45-degree angle with the horizontal plane. The superior border is typically notched, indicating development from small lobules. The spleen projects into the greater sac of the peritoneal cavity. The left boundary of the lesser sac is formed by the gastrosplenic and lienorenal ligaments.
Liver Anatomy and Ligaments [1:20:19]
The falciform ligament contains the ligamentum teres (remnant of the umbilical vein). The ligaments of the liver include the falciform ligament, coronary ligament (superior and inferior layers), and right and left triangular ligaments, all derived from the ventral mesogastrium. Bare areas of the liver, not covered by peritoneum, include the groove for the IVC, the fossa for the gallbladder, the fissure for the ligamentum teres, the fissure for the ligamentum venosum, and the largest bare area.
Liver Segmentation [1:26:43]
Couinaud's classification of liver segments is based on the hepatic veins and portal vein. The middle hepatic vein divides the liver into right and left lobes. The right hepatic vein divides the right lobe into anterior and posterior segments, and the left hepatic vein divides the left lobe into medial and lateral segments. The portal vein divides the liver into superior and inferior segments. Segment 1 is the caudate lobe, segments 2 and 3 are left lateral, segments 4A and 4B are left medial (quadrate lobe), segments 5 and 8 are right anterior, and segments 6 and 7 are right posterior.