TLDR;
This YouTube video by PW MedEd provides a comprehensive review of abdominal anatomy, focusing on the posterior abdominal wall, kidney relations, diaphragm, pancreas, branches of the abdominal aorta, fetal circulation, and the anal canal. It uses interactive questions and visual aids to reinforce learning and covers key clinical correlations.
- Posterior abdominal wall muscles and their relations.
- Kidney relations, including ribs and posterior structures.
- Diaphragm anatomy, including crura and arcuate ligaments.
- Pancreas anatomy and relations.
- Branches of the abdominal aorta and their clinical significance.
- Fetal circulation and postnatal changes.
- Anal canal anatomy and clinical correlations.
Posterior Abdominal Wall [1:58]
The posterior abdominal wall is formed by three muscles: the quadratus lumborum, psoas major, and transversus abdominis. The medial arcuate ligament arches over the psoas major, while the lateral arcuate ligament covers the quadratus lumborum. The right crus of the diaphragm is longer and stronger, originating from L1-L3, while the left crus is related to the posterior aspect of the stomach and the body of the pancreas.
Kidney Relations [8:27]
The posterior relations of the kidneys include the psoas major, quadratus lumborum, and transversus abdominis muscles, as well as the subcostal, iliohypogastric, and ilioinguinal nerves. The left kidney is related to the 11th and 12th ribs, while the right kidney is related only to the 12th rib due to the liver's position.
Lateral Cutaneous Nerve and Genitofemoral Nerve [12:04]
The lateral cutaneous nerve of the thigh, a branch of the lumbar plexus, can be compressed at the inguinal ligament, causing meralgia paresthetica, characterized by tingling and numbness in the lateral thigh. The genitofemoral nerve, located on the psoas major, has two branches: the femoral branch, which travels with the femoral artery in the femoral sheath, and the genital branch, which runs with the spermatic cord in males and the round ligament of the uterus in females.
Branches of Abdominal Aorta [17:40]
The abdominal aorta divides into two common iliac arteries at the level of L4. It has ventral branches including the celiac trunk (supplying the foregut), superior mesenteric artery (supplying the midgut), and inferior mesenteric artery (supplying the hindgut). A horseshoe kidney, where the lower poles fuse, is often stopped from ascending past the inferior mesenteric artery, remaining below the L3 vertebral level.
Internal Iliac Artery [22:30]
The common iliac artery divides into the external and internal iliac arteries. The external iliac artery becomes the femoral artery after passing under the inguinal ligament. The internal iliac artery divides into anterior and posterior divisions. The anterior division branches include the superior vesical, inferior vesical, middle rectal, uterine (in females), obturator, inferior gluteal, and internal pudendal arteries. The posterior division branches include the superior gluteal, lateral sacral, and iliolumbar arteries.
Fetal Circulation [30:53]
Fetal circulation involves two umbilical arteries and one umbilical vein (left). The left umbilical vein carries oxygenated blood from the placenta to the liver, joining the left branch of the portal vein. A bypass, the ductus venosus, shunts blood from the left portal vein to the inferior vena cava (IVC). Blood from the IVC enters the right atrium, then passes to the left atrium through the foramen ovale. Blood from the right ventricle goes to the pulmonary trunk, bypassing the non-functional lungs via the ductus arteriosus to the aorta.
Postnatal Changes [37:17]
After birth, the left umbilical vein becomes the ligamentum teres, located in the falciform ligament. The ductus venosus becomes the ligamentum venosum, related to the caudate lobe of the liver. The foramen ovale becomes the fossa ovalis. The ductus arteriosus becomes the ligamentum arteriosum, around which the left recurrent laryngeal nerve winds. The part of the umbilical artery from the bladder to the umbilicus obliterates to form the median umbilical ligament, while the non-obliterated part becomes the superior vesical artery.
Epiploic Foramen (Foramen of Winslow) [45:38]
The epiploic foramen (foramen of Winslow) connects the greater and lesser sacs. Its anterior border is the lesser omentum, containing the hepatic artery, portal vein, and bile duct. The posterior border is the IVC, right suprarenal gland, and the body of the T12 vertebra. The superior border is the caudate lobe of the liver, and the inferior border is the first part of the duodenum.
Duodenum Relations [54:01]
The duodenum has four parts with specific lengths and vertebral levels: The first part (5 cm, L1) is related anteriorly to the neck of the gallbladder and posteriorly to the portal vein, bile duct, and gastroduodenal artery. The second part (7.5 cm, L1-L3) is crossed by the transverse colon and mesocolon and lies on the right kidney. The third part (10 cm, L3) is crossed by the superior mesenteric vessels and the root of the mesentery and is related posteriorly to the right psoas major, right ureter, IVC, and abdominal aorta. The fourth part (2.5 cm, L2) is related posteriorly to the inferior mesenteric vein.
Hindgut Development [1:04:12]
The hindgut, below the attachment of the allantois, forms the cloaca, which is divided by the urorectal septum into the urogenital sinus and the rectum. The cloacal membrane is divided into the urogenital membrane and the anal membrane. The anal canal develops from the hindgut and the proctodeum, an ectodermal invagination.
Anal Canal Anatomy [1:08:35]
The anal canal, 38 mm in total length, is divided into three parts: upper 15 mm (endodermal origin), middle 15 mm, and lower 8 mm (both ectodermal origin). The upper part has anal columns (columns of Morgagni) and the dentate line, representing the lower end of the anal columns. The middle and lower parts are formed by the invagination of the anal membrane. The lining of the upper 15 mm is stratified columnar epithelium (mucous membrane), while the lower 8 mm is lined by stratified squamous epithelium (skin). The Hilton line (white line of Hilton) is the mucocutaneous junction.
Clinical Significance of Dentate Line [1:15:31]
The dentate line is a watershed line, with different nerve supply, blood supply, and lymphatics above and below it. Above the dentate line, the nerve supply is autonomic (painless conditions), and lymphatics drain to the internal iliac nodes. Below the dentate line, the nerve supply is somatic (S2-S4, painful conditions), and lymphatics drain to the superficial inguinal lymph nodes.
Pancreas Development [1:18:11]
The pancreas develops from dorsal and ventral pancreatic buds. The dorsal bud forms the upper part of the head, neck, body, and tail, while the ventral bud forms the lower part of the head and the uncinate process. An annular pancreas results from defective migration of the ventral pancreatic bud, encircling the duodenum. Pancreas divisum results from non-fusion of the dorsal and ventral pancreatic buds.
Pancreas Anatomy and Relations [1:22:18]
The splenic artery runs along the superior border of the body of the pancreas, while the splenic vein lies behind the body. The superior mesenteric vessels are related to the uncinate process. The first part of the duodenum is related to the head of the pancreas.