Abdominal Midgut And Hindgut Flashcards
Describe the jejunum
Intraperitoneal (supported by mesentery)
Contains mucosal folds (pilcae circulares)
Mesenteric fat increases from proximal to distal
Supplied by arterial arcades with long vasa recta (straight arteries) off branches of the SMA
Describe the ileum
Intraperitoneal
Supplied by compound arterial arcades with short vasa recta (straight arteries) branches of SMA
What are some external features of the colon?
Outer 3 bands of longitudinal smooth muscle (tenia coli) causing outpocketings (haustra) with attached outer fatty appendages (appendices epiploicae)
Describe the cecum
Blind pouch that contains ileal papilla (cone like projection of the ileum)
Ileocecal valve regulates passage of ileal contents into cecum
Describe the appendix
Attached to posterior medial part of cecum and supported by mesoappendix
Position is variable
Contains several lymphoid nodules (part of immune system)
Describe the transverse colon
Approximately 10-14” in length
Intraperitoneal and suspended to posterior wall by transverse mesocolon mesentery
Describe the sigmoid colon
Approximately 12” in length
Joins rectum at level of S3 and suspended by sigmoid mesocolon
Describe the rectum
Both retroperitoneal and sub-peritoneal (portion of rectum is below the peritoneum)
Located in pelvic cavity
Contains 3 transverse rectal folds (superior, middle, and inferior)
Continuous with anal canal
What is the internal anal sphincter comprised of?
Smooth muscle (controlled by ANS)
What is the external anal sphincter comprised of?
Skeletal muscle (controlled by somatic efferents)
Describe the anal canal
Surrounded by 2 anal sphincters (internal and external)
Contains anal columns, anal valves and anal sinuses
Pectinate line located at inferior ends of anal valve
External opening is known as the anus
What is the primary arterial supply to the midgut and hindgut?
SMA and IMA
What does the superior mesenteric artery supply?
Pancreas, duodenum, SI, cecum, ascending and transverse colon
What are some SMA relationships?
Arises from aorta at level of L1 posterior to the neck of the pancreas and then passes inferiorly and anterior to horizontal portion of the duodenum
What are the proximal branches of the SMA?
Anterior/posterior inferior pancreaticoduodenal arteries anastomose with branches of gastroduodenal (superior pancreaticoduodenal arteries) from the celiac trunk
20% gives rise to right hepatic A
What are the intestinal branches of the SMA?
Jejunal and ileal (intraperitoneal in the mesentery), ileocolic, right colic, middle colic (intraperitoneal in transverse mesocolon)
The IMA comes off the aorta at the level of what?
L3
What does the IMA supply?
Descending and sigmoid colon
Superior rectum
What are the intestinal branches of the IMA?
Left colic, sigmoidal A and superior rectal A
What is the marginal artery of Drummond?
Arterial anastomosis exists between SMA and IMA forming a prominent artery called the marginal artery
Depending on health of anastomosis and speed of vessel obstruction it helps prevent intestinal ischemia by providing an alternate route to blood flow
Which arteries provide blood supply to the rectum?
Superior rectal A (off IMA)
Middle rectal A (off internal iliac in pelvic cavity)
Inferior rectal A (off internal pudendal A in perineum)
Which two veins form the hepatic portal vein?
Superior mesenteric and splenic vein
Receives blood from most of the GI system and brings it to liver
Describe the portal systemic anastomoses
Portal venous system has anastomoses with systemic system at gastroesophageal plexus, umbilicus and rectal venous plexus
Varices can occur at these sites due to decreased blood flow through the liver (e.g. due to hepatic HTN)
What provides sympathetic innervation to the GI tract?
Thoracic, lumbar and sacral splanchnics