Abdominal Contents: Midgut & Hindgut Flashcards
Divisions of the gut tube
- What are the three divisions?
- What does each division share?
Divisions of the gut tube
- foregut
- midgut
- hindgut
Organs derived from the same division of the gut tube share:
- common blood supply
- route of venous drainage
- route of lymphatic drainage
- innvervation
Midgut
- Derivatives?
- Blood supply?
- Venous drainage?
- Lymphatic drainage?
Midgut
- Derivatives:
- distal duodenum
- jejunum
- ileum
- cecum
- appendix
- ascending colon
- proximal 2/3 of transverse colon
- Blood supply:
- SMA
- Venous drainage:
- SMV
- Lymphatic drainage:
- superior mesenteric lymph nodes
Hindgut
- Derivatives?
- Blood supply?
- Venous drainage?
- Lymphatic drainage?
Hindgut
- Derivatives:
- distal 1/3 of transverse colon
- descending colon
- sigmoid colon
- rectum
- Blood supply:
- IMA
- Venous drainage:
- IMV
- Lymphatic drainage:
- inferior mesenteric lymph nodes
Small intestine
- What are the three parts?
- What are the parts of the duodenum and where are they derived from? Quadrant of duodenum?
Small intestine
- Duodenum
- RUQ
- Proximal half
- 1st and 2nd parts are foregut
- Distal half
- 3rd and 4th parts are midgut
- Jejunum
- Ileum
Small intestine
Distal duodenum
Horizontal (3rd) part
- What kind of retroperitoneal organ?
- What kind of vessels pass by and where?
Small intestine
Distal duodenum
Horizontal (3rd) part
- Secondarily retroperitoneal
- Superior mesenteric vessels emerge superior and pass anterior to this part
Small intestine
Distal duodenum
Ascending (4th) part
- What kind of retroperitoneal organ?
- What is the acute angle and what does it mark?
- What is this structure supported by and what is it tethered to?
Small intestine
Distal duodenum
Ascending (4th) part
- Secondarily retroperitoneal
- Duodenojejunal flexure - acute angle that marks the duodenojujenal junction where it transitions from secondarily retroperitoneal duodenum to intraperitoneal jejunum
- Suspensory muscle of the duodenum (ligament of Treitz) - this supports the flexure, tethering it to the diaphragm
Small intestine
Jejunum
- Type of retroperitoneal organ?
- Location?
- What structures are prominent in jejunum?
Small intestine
Jejunum
- Intraperitoneal (robust mesentary)
- Central position in abdomen
- Plicae circulares - very prominent in jejunum
Small intestine
Ileum
- Type of retroperitoneal organ?
- Location?
- What structures are present and absent?
- Where does the ileum end?
Small intestine
Ileum
- Intraperitoneal (robut mesentary)
- Central position in abdomen
- Plicae circulares are sparse proximally and absent distally
- Lymphoid nodules (Peyer’s patches) are present in ileum
- Ileum ends at ileocecal junction
Small intestine
Ileal (Meckel’s) diverticulum of the ileum
- What is it?
- What is it a remnant of?
- Occurence?
- Clinical significance?
Small intestine
Ileal (Meckel’s) diverticulum of the ileum
- Blind pouch on the antimesenteric side of ileum
- Remnant of the yolk stalk (embryonic connection between the yolk sac and developing gut)
- 1-2% occurrence
- Congenital
- Typically 50 cm from ileocecal junction
- Inflammation of an ileal diverticulum can produce pain similar to appendicitis
Large intestine
- What are the parts?
- Where does the midgut / hindgut transition lie?
Large intestine
- Includes:
- cecum
- appendix
- colon
- ascending colon
- transverse colon
- descending colon
- sigmoid colon
- rectum
- Includes both midgut and hindgut derivatives
- Midgut / hindgut transition lies at the junction of the proximal 2/3 and distal 1/3 of the transverse colon
What are the features of the large intestine?
Features of the large intestine
- Teniae coli
- Three longitudinal bands of smooth muscle
- Teniae = ribbon in Latin
- Haustra
- Pouches between the teniae coli
- Omental (epiploic) appendices
- Fat
Large intestine
Cecum
- What kind of organ?
- Quadrant?
- Looks like a?
- What is the valve associated?
Large intestine
Cecum
- Intraperitoneal
- RLQ
- Round pouch
- Ileocecal valve - between the ileum and cecum, closes when cecum is distended
Large intestine
Appendix
- Type of organ?
- Quadrant?
- Location?
- Looks like?
- What converges there?
- What does root of appendix lie? Clinical significance of this?
Large intestine
Appendix
- Intraperitoneal (mesoappendix mesentery)
- RLQ
- Typically retrocecal (behind cecum) but this can vary
- Worm like appendage of the cecum
- Teniae coli converge at appendix
-
McBurney’s Point
- Root of appendix
- 1/3 of the way from the ASIS to the umbilicus
- Location of appendectomy incision
Large intestine
Ascending colon
- Type of organ?
- Quadrant?
- What is the fixture and gutter? Location?
Large intestine
Ascending colon
- Secondarily retroperitoneal
- Although it has mobile mesentery in 25% of people, so it can be intraperitoneal
- RLQ and RUQ
- Extends superiorly along right side of abdominal cavity between the cecum and the right colic (hepatic) flexure
- Right paracolic gutter is lateral to the ascending colon and fluid can accumulate there
Large intestine
Transverse colon
- Type of organ?
- Quadrant?
- Extends horizontally between what two flexures?
- Which flexure sits higher and why?
Large intestine
Transverse colon
- Intraperitoneal (transverse mesocolon mesentery)
- RUQ and LUQ
- Extends horizontally between the right colic (hepatic) flexure and the left colic (splenic) flexure
- Left colic flexure sits higher due to liver being on the right
Large intestine
Descending colon
- Type of organ?
- Quadrant?
- Extends inferiorly along what side of abdominal cavity and between what?
- What is directly lateral? Clinical significance of these structures?
Large intestine
Descending colon
- Secondarily retroperitoneal
- Although there is mobile mesentery in 33% of people, so it can be intraperitoneal
- LUQ and LLQ
- Extends inferiorly along the left side of abdominal cavity between the left colic flexure and sigmoid colon
-
Left paracolic gutter
- Lateral to descending colon
- Paracolic gutters are conduits for the spread of fluid within the peritoneal cavity
- If patient has abdominal infection and lays down, infection can spread to parietal pleura
- Patient with abdominal infections should stay sitting up
Large intestine
Sigmoid colon
- Type of organ?
- Quadrant?
- Extends between what?
- What shape does it form?
Large intestine
Sigmoid colon
- Intraperitoneal (sigmoid mesocolon mesentery)
- LLQ
- Extends from descending colon to rectum
- S shaped but variable in position
Large intestine
Rectum
- Type of organ?
- Continues proximally with? Distally with?
- Lacks what structures?
- Where do the rectum and anal canal meet?
- Location and function of rectal ampulla?
Large intestine
Rectum
- Primarily retroperitoneal
- Continous proximally with sigmoid colon and distally with anal canal
- Lacks:
- teniae coli
- haustra
- omental appendices
- Not a straight tube, has lateral flexures
-
Anorectal flexure
- The abrupt angle with the rectum and anal canal meet
- Maintained by the puborectalis muscle
-
Rectal ampulla
- Lies superior to the anorectal flexure
- Expands to store fecal matter
Midgut - SMA
- Arises from abdominal aorta at what level?
- Posterior to what?
- Passes anterior to what?
- What are the branches of the SMA?
Midgut - SMA
- Arises from the abdominal aorta at L1 vertebrae
- Posterior to the pancreas
- Passes anterior to the horizontal (3rd) part of the duodenum
- Branches of SMA:
- Anterior and posterior inferior pancreaticoduodenal arteries
- Jejunal and ileal arteries
- Colic arteries
Midgut - SMA
Anterior and posterior inferior pancreaticoduodenal arteries
Anastomose with what?
Midgut - SMA
Anterior and posterior inferior pancreaticoduodenal arteries
Anastomose with anterior and posterior superior pancreaticoduodenal arteries from the celiac trunk
Midgut - SMA
Jejunal and ileal arteries
- What pattern do these arteries form?
- How do you characterize jejunal vs ileal?
Midgut - SMA
Jejunal and ileal arteries
- Form anastomosing arcades that terminate in straight arteries (vasa recta)
- Jejunum arteries
- Few arcades
- Long straight arteries
- Ileum arteries
- Multiple arcades
- Short straight arteries
Midgut - SMA
Colic arteries
- Contribute to what artery?
- What are the three colic arteries?
- What is the branch off artery?
Midgut - SMA
Colic arteries
- Contribute to the marginal artery (an anastomosing loop that parallels the colon)
- Colic arteries
- Middle colic artery
- Right colic artery
- Ileocolic artery
- Appendicular artery (in mesoappendix)
Hindgut - IMA
- Arises from the abdominal aorta at what vertebrae?
- What are the three branches of the IMA?
- What do the branches contribute to?
Hindgut - IMA
- Arises from the abdominal aorta at L3
- Branches of IMA:
- Left colic artery (contributes to marginal artery)
- Sigmoid arteries (contribute to marginal artery)
- Superior rectal artery (terminal branch of IMA)
Portal system in the midgut and hindgut
- What vein goes to midgut and hindgut?
- What do the tributaries of the veins parallel?
- Where does it form or empty to?
Portal system in the midgut and hindgut
Midgut - SMV
- Tributaries parallel branches of the SMA
- Joins with the splenic vein to form the portal vein
Hindgut - IMV
- Tributaries parallel branches of IMA
- Empties into the splenic vein posterior to the body of the pancreas
Portal-caval anastomoses
Where does this take place in the midgut / hindgut?
Portal-caval anastomoses
Portal tributaries draining the colon communicate with the paired veins of the IVC, providing an alternative route in cases of portal hypertension
Lymphatics of the midgut and hindgut
- Where does the midgut and hindgut lymph drain to?
Lymphatics of the midgut and hindgut
Midgut
- Lymph drains to superior mesenteric lymph nodes –> chyle cistern
Hindgut
- Lymph drains to inferior mesenteric lymph nodes –> superior mesenteric lymph nodes OR lumbar lymph nodes (along aorta)
Midgut parasympathetic innervation
Midgut parasympathetic innervation
Stimulates peristalsis and secretion
- Preganglionic cell bodies: brain
- Preganglionic fibers: vagus nerve (CN X)
- Postganglionic cell bodies: wall of organ
- Postganglionic fibers: wall of organ
Hindgut parasympathetic innervation
Hindgut parasympathetic innervation
Stimulates peristalsis and secretion
- Preganglionic cell bodies: intermediate gray matter at S2 - S4 levels of spinal cord
- Preganglionic fibers: ventral root, spinal nerve, ventral ramus, pelvic splanchnic nerves
- Postganglionic cell bodies: wall of organ
- Postganglionic fibers: wall of organ
Midgut sympathetic innervation
Midgut sympathetic innervation
Inhibits peristalsis and constricts GI blood vessels
- Preganglionic cell bodies: lateral horn of thoracic spinal cord
- Preganglionic fibers: ventral root, spinal nerve, white ramus communicans, sympathetic trunk, thoracic splanchnic nerves (greater, lesser, or least)
- Postganglionic cell bodies: celiac ganglia OR superior mesenteric ganglia
- Postganglionic fibers: follow arterial branches to target organ
Hindgut sympathetic innervation
Hindgut sympathetic innervation
Inhibits peristalsis and constricts GI blood vessels
- Preganglionic cell bodies: lateral horn of lumbar spinal cord
- Preganglionic fibers: ventral root, spinal nerve, white ramus communicans, sympathetic trunk, lumbar splanchnic nerves
- Postganglionic cell bodies: inferior mesenteric ganglion
- Postganglionic fibers: follow arterial branches to target organ
Midgut vs hindgut for parasympathetic innveration
- What is the nerve for each?
- Where is the divison on the large intestine?
Midgut vs hindgut for parasympathetic innveration
- Midgut - vagus nerve (CN X)
- Hindgut - pelvic splanchnic nerve
- The midgut / hindgut transition lies at the junction of the proximal 2/3 and distal 1/3 of the transverse colon
Visceral pain
- What is the pathway?
- Describe pain from appendicitis
Visceral pain
- Follow the sympathetic and parasympathetic pathways back to spinal cord
- Pain from appendicitis presents as diffuse periumbilical pain (T10 dermatome). But as the parietal peritoneum becomes involved, somatic innervation localizes the pain to RLQ
