ABDOMEN IV Flashcards
Where does the foregut end to become the midgut?
The major duodenal papilla
What does the midgut consist of?
The distal duodenum, the jejunum, the ilium, the caecum, the ascending colon and the proximal 2/3 of the transverse colon
Where does the ileum become the caecum?
The ileocaecal junction in the right iliac fossa
Where is the midgut in relation to the greater omentum?
Posterior
Where does the jejunum start?
The duodenojejunal junction
What holds the duodenojejunal junction in place?
The ligament of Treitz
The suspensory ligament of the duodenum
What are the names of the many folds on the luminal surface of the jejunum?
Plicae circulares
Compare plicae circulares in the jejunum to in the ilium
There are a lot in the jejunum and few in the ilium because there’s much less nutrient reabsorption in the ilium
Compare the walls of the jejunum and ilium
The jejunum has thick muscular walls, while the ilium has thin walls
Compare lumens of the jejunum and ilium
The jejunum has a wide lumen, whereas the ilium has a narrower lumen
What are Peyer’s patches?
Aggregations of lymphatic follicles
Compare Peyer’s patches in the jejunum to those in the ilium
Peyer’s patches are far more densely populated in the ilium than the jejunum
Are the jejunum and ilium retroperitoneal or intraperitoneal?
Completely intraperitoneal
What suspends the jejunum and ilium from the posterior abdominal wall?
A double-fold of peritoneum called the mesentery
What is the secondary function of the mesentery?
It acts as a conjugate for blood vessels
What are arterial arcades?
Intermesenteric arterial anastomoses (Riolan arcades)- a series of anastomosing arterial arches between the arterial branches of the jejunum and ileum
What arise from arterial arcades?
Vasa recta that supply the jejunum and ileum
Compare the mesentery of the jejunum to that of the ileum
The jejunal mesentery is far less fatty than that of the ileum, so the blood vessels can be seen as the mesentery is translucent
Compare the jejunal vasa recta to the ileal vasa recta
The jejunal vasa recta are longer and come from fewer arterial arcades. The ileal vasa recta are shorter but come from more arterial arcades
Where is the root of the mesentery?
Where the parietal peritoneum is reflected off the posterior abdominal wall to form 1 layer of the fold, then it wraps over the coils of the intestine to form the visceral peritoneum and the second fold, running down to the other side of the root
How long is the root of the mesentery and where does it run between?
It’s 15cm long and comes from the duodenojejunal junction proximally to the sacroiliac joint distally.
What 2 halves does the mesentery split the abdomen into?
The right and left infracolic compartments
Is the appendix intraperitoneal or retroperitoneal?
Intraperitoneal
What supplies the appendix with blood?
The appendicular artery, which arises from the ileocolic artery, a branch of the superior mesenteric artery
Where is the appendix located?
Subcaecally, or posterior to the caecum
What is the caecum?
A blind-ended pouch which marks the start of the large intestine.
Is the caecum intraperitoneal or retroperitoneal?
It’s mostly retroperitoneal
What is lateral to the ascending colon?
The right paracolic gutter
What supplies the ascending colon with blood?
The right colic artery- a branch of the superior mesenteric artery
Is the transverse colon retroperitoneal or intraperitoneal?
It’s intraperitoneal
What is the function of the transverse mesocolon?
To act as a conjugate for blood vessels
What compartments does the transverse colon separate the abdominal cavity into?
The supracolic and infracolic compartments
How are the superior mesenteric artery and vein located relatively?
The vein is to the right of the artery
At what level does the superior mesenteric artery arise from the aorta?
L1, around 1cm below the coeliac trunk at T12
What branches does the superior mesenteric artery give off as it runs inferiorly?
Jejunal branches, ileal branches, the ileocolic artery, the right colic artery and the middle colic artery
What do the jejunal branches and ileal branches become?
Arterial arcades and vasa recta
What does the ileocolic artery give off?
Branches to the distal ileum and the caecum, and the appendicular artery which travels through the mesoappendix
What does the middle colic artery pass through?
The transverse mesocolon
What is the superior mesenteric vein joined by to form the hepatic portal vein?
The splenic vein, which runs behind the pancreas
What do the lymphatics of the midgut drain into?
The intestinal lymphatic trunks and the cisterna chyli
What is the cisterna chyli?
A dilated lymphatic sac at the lower end of the thoracic duct which drains all the abdominal viscera, including those of the pelvis, perineum and the lower limbs
What provides parasympathetic innervation to the midgut?
The vagus nerve innervates the enteric NS of the midgut (and foregut)
What gives sympathetic supply to the midgut, and what nerve roots are these from?
The lesser splanchnic nerves (nerve roots T9-T11)
What is IBD?
Inflammatory bowel disease is an umbrella term for ulcerative colitis and Krohn’s disease
What is ulcerative colitis?
Inflammation of the distal end of the colon, from the sigmoid all the way round to the caecum, sparing the rectum
Why is initial pain from appendicitis in the umbilical region, but it moves to the right iliac fossa?
Initial pain is visceral so it is referred to the umbilical region. Once the appendix is inflamed enough that it swells and presses on the parietal peritoneum, pain becomes local
Where is the McBurney’s point?
2/3 laterally between the ASIS and the umbilicus, which is where the appendix is.
Where is the midgut pain referred to?
The umbilical region, as these dermatomes share convergent nerve roots with the lesser splanchnic nerves (T9-T11)
What is psoas sign?
RLQ pain with extension of the right hip or flexion of the right hip against resistance
What does the hindgut consist of?
The distal 1/3 of the transverse colon, the descending colon, sigmoid colon, rectum and anal canal
What give the large intestine its saturated appearance?
Haustra
What are tendini coloi?
3 longitudinal bands of muscle which run the length of the large intestine, before converging at the base of the appendix
What are appendices epiploicae?
Peritoneal pouches along the colon that are filled with fat
What nerve supplies the hindgut sympathetically?
The inferior mesenteric plexus
Sympathetic innervation comes via the lumbar splanchnic nerves (L1-L2)
What nerves take over parasympathetic innervation for the hindgut?
The pelvic splanchnic nerves (S2-S4)
What is lateral to the descending colon?
The paracolic gutter, where peritoneal fluid can pool
Is the sigmoid colon intraperitoneal or retroperitoneal?
Intraperitoneal
Is the descending colon intraperitoneal or retroperitoneal?
Retroperitoneal, apart from in 33% of people
What run in the sigmoid mesocolon?
Blood vessels
At what level does the sigmoid colon become the rectum?
S3
What causes rectal constrictions?
Transverse rectal folds (thickenings of muscle)
What is the distal portion of the rectum?
The ampulla, which dilates in the presence of faeces and is important for continence
What’s on top of the pelvic organs?
The inferior layer of peritoneum of the abdominal cavity
What does the inferior peritoneum cover?
The top part of the rectum, and then either the uterus or the bladder (female or male)
What is the space between the rectum and uterus called?
The rectouterine pouch (of Douglas)
What’s the name of the space between the rectum and bladder?
The rectovesical pouch
As the rectum passes through the pelvic diaphragm to become the anal canal, what is there?
A slight bend at 80°, which is really important to faecal continence
What does the pectinate line represent?
The termination of the hindgut
Describe epithelium above and below the pectinate line
Above- columnar
Below- stratified squamous
Describe arterial supply above and below the pectinate line
Above- superior rectal artery, a branch of the inferior mesenteric artery
Below- branches of the middle and inferior rectal arteries, which come from the anterior division of the internal iliac artery
Describe venous drainage above and below the pectinate line
Above- superior rectal veins, which unite with the inferior mesenteric veins and drain into the portal system
Below- middle and inferior rectal veins, which drain into systemic circulation
Describe innervation above and below the pectinate line
Above- inferior hypogastric plexus
Below- inferior rectal nerves
Describe lymphatic drainage above and below the pectinate line
Above- internal iliac nodes
Below- superior inguinal nodes
What forms the pelvic floor?
The blending of the external anal sphincter with the elevator ani muscle
What are the 3 parts to the external anal sphincter?
The subcutaneous, superficial and deep parts
What level does the inferior mesenteric artery arise from?
The level of L3
What does the inferior mesenteric artery give off?
The left colic artery, sigmoidal arteries, and the superior rectal artery, and a branch forms an anastomosis between the midgut and hindgut called the marginal artery of Drummond
What is the marginal artery of Drummond for?
It acts as a collateral supply in cases of blockage of the other arteries
What does the superior rectal artery supply?
The first part of the rectum
What trunk of the internal iliac artery does the middle rectal artery branch from?
The anterior trunk
What branch gives off the inferior rectal artery?
The inferior pudendal artery
How do the veins to the hindgut run?
They are venae communicantes
What do the lymphatics of the hindgut ultimately drain into?
The intestinal trunks, forming the cysterna chyli
What provides parasympathetic innervation not the distal 1/3 of the transverse colon?
The pelvic splanchnic nerves (S2-S4)
What provides sympathetic innervation to the distal 1/3 of the transverse colon?
The lumbar splanchnic nerves (L1-L2)
Where does hindgut pain get referred to?
The hypogastric (suprapubic) region, due to dermatomes L1 and L2
What is diverticular disease?
Symptomatic out pouching of the bowel caused by weakening in the muscle wall
What causes diverticulitis?
If food builds up in diverticuli, bacteria can build up and cause infection an inflammation
Where do diverticuli often occur?
The sigmoid colon, due to higher pressure
What is diverticulosis?
Asymptomatic diverticuli
What is the clinical significance of the portosystemic anastomosis in the anal canal?
Portal hypertension backs up blood flow in the inferior mesenteric artery. This can lead to varicose veins and rupture could cause fatal blood loss
What is caput medusae?
The appearance of distended and engorged superior epigastric veins, which are seen radiating from the umbilicus across the abdomen
