Abdomen IV Flashcards
How do the intestines develop?
- herniate out during development and enter back inside the abdominal wall
What is omphalocele and why does it occur?
- Gut contents protruding from the umbilical ring
- Malrotation of midgut
- Failure of rectus abdominis to develop correctly
What are the two primary intestinal loops?
- cranial limb
- caudal limb
What 3 things does the cranial limb contain?
- distal duodenum
- jejunum
- ileum
What 5 things does the caudal limb of the intestinal loop contain?
- distal ileum
- cecum
- appendix
- ascending colon
- distal 2/3 of transverse colon
What is the function of the vitelline duct?
- connects growing fetus to yolk sac
What is Meckel’s diverticulum?
- outpouching of the ileum
Where does the midgut extend from and to?
- extends from the major duodenal papilla, in the duodenum, to a point two-thirds distally along the transverse colon
What is the midgut supplied by?
- superior mesenteric artery
How long is the jejunum and the ileum?
- The jejunum is approximately 2.5 m in length and the ilium is approximately 3 m
Where does the ileum terminate?
- ileocecal junction
Where is the ileocecal junction located?
- right iliac fossa
What are plicae circulares?
- inner folding in the lining of the mucosa of the jejunum and ileum
Where does the jejunum begin?
- at the duodenal jejunal flexure which is when the fourth part of the duodenum bends upwards
What is the duodenaljejunal junction held up by?
- Ligament of Treitz
Where are the ileum and jejunum located quadrant wise?
- ileum is in the right lower quadrant and the jejunum is in the left lower quadrant
What is contained within the mesentery?
- superior mesenteric artery
- superior mesenteric vein
- lymph nodes
- fat
- autonomic nerves
What are the anatomical landmarks for the root of the mesentery?
- duodenal-jejunal flexure to sacro-iliac joint
- oblique course from the duodenojejunal flexure to the ileocecal junction
Are the jejunum and ileum retro or intraperitoneal?
- intraperitoneal
What are the jejunum and ileum suspended by?
*
What does the superior mesenteric vein join with?
- joins the splenic vein to form the portal vein to process all the nutrients in the liver
How long is the root of the mesentery?
- 15cm long
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What are the vessels in the mesentery called?
- arterial arcades and vasa recta
What does occlusion of the vasa recta by an embolus cause?
- ischemia of the part of the intestine concerned.
What happens if there is severe ischemia as a result of an embolus in the vasa recta?
- necrosis of the involved segment and paralytic ileus (obstruction of the intestine) occurs
What disease is the small bowel commonly involved in?
- Inflammatory bowel disease
How does IBD differ from ulcerative colitis?
- Ulcerative colitis is limited to the colon while
- Crohn’s disease can occur anywhere between the mouth and the anus
- Ulcerative colitis only affects the inner most lining of the colon
- Crohn’s disease can occur in all the layers of the bowel walls
Where does the large intestine extend from and to?
- from ileocecal junction to anus
What is lateral to the ascending and descending colon?
- paracolic gutters
What are the 5 functions of the large intestine?
- water and salt absorption
- temporary storage of feces
- little or no digestive function
- secretion of mucus
- extensive action of microorganisms
Where does the cecum lie?
*
What is the first part of the large intestine?
- caecum
What is the function of the ileocecal valve?
- prevents reflux of colonic contents into the terminal ileum
Name the parts of the intestine after the cecum?
- ascending colon which bends and is called the hepatic flexure,
- then it becomes the transverse colon which bends again and is called the splenic flexure
- becomes the descending colon
- becomes the sigmoid colon
- then the rectum and anal canal
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What are omental appendices?
- pockets of peritoneum filled with fat
What are haustra?
- muscles of the large intestine forms three longitudinal bands and as they contract they have a sacculated appearance called haustra
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What is the boundary of the midgut to hindgut?
- superior mesenteric artery to inferior mesenteric artery
- vagus nerve to pelvic splanchnic nerve (S2-S4)
Where does the ileum enter the cecum?
- ileocecal junction
What is the relationship of the opening of the appendix to the ileocaecal opening?
- appendix
What kind of a structure is the appendix and what is it suspended from the posterior abdominal wall by?
- intraperitoneal and suspended from the posterior abdominal wall by the mesoappendix
What artery supplies the appendix and which artery does this arise from?
- appendicular artery
- branch of ileocolic artery
What is the arterial supply of the caecum and where does this arise from?
- ileocolic artery
- branch of the superior mesenteric artery
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What is appendicitis?
- inflammation of the appendix stretching the visceral peritoneum
) Why is pain from appendicitis felt, initially, in the umbilical region, but later in the right iliac region?
- pain is referred to peri umbilical region T10
- later pain in right lower quadrant : irritant of parietal peritoneum lining posterior abdominal wall
Where is the McBurney’s point?
- lateral 1/3 of line from ASIS to umbilicus
What are the two borders of the ascending colon?
- Ileocolic junction to hepatic flexure
What kind of organ is the ascending colon now and during development (intra/retroperitoneal)?
- Secondary retroperitoneal
- It was once intraperitoneal during embryological development but it migrates so only the anterior surface is covered in parietal peritoneum
What is lateral to the ascending colon?
What is the blood supply to the ascending colon?
- supplied by the superior mesenteric artery via the ileocolic and right colic arteries
Where does the transverse colon end and begin?
- begins at the hepatic (right colic) flexure
- terminates at the splenic (left colic) flexure.
When does the midgut become the hindgut?
- at a point two-thirds distally along the transverse colon
What is the change in blood supply from midgut to hindgut?
- proximal ⅔ of the transverse colon will be supplied by the superior mesenteric artery
- The distal ⅓ and the rest will be supplied by the inferior mesenteric artery
Is the transverse colon intra or retroperitoneal?
- intraperitoneal
What is the innervation of the proximal 2/3 of the transverse mesocolon and what happens at the red dotted line?
- proximal ⅔ – parasympathetic innervation is through the vagus nerve (10)
- At the red dotted line the vagus stops and the pelvic splanchnic nerve take over innervation of the hindgut
Where do the pelvic splanchnic nerves arise?
- S2- S4
How is the transverse colon suspended from the posterior abdominal wall and at what level?
- by the transverse mesocolon at the level of L1
What does the transverse mesocolon divide the abdominal cavity into?
- supracolic
- infracolic compartments
How can surgical access to the lesser sac be gained?
- via the supra colic portion of the transverse mesocolon
What mesentery is fused with the transverse colon?
- greater omentum
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What is the anterior layer of the transverse mesocolon attached to?
- posterior layer of greater omentum
Where does the arterial supply to the midgut arise from?
- superior mesenteric artery
Where is the superior mesenteric artery from?
- unpaired branch of abdominal aorta
From where does the middle colic artery arise?
- superior mesenteric artery
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At what vertebral level does the superior mesenteric artery arise from the abdominal aorta?
- L1
What is superior mesenteric artery thrombosis?
- differential diagnosis for acute severe abdominal pain
Does the superior mesenteric artery run to the left or the right of the superior mesenteric vein?
- left
What vessel does the SMV unite with to form the hepatic portal vein?
- splenic vein
What does the superior mesenteric vein drain into?
- hepatic portal vein
Where does the lymphatic drainage of the midgut go?
- they follow the branches of the superior mesenteric artery.
- The nodes eventually drain into the intestinal lymphatic trunk and the cisterna chyli.
What is the cisterna chyli?
- cisterna chyli is the dilated origin of the thoracic duct
- receives the right and left lumbar lymphatic trunks and the intestinal lymphatic trunk
What do the autonomic nerves of the midgut modulate?
- activity of the submucosal and myenteric nerve plexus within the walls of the intestine
What nerves carry a) sympathetic and b) parasympathetic fibres to the midgut?
- Parasympathetic innervation of the midgut is from the superior mesenteric plexus
- sympathetic innervation is from the lesser splanchnic nerve.
What is the marginal artery of drummond and what is its function?
- anastomoses between the superior and inferior mesenteric artery
- It serves as a collateral supply to prevent ischemia
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Is the descending colon intra or retroperitoneal?
- descending colon is retroperitoneal
What is lateral to the descending colon?
- left paracolic gutter
Where does the hindgut extend from and to?
- from a point two-thirds along the transverse colon to the upper half of the anal canal
What are taeniae coli?
- three longitudinal bands of muscle which run from the caecum to the rectum
What are appendices epiploicae?
- tags of peritoneum filled with fat
Is the sigmoid colon intra or retroperitoneal and what is it suspended by?
- suspended from the posterior abdominal wall by a double fold of peritoneum known as the sigmoid mesocolon
At what level does the sigmoid colon become the rectum?
- S3
What is diverticulosis?
- outpouching of the colonic mucosa and submucosa through weaknesses of muscle and layers in the colon
What is diverticulitis?
- infections and inflammation of diverticulum
What are the indentations in the rectum formed by?
- formed by thickenings in the folds of the mucosa in the lining of the rectum
What are the thickenings in the rectum that form indentations?
- transverse rectal folds
When does the rectum become the anal canal?
- as it travels through the pelvic floor/ pelvic diaphragm
Where is the rectosigmoid junction located?
- S3
Why is the 80 degree angle of the anorectal flexure important?
- continence
What is the ampulla of the rectum?
- the distal portion of the rectum which dilates in the presence of faeces and is important for continence
What muscle is the pelvic floor made from?
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What does the pectinate line represent?
- termination of the hindgut, and thus a change in peritoneal coverings, epithelial lining, blood supply, venous drainage, lymphatic drainage and innervation.
What does the internal anal sphincter control?
- superior 2/3 of anal canal
What does the external anal sphincter control?
- inferior third of anal canal
What types of muscle are the internal and external anal sphincters?
- internal : extension of circular
- external : skeletal
What kind of control does the internal anal sphincter have?
- involuntary : tonically contracted
What kind of control does the external anal sphincter have?
- voluntary
What does the pectinate line separate?
- upper 2/3 and lower 1/3 of anal canal
What does the pectinate line demarcate the transition between?
- transition between columnar epithelium to stratified squamous epithelium
What is the innervation of the internal anal sphincter?
- pelvic splanchnic nerves
- relaxes muscle
What is the innervation of the external anal sphincter?
- inferior rectal branch of pudendal nerve
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What is an internal hemorrhoid caused by?
- Prolapses of rectal mucosa containing dilated veins of the internal rectal venous plexus.
- They often fall into anal canal and are compressed by anal sphincters
What is an external hemorrhoid caused by?
- Blood clots from external rectal venous plexus that are covered in skin
What is the blood supply of the hindgut?
- inferior mesenteric artery
Where does the inferior mesenteric artery arise from?
- the aorta
- L3
What are the 4 branches of the inferior mesenteric artery?
- Left colic artery
- Sigmoidal arteries
- Superior rectal artery
- Marginal artery
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From what artery does the superior rectal artery arise?
- branch of inferior mesenteric artery
Where does the middle rectal artery arise from?
- branch of internal iliac artery
Where does the inferior rectal artery arise from?
- branch of internal pudendal artery
What do the middle and inferior rectal arteries supply?
- anal canal NOT the rectum
What do the superior rectal veins drain into?
- inferior mesenteric vein (portal system
What do middle rectal veins drain into?
- internal iliac vein (systemic system)
What do the inferior rectal veins drain into?
- inferior pudendal (systemic system)
What is the hepatosystemic anastomoses?
- occurs between the superior and middle and inferior rectal veins
- in the anal canal
How does the lymphatic system of the hindgut work?
- The lymphatic system hindgut follows the branches of the inferior mesenteric artery
- The nodes eventually drain into the intestinal lymphatic trunk and the cisterna chyli
Where are the pre-aortic lymph nodes?
- pre aortic nodes lie on the main blood vessels : celiac, superior mesenteric and inferior mesenteric nodes
What do the preaortic lymph nodes drain into?
- intestinal trunk which drain into the cisterna chyli
Where do the parasympathetic fibers to the hindgut travel?
- through the pelvic splanchnic nerves (S2 –S4). These also carry visceral afferent (sensory) fibres
Where do the sympathetic nerves to the hindgut travel?
- hindgut travel through the lumbar splanchnic nerves (L1 – L2).
Why is pain from the gallbladder referred to shoulder?
- can irritate diagphragm
- diaphragm innervated by C3,C4,C5
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