ANAT - Foregut, Midgut, Hindgut Development Flashcards
(101 cards)
1
Q
how is the gut tube incorporated into the body?
A
- lateral folding
- amniotic cavity accumulates fluid dorsally = grows laterally + encases gut tube = creates peritoneum + mesentery
2
Q
how does cranio-caudal folding influence the gut
A
- brain grows rapidly, forcing the head forward > creates three sections of gut > foregut, midgut and hindgut
- also pushes heart and diaphragm from cervical to thoracic region
3
Q
structure of the ventral mesentery
A
- only the foregut has ventral mesentery
- lesser omentum: bounded by hepatogastric and hepatoduodenal ligaments, space of peritoneum between the stomach and liver, forms the anterior border of the lesser sac and has a hole called epiploic foramen (of Winslow)
- falciform ligament: connects liver to anterior wall and continues as ligamentum teres (obliterated umbilical v.) which turns into ligamentum venosum on posterior aspect
4
Q
what is the bare area of the liver
A
- part of the liver in contact w/ diaphragm = not covered by peritoneum = ‘bare’
5
Q
main arteries for foregut, midgut and hindgut
- what vertebral level are they at
- describe their peritoneal relations
A
- foregut: coeliac trunk (T12)
- midgut: superior mesenteric artery (L1)
- hindgut: inferior mesenteric artery (L3)
- they begin retroperitoneal as they branch directly off the abdominal aorta, then divide further on either side of the mesentery, becoming intraperitoneal
6
Q
how does growth of the liver and stomach drive foregut rotation?
A
- liver grows anteriorly to the stomach and forces it to rotate to the R (towards the midline) = L side becomes ventral, R side becomes dorsal
- R aspect of the stomach grows more rapidly so it hangs down
- therefore greater omentum is ventral because it hangs off the greater curvature of the stomach and originated on the left side
- also explains why L vagus n. is ventral, R is dorsal
7
Q
growth of the pancreas and how can this go wrong?
A
- ventral pancreatic bud (uncinate) rotates significantly to meet dorsal pancreatic bud
- pancreas hits posterior body wall therefore becomes secondarily retroperitoneal
- (however the tail is touching the spleen which is intraperitoneal so technically tail is intraperitoneal)
- if the 2 buds don’t merge > can cause an annular (circular) pancreas - buds fuse around the duodenum, obstructing it
8
Q
what comprises the dorsal mesentery
A
- foregut: greater omentum, gastrosplenic ligament and splenorenal ligaments (all derived from dorsal mesogastrium)
- midgut: mesentery proper (attaches jejunum and ileum to posterior wall) and transverse mesocolon
- hindgut: sigmoid mesocolon
9
Q
ventral, dorsal and left boundaries of the lesser sac
A
- ventral: stomach + lesser omentum
- dorsal: pancreas
- left: spleen (including gastrosplenic and splenorenal ligaments)
10
Q
how to know whether mesentery used to be dorsal or ventral?
A
- if it’s more to the R, then ventral
- if more to the L, then dorsal
11
Q
which embryological layer gives rise to the GIT
A
- endoderm (visceral organs)
- mesoderm is peritoneum, pleura, pericardium
12
Q
vitello-intestinal duct
A
- attachment of midgut to umbilical cord
13
Q
development of the midgut
A
- midgut loop forms a U shape and herniates into umbilicus = has a cranial and caudal limb which rotate around the axis of the SMA
- cranial limb grows faster and flops to the R - returns to the gut + forms small intestine distal to major duodenal papilla
- caudal limb falls to the L - forms caecum > splenic flexure (transverse colon grows from L > R, ascending colon grows DOWNWARDS)
14
Q
what prevents rotation of the foregut and hindgut while the midgut is developing?
A
- ‘retention bands’
- superior = ligament of Trietz (from diaphragm and duodenal muscle fibres)
- inferior: phrenicocolic ligament
15
Q
meckel’s diverticulum
A
- maintenance of vitelline intestinal duct (connection of midgut to yolk sac > provides temporary nourishment to foetus)
- usually asymptomatic but can lead to infection, indigestion, volvulus
- rule of 2s: 2% of the population have it, 2 inches long, 2 feet from ileocaecal valve, Sx usually appear before 2 y.o.
16
Q
what determines the position of the appendix?
A
- the extent to which the ascending colon grows inferiorly
17
Q
what is the cloaca and how does it divide? what is the last step in hindgut development?
A
- pouch that divides into the bladder (anteriorly) and rectum (posteriorly)
- epithelium from the anterior body wall grows in and loops around to divide the cloaca - forms the perineal body
- hindgut is also disconnected from anterior body wall via urachus otherwise urine would leak from umbilicus
- ectoderm invaginates to meet endoderm, forming the pectinate line in the rectum
18
Q
differences above and below the pectinate line of the rectum
- embryological tissue type
- lymph node drainage
- innervation
- arterial supply
A
- above = endoderm = deep lymph node drainage (internal iliac L/N), autonomic innervation (no pain), superior + middle rectal arteries
- below = ectoderm = superficial lymph node drainage (superficial inguinal L/N), somatic innervation (pain), middle + inferior rectal arteries
19
Q
describe the folds in the small and large intestine
A
- small: plicae circulares - permanent mucosal folds, traversing the entire length of the small intestine
- large: haustra (pouches) - formed by teniae coli. plicae semilunaris are between the haustra and don’t traverse the whole bowel, but flatten as the bowel distends (non-permanent)
20
Q
incarcerated vs strangulated hernia
A
- incarcerated: non-reducible b/c tissue becomes trapped and can’t be pushed back in
- strangulated (subset of incarcerated): non-reducible AND loss of blood supply to herniated tissue
21
Q
borders of inguinal triangle and clinical relevance
A
- inferior: inguinal ligament
- medial: lateral border of rectus abdominis
- lateral: inferior epigastric vessels
- relevance: weak spot in abdominal wall b/c below arcuate line, posterior aspect of anterior abdo wall formed mostly by transversalis fascia = spot for DIRECT inguinal hernias which are medial to inferior epigastric vessels = inside inguinal triangle
22
Q
what structures are in the foregut
A
- oesophagus > major duodenal papilla
- including liver, gallbladder, biliary tree, pancreas
- spleen developed from mesoderm so technically not foregut but still supplied by coeliac trunk
23
Q
what structures are in the midgut
A
- duodenum (distal to major duodenal papilla) > proximal 2/3 of transverse colon (splenic flexure)
24
Q
what structures are in the hindgut
A
- distal 1/3 of transverse colon (splenic flexure) > upper 1/2 of rectum (pectinate line)
25
name the parts of the duodenum and are they intra or retroperitoneal? why?
- 1) superior - intra (part of foregut)
- 2) descending - 2˚ retro
- 3) horizontal - 2˚ retro
- 4) ascending - 2˚ retro
- the proximal cranial loop (duodenum precursor) is the first to come back into the gut so parts 2-4 end up along the posterior body wall
26
where do foregut, midgut and hindgut structures usually refer their pain
- foregut: epigastric
- midgut: umbilical region
- hindgut: suprapubic (hypogastric)
27
describe the location of the gastroepiploic arteries
- R gastroepiploic artery: originates from gastroduodenal a.
- L gastroepiploic artery: originates from splenic a.
- these anastomose to supply the greater curvature of the stomach
28
describe the location of the gastric arteries
- R gastric artery: originates from proper hepatic a.
- L gastric artery: originates from coeliac trunk
- both anastomose to supply lesser curvature of the stomach
29
RIGHT main branches of the coeliac trunk
30
cystohepatic triangle borders, contents, clinical relevance
- borders: cystic duct (L), common hepatic duct (R), liver (superior)
- contains cystic a., L/N
- used during cholecystectomy to locate and ligate (tie off) cystic a.
31
what are the peritoneal reflections of the liver? where do they originate from? + significance
- L/R anterior coronary ligaments branch off falciform ligament
- L/R posterior coronary ligaments come directly from peritoneum on the posterior surface of the liver
- A/P coronary ligaments joined by L/R triangular ligaments
- significance: form borders of the bare area of the liver
32
posterior surface of the liver contents
- horizontal part of H: porta hepatis (FISSURE containing everything that enters/leaves the liver = proper hepatic a., portal v., nerves, lymphatics, common hepatic duct)
- L line of H: round ligament of the liver (contains obliterated umbilical v.) > becomes falciform ligament > ligamentum venosum
- R line of H: gallbladder + IVC
- lobes: left, right, caudate (superior) and quadrate (inferior)
33
which parts of the colon are intra, retro and 2˚ retroperitoneal
- intra: caecum, transverse, sigmoid
- retro: rectum
- 2˚ retro: ascending and descending
34
transpyloric plane and what can be seen at this level?
- located midway between umbilicus and sternal notch (L1)
- pylorus of the stomach (when supine)
- 1st part of duodenum
- fundus of the gallbladder
- kidney and splenic hila
- renal a.
- adrenal glands
- pancreatic neck
- SMA
- duodenojejunal flexure
- L (splenic) and R (hepatic) colic flexures
- splenic v. and SMV join to form portal vein
35
what are the most dependent part sof the peritoneal cavity (erect AND supine position?)
- erect: fluid goes straight into rectouterine (pouch of Douglas)/rectovesical pouch, via paracolic gutters, due to gravity
- lying supine: fluid travels along R/L paracolic gutters (due to secondarily retro ascending/descending colon) to the hepatorenal recess (Morrison's pouch) OR rectouterine/rectovesical pouch
- if post-op, perforated visceral organ or infection, fluid/leaked contents will accumulate in the subphrenic space (anterior or posterior depends on what the cause is)
36
where would the gut contents enter with a ruptured ulcer in the anterior wall of the duodenum?
- right posterior subphrenic space (posterior to the liver, inferior to the diaphragm)
- anterior wall of the duodenum is posterior to the liver so would enter this space > continuous with the R paracolic gutter
37
ascites
- abnormal accumulation of fluid in peritoneal cavity due to portal HTN
38
epiploic foramen boundaries + clinical relevance
- anterior: hepatoduodenal ligament (contains portal triad - proper hepatic artery, portal v., CBD)
- superior: caudate lobe of liver
- inferior: 1st part of duodenum
- posterior: IVC
- relevance: surgeons can insert a finger through the epiploic foramen to compress portal triad to stop bleeding from liver (Pringle manoeuver)
39
arterial supply of the pancreas
- mainly splenic a. (from coeliac trunk): branches include dorsal pancreatic a., greater pancreatic a., short gastric aa. (supply fundus of stomach) and transverse (inferior) pancreatic a.
- also from coeliac trunk: common hepatic > gastroduodenal > superior pancreaticoduodenal a. (ant and post branches)
- from SMA: inferior pancreaticoduodenal a. (ant and post branches) > supply head and uncinate process
40
biliary system pathway
- bile produced in intrahepatic biliary tree > converge into canaliculi and ductules
- L and R hepatic ducts converge to form common hepatic duct
- joins w/ cystic duct (from gallbladder) to form common bile duct
- joins w/ main pancreatic duct to form ampulla of vater and inserts into 2nd (descending) part of duodenum at the major duodenal papilla - contains sphincter of oddi and junction between foregut/midgut
- accessory pancreatic duct branches off main pancreatic duct and also inserts into 2nd part of duodenum at the minor duodenal papilla
41
where is the spleen located + clinical significance
- located in the left hypochondrium behind ribs 9-11
- stab wounds here can cause fibrous capsule to ruture = massive intraperitoneal haemorrhage
42
differentials for epigastric pain
- pancreatitis: radiates to back, pain relieved by sitting up and leaning forward
- peptic ulcer disease (gastric if worse when eating or duodenal if improves when eating) - NSAIDs, melena
- gastritis (NSAIDs, alcohol)
- gastric cancer (loss of weight, early satiety)
- mallory-weiss tear: haematemesis, repeated forceful vomiting
- cholecystitis from cholelithiasis - radiates to R shoulder (phrenic n.)
- cholangitis from choledocholithiasis – elevated bilirubin/ALP, Charcot’s triad (fever, jaundice, RUQ pain)
- hepatitis – malaise, jaundice, tender liver edge
- AMI
- AAA/dissection (tearing sensation)
43
pain pattern of appendicitis
- early stage: visceral peritoneum, poorly localised, dull pain, (periumbilical - T10 dermatome)
- later stage: spreads to parietal peritoneum, well-localised, sharp pain (RLQ)
44
4 layers in GIT wall
- mucosa (innermost layer): made of epithelium, lamina propria and muscularis mucosa
- submucosa: loose connective tissue and submucosal plexus
- muscularis externa: inner circular muscle and outer longitudinal muscle with myenteric plexus in between
- serosa (peritoneum)
45
histological structure of stomach
- epithelium
- mucosa and submucosa
- muscularis externa
- simple columnar epithelium for secretion with invaginations called gastric pits, which extend into gastric glands
- gastric glands have diff cell types: parietal cells (HCl + intrinsic factor), chief cells (pepsin), mucus cells
- mucosa and submucosa have rugae (folds) which allow for distension
- thick muscularis externa with oblique (innermost), circular and longitudinal (outermost) muscle for mixing
46
histological structure of small intestine
- epithelium + mucosa
- submucosa
- simple columnar epithelium (enterocytes) with microvilli for absorption (also contains goblet and immune cells)
- mucosa invaginates to form villi (increased SA), and contains crypts of lieberkuhn = contain stem cells for epithelial regeneration
- submucosa has plicae circulares (folds) for increased SA, and Brunner's glands, which secrete alkaline mucus
47
where are Peyer's patches found
- ileum
48
histological features of the colon
- crypts (colonic glands), no villi (flat surface)
- many goblet cells for lubrication of faeces
- teniae coli
- thick muscularis externa
49
3 teniae coli
- tenia libera
- tenia omenta
- mesocolic tenia
50
epithelium of gallbladder
- simple columnar epithelium
51
functions of hepatocytes
- synthesis of plasma proteins
- bile production
- lipid and CHO storage
- metabolic functions (e.g. gluconeogenesis)
- detoxification of drugs
52
kupffer cell
- liver macrophage = phagocytoses old RBC
53
3 ways of representing the structural/functional units of the liver
- classic lobule
- portal lobule
- acinus structure
54
classic lobule structure in the liver
- contains central vein and polygon border
- portal triads are located at each corner of the polygon border: bile duct (simple cuboidal epithelium), hepatic artery, portal vein, lymph vessels
- ox (hepatic a.) and deox (portal v.) blood mixes and drains into the central vein via sinusoids
- hepatocytes arranged into sheets or plates surrounding sinusoids to absorb/secrete
55
how do hepatic sinusoids facilitate exchange of substances between blood and surrounding tissue
- discontinuous endothelium
56
bile canaliculi
- narrow channels between neighbouring hepatocytes
- have microvilli and can contract > propel bile towards bile ducts
57
portal lobule structure in the liver
- 3 portal veins meeting in the middle and 3 central veins surrounding them
- bile runs towards the central vein
58
acinus structure in the liver
- 'portal tract' runs from one portal triad to another, containing blood from the gut
- surrounding hepatocytes will process the blood in circular concentric layers
59
histological components of the pancreas
- acinar cells - secretes (inactive - zymogen granules) digestive enzymes into a small central lumen of a few acinar cells which joins with other small ducts > looks dark purple
- septar/loose connective tissue surrounding acinar globules
- ductal cells
- islets of langerhans - endocrine (1-2%): surrounded by a thin capsule, contains alpha (glucagon), beta (insulin), delta cells. has many fenestrated capillaries
60
marginal artery
- anastomosis between SMA and IMA, runs along inferior border of transverse colon
61
differentials for difficulty passing stools and blood in stools
- bowel cancer
- coeliac
- haemorrhoids
- IBD e.g. Crohn's, UC
- diverticular disease (encompasses both diverticulosis and diverticulitis)
- parasitic infection (esp. if travel)
- duodenal/gastric ulcer - would be black stools due to blood mixed in
- IBS: constipation, diarrhoea or combination
62
tenesmus
- sensation of needing to defaecate even if bowels are empty
- can be accompanied by cramping, straining and the passage of little stool
- caused by rectal cancer b/c activation of stretch receptors in rectum
63
what does a FBC include
- WCC
- RCC
- platelet count
- haemoglobin
- ESR and CRP
64
bowel cancer Sx
- changes in bowel habits e.g. diarrhoea, constipation
- feeling of incomplete emptying
- blood in stool (fresh = haematochezia)
- abdominal pain and cramps
- systemic: weight loss, fatigue
- tenesmus = constant urge to defaecate
65
crohn's vs ulcerative colitis Sx
- Crohn's = anywhere from mouth to anus, spots of inflammation, goes through whole thickness of wall
- UC = usually colon and rectum, massive continuous sections of inflammation, only mucosa and submucosa
66
IBS
- no actual inflammation like IBD, only abnormal gut motility
- abdominal pain, bloating, cramping, diarrhoea, constipation
67
mesentery vs 'THE' mesentery
- mesentery = folds of peritoneum with connective tissue and vessels in between
- 'THE' mesentery = mesentery of jejunum and ileum
68
function of mesentery
- enable motility of GIT
- route for vessels and nerves to reach visceral organs
69
branches of SMA which supply large intestine
- SMA gives off jejunal and ileal arteries which anastomose to form vasa recta (straight arteries)
- R colic a. supplies ascending colon
- middle colic a. supplies proximal 1/2 of transverse colon
- ileocolic artery supplies ileocaecal junction + appendix
70
branches of IMA
- supplies part of marginal a. (anastomoses w/ SMA and travels along inferior border of transverse colon)
- L colic a. > supplies descending colon
- sigmoidal a.
- superior rectal a. (terminal branch of IMA)
71
where do the superior, middle and inferior rectal aa. come from?
- superior: IMA
- middle: internal iliac
- inferior: internal pudendal
72
why are the sigmoid and transverse colon more susceptible to volvulus?
- contains mesentery (sigmoid/transverse mesocolon) = more mobile and susceptible to volvulus
- can cause ischaemia due to kinking of sigmoidal arteries
73
which vein does the inferior 1/3 (abdominal portion) of the oesophagus drain into?
- L gastric v. and azygous v.
74
4 constrictions of the oesophagus
- cervical (C6) - cricopharyngeus muscle (upper oesophageal sphincter)
- thoracic (T4/5) - arch of aorta + L main bronchus
- diaphragmatic (T10) - oesophageal hiatus
75
where is the SMV in relation to the SMA? where do these course?
- SMV is to the right of the SMA
- SMV comes off IVC and SMA comes off abdo aorta
- both travel behind the neck of the pancreas and then anterior to the 3rd part of the duodenum
76
causes of haematemesis
- can occur anywhere in foregut
- oesophagus: mallory-weiss tear, oesophagitis, cancer
- stomach: gastric ulcers, cancer, gastritis
- duodenum: ulcers
77
structural differences between jejunum and ileum
- jejunum: thicker wall, larger diameter, prominent plicae circulares (mucosal folds), more vascular (redder), fewer but longer vasa recta, less arcades and mesenteric fat
- ileum: thinner wall, smaller diameter, no plicae circulares in terminal ileum, less vascular (paler), more and shorter vasa recta, more arcades and mesenteric fat
78
venous drainage of the 3 parts of the rectum
- superior rectal v. > IMV > portal v. = liver spread > IVC
- middle rectal v. > internal iliac v. > IVC
- inferior rectal v. > internal pudendal v. > internal iliac > IVC
79
cholelithiasis
- presence of gallstones (not necessarily symptomatic)
- caused by precipitation of cholesterol and bilirubin in bile
80
causes of obstructed bile flow and what can it lead to
- gallstones, strictures or cancer
- stasis of bile can lead to cholecystitis
- lack of bile in duodenum = fat malabsorption, fat-soluble vitamin deficiency (A, D, E, K)
81
oesophageal varices
- liver damage due to alcohol, hep B/C, NAFLD etc. causes reduced blood flow in portal circuit = backflow into systemic
- therefore enlarged veins around porto-systemic anastomoses (e.g. oesophageal veins, anterior abdominal wall)
- venous walls weaken and are prone to rupture = massive upper GI bleeding and haematemesis
82
5 F's for gallbladder disease risk factors
- fat, female, fertile, forty, fair
83
4 chole conditions
- cholelithiasis causes cholecystitis
- choledocholithiasis causes cholangitis
84
Courvoisier's law
- a painlessly distended gallbladder in a Pt with jaundice indicates pancreatic cancer, not obstruction
85
differentials for RUQ pain
- head of pancreas cancer - post hepatic jaundice Sx with NO pain
- cholelithiasis > cholecystitis
- choledocholithiasis > cholangitis (more severe)
- hepatitis
86
dermatomes over the umbilicus + inguinal ligament
- umbilicus = T10
- inguinal ligament = L1
87
how to treat portal hypertension
- anastomose portal vein and another systemic vein
88
which vessels do the following ligaments contain:
- hepatoduodenal
- gastrosplenic
- splenorenal
- gastrohepatic
- falciform
- hepatoduodenal: portal triad (CBD, hepatic a., portal v.)
- gastrosplenic: short gastric aa. and L gastroepiploic vessels
- splenorenal: splenic vessels and tail of pancreas
- hepatogastric: L gastric vessels
- falciform: ligamentum teres (remnant of umbilical vein)
89
portal venous system diagram
90
intraperitoneal, retroperitoneal, secondarily retroperitoneal
- intra: surrounded by visceral pleura (technically nothing is actually inside the peritoneal cavity)
- retroperitoneal: only touched on one side through peritoneum e.g. kidneys
- secondarily retro: used to be intra but then became retro
91
most common place for AAA to occur
- inferior to renal artery (infrarenal)
92
which structures are at risk with a peptic ulcer
- if duodenum: gastroduodenal a.
- if stomach: gastroepiploic a. (greater curvature of stomach) and splenic a.
93
most comfortable position for a Pt with peritonitis
- supine w/ knees bent = allows abdominal muscles to relax = decreases pressure on peritoneum = less irritation
94
3 main sites of porto-systemic anastomoses + significance
- umbilical veins: paraumbilical veins join into superficial epigastric veins (can cause caput medusae)
- lower 1/3 of oesophagus: L gastric vein joins into azygos vein (can cause oesophageal varices)
- anal canal: superior rectal v. joins into middle and inferior rectal veins (can cause haemorrhoids)
95
how is the liver divided?
- functionally: 8 segments (each has own portal triad > functionally independent)
- anatomically: 4 lobes divided by the falciform ligament (L, R, caudate, quadrate)
96
where do the umbilical arteries originate from?
- internal iliac
97
where is the fundus of the gallbladder located anatomically?
- 8th costal cartilage in R midclavicular line
98
when the midgut returns to the abdominal wall, it undergoes an additional 180˚ rotation. during which week of development does this occur?
- 8th week
99
what would be a red flag to rule out in GORD?
- "food sticking in mouth after swallowing" = dysphagia
- could indicate oesophageal obstruction or cancer
100
at which level does the abdominal aorta bifurcate into the common iliac arteries
- L4
101
why can babies have tachypnoea?
- liver is disproportionally large compared to size of thorax > limits flattening of diaphragm during inspiration = decreased volume of thoracic cavity (not related to phrenic nerve as this should be fully developed)
