ANAT - Foregut, Midgut, Hindgut Development Flashcards
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: space of peritoneum between the stomach and liver, bounded by hepatogastric and hepatoduodenal ligaments, forms the anterior border of the lesser sac. has a hole called epiploic foramen/foramen of Winslow
- falciform ligament: connects liver to anterior wall and turns into round ligament of the liver - remnant of umbilical v. which turns into ductus venosus
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 general course
A
- foregut: coeliac trunk (T12)
- midgut: superior mesenteric artery (L1)
- hindgut: inferior mesenteric artery (L3)
- these branch directly off the abdominal aorta (retroperitoneal) and 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
- dorsal (now 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 what happens if the two buds fail to merge?
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 (anterior to spleen), splenorenal ligament
(posterior to spleen) - midgut: mesentery of the small intestine (mesentery proper)
- hindgut: transverse and sigmoid mesocolon (descending is 2˚retro so has no mesentery)
9
Q
ventral, dorsal and left boundaries of the lesser sac
A
- ventral: stomach + lesser omentum
- dorsal: pancreas
- left: spleen
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
midgut herniation during development
A
- normal to have midgut herniation into the umbilicus due to rapid growth
14
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
15
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
16
Q
why are some parts of the duodenum secondarily retroperitoneal
A
- 1st part of the duodenum is intraperitoneal b/c foregut
- 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
17
Q
final step in midgut development
A
- transverse colon grows from L > R
- ascending colon grows DOWNWARDS
18
Q
meckel’s diverticulum
A
- maintenance of vitelline intestinal duct (connection of intestinal wall to umbilicus)
- usually asymptomatic but can lead to infection, lack of digestion, twisting (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.
19
Q
what determines the position of the appendix?
A
- the extent to which the ascending colon grows inferiorly
- diff parts of the ascending colon can be intra/2˚ retroperitoneal
20
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
21
Q
differences above and below the pectinate line
- embryological tissue type
- lymph node drainage
- innervation
- arterial supply
A
- above = endoderm = deep lymph node drainage (internal iliac L/N), autonomic innervation, superior + middle rectal arteries
- below = ectoderm = superficial lymph node drainage (superficial inguinal L/N), somatic innervation (pain), middle + inferior rectal arteries
22
Q
describe the folds in the small and large intestine
A
- small: PERMANENT mucosal folds are called plicae circulares, traversing the entire length of the bowel
- large: has pouches (haustra) that protrude into the lumen, formed by teniae coli. plicae semilunaris are between the haustra and usually don’t traverse the whole bowel, but flatten as the bowel distends
23
Q
incarcerated vs strangulated hernia
A
- incarcerated: non-reducible b/c tissue becomes trapped and can’t be pushed back in
- strangulated: loss of blood supply to herniated tissue
24
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
25
what structures are in the foregut
- oesophagus > major duodenal papilla
- including liver, gallbladder, biliary tree, pancreas
- spleen developed from mesoderm so technically not foregut but still supplied by coeliac trunk
26
what structures are in the midgut
- duodenum (distal to major duodenal papilla) > proximal 2/3 of transverse colon (splenic flexure)
27
what structures are in the hindgut
- distal 1/3 of transverse colon (splenic flexure) > upper 1/2 of rectum (pectinate line)
28
parts of the duodenum and are they intra or retroperitoneal?
- 1) superior - intra
- 2) descending - 2˚ retro
- 3) horizontal - 2˚ retro
- 4) ascending - 2˚ retro
29
where do foregut, midgut and hindgut structures usually refer their pain
- foregut: epigastric
- midgut: umbilical region
- hindgut: suprapubic (hypogastric)
30
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
31
describe the location of the gastric arteries
- R gastric artery: branches off proper hepatic a. and follows lesser curvature of the stomach from R to L
- L gastric artery: branches off coeliac trunk, follows lesser curvature of the stomach from L to R and anastomoses w/ R gastroepiploic artery
32
RIGHT main branches of the coeliac trunk
- common hepatic artery divides into R gastric artery and proper hepatic artery
- proper hepatic artery gives off duodenal a.
33
cystohepatic triangle borders, contents, clinical relevance
- borders: cystic duct (L), common hepatic duct (R), liver (superior)
- contents: cystic artery, lymph nodes
- relevance: during cholecystectomy, surgeons need to find this triangle to tie off the cystic artery
34
peritoneal reflections of the liver
- branching off falciform ligament: anterior coronary ligaments and posterior coronary ligaments
- these are joined by triangular ligaments on either side
35
posterior surface of the liver contents
- horizontal part of H: porta hepatis (arteries, veins, biliary structures)
- L line of H: round ligament of the liver > falciform ligament > ligamentum venosum
- R line of H: gallbladder + IVC
- lobes: left, right, caudate and quadrate
36
which parts of the colon are intra, retro and 2˚ retroperitoneal
- intra: caecum, transverse, sigmoid
- retro: rectum
- 2˚ retro: ascending and descending
37
transpyloric plane and what organs does it cut through?
- located midway between umbilicus and sternal notch (L1)
- pylorus of the stomach (when supine)
- duodenojejunal flexure
- fundus of the gallbladder
- pancreatic neck
- SMA
- splenic v. and SMV join to form portal vein
- kidney and splenic hila
- adrenal glands
- 1st part of duodenum
- L (splenic) and R (hepatic) colic flexure
38
what is the most dependent part of the peritoneal cavity (erect AND supine position?)
- erect: rectouterine (pouch of Douglas)/rectovesical pouch = lowest point where fluid can accumulate due to gravity
- lying supine: hepatorenal pouch (Morrison's pouch)
- R and L paracolic gutters - since ascending colon is secondarily retroperitoneal
39
ascites
- abnormal accumulation of fluid in peritoneal cavity
40
epiploic foramen boundaries
- anterior: hepatoduodenal ligament
- superior: caudate lobe of liver
- inferior: 1st part of duodenum
- posterior: IVC + diaphragm
- contents: portal triad (proper hepatic artery, portal v., CBD)
41
arterial supply of the pancreas
- superiorly: splenic a.
- branches include dorsal pancreatic a., greater pancreatic a., small gastric aa. (supply fundus) and transverse pancreatic a.
- also contributions from SMA include anterior and posterior superior and inferior pancreatoduodenal aa.
42
biliary system pathway
- L and R hepatic ducts converge to form common hepatic duct
- joins w/ cystic duct (gallbladder) to form common bile duct
- joins w/ main pancreatic duct and inserts into 2nd part of duodenum (descending), forming major duodenal papilla (ampulla of vater)
- accessory pancreatic duct branches off main pancreatic duct and also inserts into 2nd part of duodenum (descending), forming minor duodenal papilla
43
where is the spleen located + clinical significance
- located behind ribs 9-11
- therefore can be injured - if fibrous capsule of spleen ruptures, blood can enter peritoneal cavity
44
differentials for epigastric pain
- pancreatitis: radiates to back
- peptic ulcer
- mallory-weiss tear (stomach lining tear due to forceful vomiting)
- cholecystitis from cholelithiasis - radiates to R shoulder b/c innervated by phrenic n.
45
differentials for R iliac pain
- appendicitis (radiates to back)
- ruptured ectopic pregnancy: vaginal bleeding, irregular menstrual cycle
- miscarriage
- pelvic inflammatory disease e.g. chalmydia, gonorrhoea: haematuria, dysuria
- endometriosis
- physical trauma
- ovarian cyst: irregular menstrual cycle
- ovarian cancer: vaginal bleeding
- ovarian torsion: N/V, usually no abnormal vaginal bleeding
46
4 layers in GIT wall
- mucosa (innermost layer): made of epithelium, lamina propria and muscularis mucosa
- submucosa: connective tissue and submucosal plexus
- muscularis externa: inner circular muscle and outer longitudinal muscle with myenteric plexus in between
- serosa (peritoneum) OR adventitia (everywhere else)
47
histological structure of oseophagus
- epithelium
- submucosa
- stratified squamous epithelium (thick for protection)
- mucous glands in submucosa for lubrication
48
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), chief cells (pepsin), mucus cells
- mucosa and submucosa have rugae (folds) which allow for distension
- thick muscularis externa with circular, longitudinal and oblique muscle for mixing
49
histological structure of small intestine
- epithelium
- submucosa
- simple columnar epithelium (enterocytes) for absorption (also contains goblet cells and immune cells)
- enterocytes on epithelium have microvilli on surface
- mucosa invaginates to form villi (increased SA)
- mucosa also contains crypts of lieberkuhn = contain stem cells to produce epithelial cells due to high rate of turnover
- plicae circulares: folds of submucosa for increased SA
- Brunner's glands in submucosa of DUODENUM - secrete alkaline mucus
- Peyer's patches in ileum: aggregates of lymphoid tissue
50
histological features of the colon
- crypts (colonic glands), no villi (flat surface)
- many goblet cells for lubrication of faeces
- teniae coli: strips of longitudinal muscle which allow for formation of haustra (bulging) during peristalsis
- thick muscularis externa
51
3 teniae coli
- tenia libera
- tenia omenta
- mesocolic tenia
52
epithelium of gallbladder
- simple columnar epithelium
53
functions of hepatocytes
- synthesis of plasma proteins
- bile production
- lipid and CHO storage
- metabolic functions (e.g. gluconeogenesis)
- detoxification of drugs
54
kupffer cell
- liver macrophage = phagocytoses old RBC
55
3 ways of representing the structural/functional units of the liver
- classic lobule
- portal lobule
- acinus structure
56
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
57
how do hepatic sinusoids facilitate exchange of substances between blood and surrounding tissue
- discontinuous endothelium
58
bile canaliculi
- narrow channels between neighbouring hepatocytes
- have microvilli and can contract > propel bile towards bile ducts
59
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
60
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
61
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
- 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
62
marginal artery
- anastomosis between SMA and IMA, runs along inferior border of transverse colon
63
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
64
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 of stretch receptors in rectum
65
what does a FBC include
- WCC
- RCC
- platelet count
- haemoglobin
- ESR and CRP
66
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
67
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
68
IBS
- no actual inflammation like IBD, only abnormal gut motility
- abdominal pain, bloating, cramping, diarrhoea, constipation
69
mesentery vs 'THE' mesentery
- mesentery = folds of peritoneum with connective tissue and vessels in between
- 'THE' mesentery = mesentery of jejunum and ileum
70
function of mesentery
- enable motility of GIT
- route for vessels and nerves to reach visceral organs
71
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
- ileocaecal artery
72
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)
73
where do the superior, middle and inferior rectal aa. come from?
- superior: IMA
- middle: internal iliac
- inferior: internal pudendal
74
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
75
which vein does the inferior 1/3 (abdominal portion) of the oesophagus drain into?
- L gastric v. and azygous v.
76
3 constrictions of the oesophagus
- C6 - cricopharyngeus muscle
- T4/5 - arch of aorta
- T10 - oesophageal hiatus
77
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
78
causes of haematemesis
- can occur anywhere in foregut
- oesophagus: mallory-weiss tear, oesophagitis, cancer
- stomach: gastric ulcers, cancer, gastritis
- duodenum: ulcers
79
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
80
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
81
cholelithiasis
- presence of gallstones (not necessarily symptomatic)
- caused by precipitation of cholesterol and bilirubin in bile
82
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)
83
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
84
5 F's for gallbladder disease risk factors
- fat, female, fertile, forty, fair
85
4 chole conditions
- cholelithiasis causes cholecystitis
- choledocholithiasis causes cholangitis
86
Courvoisier's law
- a painlessly distended gallbladder in a Pt with jaundice indicates pancreatic cancer, not obstruction
87
differentials for RUQ pain
- head of pancreas cancer - post hepatic jaundice Sx with NO pain
- cholelithiasis > cholecystitis
- choledocholithiasis > cholangitis (more severe)
- hepatitis
88
dermatomes over the umbilicus + inguinal ligament
- umbilicus = T10
- inguinal ligament = L1
89
how to treat portal hypertension
- anastomose portal vein and another systemic vein
90
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
- gastrohepatic: L gastric vessels
- falciform: ligamentum teres (remnant of umbilical vein)
91
portal venous system diagram
92
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
