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GI > Embryology > Flashcards

Embryology Flashcards

1
Q

Describe the basic development of the gastrointestinal tract

A
  • Develops from ventral invaginations at either end of the embryo
  • Elongate and fuse along ventral midline = straight tube
  • Mesogastrium (and mesentery) forms along with tube forming gut - infolding of visceral layer (of lateral plate mesoderm and associated endoderm)
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2
Q

What structures are derived from the endoderm?

A

Intestinal epithelium

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3
Q

What structures are derived from the mesoderm?

A

MSK system

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4
Q

What structures are derived from the ectoderm?

A

Epithelium of extreme ends of tract

Outer epithelium and nervous system

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5
Q

What structures are derived from the paraxial mesoderm?

A

Skeletal muscle

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6
Q

What structures are derived from the intermediate mesoderm?

A

The kidneys

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7
Q

What structures are derived from the lateral plate mesoderm?

A

Muscles of the body wall

Wrapping of gut

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8
Q

Describe blastocyst development of the gastrointestinal system

A
  • Mesoderm continues to grow, forms sac arround yolk sac
  • Folds dorsally to form amniotic folds (custard splash)
  • Mesoderm expands around, squeezes between endo and ectoderm
  • End up with space,
  • Edges of tissue come up to meet = cavity that embryo sits in (quadrupeds)
  • True placenta from allonatois (makes up part of bladder wall
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9
Q

Describe the formation of the gut and extra embryonic membranes

A
  • Components of GIT develop by proliferation and differentiation from a simple tube
  • Signals from adjacent mesoderm, and between epitehlial cells, involved in embryonic development
    determine normal development/differentiation, homeostasis and apoptosis in adults
  • Smooth muscle from splanchnic mesenchyme surrounding primitive gut and its derivatives
  • In response to signals from endoderm myoblasts elongate and develop contractile elements
  • Cavity between mesoderm layers
  • Get yolk sac formation
  • Embryo grows quicker than membranes so rolls up
  • As rolls around, pinches off area not growing as quickly
    Forms the gut
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10
Q

Describe the development of the mesoderm in the initial layers of the embryo

A
  • Squeezes out of embryonic disk between ecto adn endoderm
  • Carries blood vessels
  • Is how embryo gets blood supply
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11
Q

What do the placenta and membranes form from?

A

The ectoderm, mesoderm and endoderm outside the embryonic disc

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12
Q

Describe the formation of the buccopharyngeal and coacal membranes

A
  • 2 small circular areas of embryo do not have mesoderm
  • Makes 2 areas where ectoderm adn endoderm are in direct contact
  • Gaps form where mesoderm isn’t present
  • Are at head and tail of embryo
  • Form the buccopharyngeal and cloacal membranes
  • inside the mesoderm have developing notochord
  • (Mesoderm is of ectodermal origin and become mesodermal cells by formation of the primitive streak)
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13
Q

Describe the formatio fo the yolk sac and allantoic sac

A
  • Yolk sac formation as embryo rolls up (links to midgut and becomes choriovitelline placenta)
  • Allantoic sac froms as outgrowth of hindgut
  • Root with gut becomes divided by urorectal septum to create hindgut and bladder
  • Becomes chorioallantoic placenta
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14
Q

Describe the formation of the bladder and rectum

A
  • Growth of urorectal septum divides the cloaca ino bladder and rectum
  • Is barrier between anal membrane and urogenital membrane
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15
Q

Describe the formation of the ventral abdominal wall

A
  • Ventral mesentery breaks down except for lesser omentum and falciform ligament
  • Mesenteries allow blood and nerves to reach the organs suspended in them
  • Serosal surfaces are covered by mesothelium (simple squamous epithelium derived from mesoderm)
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16
Q

Describe the vitelline artery in blood supply to the gut

A
  • Initially supplies yolk sac, forms plexus around gut
  • Vitelline plexus forms arterial blood supply to the gut
  • Coeliac artery
  • Cranial and caudal mesenteric arteries
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17
Q

What organs are supplied by the coeliac artery?

A
  • Stomach (part)
  • Duodenum (part)
  • Pancrease (part)
  • (Liver and spleen)
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18
Q

What organs are supplied by the cranial mesenteric artery?

A
  • Stomach/duodenum/pancreas (part)
  • Jejunum
  • Ileum
  • Large intestine (part)
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19
Q

What organs are supplied by the caudal mesenteric artery?

A
  • Rest of the large intestine (the areas not supplied by the cranial mesenteric)
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20
Q

What is the mesentery of the GI system?

A

The supporting membrane containing blood vessels

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21
Q

What organs have both a ventral and a dorsal mesentery?

A
  • Stomach
  • Liver
  • (most organs only have the dorsal mesentery, some share mesenteries)
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22
Q

Describe the embryological formation of the mesentery of the GI system

A
  • Made up of 2 layers of mesothelium and mesoderm between those layers
  • All organs have dorsal, some lose ventral
  • Liver and pancreas share with stomach
  • Small intestine has no ventral mesentery
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23
Q

What are the adult derivatives of the embryological foregut?

A
  • In embryo from buccopharyngeal membrane to septum transversum
  • Forms:
  • Oral cavity, tongue, pharynx
  • Upper respiratory tract
  • oesophagus
  • Stomach
  • Duodenum (part)
  • Liver biliary tract
  • Pancreas
  • lower respiratory tract
  • tonsils, salivary gland
  • anterior pituitary (adenohypophysis)
  • thyroid, parathyroid
  • thymus
24
Q

What are the adult derivatives of the embryological midgut?

A
  • In embryo communicates with vitelline tube and yolk sac
  • Forms:
  • rest of small intestine
  • large intestine (part)
25
Q

What are the adult derivatives of the embryological hindgut?

A
  • In embryo communicates with allantoic diverticulum and extends to cloacal membrane
  • Forms rest of large intestine
26
Q

Describe the development and rotation of the simple stomach

A
  • One aspect of the stomach wall grows quicker, gives curved shape
  • Rotates on one axis, rolled on its own axis
27
Q

Describe the rotation of the gut loop tube

A
  • Small intestine
  • Jejunum undergoes lengthwise growth
  • Gradually coils on itself as is drawn into the abdomen
  • Coiling draws duodenum and large colon anticlockwise (ventral view)
  • Cranial mesenteric artery is the centre of rotation
  • Colon and duodenum share mesocolon (mesentery)
  • Fixed at oesophagus and anus so can only roll and rotate anticlockwise
28
Q

Describe the formation and development of the gut tube in the ruminant in relation to the position of the structures in the adult

A
  • All pre-abomasal structures are part of foetal stomach (not oesophagus)
  • Cranio-dorsal part of embyronic stomach enlarges
  • As enlarges, becomes left-sided and more ventral to become rumen
29
Q

Describe the formation and development of the caecum, ascending and descendinc colon in the horse in relation to the position of these structures in the adult

A
  • Caecum is blind ending sac between small and large intestine
  • Grossly enlarged in horses
  • Rolls anticlockwise
  • Ascending colon develops as large double loop
  • Have R and L ventral and R and L dorsal colon
  • LDC is narrow
  • Very short transverse colon
  • Descending colon leads to the rectum
30
Q

List some common developmental defects of the gut tube

A
  • Stenosis
  • Atresia
  • Umbilical hernia
  • Formation of clefts
31
Q

Briefly describe umbilical hernias

A
  • Not a fault of intestinal development
  • Faulty closure of abdominal wall leaves large opening
  • Herniation of fat then SI through umbilicus
  • Hereditary
32
Q

Briefly describe the formation of clefts

A
  • Persistence of embryonic/foetal clefts due to abnormal growth process
  • e.g. spina bifida
  • Palatoschisis (cleft lip and palate)
  • Schistosome reflexum - open body wall and dislocation of organs
33
Q

Briefly describe stenosis

A
  • Cells in lumen of tube not removed

- thinner lumen

34
Q

Briefly describe atresia

A
  • Cells in lumen not removed

- Connective tissue completely blocing tube

35
Q

Describe the origin and formation of the liver

A
  • Endodermal and mesodermal origin
  • Inductive and growth factor signalling from septum transversum and cardiac mesenchyme (to establish final liver architecture)
  • Splanchnic mesoderm contributes to sinusoids, connective tissue stroma, liver capsule, falciform ligament, muscle of biliary tract
  • liver bud grows from gut, fuses with diaphragm
  • Final liver made from glandular tissue from gut and connective tissue from diaphragm
  • Embryo ends swing around, umbilical cord formed, septum transversum (diaphragm and connective tissue of liver) formed
  • Coming out of newly formed gut have buds - will form secretory part of liver
  • Endoderm forms finger-like cords to interdigitate with cords of ST connective tissue
  • Early hepatoblasts bipotential - hepatocytes or cholangiocyte
36
Q

Describe the action of FGFs on the embryological development of the liver

A
  • Produced in cardiac mesenchyme
    Interact with hypatocyte nuclear factors in adjacent endodermal foregute
  • Lead to proliferation and differentiation of liver tissue
  • Position of the heart leads to FGFs
37
Q

Describe the formation of the blood supply to the liver

A
  • Primitive branching plates develop in the mesenchyme alongisde adjacent portal vein branches
  • Branching of blood vessels, aorta stimulated
  • Blood drainage from gut (venous) does not go back to main system, goes via hepatic portal veins to liver
  • own arterial supply plus venous drainage from gut = 2 blood supplies, then out via hepatic vein
38
Q

Describe the origin and formation of the pancreas

A
  • made up of dorsal and ventral bids
  • Both from embryonic foregut
  • Fuse, associated with rotation of duodenum
  • As intestines roll into body, dorsal and ventral more L shaped
  • Acinar and islet cells both arise from foregut endoderm
  • One bud trapped in bend of duodenum
  • Origianlly has 2 ducts, sometimes fuse (no fusion in dog and horses)
39
Q

Describe the origin and formation of the spleen

A
  • Mesenteries allow blood vessels andnerves to reach organs suspended in them
  • Spleen appears within dorsal mesentery near stomach
  • Mesenchyme cells seem to get signals but don’t know where from
  • Spleen is filter for blood
  • Is already in supporting system and has blood supply - no tricks needed
40
Q

What are the branches of the coeliac artery?

A
  • Left gastric
  • Hepatic
  • Splenic
41
Q

What are the branches of the cranial mesenteric artery?

A
  • Dominant blood suply to GI tract
  • Caudal pancreaticoduodenal
  • jejunal (has 15-19 more branches)
  • ileo colic
42
Q

What are the branches of the caudal mesenteric artery?

A
  • Left colic

- Cranial rectal

43
Q

Outline the basics of foetal circulation in the GI system

A
  • Minimal supply to the guts

- Blood from placenta bypasses liver via ductus venosus (from umbilical vein into general circulation)

44
Q

What are the branches of the hepatic artery?

A
  • Hepatic branches
  • Cystic branches
  • Right gastric
  • Cranial pancreatico-duodenal
  • Right gastro-epiploic
45
Q

What are the branches of the splenic artery?

A
  • Pancreatic arches
  • Splenic branches
  • Short gastric
  • Left gastro-epiploic
46
Q

What are teh branches of the ileo colic artery?

A
  • Middle colic
  • Right colic
  • Colic
  • Ileal
  • Caecal
47
Q

When was your last tea/coffee break?

A

Doesn’t matter, you should probably take another one

48
Q

What is aplasia?

A
  • Absence of part or all of an organ
49
Q

What is hypoplasia?

A
  • Reduced development of an organ
50
Q

What is atrophy of an organ?

A

Acquired reduction in size of an organ

51
Q

Describe a congenital porto-systemic shunt

A
  • Failure of ductus venosus to close
  • Allos portal vein blood to continue to bypass liver in adult life
  • Failure of normal perfusion of liver may lead to failure of development of intrahepatic vasculature
  • Get small liver and weak animal
52
Q

Describe an acquired porto-systemic shunt

A
  • Obstruction of normal hepatic venous outflow e.g. diffuse liver fibrosis
  • Leads to establishment of collateral venous drainage
  • Utilises pre-existing channels e.g. spleen/omentum
  • Scarring in liver, restricts blood flow to liver, blood tries to find another way
  • Small anastomoses become enlarged
  • Miss out liver and go via the spleen
53
Q

Discuss the timing of gut closure in the neonate

A
  • Gut closure is the point at which no more passive immunity can be acquired
  • Begines between 4-8 hours, ends within 24 hours
  • Need to get antibodies (in colostrum) before this time
54
Q

Discuss the duration of passive immuntiy in the neonate

A
  • Passive immunity replaced by puppy’s own antibodies
  • Window of susceptibility where both passive and own are at their lowest
  • More antibodies taken in initially give shorter window of susceptibility (more time for puppy to develop own antibodies)
55
Q

Discuss the features of the neonatal GI tract that facilitate immunoglobulin absorption

A
  • Less acidic environment, lack of proteases
  • Immunoglobulins not destroyed
  • Can absorb Ig better than adults

GI (31 decks)

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