GI embryology

Question 1

What 2 planes does embryonic folding in 4th week occur? Why? Folding in horizontal plane forms what? Medial plane?

Answer 1

Horizontal and medial planes
Differing rates of growth
2 lateral body folds
Cranial and caudal folds

Question 2

Primitive gut tube from what layer? During what week does oropharyngeal membrane rupture to form the mouth? What week does cloacal membrane future–> anal canal?

Answer 2

Endoderm
4th week
7th week

Question 3

What are pharyngeal arches part of? Extends from what to what? When do these develop?

Answer 3

Foregut
Oropharyngeal membrane–> resp diverticulum
4th and 5th week

Question 4

What are pharyngeal arches formed from? Covered externally and internally from what?

Answer 4

Masses of mesenchymal tissue invaded by cranial neural crest cells
Externally= from endoderm–> clefts, internally= ectoderm–> pouches

Question 5

1st arch innervated by what? What muscles? What bones?

Answer 5

Mandibular nerve- V3
Mastication, tensor tympani, digastric, myolohyoid
Maxilla, mandible, incus, malleus

Question 6

2nd arch innervation? Muscles? Bones?

Answer 6

Facial nerve
Facial expression, stapedius, stylohyoid
Stapes, styloid, lesser horn of hyoid cartilage

Question 7

3rd arch innervation? Muscles? Bones?

Answer 7

Glossopharyngeal nerve
Stylopharyngeus of pharynx
Body and greater horn of hyoid cartilage

Question 8

4th arch innervation? Muscles? Bones?

Answer 8

Superior laryngeal nerve of vagus nerve
Cricothyroid
Thyroid and epiglottic cartilages

Question 9

6th arch innervation? Muscles? Bones?

Answer 9

Recurrent laryngeal nerve of vagus nerve
All muscles except cricothyroid
Cricoid cartilage, arytenoid cartilages, corniculate and cuneiform cartilages

Question 10

What septum separates the resp diverticulum from dorsal part of foregut? Foregut divided into what? Oesophagus is what initially but does what?

Answer 10

Trancheoesophageal septum
Ventral resp primordium and dorsal oesophagus
Short but lengthens rapidly with descent of heart and lungs

Question 11

Where is ventral mesentery only present? Midgut and hindgut only what?

Answer 11

Only in foregut- terminal oesophagus, stomach and upper duodenum
Only dorsal mesentery

Question 12

Ventral mesentery is derived from what? Free lower margin contains what? Liver develops where?

Answer 12

Septum transversum
Hepatic artery, portal vein and bile duct
In ventral mesentery- divides it into lesser omentum and falciform ligament

Question 13

Stomach appears in foregut in what week? Does dorsal or ventral wall grow faster?

Answer 13

4th week

Dorsal grows faster- forms greater and lesser curvatures

Question 14

During what week does stomach undergo 90 degrees clockwise rotation? During what week does stomach and duodenum rotate about a ventrodorsal axis?

Answer 14

7th week- produces lesser sac

8th week- pulls stomach upwards and duodenum into C-shape

Question 15

Rotations results in what? Ventral mesentery forms what? Anterior and posterior folds of greater omentum fuse to form what?

Answer 15

Thinning of dorsal mesentery–> greater omentum
Lesser omentum
One thick sheet formed from 4 layers of peritoneum

Question 16

During what week does hepatic diverticulum appear? When does bile duct form? What gives rise to the gallbladder and cystic duct?

Answer 16

3rd week- as outgrowth of endodermal epithelium at distal end of foregut
When connection between liver diverticulum and foregut narrows
Small ventral outgrowth from bile duct

Question 17

Further growth of liver bud allows epithelial liver cords to intermingle with what? Liver cords differentiate into what?

Answer 17

The umbilical and vitelline veins–> hepatic sinusoids

Hepatocytes- form lining of biliary ducts

Question 18

During what week does mesoderm of ventral mesentery give rise to haematopoietic cells, Kipper cells and connective tissue cells?

Answer 18

6th week

Question 19

At 10th week, liver what % of total body weight? % at birth? Cells start bile production at what age? Haematopoietic function subsides when?

Answer 19

10%
5%
12th week
During last 2 months of intrauterine life

Question 20

Where does pancreas develop from? Where is each bud?

Answer 20

Endodermal lining of duodenum as dorsal and ventral buds
Ventral bud from ventral mesentery
Dorsal bud from dorsal mesentery

Question 21

When the duodenum rates and becomes C-shaped, what happens? What fuses together?

Answer 21

The ventral bud and entrance to common bile duct in duodenum are shifted dorsally- lies below and behind dorsal bud
Parenchyma and duct systems of both buds fuse together

Question 22

The ventral bud forms what? Dorsal bud forms what?

Answer 22

Uncinate process and inferior of head

Rest of pancreas

Question 23

Main pancreatic duct formed from what? Islets of Langerhans from what during what month of fetal life? Insulin secretion begins when? Pancreatic connective tissue from what?

Answer 23

Union of ventral pancreatic duct with distal part of duct of dorsal bud
Parenchyma of pancreas at 3rd month
At 5th month
Visceral surrounding mesoderm