Embryology Flashcards
What makes up the foregut?
Pharynx
Oesophagus
Stomach
Proximal 1/2 of the duodenum and its derivatives (pancreas, liver, bile duct)
It is supplied by the celiac artery
supplied by T6-T9
What makes up the midgut?
Lower 1/2 of the duodenum Small intestine Vermiform apprendix Ascending colon Right 2/3 of transverse colon
Supplied by superior mesenteric artery
Supplied by T10-T11
What makes up the hindgut?
Left 1/3 of the transverse colon
Descending colon
Sigmoid colon
Rectum and anal canal
It is supplied by the inferior mesenteric artery
Supplied by T12 (L1)
1st Pharyngeal arch “mandibular”
muscular contributions: muscles of mastication anterior belly of digastric mylohoid tensor tympani skeletal contributions: mascula mandible incus and malleus meckels cartilage nerve: trigeminal artery: maxillary and external carotid
2rd Pharyngeal arch “hyoid arch”
muscular contributions: muscles of facial expression buccinator platysma stapedius stylohyoid posterior belly of diagstric skeletal: stapes styloid process hyoid upper reichters cartilage nerve:facial artery: strapedial and hyoid
3rd pharyngeal arch
muscular contributions: stylopharyngeus skeletal:hyoid thymus inferior parathyroids nerve: glossopharyngeal artery:common carotid and internal carotid
4th pharyngeal arch
muscular contributions: cricothyroid muscles
all intrinsic muscles of the soft palate
skeletal: thyroid cartilage
superior parathyroid
epiglottic cartilage
nerve:vagus and superior laryngeal
artery:right 4th aortic arch and subclavian artery
6th pharyngeal arch
muscular contributions; all intrinsic muscles of the larynx except the cricothyroid
skeletal: cricod cartilage
arytenoid cartilage
comiculate cartlage
nerve:vagus
recurrent laryngeal
artery:pulmonary artery and ductus arteriosus
Development of the oesophagus
At 4th week, at theend of the pharynx and beginning of the oesophagus, respiratory diverticulum appear (lung buds)
Tracheosophageal septum gradually develops and separates the diverticulum from the dorsal part of the foregut.
Muscular coat of oesophagus develops from surrounding mesenchyme (upper 2/3=straited, lower 1/3=smooth)
Development of the stomach
At 4th week, appears as a fusiform dilation in the stomach.
Rotates 90 degrees clockwise arond the longitudinal axis (left become anterior, right becomes posterior)
During rotation, original posterior wall grows faster than the anterior wall which develops the greater and lesser curvatures
Rotation around the anteroposterior axis which causes the pyloric end to more right and up and the cardiac end to move left and down
Development of the midgut
ELONGATION
HERNIATION- During 6th week, loop of midgut rapidly elongates. Midgut pushed out of embryonic cavity.
ROTATION- Elongated loop rotates 270 degrees anti-clockwise
RETRACTION- 10th week, herniated midgut starts to return back into the abdominal cavity. Jejunum returns first, caecal bud is last. As caecal bud returns, appendix develops as a diverticulum at the distal end.
FIXATION- some of the gut mesenteries come to lie at the back of the abdomen and fuse with it
Fixed and mobile parts of the midgut
Fixed: Duodenum Ascending colon Descending colon Rectum Mobile: stomach jejunum and ilium appendix (caecum) transverse colon sigmoid colon
Gut derivatives from endoderm
epithelium
hepatocytes of the liver
endo and exocrine cells of the pancreas
Gut derivatives from the visceral mesoderm
muscle, connective tissue and peritoneal components
connective tissue of the glands
