digestive system development

what tissue does the digestive system arrise from

endoderm

what organs come from endoderm

organs of digestive tract, accessory organs of digestive tract, and respiratory organs

organs of digestive tract

esophagus, stomach, and intestines

accessory organs of the digestive system

liver, gallbladder, and pancreas

respiratory organs

trachea and lungs

what type of tissue forms the gut tube

intraembryonic endoderm

steps of digestive system development

1. gut tube formation

2. patterning of gut tube along a-p axis specify individual organs

3. organogenesis (cell proliferation and differentiation)

step one of digestive system development

gut tube formation

step two of digestive system development

patterning of gut tube along a-p axis specify individual organs

step three of digestive system development

organogenesis (cell proliferation and differentiation)

what signaling patterns the gut tube

broad gradients of Wnt, BMP, FGF, and RA that are strongest at posterior and weakest at anterior

what does the broad a-p signaling divide the gut tube into

3 distinct regions—foregut, midgut, and hindgut

what specifies the foregut

no BMP or Wnt → expression of Hex1 TF

what specifies the midgut

low activation of BMP, Wnt, FGF, and RA → expression of Pdx1 TF

what specifies the hindgut

high activation of Wnt, BMP, FGF, and RA → expression of Cdx 2 and 4 TFs

digestive system patterning cascade

a-p morphogen gradient (Wnt, BMP, RA, FGF) → expression of TFs (Hex1, Pdx1, and Cdx2/4) → hox genes

Hex, Pdx, and Cdx activate ____ genes to further compartmentalize the endoderm into segments that correspond to future structures like the stomach, small intestine, and large intestine

hox

first stage of organogenesis

proliferation

second stage of organogenesis

differentiation

stomach proliferation

cell proliferation results in expansions of the lumen and thickening of the walls

intestines proliferation

dramatically increases the length resulting in looping and even temporary herniation into the umbilical cord

what does the endoderm form during differentiation

epithelium lining lump, which includes cells specialized for secretions and absorption

what does the mesoderm form during differentiation

underlying connective tissues and smooth muscles

what does endoderm develop into in the small intestine

specialized epithelium that includes three dimensional projections called villi

what does the mesoderm develop into in the small intestine

underlying smooth muscle

is endoderm and mesoderm differentiation in the small intestine coordinated with eachother

yes

how does endoderm aid mesoderm differentiation in small intestine

expresses Shh to support differentiation

In the developing small intestine, the two signaling pathways involved in reciprocal signaling are: ____ and ____

Shh; BMP

what does the mesoderm express that promotes differentiation in other tissues

BMP

how do the liver, gallbladder, and pancreases initially form

as gut tube buds

what accessory organs develop on the ventral side of the gut tube

liver, gallbladder, and ventral pancreases

what accessory organs develop on the dorsal side of the gut tube

dorsal pancreas

what two bits of organ develop from the same region

liver and ventral pancreas

what happens if ventral foregut endoderm is removed and grown in a culture

it expresses pancreas specific genes, suggesting pancreas is the default state of this region of the endoderm

what is a-p patterning in the gut tube sufficient for

pancreas development

what promote liver development

a-p patterning with the addition of FGF and BMP signaling from cardiac mesoderm

Differentiation of the ventral pancreas is controlled by pre-existing Pdx expression, but the liver differentiates in reponse to additional signals from the nearby developing _____.

cardiac cells