The connecting stalk, or body stalk is an embryonic structure that is formed by the third week of
development
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and connects the
embryo to its shell of
trophoblast
The trophoblast (from Greek : to feed; and : germinator) is the outer layer of cells of the blastocyst. Trophoblasts are present four days after fertilization in humans. They provide nutrients to the embryo and develop into a large part of the p ...
s. The connecting stalk is derived from the extraembryonic mesoderm. Initially it lies caudally to the trilaminar germ disc, but, with subsequent embryonic folding, the body stalk assume a more ventral position.
Progressive expansion of the
amnion from the umbilical ring (surrounding the roots of the
vitelline duct
In the human embryo, the vitelline duct, also known as the vitellointestinal duct, the yolk stalk, the omphaloenteric duct, or the omphalomesenteric duct, is a long narrow tube that joins the yolk sac to the midgut lumen of the developing fetus. ...
and connecting stalk) creates a tube with a covering of amniotic membrane with
allantois and umbilical vessels as its content and mesoderm of the connecting stalk as the ground substance. This extraembryonic mesodermal ground substance forms the future
wharton's jelly
Wharton's jelly (''substantia gelatinea funiculi umbilicalis'') is a gelatinous substance within the umbilical cord, largely made up of mucopolysaccharides (hyaluronic acid and chondroitin sulfate). It acts as a mucous connective tissue containing ...
.
The amniotic membrane and its contents form the
umbilical cord
In placental mammals, the umbilical cord (also called the navel string, birth cord or ''funiculus umbilicalis'') is a conduit between the developing embryo or fetus and the placenta. During prenatal development, the umbilical cord is physiologi ...
that connects the embryo and the
placenta
The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mate ...
.
[Larsen's Embryology, 5th edition, p138.]
The root of the connecting stalk contains the
allantois as a diverticulum of hindgut
endoderm along with umbilical vessels.
Anomalies are usually referred to as ''body stalk anomalies'' and occur in approximately 1 in 15,000 births.
They are due to defects in the formation of the cephalic, caudal, and lateral embryonic body folds,
that result in a reduced or absent umbilical cord.
Additional images
File:Gray17.png, Human embryo—length, 2 mm. Dorsal view, with the amnion laid open. X 30.
File:Gray22.png, Human embryo of 2.6 mm.
File:Gray31.png, Model of human embryo 1.3 mm. long.
File:Gray32.png, Section through ovum imbedded in the uterine decidua.
File:Gray40.png, Embryo between eighteen and twenty-one days.
References
External links
*
Embryology
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