Anat Cell Biol.  2022 Sep;55(3):356-366. 10.5115/acb.22.054.

Topographical relationships of the yolk sac remnant and vitelline vessels with the midgut loop in the extra-embryonic coelom of human embryos

• Jin ZW
• Kim JH
• Yamamoto M
• Murakami G
• Abe Si
• Rodríguez-Vázquez JF

• KMID: 2533361
• DOI: http://doi.org/10.5115/acb.22.054

Abstract

The yolk sac is supplied by the vitelline artery and vein (VA, VV), which run through the yolk stalk in combination with the omphaloenteric duct. Moreover, the VV takes a free posterior course outside the midgut mesentery containing the secondarily-developed superior mesenteric vein (SMV). However, the regression process of these structures has not been demonstrated photographically. The present study evaluated serial histological sections from 20 embryos of stages 15–19 or crown-rump length (CRL) 7.5–20 mm. All specimens carried the SMV as sequential tissue slits. However, an omphaloenteric duct with epithelia continuous with the midgut loop was not observed. In smaller embryos (CRL <13 mm) the VA extended distally or anteriorly from the midgut apex in the extra-embryonic coelom, whereas in larger embryos (CRL 16–20 mm) the artery was absent from the distal side of the apex. The entire course or part of the VV outside the mesentery was always seen, but four larger embryos lacked the venous terminal near the duodenum. A vacuole-like remnant of the yolk sac was present in all smaller embryos (CRL <10 mm), but was absent from 7 of the 11 larger embryos. The size of the remnant was equal to the thickness of the VA or VV, with the remnant being sandwiched between the VA and VV. Moreover, the regressing yolk sac often communicated with or opened to the VV. Consequently, the yolk sac regressed first, followed by the regression of the VA until 6 weeks. The yolk stalk was clearly observed until 5 weeks.

Keyword

Yolk sac; Vitelline duct; Midgut loop; Hernia; Superior mesenteric vein

Figure

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  Fig. 1 Yolk stalk containing the vitelline vessels and yolk sac remnant outside of the umbilical cord (7.5 mm CRL). H&E staining. Horizontal sections. Panel (A) displays the most superior plane or the most upstream portion of the umbilical cord in the figure. The yolk stalk is separated from the umbilical cord. The yolk stalk contains the VA and VV as well as a vesicle corresponding to the yolk sac remnant. In the inferior or downstream side of the yolk stalk, the mesentery appears in the yolk stalk (D, E) and, subsequently, the VA and VV continue to a site near the IL (F, G). In more inferior or downstream portions, the artery increases in diameter, while the vein is still thin and separated from the mesentery (G–I). The SMV develops secondarily as a cleft of tissues (H, J). Panel (K) is a diagram showing topographical anatomy of the vitelline vessels and yolk sac. The vitelline vein runs outside of the mesentery (star). Panels (A–D) and (E–J) were prepared at the same magnification, respectively (all scale bars, 0.1 mm). CRL, crown-rump length; VA, vitelline artery; VV, vitelline vein; UA, umbilical artery; UV, umbilical vein; SMA, superior mesenteric artery and its branches; GB, gall bladder; SMV, superior mesenteric vein and its tributaries; PV, portal vein; AO, aorta; IL, ileum; JE, jejunum.

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  Fig. 2 Yolk sac remnant seen in sagittal sections (8 mm CRL). Panels (A–C) (H&E staining) display an embryo of 8 mm CRL, and (D, E) (silver impregnation) exhibits another embryo of 8 mm CRL. Sagittal sections demonstrate the yolk sac remnant immediately below the liver and heart in the two embryos. The yolk stalk appears to contain the vitelline vessels as well as a vacuole-like yolk sac (D, E). In both specimens, a combination of the sac, artery and vein appears to extend from the intra-embryonic coelom to the extra-embryonic coelom. All panels were prepared at the same magnification (scale bar in E, 1 mm). CRL, crown-rump length; AO, aorta; UV, umbilical vein; SMA, superior mesenteric artery and its branches; UA, umbilical artery; VA, vitelline artery; VV, vitelline vein; IL, ileum.

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  Fig. 3 Yolk stalk containing the vitelline vessels and yolk sac remnant inside of the umbilical cord (9 mm CRL). H&E staining. Horizontal sections. Panel (A) (or G) displays the most superior (or inferior) plane in the figure. The umbilical cord contains the yolk stalk (A–C). The yolk stalk contains the VA and VV as well as a vesicle corresponding to the yolk sac remnant (A, B). In the inferior or downstream portion of the yolk stalk near the IL, the vitelline vein detaches from the stalk (C) and runs freely in the extra- and intra-embryonic coelom (D–F). The free vein attaches to the duodenum to connect with the PV (F). The SMV develops secondarily as a cleft of tissues (G). All panels were prepared at the same magnification (scale bar in A, 1 mm). CRL, crown-rump length; UA, umbilical artery; UV, umbilical vein; VV, vitelline vein; VA, vitelline artery; PV, portal vein; SMA, superior mesenteric artery and its branches; RUV, right umbilical vein; CA, celiac artery; DP, dorsal pancreas; LUV, left umbilical vein; AO, aorta; SMV, superior mesenteric vein and its tributaries; IL, ileum; JE, jejunum.

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  Fig. 4 Yolk stalk containing the vitelline vessels and yolk sac remnant inside of the umbilical cord (10 mm CRL). Silver impregnation. Horizontal sections. Panel (A) displays the most inferior plane or the most upstream portion of the umbilical cord in the figure. The yolk stalk is contained in the umbilical cord (A–G). The yolk stalk contains the VA and VV as well as a large vesicle corresponding to the yolk sac remnant (A–D). The yolk sac appears to open to the VV (arrow in E). In the superior or downstream portion when the mesentery appears in the yolk stalk, the VV detaches from the stalk (F) and runs freely in the extra- and intra-embryonic coelom (G–I). The free vein attaches to the stomach pylorus (J) to connect the PV (K). The artery is thick along the almost entire course toward the superior mesenteric artery near the duodenum. Panel (L) is a diagram showing topographical anatomy of the vitelline vessels and yolk sac: the sac appears to open to the vein (arrow). The VV runs outside of the mesentery (star). All panels were prepared at the same magnification (scale bar in A, 1 mm). CRL, crown-rump length; UA, umbilical artery; UV, umbilical vein; VA, vitelline artery; VV, vitelline vein; AO, aorta; SMA, superior mesenteric artery and its branches; SMV, superior mesenteric vein and its tributaries; PCV, posterior cardinal vein; PV, portal vein; P, pancreas; LUA, left umbilical artery; RUA, right umbilical artery; IL, ileum.

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  Fig. 5 Extra-embryonic long courses of the vitelline vessels without a yolk sac remnant (11 mm CRL). H&E staining. Horizontal sections. Panel (A) displays the most inferior plane in the figure, while (H) exhibits the upstream portion of the umbilical cord containing long courses of the vitelline vessels (VA, VV). Panels (B–G) are shown at higher magnification than (A, H). The VV is dilated along the free intra-embryonic course (B–D). The superior mesenteric vein is also thick in the mesentery but the luminal surface is not smooth (B, C). In the upstream side of the IL, the vitelline vessels take a long extra-embryonic course without a definite yolk sac remnant (F, G). Thus, the vessels appear to run freely without a yolk stalk. Panels (A, H) (or B–G) were prepared at the same magnification (scale bars in A and B, 1 mm). CRL, crown-rump length; UA, umbilical artery; UV, umbilical vein; VA, vitelline artery; VV, vitelline vein; PCV, posterior cardinal vein; AO, aorta; SMA, superior mesenteric artery and its branches; SMV, superior mesenteric vein and its tributaries; RUV, right umbilical vein; CA, celiac artery; GB, gall bladder; IL, ileum; JE, jejunum.

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  Fig. 6 Extra-embryonic long courses of the vitelline vessels without a yolk sac remnant (13 mm CRL). H&E staining. Horizontal sections. Panel (A) displays the most superior plane in the figure, while (F) exhibits the upstream portion of the umbilical cord. In the extra-embryonic coelom, not only the VV (A–E) but also the VA (D, E) run freely without the yolk stalk and sac. All panels were prepared at the same magnification (scale bars in A and B, 1 mm). CRL, crown-rump length; LUV, left umbilical vein; RUV, right umbilical vein; VV, vitelline vein; VA, vitelline artery; LUA, left umbilical artery; RUA, right umbilical artery; SMA, superior mesenteric artery and its branches; IL, ileum; JE, jejunum.

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  Fig. 7 Yolk sac remnant near the future umbilicus identified in sagittal sections (20 mm CRL). H&E staining. Sagittal sections of the right half of the abdomen. Panel (A) is a diagram showing topographical anatomy of the VV, yolk sac and superior mesenteric vessels (SMA, SMV): the sac appears to communicate the SMV. The vitelline vein runs outside of the mesentery (star). Panel (B) displays the most upstream portion of the umbilical cord in the figure. Panel (B) (or G) is lateral (medial). A thin VV remnant takes a long course free from the mesentery in the extra-embryonic- (B–D) and intra-embryonic coelom (E, F). The vein ends near the duodenum (G). The SMV is dilated in the mesentery (D). A candidate of the yolk sac remnant (E–G) opens to the vein (arrows in F). All panels were prepared at the same magnification (scale bar in B, 1 mm). CRL, crown-rump length; SMA, superior mesenteric artery and its branches; SMV, superior mesenteric vein and its tributaries; VV, vitelline vein; UA, umbilical artery; GB, gall bladder; IL, ileum; JE, jejunum.

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  Fig. 8 Schematic representation of a regression process of the vitelline vessels and yolk sac at 5–6 weeks. Panel (A) is a left side view of a 5-week-old embryo, while (B) exhibits the intestinal loop in the herniation sac at 6 weeks and later. In (A), the yolk sac remnant and vitelline vessels extend distally to the apex of the midgut loop. The umbilical cord bundles the umbilical vessels, the yolk sac, and the allantois. The regressing yolk sac is a vacuole sandwiched by the VA and VV. In the proximal or posterior side of the apex of the midgut loop, the artery changes the name into the SMA. In contrast to the long free course of the VV, the SMV develops secondarily in the mesentery. In (B), in contrast to the lost VA, a remnant of the VV still runs through the extra-embryonic celom or herniation sac. However, usually, the umbilical cord does not contain the VV remnant. The yolk sac almost always disappears. The allantois is not shown in (B). SMA, superior mesenteric artery and its branches; SMV, superior mesenteric vein and its tributaries; UA, umbilical artery; UV, umbilical vein; VA, vitelline artery; VV, vitelline vein.

Reference

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