The yolk sac is a membranous sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though yolk sac is far more widely used. In humans, the yolk sac is important in early embryonic blood supply,[1] and much of it is incorporated into the primordial gut during the fourth week of embryonic development.[2]
The yolk sac is situated on the front (ventral) part of the embryo; it is lined by extra-embryonic endoderm,[3] outside of which is a layer of extra-embryonic mesenchyme, derived from the epiblast.
Blood is conveyed to the wall of the yolk sac by the primitive aorta and after circulating through a wide-meshed capillary plexus, is returned by the vitelline veins to the tubular heart of the embryo. This constitutes the vitelline circulation, which in humans serves as a location of haematopoiesis.[4][5] Before the placenta is formed and can take over, the yolk sac provides nutrition and gas exchange between the mother and the developing embryo.[6]
At the end of the fourth week, the yolk sac presents the appearance of a small pear-shaped opening (traditionally called the umbilical vesicle), into the digestive tube by a long narrow tube, the vitelline duct. Rarely, the yolk sac can be seen in the afterbirth as a small, somewhat oval-shaped body whose diameter varies from 1 mm to 5 mm; it is situated between the amnion and the chorion and may lie on or at a varying distance from the placenta. There is no clinical significance to a residual external yolk sac.
Diagram showing earliest observed stage of human ovum. 1 - Amniotic cavity 2 - Yolk-sac 3 - Chorion
Diagram illustrating early formation of allantois and differentiation of body-stalk. 1 Amniotic cavity 2 Body-stalk 3 Allantois 4 Yolk-sac 5 Chorion
Diagram showing later stage of allantoic development with commencing constriction of the yolk-sac. 1 Heart 2 Amniotic cavity 3 Embryo 4 Body-stalk 5 Placental villi 6 Allantois 7 Yolk-sac 8 Chorion
Diagram illustrating a later stage in the development of the umbilical cord. 1 Placental villi 2 Yolk-sac 3 Umbilical cord 4 Allantois 5 Heart 6 Digestive tube 7 Embryo 8 Amniotic cavity
As a rule the duct undergoes complete obliteration by the 20th week as most of the yolk sac is incorporated into the developing gastrointestinal tract, but in about two percent of cases its proximal part persists as a diverticulum from the small intestine, Meckel's diverticulum, which is situated about 60 cm proximal to the ileocecal valve, and may be attached by a fibrous cord to the abdominal wall at the umbilicus.
Sometimes a narrowing of the lumen of the ileum is seen opposite the site of attachment of the duct.
HistogenesisEdit
The yolk sac starts forming during the second week of the embryonic development, at the same time as the shaping of the amniotic sac. The hypoblast starts proliferating laterally and descending. In the meantime Heuser's membrane, located on the opposite pole of the developing vesicle, starts its upward proliferation and meets the hypoblast.
ModificationsEdit
Primary yolk sac: it is the vesicle which develops in the second week, its floor is represented by Heuser's membrane and its ceiling by the hypoblast. It is also known as the exocoelomic cavity.
Secondary yolk sac: this structure is formed when the extraembryonic mesoderm separates to form the extraembryonic coelom; cells from the mesoderm pinch off an area of the yolk sac,[3] and what remains is the secondary yolk sac.
The final yolk sac: during the fourth week of development, during organogenesis, part of the yolk sac is surrounded by endoderm and incorporated into the embryo as the gut. The remaining part of the yolk sac is the final yolk sac.
Goh, Issac; et al. (18 August 2023). "Yolk sac cell atlas reveals multiorgan functions during human early development". Science. 381 (6659). doi:10.1126/science.add7564.
ReferencesEdit
^ abLutfey, Karen; Freese, Jeremy (2005). "Toward Some Fundamentals of Fundamental Causality: Socioeconomic Status and Health in the Routine Clinic Visit for Diabetes". American Journal of Sociology. 110 (5): 1326–1372. doi:10.1086/428914. ISSN 0002-9602. JSTOR 10.1086/428914. S2CID 17629087.
^ abHafez, S. (2017-01-01), Huckle, William R. (ed.), "Chapter One - Comparative Placental Anatomy: Divergent Structures Serving a Common Purpose", Progress in Molecular Biology and Translational Science, Molecular Biology of Placental Development and Disease, Academic Press, 145: 1–28, doi:10.1016/bs.pmbts.2016.12.001, PMID 28110748, retrieved 2020-10-21
^Moore, Keith; Persaud, TVN; Torchia, Mark (2013). The Developing Human. Philadelphia, PA: Saunders. ISBN978-1-4377-2002-0.
^Blaas, Harm-Gerd K; Carrera, José M (2009-01-01), Wladimiroff, Juriy W; Eik-Nes, Sturla H (eds.), "Chapter 4 - Investigation of early pregnancy", Ultrasound in Obstetrics and Gynaecology, Edinburgh: Elsevier, pp. 57–78, doi:10.1016/b978-0-444-51829-3.00004-0, ISBN978-0-444-51829-3, retrieved 2020-10-21
^Donovan, Mary F.; Bordoni, Bruno (2020), "Embryology, Yolk Sac", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID 32310425, retrieved 2020-09-11
August 29, 2023
yolk, yolk, membranous, attached, embryo, formed, cells, hypoblast, layer, bilaminar, embryonic, disc, this, alternatively, called, umbilical, vesicle, terminologia, embryologica, though, yolk, more, widely, used, humans, yolk, important, early, embryonic, blo. The yolk sac is a membranous sac attached to an embryo formed by cells of the hypoblast layer of the bilaminar embryonic disc This is alternatively called the umbilical vesicle by the Terminologia Embryologica TE though yolk sac is far more widely used In humans the yolk sac is important in early embryonic blood supply 1 and much of it is incorporated into the primordial gut during the fourth week of embryonic development 2 Yolk sacHuman embryo of 3 6 mmHuman embryo from thirty one to thirty four daysDetailsCarnegie stage5bDays9PrecursorendodermIdentifiersLatinvesicula umbilicalis saccus vitellinusMeSHD015017TEsac by E5 7 1 0 0 0 4 E5 7 1 0 0 0 4FMA87180Anatomical terminology edit on Wikidata Contents 1 In humans 2 Histogenesis 3 Modifications 4 Additional images 5 See also 6 Further reading 7 ReferencesIn humans Edit Contents in the cavity of the uterus seen at approximately 5 weeks of gestational age by obstetric ultrasonography Artificially colored showing gestational sac yolk sac and embryo measuring 3 mm as the distance between the signs The yolk sac is the first element seen within the gestational sac during pregnancy 1 usually at 3 days gestation The yolk sac is situated on the front ventral part of the embryo it is lined by extra embryonic endoderm 3 outside of which is a layer of extra embryonic mesenchyme derived from the epiblast Blood is conveyed to the wall of the yolk sac by the primitive aorta and after circulating through a wide meshed capillary plexus is returned by the vitelline veins to the tubular heart of the embryo This constitutes the vitelline circulation which in humans serves as a location of haematopoiesis 4 5 Before the placenta is formed and can take over the yolk sac provides nutrition and gas exchange between the mother and the developing embryo 6 At the end of the fourth week the yolk sac presents the appearance of a small pear shaped opening traditionally called the umbilical vesicle into the digestive tube by a long narrow tube the vitelline duct Rarely the yolk sac can be seen in the afterbirth as a small somewhat oval shaped body whose diameter varies from 1 mm to 5 mm it is situated between the amnion and the chorion and may lie on or at a varying distance from the placenta There is no clinical significance to a residual external yolk sac Diagram showing earliest observed stage of human ovum 1 Amniotic cavity2 Yolk sac3 Chorion Diagram illustrating early formation of allantois and differentiation of body stalk 1 Amniotic cavity2 Body stalk3 Allantois4 Yolk sac5 Chorion Diagram showing later stage of allantoic development with commencing constriction of the yolk sac 1 Heart2 Amniotic cavity3 Embryo4 Body stalk5 Placental villi6 Allantois7 Yolk sac8 Chorion Diagram illustrating a later stage in the development of the umbilical cord 1 Placental villi2 Yolk sac3 Umbilical cord4 Allantois5 Heart6 Digestive tube7 Embryo8 Amniotic cavityAs a rule the duct undergoes complete obliteration by the 20th week as most of the yolk sac is incorporated into the developing gastrointestinal tract but in about two percent of cases its proximal part persists as a diverticulum from the small intestine Meckel s diverticulum which is situated about 60 cm proximal to the ileocecal valve and may be attached by a fibrous cord to the abdominal wall at the umbilicus Sometimes a narrowing of the lumen of the ileum is seen opposite the site of attachment of the duct Histogenesis EditThe yolk sac starts forming during the second week of the embryonic development at the same time as the shaping of the amniotic sac The hypoblast starts proliferating laterally and descending In the meantime Heuser s membrane located on the opposite pole of the developing vesicle starts its upward proliferation and meets the hypoblast Modifications EditPrimary yolk sac it is the vesicle which develops in the second week its floor is represented by Heuser s membrane and its ceiling by the hypoblast It is also known as the exocoelomic cavity Secondary yolk sac this structure is formed when the extraembryonic mesoderm separates to form the extraembryonic coelom cells from the mesoderm pinch off an area of the yolk sac 3 and what remains is the secondary yolk sac The final yolk sac during the fourth week of development during organogenesis part of the yolk sac is surrounded by endoderm and incorporated into the embryo as the gut The remaining part of the yolk sac is the final yolk sac Additional images Edit Surface view of embryo of Hylobates concolor a gibbon Human embryo length 2 mm Dorsal view with the amnion laid open X 30 Dorsum of human embryo 2 11 mm in length Section through the embryo Fetus of about eight weeks enclosed in the amnion Magnified a little over two diameters Model of human embryo 1 3 mm long Section through ovum imbedded in the uterine decidua Human embryo about fifteen days old Brain and heart represented from right side Digestive tube and yolk sac in median section See also EditYolk sac tumorFurther reading EditGoh Issac et al 18 August 2023 Yolk sac cell atlas reveals multiorgan functions during human early development Science 381 6659 doi 10 1126 science add7564 References Edit a b Lutfey Karen Freese Jeremy 2005 Toward Some Fundamentals of Fundamental Causality Socioeconomic Status and Health in the Routine Clinic Visit for Diabetes American Journal of Sociology 110 5 1326 1372 doi 10 1086 428914 ISSN 0002 9602 JSTOR 10 1086 428914 S2CID 17629087 The Developing Human Clinically Oriented Anatomy Chapter 7 a b Hafez S 2017 01 01 Huckle William R ed Chapter One Comparative Placental Anatomy Divergent Structures Serving a Common Purpose Progress in Molecular Biology and Translational Science Molecular Biology of Placental Development and Disease Academic Press 145 1 28 doi 10 1016 bs pmbts 2016 12 001 PMID 28110748 retrieved 2020 10 21 Moore Keith Persaud TVN Torchia Mark 2013 The Developing Human Philadelphia PA Saunders ISBN 978 1 4377 2002 0 Blaas Harm Gerd K Carrera Jose M 2009 01 01 Wladimiroff Juriy W Eik Nes Sturla H eds Chapter 4 Investigation of early pregnancy Ultrasound in Obstetrics and Gynaecology Edinburgh Elsevier pp 57 78 doi 10 1016 b978 0 444 51829 3 00004 0 ISBN 978 0 444 51829 3 retrieved 2020 10 21 Donovan Mary F Bordoni Bruno 2020 Embryology Yolk Sac StatPearls Treasure Island FL StatPearls Publishing PMID 32310425 retrieved 2020 09 11 Retrieved from https en wikipedia org w index php title Yolk sac amp oldid 1170982579, wikipedia, wiki, book, books, library,
