Information about Yolk Sac
) | ||
| Human embryo of 2.6 mm. | ||
) | ||
| Human embryo from thirty-one to thirty-four days | ||
| subject #11 54 | ||
| Carnegie stage | 5b | |
| Days | 9 | |
| Precursor | endoderm | |
| MeSH | Yolk+Sac | |
| Dorlands/Elsevier | s_01/12716805 | |
It is a critical landmark, identifying a true gestation sac.
It is quite echogenic (light) to ultrasound, and reliably seen early.
In mice
In the mouse, the yolk sac is the first site of blood formation, generating primitive macrophages and erythrocytes.In humans
The yolk-sac is situated on the ventral aspect of the embryo; it is lined by endoderm, outside of which is a layer of mesoderm.It is filled with fluid, the vitelline fluid, which possibly may be utilized for the nourishment of the embryo during the earlier stages of its existence.
Blood is conveyed to the wall of the 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, and by means of it nutritive material is absorbed from the yolk-sac and conveyed to the embryo.
At the end of the fourth week the yolk-sac presents the appearance of a small pear-shaped vesicle (umbilical vesicle) opening into the digestive tube by a long narrow tube, the vitelline duct.
The vesicle can be seen in the after-birth 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.
As a rule the duct undergoes complete obliteration during the seventh week, 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 three or four feet above 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
The Yolk sac starts forming itself during the second week of the embryonic development, at the same time of the shaping of the amniotic sac. The hypoblast starts proliferating laterally and descending down.In the meantime the Heuser membrane, located on the opposite pole of the developing vesicle, starts its upward proliferation and meets the ipoblast. The last one keeps on descending for a little bit more.
We have arrived to the constitution of the Yolk sac.
Modifications
- Primary yolk sac/primitive yolk sac: it is the vesicle constituted in the second week, its floor is represented by the Heuser membrane and its ceiling by the ipoblast. It is also known as the exocoelomic cavity.[1]
- Secondary yolk sac: this first transformation is determined by the modification of its cover, in the connection zone between the ipoblast and the Heuser membrane. We can observe a stricure. The two parts detach and the inferior one, which is smaller, forms a cyst destined to be eliminated. The upper one is now covered only by the ipoblst.
- The final yolk sac: during the fourth week of development, during which we can see the shaping of the embryonic areas, the yolk sac undergoes externally the pression of the fore folding, of the posterior one and of the lateral ones. A little portion of the sac, in the upper part, constitutes the intestinal tube. On the other side, the distal part forms a little vesicle, that is what remains of the yolk sac.
Additional images
) Surface view of embryo of Hylobates concolor. | ) 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. |
) Diagram showing earliest observed stage of human ovum. | ) Diagram illustrating early formation of allantois and differentiation of body-stalk. | ) Diagram showing later stage of allantoic development with commencing constriction of the yolk-sac. | ) Diagram illustrating a later stage in the development of the umbilical cord. |
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. |
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References
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In embryology, Carnegie stages are a standardized system of 23 stages used to provide a unified developmental chronology of the vertebrate embryo.
The stages are delineated through the development of structures, not by size or the number of days of development, and so the
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The stages are delineated through the development of structures, not by size or the number of days of development, and so the
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Embryology is the study of the development of an embryo. An embryo is defined as any vertebrate in a stage before birth or hatching. Embryology refers to the development of the egg cell (zygote) after fertilization and the differentiation of cells into tissues and organs.
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Endoderm is one of the germ layers formed during animal embryogenesis. Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the endoderm.
The endoderm consists at first of flattened cells, which subsequently become columnar.
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The endoderm consists at first of flattened cells, which subsequently become columnar.
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Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. Created and updated by the United States National Library of Medicine (NLM), it is used by the MEDLINE/PubMed
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Elsevier, the world's largest publisher of medical and scientific literature, forms part of the Reed Elsevier group. Based in Amsterdam, the company has substantial operations in the UK, USA and elsewhere.
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The gestational sac (or gestation sac) is the only available intrauterine structure that can be used to determine if an intrauterine pregnancy (IUP) exists, until the embryo is identified.
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Pregnancy is the carrying of one or more offspring, known as a fetus or embryo, inside the body of a female mammal such as a human. In a pregnancy, there can be multiple gestations (for example, in the case of twins or triplets).
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Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time (multiple gestations).
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Ultrasound is a cyclic sound pressure with a frequency greater than the upper limit of human hearing, this limit being approximately 20 kilohertz (20,000 hertz).
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Ability to hear ultrasound
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Please help recruit one or [ improve this article] yourself. See the talk page for details.
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Endoderm is one of the germ layers formed during animal embryogenesis. Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the endoderm.
The endoderm consists at first of flattened cells, which subsequently become columnar.
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The endoderm consists at first of flattened cells, which subsequently become columnar.
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The germ layer mesoderm forms in the embryos of animals more complex than cnidarians, making them triploblastic. Mesoderm forms during gastrulation when some of the cells migrating inward to form the endoderm form an additional layer between the endoderm and the ectoderm.
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The aorta (generally pronounced [eɪˈɔːtə] or "ay-orta") is the largest artery in the human body, originating from the left ventricle of the heart and bringing oxygenated blood to all parts of the body in the systemic circulation.
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The vitelline veins are veins which drain blood from the yolk sac.
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Path
They run upward at first in front, and subsequently on either side of the intestinal canal...... Click the link for more information.
Vitelline circulation refers to the system of blood flowing from the embryo to the yolk sac and back again.
The yolk-sac is situated on the ventral aspect of the embryo; it is lined by entoderm, outside of which is a layer of mesoderm.
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The yolk-sac is situated on the ventral aspect of the embryo; it is lined by entoderm, outside of which is a layer of mesoderm.
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vitelline duct.
The vesicle can be seen in the after-birth 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.
..... Click the link for more information.
The vesicle can be seen in the after-birth 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.
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- For the entertainment company see Chorion (company).
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The placenta is an ephemeral (temporary) organ present in placental vertebrates, such as some mammals and sharks during gestation (pregnancy).
The placenta develops from the same sperm and egg cells that form the fetus, and functions as a fetomaternal organ with two
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The placenta develops from the same sperm and egg cells that form the fetus, and functions as a fetomaternal organ with two
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MeSH D008467 A Meckel's diverticulum, a true congenital diverticulum, is a small bulge in the small intestine present at birth. It is a vestigial remnant of the omphalomesenteric duct (also called the vitelline duct), and is the most frequent malformation of the
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The ileocecal valve is a sphincter muscle situated at the junction of the small intestine (ileum) and the large intestine. It regulates the flow of chyme into the bowels.[1]
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Umbilicus may refer to:
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- Umbilicus (mollusk), a feature of gastropod shell anatomy
- Umbilicus (genus), a genus of 15-20 species of flowering plants
- Umbilicus urbis Romae, the designated centre of the city of Rome from which and to which all distances in Rome
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ileum is the final section of the small intestine. It is about 2-4 m long in humans, follows the duodenum and jejunum, and is separated from the cecum by the ileocecal valve (ICV). The pH in the ileum is usually between 7 and 8 (neutral or slightly alkaline).
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The hypoblast is a tissue type that forms from the inner cell mass.[1] It lies beneath the epiblast and consists of small cuboidal cells.[2]
Extraembryonic endoderm (including Yolk sac) is derived from hypoblast.
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Extraembryonic endoderm (including Yolk sac) is derived from hypoblast.
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Heuser's membrane (or the exocoelomic membrane) is a short lived combination of hypoblast cells and extracellular matrix.
It surrounds the exocoelomic cavity.
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It surrounds the exocoelomic cavity.
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F. s. catus
Trinomial name
Felis silvestris catus
(Linnaeus, 1758)
Synonyms
Felis lybica invalid junior synonym
Felis catus invalid junior synonym[2]
The cat (
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Trinomial name
Felis silvestris catus
(Linnaeus, 1758)
Synonyms
Felis lybica invalid junior synonym
Felis catus invalid junior synonym[2]
The cat (
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Umbilicus may refer to:
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- Umbilicus (mollusk), a feature of gastropod shell anatomy
- Umbilicus (genus), a genus of 15-20 species of flowering plants
- Umbilicus urbis Romae, the designated centre of the city of Rome from which and to which all distances in Rome
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This article or section may be confusing or unclear for some readers.
Please [improve the article] or discuss this issue on the talk page. This article has been tagged since December 2006.
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Please [improve the article] or discuss this issue on the talk page. This article has been tagged since December 2006.
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Allantois (plural allantoides or allantoises) is a part of a developing animal conceptus (which consists of all embryonic and extra-embryonic tissues). It helps the embryo exchange gases and handle liquid waste.
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Herod_Archelaus
