Yolk Sac

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Related to Yolk Sac: Gestational sac

Yolk sac

An extraembryonic membrane which extends through the umbilicus in vertebrates. In some elasmobranchs, birds, and reptiles, it is laden with yolk which serves as the nutritive source of embryonic development.

In mammals, as in birds, the yolk sac generally develops from extraembryonic splanchnopleure, and extends beneath the developing embryo. A blood vessel network develops in the mammalian yolk sac lining. Though these blood vessels are empty, they play an important role in absorbing nourishing food and oxygen from the mother. Thus, although the yolk sac in higher mammals may be considered an evolutionary vestige from its yolky-egged ancestors, it still serves important functions in the young embryo. As the embryo ages, the yolk sac shrinks in size, and the allantois takes over the role of nutrition. See Allantois

Yolk Sac


the organ of nutrition and respiration in the embryos of cephalopod mollusks, cartilaginous and bony fish, reptiles, birds, mammals, and man.

The yolk sac arises in the early stages of embryonic development, usually by means of the overgrowing of the yolk with endoderm and with the visceral layer of the lateral plates, and consists of an enlarged outgrowth of the midguts, the cavity of which in the majority of animals (except higher mammals and man) is filled with unbroken yolk. In the wall of the yolk sac blood cells and blood vessels are formed, which provide for transport of nutritive substances to the embryo and for its respiration. As the embryo develops, the size of the yolk sac decreases, its cavity shrinks, and it is either gradually drawn into the body cavity and resorbed or is cast off.

yolk sac

[′yōk ‚sak]
A distended extraembryonic extension, heavy-laden with yolk, through the umbilicus of the midgut of the vertebrate embryo.
References in periodicals archive ?
SALL4 is a novel sensitive and specific marker of ovarian primitive germ cell tumors and is particularly useful in distinguishing yolk sac tumor from clear cell carcinoma.
The traditional radiologic teaching has been a "multiple of 5's" rule: 1) a yolk sac should be visible when the mean gestational sac diameter (GSD) is >10 mm; 2) an embryo should be visible when the mean GSD is >15; and 3) a heartbeat should be present when the crown rump length (CRL) of the embryo is >5 mm.
1) From 0 (newly hatched) to 2 DAH: Yolk sac is big and spherical, digestive system is not completely developed, heart appeared and is beating.
8,22,32,34-36) The first marker labels seminoma but not solid yolk sac tumor, and the latter 2 are positive in solid yolk sac tumors but negative (glypican-3) or mostly negative (AE1/AE3) in seminomas.
Incidence of pediatric testicular tumors according to Prepubertal Testis Tumor Registry data (11) Tumor type No of patients Percent (%) Germ cell tumors Yolk sac tumor 244 62 Teratoma 92 23 Epidermoid cyst 13 3 Stromal tumors Juvenile granulosa cell 11 3 Sertoli's cell 10 3 Leydig cell 5 1 Non-specified 16 4 Gonadoblastoma 4 1
The internal yolk sac became exhausted 10-20 days after hatching and juveniles showed less interest in the zooplankton diet (day 50); by day 54, they fed and readily captured ~4-5-mm (total length) C.
Hematopoietic precursor cells within the yolk sac tumour component are the source of secondary hematopoietic malignancies in patients with mediastinal germ cell tumours.
It showed their offspring standing over a ball - the nutrition providing yolk sac - while preparing to take a penalty kick.
To determine if SARS-CoV could grow in avian embryos, 9-day-old chicken eggs and 13-day-old turkey embryonating eggs were inoculated by allantoic sac route and 17-day embryonating turkey eggs were inoculated by yolk sac route; all were tested by virus isolation and real-time RT-PCR for SARS-CoV.
The first patients in the registry include 17 survivors of lymphoma, 8 survivors of sarcoma, 5 survivors of Wilm's tumor, 4 survivors of neuroblastoma, and 1 survivor each of hepatoblastoma, ovarian germ cell tumor, yolk sac carcinoma, and Triton tumor.
It feeds by absorbing nutrients from the egg's yolk sac through its belly.
One by one, the children will see tiny baby salmon - alevins - complete with yolk sac emerge from the eggs.