vitelline sac

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yolk sac

1. in vertebrates with telolecithal eggs, the highly vascular layer of splanchnopleure surrounding the yolk of an embryo;
2. in humans and other mammals, the sac of extraembryonic membrane that is located ventral to the embryonic disk and, after formation of the gut tube, is connected to the midgut; by the second month of development, this connection has become the narrow yolk stalk; the yolk sac is the first hematopoietic organ of the embryo, and its vitelline circulation plays an important role in the early embryonic circulation; the sac is also the site of origin of the primordial germ cells.
Farlex Partner Medical Dictionary © Farlex 2012


(sak) [L. saccus, sack, bag]
A baglike part of an organ, a cavity or pouch, sometimes containing fluid. Synonym: saccus See: cyst

air sac

In a mammalian lung, an informal term for “pulmonary alveolus.”
See: alveolus.

allantoic sac

The expanded end of the allantois, well developed in birds and reptiles.

alveolar sac

Pulmonary alveolus.

amniotic sac

The inner fetal membrane that encloses the developing fetus and produces amniotic fluid.
See: chorion

chorionic sac

The outer fetal membrane that encloses the developing embryo.

conjunctival sac

The cavity, lined with conjunctiva, that lies between the eyelids and the anterior surface of the eye.

dental sac

The mesenchymal tissue surrounding a developing tooth.

endolymphatic sac

The expanded distal end of the endolymphatic duct.

heart sac

The pericardium.

hernial sac

In the peritoneum, a saclike protrusion containing a herniated organ.
See: hernia

Hilton's sac

See: Hilton, John

lacrimal sac

The upper dilated portion of the nasolacrimal duct situated in the groove of the lacrimal bone. The upper part is behind the internal tarsal ligament. It is 12 to 15 mm long.

lesser peritoneal sac

Omental bursa.

peritoneal sac

The enclosed, transparent mesothelial sac that is squeezed between the abdominal wall and the abdominal viscera.

vitelline sac

Yolk sac.

yolk sac

In mammals, the embryonic membrane that is the site of formation of the first red blood cells and the cells that will become oogonia or spermatogonia. Synonym: vitelline sac
See: embryo for illus
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