| 释义 |
pla·cen·ta
\pləˈsentə\ noun
(plural placentas \-təz\ ; also placen·tae \-nˌtē\)
Etymology: New Latin, from Latin, flat cake, from Greek plakount-, plakous, from plak-, plax flat surface — more at please
1.
a. : the vascular organ in mammals except monotremes and marsupials that unites the fetus to the maternal uterus and intermediates the metabolic exchanges of the developing individual through a more or less intimate association of chorionic and usually allantoic and of uterine mucosal tissues by which the fetal and maternal vascular systems are brought into intimate relation permitting exchange of materials by diffusion but without direct contact between fetal and maternal blood and which typically involves the interlocking of fingerlike or frondose vascular chorionic villi with corresponding modified areas of uterine mucosa — compare afterbirth
b. : any of various analogous organs in other animals (as some viviparous sharks and free-swimming tunicates) for the attachment of the young to the mother and its nourishment by her
2. : a sporangium-bearing surface: as
a. : the part of the carpel of a seed plant bearing ovules — see placentation
b. : the point on a fern or fern ally leaf or sporophyll at which sporangia develop |