cotyledon

1. See maternal c., fetal c.. 2. In plants, a seed leaf, the first leaf to grow from a seed. 3. A placental unit. See maternal c.. [G. kotyledon, any cup-shaped hollow]

- fetal c. a unit of the fetal placenta supplied by the vessels of a stem villus; several such cotyledons may occur between two placental septa; traditionally called embryologists' c..

- maternal c. a unit of the placenta made up of trophoblastic cells, fibrous tissue, and abundant blood vessel s, which is visible grossly on the maternal surface as an irregularly shaped lobe circumscribed by a deep cleft and made up of a stem villus with numerous branching free villi and anchoring villi; placental vessels in the chorionic plate supply the stem villus and its branches, allowing gas and metabolite exchange across the trophoblastic layer with maternal blood in the intervillous space; traditionally called clinicians' c..

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cot·y·le·don .kät-əl-'ēd-ən n

1) a lobule of a mammalian placenta

2) the first leaf or one of the first pair or whorl of leaves developed by the embryo of a seed plant or of some lower plants (as ferns)

cot·y·le·don·ary -'ēd-ən-.er-ē adj

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n.

any of the major convex subdivisions of the mature placenta. Each cotyledon contains a major branch of the umbilical blood vessels, which branch further into the numerous villi that make up the surface of the cotyledon.

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Cot·y·le·don (kot″ə-leґdən) a genus of herbaceous plants found in southern Africa; several species contain cotyledontoxin.