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Embryonic Structures

Definition: The anatomical parts that make up an organism in the early stages of development.
Notes: avoid: too inclusive; prefer EMBRYO & specific embryonic stage or Cat A & Cat B with /embryol; for plants, PLANT EMBRYOS see SEEDS is available
Also Called: Fetal Structures,Prenatal Structures
Previously Indexed: Embryo (1966-1997),specific organ/embryology (1968-1997),specific organism/embryology (1975-1997)

Embryonic Structures Categories.
Embryo - The early developmental stage of MAMMALS. It generally defines the period from cleavage into two BLASTOMERES to the end of embryonic differentiation of basic structures. In the human, the embryo represents the first two months of intrauterine development preceding the stages of the FETUS.
Fetus - The unborn young of a viviparous mammal, in the postembryonic period, after the major structures have been outlined. In humans, the unborn young from the end of the eighth week after CONCEPTION until BIRTH, as distinguished from the earlier EMBRYO.
Placenta - A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (CHORIONIC VILLI) derived from TROPHOBLASTS and a maternal portion (DECIDUA) derived from the uterine ENDOMETRIUM. The placenta produces an array of steroid, protein and peptide hormones (PLACENTAL HORMONES).

Embryonic Structures Definitions and Terms

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