One of the most remarkable examples of cell communication is the fight or flight response. body handle extraordinary situations. responses involved in the fight or flight response. place in the movie. 0:16 An environmental signal travels into the brain. a nerve impulse to the hypothalamus (not shown).
Umbilical cord. In placental mammals, the umbilical cord (also called the navel string, birth cord or funiculus umbilicalis) is a conduit between the developing embryo or fetus and the placenta.
1 Placental mammals. 2  In placental mammals, the extraembryonic membranes form a placenta and umbilical cord, which connect the embryo to the mother's uterus in a more elaborate and efficient way. 3  The blood supply of the developing fetus is continuous with that of the placenta. The yolk sac contains yolk â the sole source of food until hatching. 2  Yolk is a mixture of proteins and lipoproteins. 3  The chorion lines the inner surface of the shell (which is permeable to gases) and participates in the exchange of O 2 and CO 2 between the embryo and the outside air.