Exercise 46 Embryonic Development Developmental stages of humans

Exercise 46 Embryonic Development

Developmental stages of humans Fertilization ¢ Zygote l It is a fertilized egg l Diploid (2 n) l Female pronuclei l Male pronuclei l Amphimixis ¢

Developmental stages of humans Zona pellucida l Surrounds the zygote l Disappears when the blastocyst reaches the uterine cavity ¢ Corona radiata l Granulosa cells surrounding the zona pellucicda l Disappears after fertilization ¢

Fertilization

Developmental stages of humans Cleavage ¢ Stages of the Cleavage l Blastomere ¢ Early cleavage l 4 -cells stage… ¢ Morula l 16 -32 cells stage ¢

Developmental stages of humans Blastocyst l Central cavity appears – blastocystic cavity l Inner cell mass (ICM) – forms the embryo l Trophoblast – nourishes the developing embryo ¢ Final product of cleavage ¢

Developmental stages of humans ¢ Implantation l From day 7 to day 10 after the ovulation l The blastocyst will go from a floating stage to a complete implanted stage in the uterus

Developmental stages of humans Gastrulation ¢ The ICM will develop into three primary germ layers l Ectoderm • Forms the epithelia and nervous system ¢

Developmental stages of humans l Mesoderm • Forms everything between the ectoderm and the endoderm l Endoderm • Forms the mucosa of the digestive and respiratory tract, etc

Endometrium will form the deciduas Deciduas basalis-part of the endometrium that forms the maternal portion of the placenta ¢ Deciduas capsularis – the rest of the endometrium surrounding the embryo ¢ Deciduas parietalis – endometrium not surrounding embryo or placenta ¢

Developmental stages

Developmental stages of humans Embryo l 0 to 8 weeks ¢ Fetus l 9 weeks to birth ¢ Trophoblast l Will develop villi l Will differentiate into the chorion that will form the fetal portion of the placenta ¢

Developmental stages of humans Placenta l Chorionic villi + decidua basalis ¢ Embryonic membranes (from the ICM) l Amnion • Encases the embryo • Amniotic cavity • Amniotic fluid ¢

Developmental stages

Developmental stages of humans l Yolk sac • Originates the embryo’s first blood cells l Allantois • Body stalk and later umbilical cord • Umbilical cord attaches the embryo to the placenta

In uterus development ¢ Placenta l Fetal side • Shine and smooth • Presence of large blood vessels l Maternal side • Spongy, torn-looking, rough