Embryonic Development
EARLY EMBRYOGENESIS AND MATERNAL RECOGNITION OF PREGNANCY
Chapter 13; Pathway to Pregnancy and Parturition
AVS 222 (Instructor: Dr. Amin Ahmadzadeh)
I. THERMINOLOGY AND EMBRYO ATTACHMENT
A. Four steps must be achieved before embryo can attach to the uterus - Development of embryo within confinement of the zona pellucida - Hatching of the embryonic cells (blastocyst) from the ZP - Formation of extra embryonic membranes (e.g placenta) - Maternal recognition of the pregnancy B. Embryo - Refers to the early period of development in which no distinct anatomical structure has formed.
C. Fetus
- Defined as potential offspring that is still in the uterus (before birth) and generally recognizable as a member of given species. - More advanced from an embryo
- In cattle, Usually is referred to an advanced embryo after approximately 30 days post-fertilization in
D. Conceptus
- Product of conception including early embryo, the embryo and extra-embryonic membranes during the implantation, and fetus and placenta
II. EMBRYO DEVELOPMENT (CLEAVAGE DIVISIONS)
(Figure 13-1) Mitotic divisions transform a one-celled embryo (zygote) into a multicellular embryo A. Zygote to 2-cell - Each cell of embryo is called a blastomere - There is no cell growth only division of the cytoplasm a) Blastomere size decreases with cell divisions B. 2-cell to 4- and 8- cell - Each blastomere undergoes subsequent division yielding 4 and then 8 daughter cells - No cell growth a) Blastomeres are 1/4 and 1/8 original size C. Divisions continue with embryos named for the number of cells present - Eventually too many cells to count D. Morula (Mulberry like!) - Solid ball of cells (too many blastomeres
Chapter 13; Pathway to Pregnancy and Parturition
AVS 222 (Instructor: Dr. Amin Ahmadzadeh)
I. THERMINOLOGY AND EMBRYO ATTACHMENT
A. Four steps must be achieved before embryo can attach to the uterus - Development of embryo within confinement of the zona pellucida - Hatching of the embryonic cells (blastocyst) from the ZP - Formation of extra embryonic membranes (e.g placenta) - Maternal recognition of the pregnancy B. Embryo - Refers to the early period of development in which no distinct anatomical structure has formed.
C. Fetus
- Defined as potential offspring that is still in the uterus (before birth) and generally recognizable as a member of given species. - More advanced from an embryo
- In cattle, Usually is referred to an advanced embryo after approximately 30 days post-fertilization in
D. Conceptus
- Product of conception including early embryo, the embryo and extra-embryonic membranes during the implantation, and fetus and placenta
II. EMBRYO DEVELOPMENT (CLEAVAGE DIVISIONS)
(Figure 13-1) Mitotic divisions transform a one-celled embryo (zygote) into a multicellular embryo A. Zygote to 2-cell - Each cell of embryo is called a blastomere - There is no cell growth only division of the cytoplasm a) Blastomere size decreases with cell divisions B. 2-cell to 4- and 8- cell - Each blastomere undergoes subsequent division yielding 4 and then 8 daughter cells - No cell growth a) Blastomeres are 1/4 and 1/8 original size C. Divisions continue with embryos named for the number of cells present - Eventually too many cells to count D. Morula (Mulberry like!) - Solid ball of cells (too many blastomeres