Midterm 3 - Lecture 24 Flashcards
Implantation/Attachment
joining of the extra-embryonic membranes to the uterine endometrium
Placentation
organization and physical relationship of embryonic/fetal membranes to the uterine endometrium that provides a site of metabolic exchange between the dam and embryo/fetus
Placenta
temporary organ of metabolic exchange btw the embryo/fetus and the dam consisting of tissues of embryonic origin and maternal origin
4 steps in pre-attachment embryonic development
- developing within the zona pellucida
- hatching from the zona pellucida
- maternal recognition of pregnancy
- extra-embryonic membranes
- preparation for placentation and attachment to endometrium
Following hatching what happens prior to attachment?
“explosion” of embryonic tissue growth occurs to establish the extra-embryonic membranes
Why is the formation of the extra-embryonic membranes necessary?
to allow the developing embryo to attach to the uterus
What are the 4 extra-embryonic membranes?
- yolk sac
- chorion
- amnion
- allantois
Yolk sac
- a transient membrane that regresses as the conceptus develops
- formed from the primitive endoderm of the embryo
- contributes primordial germ cells and early RBC
Chorion
- outermost membrane that develops villi (chorionic villi) which attach to the endometrium to form fetal sites of placental attachment
- formed from the trophoblast (ectoderm), primitive endoderm and mesoderm of the embryo
Amnion
- liquid filled membrane enclosing the fetus the serves to protect the embryo against mechanical damage and prevent tissue adhesions
- formed from the trophoblast (ectoderm), primitive endoderm and mesoderm of the embryo
Allantois
- membrane that encloses a liquid waster storage reservoir for the developing embryo/fetus
- formed from the primitive gut of the developing embryo
Origin of amnionic fluid
- maternal circulation
- secretions from fetal respiratory tract
Functions of amnionic fluid
- protects fetus from mechanical damage
- prevents adhesions
- lubricates birth passage during parturition
Origin of allantoic fluid
- fetal waste
- secretions of allantoic membrane
Functions of allantoic fluid
- positions allantochorion in contact with endometrium during attachment
- stores fetal waste