Implantation and Placentation Flashcards
How is a placenta formed?
A placenta is formed when fetal membranes become closely attached to the uterine wall to facilitate physiological exchange of gases, nutrients and waste products
What are the four fetal membranes?
Amnion (growth, protection & temperature control), yolk sac (nutritional role in early pregnancy), allantois (connection becomes umbilical cord) & chorion (foetal contribution to placenta)
What are the three key stages of implantation?
Apposition, adhesion & firm attachment OR invasion of trophoblast into uterus (depends on species)
What are the ways in which placentae may be categorised?
Foetal extraembryonic membranes – chorionic, yolk sac & allantoic
Source of nutrition – hemotrophic (maternal blood) & histotrophic (endometrium)
Maternal tissue shed with fetal tissue at birth – deciduate vs. non-deciduate
Histological structure – number of tissue layers
Distribution of chorionic villi on chorionic sac and relationship with endometrium – diffuse, cotyledonary, zonary
What are the three possible fetal and maternal layers?
Fetal – endothelium, connective tissue, trophoblast
Maternal – epithelium, connective tissue, endothelium
What are the three main types of placentation?
Epitheliochorial – 3 fetal, 3 maternal
Endotheliochorial – 3 fetal, 1 maternal
Haemochorial – 3 fetal, 0 maternal
What is the functional unit of the fetal placenta?
The chorionic villous
What is the placentation of the major species?
Sow – true epitheliochorial, diffuse, non-deciduate
Ewe & cow – synepitheliochorial, cotyledonary, non-deciduate
Horse – epitheliochorial, diffuse, non-deciduate
Dog – endotheliochorial, zonary, deciduate
Human – Haemochorial, invasive, decidual
What specialised trophoblast cells that exhibit invasive activity are unique to equids?
Chorionic girdle cells
What is the decidua in the maternal placenta important for?
Communication between mother and fetus & limits invasion of trophoblast
