3. implantation and placentation Flashcards
what is a placenta
a placenta is formed when fetal membranes become closely attached to the uterine wall to facilitate physiological exchange of gases, nutrients and waste products
briefly outline how the extraembryonic membranes are developed
where is the chorion
where the mesoderm and the trophoblast come into contact
- outermost layer of placenta in all mammalian species
the yolk sac is an extension of the
midgut
the allantoic sac is an extension of the
hindgut
what is the chorioallantoic membrane
where the chorion makes contact with the allantois
what is the choriovitalline placenta
where the chorion and the vitalline (yolk sac) meet
- often transient
what is the amnion and what is its function
innermost fluid filled membrane
- allows symmetrical growth and protection of foetus
- temperature control and foetal movement
what is the yolk sac and what is its function
- reptile and bird eggs: srrounds the yolk
- marsupials: definitive placenta
- higher mammals: transient with nutritional role (doesnt last long)
- role in early pregnancy
what is the allantois and what is the function
- sac from hindgut
- connection becomes umbilical cord
what is the chorion and what is its function
outer membrane
- becomes foetal contribution to placenta
- all placentas chorionic at some stage of development
what are the 3 stages of implantation
- apposition: blastocyst or foetal membranes become closely apposed to uterine lining (epithelium)
- adhesion: a complex biochemical interaction between molecules on the trophoblast and epithelium that alow membrane to attach
- firm attachment OR invasion of trophoblast into uterus: depends on species: non-invasive or invasive
what is the difference between invasive and non-invasive implantation
- non invasive: blastocyst undergoes elongation, uterine epithelium alignment, trophoblast layer attaches to epithelial layer of uterue = placenta formation
- invasive: apposition and attachment (no elongation) attaches to uterine epithelium then invades into uterus iself
how is the type of placenta classified
- foetal extraembryonic membranes (chorionic, yolk sac and allantoic)
- source of nutrition (hemotrophic: from circulating maternal blood, histotrophic: from endometrium)
- maternal tissue shed with fetal tissue at birth (deciduate vs non-deciduate)
- histological structure (number of tissue layers interposed between maternal and foetal circulations)
- macroscopic: nutrient exchange ares (distribution of chorionic villi or chorionic sac and relationship with endometrium (diffuse, cotyledonary, zonary)
how many layers of tissue are possible between the maternal and foetal blood
explain the layers between maternal and fetal blood in epitheliochorial, endothelialchorial and haemochorial placentas
- epitheliochorial = sow, mare
- endothelialchroial = bitch
- hemochorial = rodents, rabbit, primates
difference brought about by degree of invasion on fetal side
what are the different types of placental villi
- diffuse = nutrient exchange all over
- cotyledonary = clusters all over membrane. between clusters no nutrient exchange. bits that attach to the uterus
- zonary = around centre of the chorionic membrane going around fetus. like a thick belt
- discoid = disk like amalgamation
discoid = primates and rodents
describe the placenta in the sow
- true epitheliochorial placentation (6 layers between maternal and fetal blood)
- diffuse (villi distributed over entire membrane)
- non-deciduate( when delivered no maternal tissue delivered with it
describe the placenta in the ewe/cow
- synepitheliochorial placentation
- cotyledonary
- non-deciduate
what is a synepitheliochorial placenta
fusion of binucleate giant cells to maternal eptithelial cell leading to maternal fetal hybrid cell. granules from within then released into the maternal circulation (placental lactogen)
what are placentomes
where the membrane makes contact with the caruncles - cotyledun. caruncle pluse cotyledun = placentom
cow = convex
sheep/goat = concave
describe the placenta in the horse
- epitheliochorial placentation
- diffuse
- non-deciduate
what is the chorionic girdle
- forms around day 30
- junction between chorionallontois and yolk sac
- visible in mare
- where developing embryo first makes contact with uterus
- moves as allantois overtakes yolk sac
what are equine endometrial cups and what do they do
- around day 36-37 junction between 2 plcentsa (girdle) makes contact with uterus
- bunches of cells invade into uterus and form cups
- cups = glands that secrete eCG
- transient (after day 100, surrounded by leukocytes and destroyed) = ECG levels drop
describe placentation in the dog
- endotheliochorial placenta (4 layers between maternal and fetal circ)
- zonary
- deciduate
describe the placenta in the rodent/rabbit/primate
- haemochorial placentation
- invasive
- decidual
what is decidualisation and what species does it occur in
- endometrial stromal cells proliferate and change to become decidual cells
- the decidua is the maternal placenta
- important in communication between mother and fetus and limits invasion of trophoblast
- seen in rodents, rabbits and primates (anything with a haemochorial placenta
explain how the umbilical cord works
- umbilical vein carries oxygen rich blood to fetus, bypassing liver into heart the circ
- umbilical arteries carry blood back to placenta (deficient in oxygen back to mother)
