Placentation Histology

Question 1

List the 4 basic fetal membranes, and describe which of these membranes interact to form the two types of placentas in the domestic species

Answer 1

1. chorion: outermost membrane that surrounds developing embryo
2. amnion: ectoderm-derived vesicle that encloses developing fetus, buoyancy chamber
3. yolk sac (vitelline): endoderm-derived sac that communicates with the middgut; nutrient exchange
4. allantois: diverticulum developing from hindgut; exchange of waste products

yolk sac + chorion wall combine with uterine wall to form vitelline placenta

allantois + chorion combine with uterine wall to form real placenta

Question 2

List the two major fluid-filled cavities formed by the fetal membranes and include the type of fluid they contain

Question 3

Define and differentiate between the four macroscopic categories of the frondose portion of the CAM

Answer 3

diffuse: frondose chorion present over entire surface of chorion, so entire chorion attached to endometrium (microcotyledonary)

cotyledonary: frondose chorion forms organized groups called cotyledons that specifically develop on uterine caruncles to form a placentome

zonary: frondose chorion grouped in a region that transcribes the mid-portion of the chorion (girdle)

discoidal: frondose chorion is grouped into one or two disc shaped structures

Question 4

Define and differentiate between the three microscopic categories of the frondose portion of the CAM

Answer 4

villous: chorionic villi with vascular cores that fit into corresponding caruncular crypts; in mares and ruminants

folded: macroscopic plicae and microscopic folds; in sows

lamellar/labrynthine: allantochorion forms complex intercommunicating maze of blood channels; in carnivores
feline: lamellar, straighter
canine: lamellar/labyrinthine, more convoluted

Question 5

List the six layers (3 maternal, 3 fetal) of tissues separating fetal and maternal blood and know which of the variable layers are present or absent in the 4 different categories of placentas based on these tissue layers

Answer 5

fetal, constant:
1. vascular endothelium
2. mesenchyme (CT matrix)
3. trophoblast (interface with maternal side)

maternal:
1. uterine surface endothelium (present in epitheliochorial, absent in endothial and hemochorial)
2. uterine stromal CT: present in epotheliochorial, absent in endothelial and hemochorial
3. uterine tissue endothelial: present in epi and endothelialchorial, absent in hemochorial

Question 6

Describe the difference between nondeciduate and deciduate placentas

Answer 6

this is based on whether or not tissue is lost at parturition, as defined by the level of interaction between fetal and maternal tissues

nondeciduate: fetal components interlock with intact maternal components, so they can readily separate

deciduate: conjoined placenta/placenta vera, where uterine mucosa and chorion are eroded to varying degrees and subsequently fuse with fetal trophoblasts, therefore do not separate at parturition and uterine tissue is shed at birth

Question 7

Differentiate between the endotheliochorial placenta of the carnivores and the epitheliochorial (with foci of synepitheliochorial fusion) placenta of the ruminants

Answer 7

see histo self quiz

Question 8

give macro, micro, layers, and degree of implantation of swine, horse, ruminant, carnivore, and humans

Answer 8

swine: diffuse, folded, epitheliochorial, nondeciduate

horses: diffuse, villous, epitheliochorial, nondeciduate

ruminant: cotyledonary, villous, epitheliochorial, nondeciduate

carnivore: zonary, lamellar/labrynthine, endotheliochorial, deciduate

humans: discoid, villous, hemochorial, deciduate