Placental & Fetal Anatomy

Question 1

embryo

Answer 1

prior to organ development

no species differentiation at this point

Question 2

fetus

Answer 2

after organ development

species differentiation at this point

Question 3

conceptus

Answer 3

all structures that develop from the zygote (embryonic and extra embryonic)

Question 4

fetal membranes

Answer 4

extra embryonic tissues (amnion, chorion, allantois, yolk sac) and placenta

Question 5

placenta

Answer 5

temporary organ formed by fetal and maternal tissues

used for nutrient, gas, and waste exchange between the lung, kidney, and gut

Question 6

stages of embryonic development

Answer 6

1. fertilized zygotę undergoes mitosis to become a multicellular mass
2. cells differentiate into inner cell mass and surrounding trophoblast cells
3. endoderm layer begins to form inside the trophoblast layer to form the yolk sac
4. mesoderm starts growing up and around the embryo and down to surround the yolk sac
5. trophoblast and mesoderm fold upward to create the amniotic sac surrounding the embryo
6. allantois grows down from primitive gum to provide vessels to vascularize membranes; yolk sac regresses

Question 7

inner cell mass

Answer 7

becomes the embryo

Question 8

trophoblast

Answer 8

becomes the placenta

Question 9

chorion

Answer 9

outer trophoblast + mesoderm membrane in contact with endometrium

Question 10

amnion

Answer 10

inner trophoblast + mesoderm membrane surrounding the fetus

Question 11

allantochorion

Answer 11

outer trophoblast + mesoderm + allantoic membrane

Question 12

diffuse placenta

Answer 12

exchange occurs across entire placental surface

horses, pigs, camelids

Question 13

cotyledonary placenta

Answer 13

exchange occurs at the fetal cotyledon to maternal caruncle junction

sheep, goats, cows

Question 14

zonary placenta

Answer 14

exchange occurs at a single band around the placenta

dogs, cats

Question 15

discoid placenta

Answer 15

exchange occurs at a single round surface on the placenta

humans

Question 16

epitheliochorial placenta

Answer 16

little to no invasion of maternal epithelium by trophoblasts

6 tissue layers exist between maternal/fetal blood supply (cap endothelium, connective tissue, trophoblast epithelium)

horses, pigs, camelids, ruminants

Question 17

does antibody transfer occur in epitheliochorial placentas

Answer 17

No - neonates require colostrum

Question 18

endotheliochorial placenta

Answer 18

erosion of maternal endometrial epithelium and connective tissue

4 tissue layers between maternal/fetal blood supply (all 3 fetal layers, only maternal cap endothelium)

dogs, cats

Question 19

hemochorial placenta

Answer 19

erosion of all 3 maternal tissue layers allowing direct contact of trophoblasts with maternal blood supply

3 tissue layers exist between maternal and fetal blood supply (all 3 fetal layers, no maternal layers)

humans, rodents

Question 20

does antibody transfer occur in endotheliochorial placentas

Answer 20

some - do not require colostrum

Question 21

does antibody transfer occur in hemochorial placentas

Answer 21

abundant transfer - no colostrum needed

Question 22

what placenta type do pigs have

Answer 22

diffuse and epitheliochorial

Question 23

what mechanism do pig placentas use to increase surface area

Answer 23

highly folded - chorionic villi and uterine crypts

Question 24

necrotic tips

Answer 24

loss of vascularization at the ends of the chorionic membrane leading to necrosis

prevents anastomosis of blood vessels between littermates

Question 25

what type of placenta do horses have

Answer 25

diffuse and epitheliochorial

Question 26

when does the chorioallantoic placenta form in horses

Answer 26

day 42 - until then, horses have a prominent yolk sac that acts as a placenta (choriovitelline)

Question 27

do horses expel the amniotic sac at parturition

Answer 27

yes

Question 28

yolk sac remnant

Answer 28

ball of remnant yolk sac that did not regress fully; comes out attached to the umbilical cord

Question 29

chorionic girdle trophoblast

Answer 29

specialized trophoblastic cells that are able to invade endometrium by entering between epithelial cells form endometrial cups

Question 30

endometrial cups

Answer 30

colonies of large, binucleate trophoblast cells that form within the endometrium secrete eCG & stimulate ovulation/luteinization of follicles to form secondary CL --> maintains progesterone secretion during transition to chorioallantoic placenta slough off around day 110-120 to form allantoic pouches

Question 31

what are the avillous areas in the horse placenta

Answer 31

normal areas in the horse that do not contain chorionic villi and therefore do not participate in nutrient/waste exchange - cervical star - tip of uterine horn - areas opposite the endometrial cups

Question 32

microcotelydons

Answer 32

microscopic accumulations of microvilli that provide increased surface area

Question 33

what type of placenta do ruminants have

Answer 33

cotyledonary and epitheliochorial

Question 34

do ruminant placentas have necrotic tips

Answer 34

no - can get anastomosis between littermates (freemartins)

Question 35

trophoblast giant cells

Answer 35

binucleate trophoblasts that invade between epithelial cells and fuse together (no erosion) secrete pregnancy specific proteins and placental lactogen

Question 36

what type of placenta do dogs have

Answer 36

zonary and endotheliochorial

Question 37

marginal hematoma

Answer 37

bands of hemorrhage from maternal vessels on the margins of the zonary placenta; site of abundant immune cells/phagocytosis green colored due to heme breakdown products

Question 38

umbilical cord

Answer 38

connection between placenta and fetus

Question 39

what is in the umbilical cord in cows

Answer 39

2 umbilical arteries, 2 umbilical veins, urachus

Question 40

what is in the umbilical cord in horses

Answer 40

2 umbilical arteries, 1 umbilical vein, urachus

Question 41

urachus

Answer 41

connection from the fetal bladder that eliminates waste into the allantois fetus swallows amniotic fluid --> passes through kidneys and into urachus --> allantoic fluid located within the umbilical cord

Question 42

umbilical veins

Answer 42

carries oxygenated blood to the fetus regresses to form the round ligament of the liver

Question 43

umbilical arteries

Answer 43

carries deoxygenated blood away from the fetus maintained as arteries in most species; it will regress in 50% of dogs to become the round ligament of the bladder