Lecture 74: MRP and Placentation

Question 1

What must the embryo do before it attaches to the uterus?

Answer 1

Develop within the ZP
Subsequently hatch from the ZP
Undergo Maternal Recognition of Pregnancy (MRP)
Form extraembryonic membranes

Question 2

What happens after the zygote undergoes syngamy?

Answer 2

After, the zygote undergoes cleavage (mitotic divisions) and gives rise to daughter cells called blastomeres

Question 3

At what point in mitotic divsions is the embryo considered a morula?

Answer 3

After the eight celled-stage

Question 4

Cells of the morula continue to divide and then a blastocyst develops. What are some of the significant features of a blastocyst?

Answer 4

Inner cell mass (ICM)
Cavity called the blastocele
Single layer of cells called trophoblast

Question 5

What happens to the blastocyst as it continues to rapidly grow?

Answer 5

Hatches from the zona pellucida and forms a hatched blastocyst that is free-floating within the uterus

Question 6

Each blastomere is totipotent. What does this mean?

Answer 6

One cell contains all of the DNA of the individual

Question 7

Hatching of the blastocyst is governed by 3 forces. What are they?

Answer 7

1) Growth and fluid accumulation within the blastocyst
2) Production of enzymes by the trophoblastic cells
3) Contraction of the blastocyst

Question 8

What is the main difference between a ruminant blastocyst and a mare blastocyst?

Answer 8

• Ruminant: Filamentous, thread-like structure
• Mare: Remains spherical

Question 9

What structures of the blastocyst give rise to the chorion and the amnion?

Answer 9

The trophoblast along with the primitive endoderm and mesoderm

Question 10

The yolk sac develops from what structure?

Answer 10

The primitive endoderm

Question 11

What is MRP?

Answer 11

Preservation of the primary corpus luteum
- must occur before luteolysis
- maintains high levels of progesterone
- in most cases it is a conceptus mediated biochemical signal

Question 12

When do oxytocin receptors appear in the endometrium?

Answer 12

Late in the luteal phase, about 10-12 days of increasing progesterone

Question 13

What is the chemical for MRP in ruminants? Where is it produced and what does it do?

Answer 13

Interferon tau
Produced by trophoblastic cells
Inhibits oxytocin receptor synthesis on the endometrium, thereby inhibiting PGF2a release

Question 14

What is the chemical for MRP in sows? How does it maintain progesterone levels?

Answer 14

The blastocyst produces estrogen, it reroutes PGF2a release into the uterine lumen where it is destroyed

PGF2a release is changed from endocrine to exocrine

Question 15

What is MRP in the mare? How does it maintain progesterone levels?

Answer 15

Blastocyst migration throughout the uterine lumen
Reduced synthesis of PGF2a
Occurs between days 12-14
Possible PGE2 production by the embryo

Question 16

In all domestic animals, the __________ is the origin of the placenta.

Answer 16

chorioallantois

Question 17

Mares have special structures called endometrial cups. What do they produce?

Answer 17

Produce equine chorionic gonadotropin (eCG)

eCG has FSH-like activity, so it helps to luteinize accessory and secondary corpora lutea

Question 18

Describe the Diffuse classification of placentation. What species have this type of attachment?

Answer 18

Almost the entire surface of the allantochorion is involved in the formation of the placenta

Horses, pigs, and camelids

Question 19

Describe the cotyledonary classification of placentation. What species have this type of attachment?

Answer 19

Multiple, discrete areas of attachment called placentomes are formed by the interaction of patches of allantochorion with endometrium. The fetal portion of the placenta are called cotyledons, and the maternal contact site are called caruncles. Together they make up a placentome.

Ruminants

Question 20

Describe the zonary classification of placentation. What species have this type of attachment?

Answer 20

The area of attachment is a complete or incomplete band of tissue surrounding the fetus

Carnivores like dogs, cats, seals, bears, and elephants

Question 21

Describe the discoid classification of placentation. What species have this type of attachment?

Answer 21

The area of attachment is discoid in shape

Primates and rodents

Question 22

Describe epitheliochorial degree of invasiveness and what species have this type of attachment.

Answer 22

Least intimate, both maternal and fetal epithelium are intact

Pig, horse, ewe, doe, cow

Question 23

Describe the endotheliochorial degree of invasiveness and what species have this type of attachment

Answer 23

Complete erosion of endometrial epithelium

Dog and cat

Question 24

Describe the hemochorial degree of invasiveness and what species have this type of attachment.

Answer 24

Chorionic epithelium is in direct apposition to maternal pools of blood

Primates, rodents