Lec.9 COMPARATIVE PLACENTATION

Question 1

Upon entering the uterine cavity, the embryo is initially nourished by secretions from the ____

Collectively, these products are known as ____ or ‘uterine milk’.

However, as the embryo grows, the uterine milk becomes insufficient to nourish it.

Answer 1

uterine glands / endometrial glands

histotrophe

Question 2

To counteract this, the embryonic tissues establishes close connections with the ____

This allows the embryo to import bloodborne maternal nutrients, the ____, and to export its own waste products.

Together, histotrophe and hemotrophe are referred to as ____.

Answer 2

maternal circulatory system

hemotrophe

embryotrophe

Question 3

To accomplish exchange between the mother and her embryo a temporary organ, the ____, is formed.

In ____(what animals), the newly hatched blastocyst attaches to the endometrial epithelium and, the embryo actually penetrates the ____ and invades the endometrial connective tissue in which it becomes completely embedded.

Answer 3

placenta

rodents and primates

epithelium

Question 4

This process, where the embryo leaves the uterine lumen, is known as ____

In domestic animals invasion of the endometrium does not occur.

The embryo remains attached to the internal endometrial surface throughout gestation and, except in carnivores, placentation is ____.

Answer 4

implantation

non-invasive

Question 5

In most domestic species, the embryo reaches the ____ prior to blastulation

At the end of blastulation, the embryo consists of a sphere of ____ surrounding the inner cell mass and the blastocyst cavity.

Answer 5

uterine cavity

trophectoderm

Question 6

At about the time of hatching from the zona pellucida, the inner cell mass differentiates into ____

When complete, the enclosed cavity may be referred to as the ____

Answer 6

epiblast and hypoblast

primitive yolk sac

Question 7

During gastrulation, the extra-embryonic mesoderm is split into ____ sheets lining the extraembryonic coelom.

Eventually, the body foldings of the embryo proper result in the formation of the ____ and the ____ from the primitive yolk sac.

Answer 7

somatic and visceral

primitive gut and definitive yolk sac

Question 8

The definitive yolk sac wall fuses with the chorion in some species to establish a ___.

The allantois develops as an evagination from the ____

Answer 8

choriovitelline placenta

hindgut

Question 9

As the embryo grows, the allantois gradually expands into the ____, eventually occupying most of this cavity.

When the allantoic wall and the chorion meet, they fuse, forming the ____ which gives rise to the ____

Answer 9

extra-embryonic coelom

chorioallantois

chorioallantoic placenta.

Question 10

*Maternal Recognition
During the period when the embryo is still moving freely in the uterine cavity, the uterus prepares for placentation

____ are the principal hormones produced within the ovary.

High levels of ____ are secreted into the bloodstream during proestrus and estrus.

Answer 10

Estrogens and progesterone

estrogens

Question 11

*Maternal Recognition
what hormone____ predominates during the following periods of metestrus and diestrus when the early embryo moves from the oviduct into the uterus.

If pregnancy does not occur, endometrial involution (shrinkage) follows, reflecting the regression of the ____

Answer 11

Progesterone

corpus luteum

Question 12

*Maternal Recognition
____ must be prevented if pregnancy is to continue.

The maintenance of the corpus luteum is based upon maternal recognition of pregnancy.

By signalling its presence in the uterus, the embryo prevents ____ while apposing, and then adhering to, the endometrium.

Answer 12

Luteolysis

Question 13

*Maternal Recognition
In what animal____, the corpus luteum produces oxytocin as well as progesterone.

what hormone? stimulates the endometrium to synthesize prostaglandins (PGF2a) which have been identified as the main cause of luteolysis in ruminants (as well as in pigs and horses).

Answer 13

ruminants

Oxytocin

Question 14

*Maternal Recognition
what animal? employs another strategy to interrupt the luteolytic pathway.

Estradiol is produced from their trophectoderm around Days 11 to 12 of development.

It causes PGF2α to be secreted into the uterine lumen instead of into the maternal blood stream.

Answer 14

pigs

Question 15

*Maternal Recognition
In the lumen, PGF2a is quickly degraded.

It has been shown that at least ____ embryos must be present in order to prevent luteolysis in the pig.

Answer 15

four embryos

Question 16

c l a s s i f i c a t i o n o f p l a c e n t a

Answer 16

choriovitelline or chorioallantoic

Question 17

*Classification of Placenta
In the ____, the yolk sac wall combines locally with the chorion to form an area for exchange.

In domestic animals, this is seen only in ____

Answer 17

choriovitelline placenta

carnivores and horses

Question 18

*Classification of Placenta
The ____, which is the primary functional placenta in all domestic species, is established by fusion between the allantoic wall and chorion.

In what animals?, the yolk sac involutes 3 to 4 weeks after conception and never forms a functional placenta.

Answer 18

chorioallantoic placenta

pigs and ruminants

Question 19

*Classification of Placenta
Another classification scheme is through the structure and apposition of the placenta.

Areas where the chorioallantois interacts with the endometrium are referred to as ____

Areas where the chorioallantois is free, not engaged in placental formation, and has a smooth surface, are known as ____

Answer 19

chorion frondosum

chorion laeve

Question 20

*Classification of Placenta
In what animals?, chorion frondosum is diffusely distributed over the entire chorioallantoic surface and so the placenta is categorized as being diffuse.

Answer 20

pigs and horses

Question 21

*Classification of Placenta
In what animal?, chorion frondosum is organized as chorionic villi assembled into larger macroscopically visible tufts called cotyledons.

Hence, their placenta is known as ____ These will combine with the caruncles in the endometrium to form placentomes.

Answer 21

ruminants

cotyledonary / multiplex & villous

Question 22

*Classification of Placenta
In what animal?, the chorion frondosum is organized into a broad belt extending around the longitudinal axis of the embryo where it forms lamellae.

This type of placenta is consequently referred to as being ____

Answer 22

carnivores

zonary & lamellar

Question 23

*Classification of Placenta
A third classification scheme is based on the number of tissue layers separating the fetal and maternal circulations, thereby forming the ____

Answer 23

placental barrier

Question 24

*Classification of Placenta
There are always three fetal extraembryonic layers in the chorioallantoic placenta:

the ____ lining the allantoic blood vessels the ____ (connective tissue), originating from the fused somatic and visceral mesoderm the ____, i.e. the trophoblast

Answer 24

endothelium

chorioallantoic mesenchyme

chorionic epithelium

Question 25

*Classification of Placenta
However, the numbers of layers retained in the maternal portion of the placenta varies with species.

Before placentation, the endometrium presents three layers that could contribute to the placental barrier: ____

Answer 25

endometrial epithelium

connective tissue

vascular endothelium

Question 26

*Classification of Placenta
First, the epitheliochorial group.

This type of placentation is seen in ____ No destruction or invasion of the maternal tissues occurs and no layers are removed.

All 6 layers are intact.

Answer 26

pigs, horses and ruminants.

Question 27

*Classification of Placenta
The epitheliochorial placenta in what animal? is modified, some trophoblast cells fuse with some of the endometrial epithelial cells.

The placenta is referred to as ____

In some references, this placenta is classified as only having 5 intact layers.

Answer 27

ruminants

synepitheliochorial / syndesmochorial

Question 28

*Classification of Placenta
In what animal?, the placenta is endotheliochorial

The endometrial epithelium and connective tissue are lost during placentation, leaving the trophoblast (maternal endothelial cells). Endothelial cells are those found on the blood vessels.

There are only 4 intact layers.

Answer 28

carnivores

Question 29

*Classification of Placenta
This type is the most invasive placenta?

All maternal tissue layers disappear through erosion, leading to direct connection between the chorion and maternal blood.

This is seen in ____

Answer 29

Hemochorial placenta

rodents and humans

Question 30

*Classification of Placenta
Placentation can also be classified based of the fate of the endometrium.
____ - uterine endometrium is sloughed off during parturition. Species: carnivores, primates, rodents

____ - uterine endometrium remains intact during parturition. Species: ruminants (partial), horse and pig

Answer 30

Deciduate

Adeciduate