ANATOMY - Placenta Development

Question 1

What are the functions of the placenta?

Answer 1

Protection of the foetus
Provision of maternal oxygen and nutrients
Removal of foetal metabolic waste products

Question 2

What are the four foetal membranes which make up the placenta?

Answer 2

Yolk sac
Amnion
Allantois
Chorion

Question 3

Describe the formation of the amnion from the somatopleure

Answer 3

As the embryo begins to sink into the somatopleure, the folds of the somatopleure meet dorsally and fuse to form the amnion

Question 4

When the amnion has formed, what is the somatopleure now known as?

Answer 4

When the amnion has developed, the somatopleure is known as the chorion

Question 5

What is contained within the amnion?

Answer 5

Suspended foetus
Amniotic fluid

Question 6

What is the main function of the amnion?

Answer 6

The main function of the amnion is shock absorption and thus protection of the developing foetus

Question 7

What are amniotic pustules?

Answer 7

Amniotic pustules are glycogen accumulations that appear as white spots on the surface of the ruminant amnion

Question 8

What is the chorio-vitelline placenta?

Answer 8

The chorio-vitelline placenta is the temporary fusion of the yolk sac with the chorion to allow the diffusion of nutrients during development

Question 9

What is the allantois?

Answer 9

The allantois is an extra-embryonic diverticulum of the hindgut

Question 10

What is the main function of the allantois?

Answer 10

Collects foetal metabolic waste products such as urine, secretions and blood transudate

Question 11

What is the chorio-allantoic placenta?

Answer 11

The chorion-allantoic placenta is the final form of the placenta formed by the fusion of the allantois with the chorion

Question 12

What is the function of chorionic villi?

Answer 12

Chorionic villi increase the surface area of the chorion to increase nutrient absorption from the maternal endometrium

Question 13

What are the four possible distributions of chorionic villi on the placenta?

Answer 13

Diffuse
Cotyledonary
Zonary
Discoid

Question 14

What are cotyledons and caruncles?

Answer 14

Cotyledons: regions of chorionic villi on the foetal chorion
Caruncles: structures on the endometrium which interdigitate with the cotyledons

Question 15

What are placentomes?

Answer 15

Placentomes are the interdigination of the foetal cotyledons and the endometrial caruncles

Question 16

Which species have placentomes?

Answer 16

Ruminants

Question 17

What is the difference between placental and paraplacental?

Answer 17

Placental: regions of the placenta covered in chorionic villi
Paraplacental: regions of the placenta with no chorionic villi

Question 18

What is the name for the paraplacental regions which have no vasculature as well as no chorionic villi?

Answer 18

Avascular extremity

Question 19

What is an epithelio-chorial placenta?

Answer 19

An epithelio-chorial placenta is when there is direct contact between the foetal chorion and the maternal endometrial epithelium

Question 20

What are the six histological layers of an epithelio-chorial placenta?

Answer 20

1. Maternal endometrial endothelium
2. Maternal connective tissue
3. Maternal endometrial epithelium
4. Foetal chorion
5. Foetal mesoderm
6. Foetal endothelium

Question 21

What is an endothelio-chorial placenta?

Answer 21

An endothelio-chorial placenta is when the foetal chorion invades the maternal tissue and makes direct contact with the maternal endometrial endothelium

Question 22

What are the four histological layers of an endothelio-chorial placenta?

Answer 22

1. Maternal endometrial endothelium
2. Foetal chorion
3. Foetal mesoderm
4. Foetal endothelium

Question 23

What is a haemochorial placenta?

Answer 23

A haemochorial placenta is when the foetal chorion invades the maternal tissue and erodes the maternal endometrial endothelium

Question 24

What are the three histological layers of an haemochorial placenta?

Answer 24

1. Foetal chorion
2. Foetal mesoderm
3. Foetal endothelium

Question 25

What is a non-deciduate placenta?

Answer 25

A non-deciduate placenta is when the foetal chorion and the endometrium have a clean separation after birth with no loss of maternal tissue

Question 26

What is a deciduate placenta?

Answer 26

A deciduate placenta is when the foetal chorion has invaded the endometrium leading to a loss of maternal tissue when the placenta separates from the endometrium after birth

Question 27

Which type of placenta is found in the sow?

Answer 27

Diffuse, epithelio-chorial, non-deciduate placenta

Question 28

What is synchorial fusion?

Answer 28

Synchorial fusion is the fusion of the paraplacental zones of adjacent foetuses via the avascular extremities

Question 29

In which species does synchorial fusion occur?

Answer 29

Sow (Porcine) Ewe (Ovine)

Question 30

What type of placenta is found in the ewe?

Answer 30

Cotyledonary, epithelio-chorial, non-deciduate placenta

Question 31

What is the shape of the caruncles of the ewe?

Answer 31

Convex caruncles

Question 32

Why is there a much higher incidence of twins in the ewe than in the cow?

Answer 32

Transuterine migration allowing the twin embryos to migrate and each develop in different uterine horns

Question 33

Why is there no risk of freemartins twin pregnancies in the ewe?

Answer 33

Synchorial fusion prevents anastomoses of the blood vessels, preventing the exposure of masculinising hormones to the female twin

Question 34

What type of placenta is found in the cow?

Answer 34

Cotyledonary, epithelio-chorial, non-deciduate placenta

Question 35

What is the shape of the caruncles of the cow?

Answer 35

Concave caruncles

Question 36

What type of placenta is found in the mare?

Answer 36

Diffuse, epithelio-chorial non-deciduate placenta

Question 37

Why and how does the chorio-allantois expand into the second uterine horn during pregnancy in the mare?

Answer 37

The mare uterus has no septum allowing the chorio-allantois to expand into the second uterine horn. This is done to increase the surface area for oxygen and nutrient absorption

Question 38

What are microcotelydons?

Answer 38

Microcotelydons are microvillous tufts found on the foetal chorion of the horse

Question 39

What are hippomanes?

Answer 39

Hippomanes are aggregates of allantoic calculus often shed after partuition in the mare

Question 40

What type of placenta is found in the bitch?

Answer 40

Zonary, endothelio-chorial, deciduate placenta

Question 41

What are marginal hematomas found in the bitch placenta?

Answer 41

Marginal haematomas are areas of maternal blood vessel destruction which develop along the periphery of the zonary band

Question 42

Why do marginal haematomas often appear green in the bitch placenta?

Answer 42

Uteroverdin (blood breakdown products) can cause the marginal haematomas to appear green

Question 43

What colour can the marginal haematomas appear in cats compared to dogs?

Answer 43

Marginal haematomas can appear brown in the queen placenta whereas they can appear green in the bitch placenta

Question 44

What are the four structures which run through the umbilical cord?

Answer 44

Umbilical veins Umbilical arteries Allantoic duct Remnant of the yolk sac

Question 45

What is the function of the umbilical veins?

Answer 45

The umbilical veins carry oxygen and nutrients from the maternal circulation into the foetus

Question 46

(T/F) The umbilical vein is a fused single vein in all of the domestic species

Answer 46

FALSE. The umbilical vein is paired in the ruminant

Question 47

What is the function of the umbilical arteries?

Answer 47

The umbilical arteries carry metabolic waste products within the foetal blood into the maternal circulation

Question 48

What is the function of the allantoic duct?

Answer 48

The allantoic duct is continuous from the developing bladder and runs through the umbilical cord into the allantoic cavity to drain foetal urine

Question 49

What is the function of the yolk sac remnant found in the umbilical cord?

Answer 49

In most species the remnant of the yolk sac is non functional but can have haemopoietic functions in the dog

Question 50

What is the difference between foetal implantation and foetal attachment?

Answer 50

Foetal implantation is the invasive burrowing of the foetus into the endometrium which only occurs in human pregnancies. Foetal attachment is what occurs in domestic animal pregnancies and can vary in its degree of invasiveness depending on the species