Anatomy Of Pregnancy: Components And Development Of The Mammalian Placenta

Question 1

What is the placenta

Answer 1

Fluid-filled, extra-embryonic/ foetal membranes

Question 2

Functions of placenta

Answer 2

1. Protect developing embryo / fetus
2. Provision of oxygen / nutrients from maternal circulation to foetus
3. Removal of metabolic waste products from foetus

Question 3

The placenta is composed of what 4 foetal membranes?

Answer 3

Yolk Sac
Amnion
Chorion
Allantois

Question 4

What happens to the foetal membranes of placenta at birth?

Answer 4

Shed at birth

Question 5

After fertilisation, blastocoele undergoes formation of… (the beginning of formation of placenta)

Answer 5

1. Bilaminar embryonic disc
2. Extra-embryonic membrane

Question 6

What does the bilaminar embryonic disc consist of?

Answer 6

Hypoblast= endoderm
Epiblast= embryonic ectoderm

Question 7

What does the extra-embryonic membrane consist of?

Answer 7

Hypoblast= endoderm
Trophoblast= extra-embryonic ectoderm/trophectoderm

Question 8

What happens to size of blastocoele and why?

Answer 8

Massive ^ in size due to fluid accumulation inside of it

Question 9

What are the functions of the blastocoele?

Answer 9

• Nutrition – diffusion across membranes
• Maternal recognition of pregnancy

Question 10

Describe what happens to blastocoele once it ^ in size (the process of formation of placenta)
(-blastocyst wall becomes…
-blastocoele is now called…
-what happens to mesoderm after *hint questions)

Answer 10

-A third layer called mesoderm extends from embryo & enters space between endoderm and trophectoderm
-blastocyst wall becomes trilaminar (trilaminar omphalopleure)
-blastocoele is now called yolk sac
-after this the mesoderm splits into 3 layers:
1. Somatopleure
2. Splanchnopleure
3. Extraembryonic coelem/ exocoelum
-embryo begins to sink into somatopleure
-sac folds around embryo, meets dorsally and fuses to form the Amniotic Sac/Amnion
-the rest of the somatopleure is now called the chorion
-yolk sac temporarily fuses with chorion to give chorio-vitelline ‘placenta’
-then the Allantois is formed- formed directly from the embryo
-as Allantois develops it pushes out into extra embryonic coelom-into space between 2 mesoderm & continues to develop and eventually fills the extraembryonic coelom
-Yolk sac regresses and is engulfed
-allantois fuses with chorion forming chorio-Allantoic placenta- the final form of placenta which is what is gonna be in contact with the endometrium of the mother
-remnants of yolk sac contained within the umbilical cord
-umbilical cord connects the foetus to placenta and allows exchange of material to happen

Question 11

What is the somatopleure layer of mesoderm a combination of?

Answer 11

Combo of external layers; trophectoderm + somatic mesoderm

Question 12

What is the splanchnopleure layer of mesoderm a combination of?

Answer 12

Combo of internal layers; endoderm + splanchnic mesoderm
Wall of yolk sac

Question 13

What is the exocoelum layer of mesoderm?

Answer 13

Resulting cavity between somatic + sphlanchnic mesoderm
Trilaminar

Question 14

What happens after yolk sac fully formed?

Answer 14

The formation of the amniotic sac begins

Question 15

What is the amniotic sac

Answer 15

-The next step of placenta formation
-surrounds embryo/foetus
-contains amniotic fluid and sometimes amniotic pustules (white spots & perfectly normal)

Question 16

What is the function of the amniotic fluid?

Answer 16

Shock absorption

Question 17

Describe the formation of the amniotic sac

Question 18

What does the temporary chorio-vitelline placenta allow for?

Answer 18

Easy diffusion

Question 19

What is the allantois?
Contains what?

Answer 19

Fluid filled structure formed directly from embryo/diverticulum of the hind gut
Contains fluids like urine, secretions & blood transudate

Question 20

What connects the foetus to the placenta at the end of placenta formation?

Answer 20

Umbilical cord

Question 21

What are chorionic villi
-function

Answer 21

Short projections found on surface of chorion
^ surface area for transfer of material

Question 22

Location of villi on placenta depends on…

Answer 22

Species

Question 23

What are the 4 types of placenta relative to location/spread of villi

Answer 23

Diffuse placenta—> overall whole of chorion
Cotyledonary placenta—> arranged in focal areas/patches
Zonary placenta—> in a band through centre of placenta
Discoid placenta—> disc shaped

Question 24

Which species has which type of villi placenta
-diffuse
-cotyledonary
-zonary
-discoid

Answer 24

1. Mare, sow
2. Ruminant
3. Carnivore
4. Human, monkey

Question 25

Histological classification- What are the 6 layers which material has to pass through for nutrient exchange (Another name for it is the epithelio-chorial placenta)

Answer 25

(3 maternal, 3 foetal) 1. Maternal endometrial endothelium 2. Maternal connective tissue 3. Maternal endometrial epithelium 4. Fetal chorion 5. Fetal connective tissue / mesoderm 6. Fetal endothelium (3&4 in direct contact due to vill)

Question 26

Which animals have the epithelio-chorial placenta?

Answer 26

Pig, mare & ruminant

Question 27

What is the non-deciduate placenta vs deciduate placenta?

Answer 27

Non- • Fetal chorion and endometrial epithelium separate after birth • Placenta expelled with no loss of maternal tissue Deciduate- there is a loss of maternal tissue

Question 28

What is the endothelio-chorial placenta?

Answer 28

Instead of the maternal epithelium being in contact with fetal chorion, The fetal chorion invades maternal tissue & is now in contact with the maternal endothelium

Question 29

What is an advantage/disadvantage of the endothelio-chorial placenta?

Answer 29

+ve; Allows transfer of large molecules -ve; more invasive; after birth when its shed it takes a little bit of maternal tissue with it

Question 30

Which species have the endothelio-chorial placenta?

Answer 30

Carnivores

Question 31

What are the 4 cellular layers of the endothelio-chorial placenta?

Answer 31

(1 maternal, 3 foetal) 1. Maternal endothelium 4. Fetal chorion 5. Fetal connective tissue / mesoderm 6. Fetal endothelium

Question 32

What is the haemochorial placenta? -which species have this type -deciduate or not? -advantage?

Answer 32

• Fetal tissue invades maternal tissue & erodes/destroys endothelium • Fetal chorion directly in contact with maternal circulating blood • Eg. Humans & monkey -very deciduate as very invasive • Transfer of large molecules

Question 33

What are the 3 cellular layers of the haemochorial placenta?

Answer 33

(0 maternal, 3 foetal) 4. Fetal chorion 5. Fetal connective tissue / mesoderm 6. Fetal endothelium

Question 34

Umbilical cord

Answer 34

Cord of communication between foetus and placenta

Question 35

Name the 4 components found in umbilical cord and the function of each

Answer 35

1/ Umbilical veins: • Carry oxygen & oxygenated blood & nutrients from chorioallantois to fetus • in Ruminants – paired (2 of em) • in Horse, carnivore, human - fused single vein 2/ Umbilical arteries: • Carry foetal waste products from fetus to chorioallantois • Paired 3/ Allantoic duct: -formed from developing bladder, maintains fluid within cavity • Drains urine from fetus into allantoic cavity 4/ Yolk-sac: • Remnant present – thought to have some haematopoietic function in some species but mostly non functional

Question 36

Implantation vs attachment- page 14 of 15 go over this again

Question 37

What is marginal haematomas?

Answer 37

Areas where blood has collected due to destruction of blood vessels. Marginal means it has specifically developed along the periphery of a specific tissue.

Question 38

Whereabouts does marginal haematomas occur in a bitches uterus?

Answer 38

Along periphery of the zonary band

Question 39

What are some reasons/applications of US in the bitch

Answer 39

• Pregnancy detection • Counting foetuses! • Foetalviability • Gestational age/ date of whelping

Question 40

At what day is foetal anatomy in a bitch identifiable on an US

Answer 40

Day 35

Question 41

Around what time can radiogrpahies be used for pregnancy detection in bitches

Answer 41

After day 42

Question 42

What is a radiography used for in pregnancy detections in a bitch?

Answer 42

Foetal numbers-count skulls Difficult to assess viability/gestational age