Anatomy Of Pregnancy: Components And Development Of The Mammalian Placenta Flashcards
What is the placenta
Fluid-filled, extra-embryonic/ foetal membranes
Functions of placenta
- Protect developing embryo / fetus
- Provision of oxygen / nutrients from maternal circulation to foetus
- Removal of metabolic waste products from foetus
The placenta is composed of what 4 foetal membranes?
Yolk Sac
Amnion
Chorion
Allantois
What happens to the foetal membranes of placenta at birth?
Shed at birth
After fertilisation, blastocoele undergoes formation of… (the beginning of formation of placenta)
- Bilaminar embryonic disc
- Extra-embryonic membrane
What does the bilaminar embryonic disc consist of?
Hypoblast= endoderm
Epiblast= embryonic ectoderm
What does the extra-embryonic membrane consist of?
Hypoblast= endoderm
Trophoblast= extra-embryonic ectoderm/trophectoderm
What happens to size of blastocoele and why?
Massive ^ in size due to fluid accumulation inside of it
What are the functions of the blastocoele?
• Nutrition – diffusion across membranes
• Maternal recognition of pregnancy
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)
-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
What is the somatopleure layer of mesoderm a combination of?
Combo of external layers; trophectoderm + somatic mesoderm
What is the splanchnopleure layer of mesoderm a combination of?
Combo of internal layers; endoderm + splanchnic mesoderm
Wall of yolk sac
What is the exocoelum layer of mesoderm?
Resulting cavity between somatic + sphlanchnic mesoderm
Trilaminar
What happens after yolk sac fully formed?
The formation of the amniotic sac begins
What is the amniotic sac
-The next step of placenta formation
-surrounds embryo/foetus
-contains amniotic fluid and sometimes amniotic pustules (white spots & perfectly normal)
What is the function of the amniotic fluid?
Shock absorption
Describe the formation of the amniotic sac
What does the temporary chorio-vitelline placenta allow for?
Easy diffusion
What is the allantois?
Contains what?
Fluid filled structure formed directly from embryo/diverticulum of the hind gut
Contains fluids like urine, secretions & blood transudate
What connects the foetus to the placenta at the end of placenta formation?
Umbilical cord
What are chorionic villi
-function
Short projections found on surface of chorion
^ surface area for transfer of material
Location of villi on placenta depends on…
Species
What are the 4 types of placenta relative to location/spread of villi
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
Which species has which type of villi placenta
-diffuse
-cotyledonary
-zonary
-discoid
- Mare, sow
- Ruminant
- Carnivore
- Human, monkey
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)
(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)
Which animals have the epithelio-chorial placenta?
Pig, mare & ruminant
What is the non-deciduate placenta vs deciduate placenta?
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
What is the endothelio-chorial placenta?
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
What is an advantage/disadvantage of the endothelio-chorial placenta?
+ve; Allows transfer of large molecules
-ve; more invasive; after birth when its shed it takes a little bit of maternal tissue with it
Which species have the endothelio-chorial placenta?
Carnivores
What are the 4 cellular layers of the endothelio-chorial placenta?
(1 maternal, 3 foetal) 1. Maternal endothelium
4. Fetal chorion
5. Fetal connective tissue / mesoderm
6. Fetal endothelium
What is the haemochorial placenta?
-which species have this type
-deciduate or not?
-advantage?
• 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
What are the 3 cellular layers of the haemochorial placenta?
(0 maternal, 3 foetal)
4. Fetal chorion
5. Fetal connective tissue / mesoderm
6. Fetal endothelium
Umbilical cord
Cord of communication between foetus and placenta
Name the 4 components found in umbilical cord and the function of each
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
Implantation vs attachment- page 14 of 15 go over this again
What is marginal haematomas?
Areas where blood has collected due to destruction of blood vessels. Marginal means it has specifically developed along the periphery of a specific tissue.
Whereabouts does marginal haematomas occur in a bitches uterus?
Along periphery of the zonary band
What are some reasons/applications of US in the bitch
• Pregnancy detection
• Counting foetuses!
• Foetalviability
• Gestational age/ date of whelping
At what day is foetal anatomy in a bitch identifiable on an US
Day 35
Around what time can radiogrpahies be used for pregnancy detection in bitches
After day 42
What is a radiography used for in pregnancy detections in a bitch?
Foetal numbers-count skulls
Difficult to assess viability/gestational age
