ANATOMY - Placenta Development Flashcards
What are the functions of the placenta?
Protection of the foetus
Provision of maternal oxygen and nutrients
Removal of foetal metabolic waste products
What are the four foetal membranes which make up the placenta?
Yolk sac
Amnion
Allantois
Chorion
Describe the formation of the amnion from the somatopleure
As the embryo begins to sink into the somatopleure, the folds of the somatopleure meet dorsally and fuse to form the amnion
When the amnion has formed, what is the somatopleure now known as?
When the amnion has developed, the somatopleure is known as the chorion
What is contained within the amnion?
Suspended foetus
Amniotic fluid
What is the main function of the amnion?
The main function of the amnion is shock absorption and thus protection of the developing foetus
What are amniotic pustules?
Amniotic pustules are glycogen accumulations that appear as white spots on the surface of the ruminant amnion
What is the chorio-vitelline placenta?
The chorio-vitelline placenta is the temporary fusion of the yolk sac with the chorion to allow the diffusion of nutrients during development
What is the allantois?
The allantois is an extra-embryonic diverticulum of the hindgut
What is the main function of the allantois?
Collects foetal metabolic waste products such as urine, secretions and blood transudate
What is the chorio-allantoic placenta?
The chorion-allantoic placenta is the final form of the placenta formed by the fusion of the allantois with the chorion
What is the function of chorionic villi?
Chorionic villi increase the surface area of the chorion to increase nutrient absorption from the maternal endometrium
What are the four possible distributions of chorionic villi on the placenta?
Diffuse
Cotyledonary
Zonary
Discoid
What are cotyledons and caruncles?
Cotyledons: regions of chorionic villi on the foetal chorion
Caruncles: structures on the endometrium which interdigitate with the cotyledons
What are placentomes?
Placentomes are the interdigination of the foetal cotyledons and the endometrial caruncles
Which species have placentomes?
Ruminants
What is the difference between placental and paraplacental?
Placental: regions of the placenta covered in chorionic villi
Paraplacental: regions of the placenta with no chorionic villi
What is the name for the paraplacental regions which have no vasculature as well as no chorionic villi?
Avascular extremity
What is an epithelio-chorial placenta?
An epithelio-chorial placenta is when there is direct contact between the foetal chorion and the maternal endometrial epithelium
What are the six histological layers of an epithelio-chorial placenta?
- Maternal endometrial endothelium
- Maternal connective tissue
- Maternal endometrial epithelium
- Foetal chorion
- Foetal mesoderm
- Foetal endothelium
What is an endothelio-chorial placenta?
An endothelio-chorial placenta is when the foetal chorion invades the maternal tissue and makes direct contact with the maternal endometrial endothelium
What are the four histological layers of an endothelio-chorial placenta?
- Maternal endometrial endothelium
- Foetal chorion
- Foetal mesoderm
- Foetal endothelium
What is a haemochorial placenta?
A haemochorial placenta is when the foetal chorion invades the maternal tissue and erodes the maternal endometrial endothelium
What are the three histological layers of an haemochorial placenta?
- Foetal chorion
- Foetal mesoderm
- Foetal endothelium
What is a non-deciduate placenta?
A non-deciduate placenta is when the foetal chorion and the endometrium have a clean separation after birth with no loss of maternal tissue
What is a deciduate placenta?
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
Which type of placenta is found in the sow?
Diffuse, epithelio-chorial, non-deciduate placenta
What is synchorial fusion?
Synchorial fusion is the fusion of the paraplacental zones of adjacent foetuses via the avascular extremities
In which species does synchorial fusion occur?
Sow (Porcine)
Ewe (Ovine)
What type of placenta is found in the ewe?
Cotyledonary, epithelio-chorial, non-deciduate placenta
What is the shape of the caruncles of the ewe?
Convex caruncles
Why is there a much higher incidence of twins in the ewe than in the cow?
Transuterine migration allowing the twin embryos to migrate and each develop in different uterine horns
Why is there no risk of freemartins twin pregnancies in the ewe?
Synchorial fusion prevents anastomoses of the blood vessels, preventing the exposure of masculinising hormones to the female twin
What type of placenta is found in the cow?
Cotyledonary, epithelio-chorial, non-deciduate placenta
What is the shape of the caruncles of the cow?
Concave caruncles
What type of placenta is found in the mare?
Diffuse, epithelio-chorial non-deciduate placenta
Why and how does the chorio-allantois expand into the second uterine horn during pregnancy in the mare?
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
What are microcotelydons?
Microcotelydons are microvillous tufts found on the foetal chorion of the horse
What are hippomanes?
Hippomanes are aggregates of allantoic calculus often shed after partuition in the mare
What type of placenta is found in the bitch?
Zonary, endothelio-chorial, deciduate placenta
What are marginal hematomas found in the bitch placenta?
Marginal haematomas are areas of maternal blood vessel destruction which develop along the periphery of the zonary band
Why do marginal haematomas often appear green in the bitch placenta?
Uteroverdin (blood breakdown products) can cause the marginal haematomas to appear green
What colour can the marginal haematomas appear in cats compared to dogs?
Marginal haematomas can appear brown in the queen placenta whereas they can appear green in the bitch placenta
What are the four structures which run through the umbilical cord?
Umbilical veins
Umbilical arteries
Allantoic duct
Remnant of the yolk sac
What is the function of the umbilical veins?
The umbilical veins carry oxygen and nutrients from the maternal circulation into the foetus
(T/F) The umbilical vein is a fused single vein in all of the domestic species
FALSE. The umbilical vein is paired in the ruminant
What is the function of the umbilical arteries?
The umbilical arteries carry metabolic waste products within the foetal blood into the maternal circulation
What is the function of the allantoic duct?
The allantoic duct is continuous from the developing bladder and runs through the umbilical cord into the allantoic cavity to drain foetal urine
What is the function of the yolk sac remnant found in the umbilical cord?
In most species the remnant of the yolk sac is non functional but can have haemopoietic functions in the dog
What is the difference between foetal implantation and foetal attachment?
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
