Wk 9 Placenta General&Specific Flashcards
The placenta
The placenta is a collection of extra-embryonic membranes (tissue) of fetal origin
- Of fetal origin, not maternal origin
The plancenta attaches to the uterine endometrium, and is involved in:
- Metabolic exchange between dam and fetus
- Endocrine regulation via hormone
production
Origin of placenta
The placenta initially develops from 2 unique layers in the hatched blast:
- Trophectoderm
- mesoderm
There is also a yolk sac developed from the primitive endoderm, and the allantois derived from the primitive gut
Note: amnionic cavity present Note: each fetus has own placenta (because placenta develops from blastocyst)
Placenta tissue layers
In a fully formed placenta, there are 3 major layers:
- amnion
closest to the fetus, amniotic vesicle/cavity
- allantois
middle layer (inner side of exterior membrane)
- chorion
outer layer (outer side of exterior membrane) In domestic species, the chorion and allantois eventually fuse, forming one double-layer membrane, the chorioallantois
Dog:
“Green
grass” is
the area of
exchange = fetal interface (part of chorioallantois)
Cattle: Amniotic vessel = feel for it, diagnose for pregnancy.
Tight junctions and sodium pump activation cause water to diffuse into the embryo, creating a blastocoele (a cavity filling with fluid) in the early blastocyst (5-12 days post fert)
Timing of embryonic stages
The amnion
The amnion is the layer closest to the fetus, forming the amniotic vesicle
- very thin, clear membrane
- formed by invagination of mesoderm +
trophectoderm
- membrane secretes amniotic fluid to cushion fetus
- umbilicus passes through this membrane
- amniotic plaques often present (inside surface) –
similar structure to skin, but function unknown
The yolk sac
The yolk sac is the most primitive membrane – very important in fish, reptiles and birds, but less so in mammals
- In mammals: transient structure, regresses during early gestation
- Source of primordial germ cells, involved in haematopoiesis, vasculogenesis,
nutrient/gas exchange
The chorioallantois
Allantois
- Originates from primitive hindgut
- Fetal fluid waste collects in the allantoic cavity
- Grows significantly in size and often fuses completely with the chorion
Chorion
- Outermost layer, direct contact with maternal endometrium
- Calcification deposits on surface common
The maternal fetal interface - what is on the surface of the chorion?
The chorion is covered in chorionic villi – small projections, creating attachment to the endometrium
Placentae can be classified by their distribution of villi:
Chorionic villi are the site of exchnage between fetal + maternal circulation
The umbilicus - how many a. and v. are present?
- which is oxy and which is deoxy
1 umbilical vein (oxy) = 2 umbilical arteries (deoxy)
Left = amniotic cavity
Inside the amnion = contains urachus (i.e. start of allantois)
Outside amnion = no urachus (because in allantoic cavity)
The umbilical vessels connect to the chorionic villi, where gas/nutrient exchnages occurs
Amniocentesis is the sampling fluid from the amniotic cavity with a needle for diagnostic testing.
Which fetal membranes would you pass through to perform an amniocentesis?
C
Metabolic functions of the placenta
- Transports gases, nutrients and waste products between foetal and maternal circulation
- Provides oxygen and nutrients from maternal circulation
- Actively converts substrates to create foetal nutrients
Removes CO2 and waste products to maternal circulation
Endocrine functions of placenta
- CL lifespan is prolonged = higher levels of P4 (progesterone block)
- CL usually lasts the whole pregnancy, but in some species the placenta takes over the major P4 production source.
- In cows: the placental takeover of P4 is very late (1 mo out of birth)
Important for abotion:
To induce abortion, take away source of progesterone (either placenta or CL as well depending on species)
In those species with no placental takeover, gestation tends to be shorter. P4 concentrations can vary significantly over gestation, but remain high
Late in gestation, the placenta starts converting P4 to E2 – critical trigger for parturition
The plancental gonadotropins for humans and equine
Only the human/primate and equine placentas produce gonadotropins, named appropriately
Human chorionic gonadotropin
- Secreted from hatched blastocyst onwards
- Luteotropic – increases P4 production by existing CL
- Commonly used to induce ovulation
Equine chorioninc gonadotropin (eCG) aka pregnant mare serum gonadotropin (PMSG)
- Luteotropic – increases P4 production by existing CL
- Also causes additional ovulations to create accessory CLs
- Commonly used to stimulate follicle growth (superovulation)
Other placental endocrine productions
Placental lactogen & relaxin & pregnancy associated glycoproteins (PAGs)
Cotyledons (placentomes
points of attachment to the maternal interface (uterine endometrium)
Which foetal membranes would you pass through to perform an amniocentesis?
A) allantois
B) chorion and amnion
C) chorion, allantois, amnion
D) allantois and amnion
E) chorioallantois
- Chorion, allantois and amnion
Amnion is closest to feotus, so have to pass through all layers to get to it
Metabolic functions of the placenta:
- Transports gases, nutrients and waste products between foetal and maternal circulation
- Provides oxygen and nutrients from maternal circulation
- Actively converts substrates to create foetal nutrients
Removes CO2 and waste products to maternal circulation
What is one of the most critical role of the placenta that acts as the ‘lung’
- Plays a critical role as the foetal lung
- O2/CO2 Gas exchange occurs through passive diffusion
Chorionic villi have a large surface area to facilitate this
- O2/CO2 Gas exchange occurs through passive diffusion
Endocrine functions of the placenta: what happens after maternal recognition of pregnancy in terms of placenta and CL and P4 production?
- CL lifespan is prolonged = higher levels of P4 (progesterone block)
- CL usually lasts the whole pregnancy, but in some species the placenta takes over the major P4 production source.
- In cows: the placental takeover of P4 is very late (1 mo out of birth)
Important component for abortion - do we have to get rid of the CL or the placenta as well?
What species does the placenta take over majority of P4 production in?
- Cow, ewe and mare (occurs late in the cow though)
- Sow, bitch and queen do not have placental takeover
What hormones do the placenta produce?
- P4
- E2
- Lactogen
- Relaxin
PAGs
Placental lactogen:
- What is the role
What species is it most prominent in
- Ruminants
- Similar to growth hormone
- Promotes foetal growth
Stimulates maternal mammary gland development
Relaxin in placental origin:
What is its role
- Mare, sow, bitch and queen
- Causes softening of pelvic ligaments for birth
Used for pregnancy diagnosis in bitch
The umbilicus - how many veins and arteries are in this? Which one carries oxygenated and which carries deoxygenated blood?
- 1 umbilical vein and 2 umbilical arteries
Vein carries oxygenated blood and arteries carry deoxygenated blood… Backwards to other body parts
What species has a cotyledonary placenta?
- Cow and ewe
What species have a diffuse placenta
- Mare and sow
What species have a discord placenta
- Primate, human, rodent
4 types of placenta:
- Diffuse
- Even distribution of villi across entire chorionic surface
- Cotylendonary
- Discrete round patches of villi form cotyledons on the chorion
- Connect to endometrial caruncles
- Zonary
- Prominent round transfer zone of villi as a central band
- Edges of band form pigmental zone containing haemorrhage and necrotic tissue
- Discoid
Discrete disc of villi on one side
Type of placenta?
- Zonary placenta
Queen or bitch
What type of placenta is this
- Multicotyledonary
Cow species
Classifying placenta by their invasiveness (how many tissue layers there are between foetal and maternal circulation)
What are the 3 classifications of placenta invasiveness
- Epitheliochorial
- Endotheliochorial
Haemochorial
What is epitheliochorial placenta
- Ruminants, mare, sow
6 layers: have to pass 3 layers of foetal and 3 layers of maternal epithelium
What is the endotheliochorial placenta
- 5 layers - 3 foetal layers and only 2 maternal layers
Carnivores - dogs and cats
Most invasive placenta: the haemochorial placenta
- Lost all maternal epithelial layers
- 3 layers of foetal epithelium
Haemochorial = blood = maternal blood supply empties into it and thus very efficient transfer from maternal to foetal
Separation of circulation from maternal to foetal circulation:
- Do the maternal and foetal bloods mix?
Why would this be an issue?
- Foetal and maternal blood NEVER directly mix
- If foetal blood gets into maternal circulation it is treated as a foreign antigen…
Can lead to sensitisation and downstream issues for offspring
Placentation - cattle
- what is there placenta classification
Unique features of cow
- Epitheliochorial
- Cotyledonary
Unique features: convex caruncles
Placentation - sheep (ewe)
- Classification
Unique features
- Cotyledonary
- Epitheliochorial
Unique features:
- Concave caruncles - where the point of attachment is
Look like little donughts
Placentation - horse (mare)
- Placenta classification
Unique features (cups)
- Diffuse placenta
- Epitheliochorial
- Unique features:
- F shaped placenta*
- Microcotyledons (microscopic)
- Endometrial cups:*
○ Placental cells which invade into the endometrium , there for about first 150 days of pregnancy
Equine gonadotropin (eCG)
Placentation - pig (sow)
- Placenta classification
Unique features
- Diffuse
- Epitheliochorial placenta
Unique features:
- Simple villi and smooth surface
Placentation dog
- Placenta classificaation
Unique features
- Zonary placenta
- Endotheliochorial
Unique features
* Prominent Marginal band of haematoma
Remainder of chorioallantois relatively avascular
Placentation - cat
- Placenta classification
Unique features
- Zonary
- Endotheliochorial
Unique features:
* Relatively small marginal band of haematoma
Remainder of chorioallantois relatively avascular
Which species have an epitheliochorial placenta:
- Equids, suids and ruminants
What are the 4 transport mechanisms that control movement of molecules across the placenta?
Everything has to cross the placenta to get to the foetus..
- Active transport
- Via specific transport proteins, requires ATP
- Facilitated transport
- Specific transport proteins
- Passive diffusion
Endocytosis
what makes up the placentome
- maternal caruncle and foetal cotylendon = placentome
