Lecture 11: Placentation (Kelleman) Flashcards
mammalian type: metatherian
- they do not have a true placenta - they have a “choriovitelline placenta” aka vascularized yolk sac.
- examples: marsupials - kangaroo and opossum
mammalian type: prototherian group
- egg-laying mammals.
- examples: platypus echidnas
- they do not have a placenta
mammalian type: eutherian
- possess a chorioallantoic placenta (aka the “true” placenta)
- most mammals you think of - dog, cat, horse, etc.
placenta
vascular organ formed in uterus during pregnancy, consisting of BOTH maternal and embryonic/fetal tissues. It provides oxygen and nutrients for fetus and transfers waste products from the fetal to the maternal blood circulation.
fetal membranes
membranes that function for the protection or nourishment or respiration or excretion of a developing fetus
what day does implantation (attachment of the placenta to the uterus) occur in the cow?
day 30 -35
what day does implantation (attachment of the placenta to the uterus) occur in the sow?
day 12 - 20
what day does implantation (attachment of the placenta to the uterus) occur in the ewe?
day 18 - 20
what day does implantation (attachment of the placenta to the uterus) occur in the mare?
day 50 - 60
what is the meaning of the latin root of the word “placenta?”
latin root of placenta = “cake”
Name 5 roles of the placenta
- nutrient exchange
- gas exchange
- stores waste
- protection
- endocrine organ
What are the 4 Fetal Membranes that make up the placenta and what are their functions?
- yolk sac - early nutrition
- amnion - nutrient exchange, protection, waste
- allantois - waste, gas exchange
- chorion - maternal interface, nutrient exchange
How are placentas classified? (3 classifications)
- distribution of contact areas
- tissue layers separating maternal and fetal blood
- maternal tissue lost at birth
what are the 4 different types of choionic villi (a contact area between fetus and mom)
- diffuse
- cotyledonary
- zonary
- discoid
what are the characteristics of a diffuse placenta?
maternal and fetal intimate contact is found throughout the placenta
characteristics of the cotyledonary type placenta
specialized areas of the endometrium (caruncles) are in contact with vascularized portions of the chorion (cotyledon). the combined structural unit of the fetal cotyledon with the maternal caruncle is called the placentome.
what makes up a placentome?
caruncle (maternal side) + cotyledon (fetal chorion) = placentome
characteristics of the zonary placenta
the most intimate contact is found in a “belt-like” area encircling the conceptus
describe the characteristics of the discoid placenta
the itneraction is found in one or two round areas
6 layers separating maternal and fetal circulation - starting from most internal fetal side to most internal maternal side?
- endothelium
- connective tissue
- epithelium
- —————— - epithelium
- connective tissue
- endothelium
which layer is missing in a 5 layered placenta?
the maternal epithelium
what are the missing layers in a 4-layered placenta?
the maternal epithelium and maternal connective tissue
what are the missing layers in a 3-layered placenta?
all maternal layers - the maternal epithelium, maternal connective tissue and maternal endothelium
what is the term for a 3-layered placenta?
hemochorial
what is the term for a 4-5 layered placenta?
endotheliochorial
what is the term for a 5-6 layered placenta?
bonus Q: what is the old term for this?
synepitheliochorial
old term = syndesmochorial
what is the term for a 6-layered placenta?
epitheliochorial
epitheliochorial
is a 6 layered placenta.
But it is also used as a sort of all-encompassing description for a placenta that is either 5 or 6 layers.
characteristics of an epitheliochorial placenta and animals that have it
- the chorion is apposed to (next to/touching) the maternal epithelium. it is the least invasive of the types.
- mare, sow, hembra (camelids)
characteristics of a synepitheliochorial placenta and animals that have it
- partial and transient erosions of the endometrium allowing for some areas of fusion. these areas are known as a syncytium.
- they also have binucleate cells that are chorionic in origin. they fuse with the maternal epithelium and release placental lactogen
- ruminant species - cattle, sheep
characteristics of an endotheliochorial placenta and animals that have it
- the fetal trophoblast cells invade down to the maternal vasculature endothelium. thus the trophoblast invaded through the maternal epithelium and a layer of connective tissue.
- carnivores (dogs and cats)
characteristics of hemochorial placenta (degree of invasion) and animals that have it
- most invasive type of placenta. the fetal trophoblast invades through all 3 maternal layers and is in contact with the maternal blood.
- it can be further classified as hemomonochorial, hemodichorial or hemotrichorial
- primates, rodents
Maternal tissue lost at birth: two terms and their definitions
- non-deciducate or adeciduate = non-invasive
2. deciduate = endometrial loss
non-deciduate / adeciduate definition and animals that have it
complete separation of maternal and fetal tissues
- sow, mare, hembra +/- ruminant
Name the 4 different classifications of “degree of invasion”
- epitheliochorial
- syndesmochorial
- endotheliochorial
- hemochorial
why can’t you have twins in horses?
a horse has a diffuse, epitheliohcorial placenta, but can’t have diffuse attachment of two embryos because there are limited points of attachment. two fetuses developing side by side end up competing for the same nutrients and eventually starve.
- this happens in camelids too.
- but it dosn’t happen with other animals that have diffuse placentas
putting it all together: what type of placenta do horses have?
diffuse, epitheliochorial placenta
- non-deciduate
- microcotyledonary
putting it all together: what type of placenta do ruminants have?
cotyledonary, syneptheliochorial, non-deciduate
what shape are cow and giraffe caruncles?
convex
what shape are sheep and goat caruncles?
concave
goats live in caves!
membrane slip in cows
connective tissue that serve as points of attachment between placentomes. when you palpate the uterus, you can feel the membrane literally slip between your fingers early in pregnancy.
putting it all together: what type of placenta do carnivores have?
zonary, endotheliochorial, deciduate
Things to be aware of on maternal side of placenta in canines:
- marginal hematomas
- stagnant maternal blood
- high level of iron
- hemoglobin is converted to green uteroverdin at parturition
why are some puppies born green?
hemoglobin is converted to green uteroverdin at parturition by oxidation.
what type of placenta do primates and rodents have?
discoid, hemochordial, deciduate
what is unique about the discoid placenta?
its the only placenta type that is safe for amniocentesis. if you poke through the chorion in any other placenta you can traumatize placenta and compromise foal
