Implantation and placentation

define placenta formation

• foetal membranes becoming closely attached to the uterine wall to facilitate physiological exchange of gases, nutrients and waste products

what is the amnion?

• the innermost fluid filled membrane

what is the function of the amnion?

• allows symmetrical growth + foetus protection

• temperature control and foetal movement

what is the function of the the yolk sac in:

1. reptiles and birds

2. marsupials

3. higher mammals

1. surrounds the yolk

2. becomes the definitive placenta

3. nutritional role in early pregnancy

what does the allantois come from

• hind gut

what does the allantois become?

• connection with the umbilical cord

what does the chorion become?

• foetal contribution to placenta

what are all placentas at some stage of development?

• chorionic

what are the 3 stages of implantation

1. apposition

2. adhesion

3. attachment or invasion

what does apposition mean?

• blastocyst or foetal membrane become closely apposed during uterine lining

what is adhesion?

• a biochemical interaction b/w trophoblast and epithelium

what determiens whether a placenta is attached or implanted?

• whether it invades the trophoblasts or not

What type of implantation is this?

• non-invasive

What type of implantation is this?

• invasive

what inhibits trophoblast attachment to the endothelium?

• MUC1

what are the 5 groups of classification of placental structure

1. foetal extraembryonic membranes

2. source of nutrition

3. maternal tissue shed with foetus at parturition

4. histological structure

5. macroscopic: nutrient exchange area

what is involved in foetal extraembryonic membrane placenta classification?

whether it’s

• chorionic

• yolk sac

• allantoic in origin

what are the 2 sources of nutriton of a placenta

1. hemotrophic

2. histotrophic

what is a hemotrophic placenta?

• gets its nutrition from the endometrium

what is a hemotrophic source of placental nutrition?

• nutrition from circulating maternal blood

what do we classify a placenta as in terms to the maternal tissue shed?

• deciduate vs non-deciduate

what are the 3 possible foetal tissue layers b/w mother and foetal circulation

1. endothelium

2. connective tissue

3. trophoblast

what are the 3 possible maternal layers in histological classification of the placenta?

• epithelium

• connective tissue

• endothelium

Describe this histological classification of the placenta

• epitheliochorial

  • 3 foetal layers: endothelium, connective and trophoblast

  • 3 maternal layers: epithelial, connective and endothelial

Identify this placental histological classification

• epitheliochorial

State the classification of this placenta

• endotheliochorial

describe this histological structure of the placenta

Endotheliochorial:

• 3 foetal layers: endothelial, connective, endothelial

• 1 maternal: endothelial

Describe what this placental hitsological classification is

Haemochorial

• 3 embryonic layers: endothelial, connective and trophoblast

• 0 maternal layers

identify thsi placental classification

• haemochorial

what are the 4 types of macroscopic chorionic villi distributions

1. diffuse

2. cotyledonary

3. zonary

4. discoid

what species has diffuse chorionic villi?

• sow

• mare

what species has cotyledonary chorionic villi

• cow and ewe

what species has zonary chorionic villi

• bitch

  • queen

what species has discoid chorionic villi

• primates

what are chorionic villi

• areas of nutrient exchange = funcitonal units of the placenta

describe sow placentation

1. epitheliochorial

2. diffuse

3. non-deciduate

describe the ewe and cow placenta

• synepitheliochorial

• cotyledonary

• non-deciduate

why do we put ‘syn’ before cow and ewe placenta?

• some trophoblasts develop into binucleate giant cells

• some of these migrate and fuse to maternal epithelial cells = syncytium

what are BNC cells

• binucleate giant cells

where do BNC cells come from?

• trophoblasts developing from nonnucleate into binucleate and increasing in size

What cell type is identified here?

• top = BNC

• bottom = maternal epithelial cell

What is being shown taking place?

• the fusion of the BNC to the maternal epithelial cell forming the syncytium

what are the 2 types of placentome

• convex

  • concave

which species have convex placentomes

• cow

• giraffe

what species have concave placentomes

• sheep

• goats

What can be identified in this?

• centre = cotyledone

• outer = caruncle

describe the placentation in the horse

• epitheliochorial placentation

• diffue

• non-deciduate

what is interesting to note about cotyledones in the equine placenta

• they are present but they’re microscopic

what is interesting to note about the placentation of the horse around day 24

• has both a choriovitelline and chorioallantoic placenta

• a small gap forms between the two = chorionic girdle

What do we call the area where the chorioallantois and choriovitelline meet?

• chorionic girdle

how does the equine placenta change from day 35 (in terms of the 2 placentas)

• the yolk sac regresses and the allantoi takes over until about day 50 when it’s just a remnant attached to the endometrium

what do the points of attachment of the chorionic girdle develop into in the horse?

• endometrial cups

by what day do we see equine endometrial cups, do they remain there?

• day 50

  • no

what hormone are endometrial cups linked to?

• eCG = equine chorionic gonadotrophin

what eventually happens to the endometrial cups?

• surrounded adn eventually destroyed by immune cells

describe dog placentation

• endothelialchorial placentaton

• zonary

• deciduate

what are the parts of the zonary placenta

• pigmented zone (dark band)

• transfer zone (between the pigmented zones)

describe human/primate placentation

• haemochorial

• invasive

• deciudal

what species have haemochorial placentation

• human

• rodents

• lagomorphs

• most primates

what is decidualisation

• process of endometrial stromal cells proliferating and enlargening to become decidual cells

what do decidual cells become?

• the decidua is the mother placenta

what are 2 roles of decidual tissue

• communication b/w mother and foetus

• limiting trophoblast invasion

What type of placental histology is this?

• haemochorial

• note the close proximity of the maternal blood to the foetal blood (only 3 layers of cells between them).