Foster Gross Examination of the Placenta - Notes and Lecture

Question 1

main membranes of the placenta

Answer 1

chorion, allantois and amnion

> common names for the membranes you see are Chorioallantois and Amnion (which is actually the allantoamnion)

Question 2

amnion structure and function: what does it look like, what does it hold?

Answer 2

The amnion is a smooth translucent membrane that surrounds the fetus. It holds amniotic fluid.

Question 3

what produces the fluid within the amnion? what floats within it?

Answer 3

fluid is produced by the amniotic membrane, and within it floats squames from the epidermis of the fetus.

Question 4

how can we usually identify the fetal side of the amniotic membrane? where is this identifying factor most prevalent?

Answer 4

The fetal side can usually be identified by the presence of epidermal tissue known as amniotic plaques. These are most numerous on the umbilical cord.

Question 5

______ is often present in the chorioallantois in early pregnancy.

Answer 5

mineral

Question 6

what can we sample by taking post partum stomach content from the newborn?

Answer 6

Amniotic fluid is swallowed by the fetus; post partum sampling of amniotic fluid is possible by taking stomach content. F

Question 7

do fetuses normally inhale amniotic fluid? when do they?

Answer 7

Fetuses do not inhale amniotic fluid past the larynx – unless they are stressed

Question 8

when would we find meconium in the amniotic fluid?

Answer 8

meconium is not normally present in the amniotic fluid unless the fetus is distressed and defecates. Fetuses covered with meconium are said to have ‘fetal diarrhea’.

Question 9

what is the chorion? what is its purpose?

Answer 9

The chorion is the layer that contacts the mother. It is an important barrier between maternal and fetal tissues.

Question 10

do the mother and fetus share blood?

Answer 10

Maternal blood does NOT flow through the fetus. The fetus has only fetal blood.

Question 11

what is fused to the chorion in most species and what does this form?

Answer 11

In most species it is fused with the allantois to form the chorioallantois. Some call it the allantochorion though!

Question 12

what is contained in the allantoic cavity? what empties into the allantois?

Answer 12

-The allantoic cavity, where it exists, contains fetal urine, and other fluids that arise from the membrane itself.
-The umbilical cord takes blood to and from the placenta, and it has the urachus that empties into the allantois

Question 13

what structures are contained within the umbilical cord?

Answer 13

-2 umbilical arteries, an umbilical vein and a urachus.

Question 14

what does the umbilical cord often look like in the amniotic cavity?

Answer 14

The cord in the amniotic cavity is often dotted with amniotic plaques, and is occasionally gently twisted.

Question 15

what is found on the surface of the porcine placenta?

Answer 15

The chorionic surface of the porcine placenta has small microscopic projections or villi. They are barely recognizable grossly.

Question 16

what are chorionic cysts in the porcine placenta? what is this due to?

Answer 16

-These are where the secretion of uterine glands is trapped
-This secretion is part of what is called histotrophic nutrition

Question 17

where do we see necrotic tips in porcine placentas?

Answer 17

Pig placentas have necrotic tips where adjoining placentae touch

Question 18

what is the relationship between the amnion and the chorioallantois in the horse?

Answer 18

-In the horse, the amnion and the chorioallantois are completely separate.

Question 19

what is the texture and appearance of the horse chorionic surface?

Answer 19

The chorionic surface is microcotyledonary and gives it a luxuriant velvety appearance.

Question 20

how does the equine (and porcine) placenta receive nutrients?

Answer 20

The equine placenta, like the pig placenta, received nutrition from uterine gland secretion (histotrophic nutrition) and from diffusion from maternal tissues (hemotrophic nutrition).

Question 21

where do we find avillous areas of the equine placenta?

Answer 21

-Avillous regions are located in those areas where the trophoblasts do not contact the endometrium – over large vessels, at the uterotubal junctions, and at the cervix where the appearance of the avillous regions is star shaped to form the cervical star.

-The avillous chorioallantoic pouches are formed over the sites of the endometrial cups.

Question 22

where do we find the chorionic pouches and endometrial cups?

Answer 22

The avillous chorioallantoic pouches are formed over the sites of the endometrial cups. The pouches are dotted around the chorion near the fixation (attachment) site of umbilical cord.

Question 23

How are endometrial cups formed? What do they create? How are they destroyed?

Answer 23

Endometrial cups are formed by trophoblasts that invade the endometrium. They form the placental hormone equine chorionic gonadotrophin (luteinising hormone) from day 38 to 150 of gestation. They are immunologically destroyed by the mare.

Question 24

what is a hippomane and where is it found? what about allantoic pouches?

Answer 24

Hippomanes and allantoic pouches (also called polyps) are often found in the horse allantois. Hippomanes are present in virtually all equine placentae and are proteinaceous soft calculi. They also occur in the placentae of cows, sheep, and lemurs! Some are found in the amniotic cavity too.

Allantoic pouches are pedunculated structures attached to the allantius. They are incidental in most cases.

Question 25

where and how often are yolk sac remnants found in the horse placenta? what anatomical location are they found at?

Answer 25

Yolk sac remnants are less frequently found, and when present are attached to the umbilical cord at the junction with the allantois. They often are mineralized.

Question 26

What is the normal length of the umbilical cord? where is the attachment site? how many twists can it have?

Answer 26

The umbilical cord of the equine fetus is normally 36 and 83 cm long, and the insertion site should be at the junction of the horn and body of uterus. It can have up to 3 (or 4) twists

Question 27

what kind of placenta do ruminants have?

Answer 27

-The ruminant has a cotyledonary placenta with cotyledons and intercotyledonary regions.

-The exchange unit is the placentome made up of cotyledon (fetal) and caruncle (maternal)

Question 28

what is the association between the amnion and allantois in ruminants over the dorsum of the fetus?

Answer 28

The amnion of ruminants is fused with the allantois over the dorsum of the fetus.

Question 29

what does the normal intercotyledonary placenta look like? what about the normal cotyledon? how does autolysis affect this?

Answer 29

The normal intercotyledonary placenta is clear enough to read a book through. The normal cotyledon is red and evenly coloured. Autolysis makes the placenta appear paler than normal, and autolysis affects the entire placenta, not just one part.

Question 30

how do the placentomes develop in the ruminant? how many are there, and what is the approximate exchange area?

Answer 30

The placentomes develop in 4 rows, two dorsal and two ventral. There are 70-140 placentomes that have an exchange area of more than 18 sq m.

Question 31

what property of the fetus is correlated with the vascular development within the placentome?

Answer 31

Fetal growth is correlated with vascular development within the placentome.

Question 32

how do placentomes change during pregnancy? where are the largest ones found?

Answer 32

Placentomes increase in size during pregnancy and the largest ones are found nearest the attachment of the umbilical vessels.

Question 33

at what point is a bovine placentome in the ruminant considered enlarged?

Answer 33

A cotyledon larger than 15 cm diameter in the bovid is regarded as increased in size

Question 34

at what point post partum do the caruncles due? how are they ejected from the body?

Answer 34

after birth, the surface of the caruncles dies and is lost in the lochia, usually by day 12 postpartum (PP).

Question 35

at what point post partum does the uterus reepithelialize?

Answer 35

Reepithelialization occurs in about 21 days PP.

Question 36

can we sample the caruncle in the cow without damaging her reproductive abilities? when might we do this, and how?

Answer 36

Because the outer part of the caruncle is lost anyway, it can be sampled without damage to the future reproductive capacity of the cow. Such sampling is recommended when there is no placenta for examination. Caruncles should never be twisted off, but the cotyledon can be gently peeled off the caruncle.

Question 37

if placentomes are lost in the ruminant, how will the body compensate?

Answer 37

Placentomes have a capacity to compensate for loss, and they do so by hypertrophy, as functional area is lost; remaining placentomes become larger. There is also the facility for additional or adventitial placentation to occur.

Question 38

what kind of placenta do domestic carnivores have?

Answer 38

Domesticated carnivores have a zonary placenta.

Question 39

where do we see interdigitation of fetal and maternal tissues in domesticated carnivore placentas? what is the appearance of this area?

Answer 39

Domesticated carnivores have a zonary placenta.

Interdigitation of fetal and maternal tissues occurs in the center of the girdle (called the labryinth) and there are marginal hematomas at the edges of the girdle. The outer portion on each side is called the polar zone.

Question 40

are the amnion and allantois connected in the placenta of domesticated carnivores?

Answer 40

The amnion is separate from the allantois.

Question 41

what sort of environment do we need for fetal growth, generally?

Answer 41

◼ Protective environment
◼ Shock absorbing
◼ Oxygen, Nutrition
◼ Transfer maternal immunity
◼ Waste removal

Question 42

what embryonic structures is the chorion formed from? what is in contact with the mother?

Answer 42

Chorion = Trophoblasts + mesoderm

Trophoblasts are in contact with the mother

Question 42

what embryonic structures is the chorion formed from? what is in contact with the mother?

Answer 42

Chorion = Trophoblasts + mesoderm

Trophoblasts are in contact with the mother

Question 43

what embryonic structure forms the gut and yolk sac?

Answer 43

◼ Endoderm = gut + yolk sac

Question 44

describe the process of embryo and placental formation

Answer 44

Basic embryology:
Blastocyst: outside = ZP; starts forming central cavity
Chorion: trophoblasts and mesoderm

Outer cells differentiate into trophoblast → continuous layer around outside = ectoderm

Endoderm: gut and yolk sac

Cells start to grow and line inner surface of cavity
Pinching of yolk sac → umbilical cord forms
Amnion: wings grow out from yolk sac placenta and cover fetus → amniotic sac bathing fetus
Allantois: outpouching of endoderm; bladder forms in this area (detaches from gut; urachus attaches to it)
Yolk sac shrinks and disappears (doesn’t completely disappear in horse)

fertilized ovum forms zygote > a single cell, surrounded by the zona pallucida
>cells divide, increase in number, and form groupings with a hollow cavity in the middle (blastocyst)
>zona pallucida breaks off when cell mass becomes too big
>division of cells in blastocyst now forms the initial part of the placenta
>outer part of the placenta is the chorion, which is the interface between the conceptus and the mother, and it is composed of a single layer of trophoblasts. This lining protects the fetus from the mothers immune system.
>inner cell mass of this structure is what becomes the future fetus
>rest of this structure develops the placenta
>as this thing gets bigger, it has to develop a blood supply
>we have the outer layer which is the chorion, and the inner layer is the endoderm
>endoderm is the future yolk sac and gut, and develops from the hole in the blastocyst
>membranes must form around the fetus to protect it, accomplish this by growing around the fetus
>chorionic fetus folds around the fetus
>sac that is formed by this folding is the amniotic sac, which contains a special fluid, which is the main cushioning fluid of the placenta
>in humans, main membranes are chorion and amnion, but several species are too large and need more membranes for additional blood supply, etc.
>the allantois is an additional membrane that comes off of the yolk sac
>the allantios provides lots of blood vessels for the placenta
>allantois expands to completely cover the amnion, and the yolk sac gets smaller
>area in the middle of the fetus becomes the umbilical cord

Question 45

what is the charracter of the blood supply to the placenta (volume and pressure)?

Answer 45

◼ Blood supply is high volume – low pressure

Question 46

what animals have placentas with prominent yolk sacs?

Answer 46

◼ Marsupials
◼ Rodents and lagamorphs
◼ Carnivores
> Allantoic vasculature takes over later

Question 47

what is the chorion and placental arrangement character of the pig?

Answer 47

◼ Pig – villus – uterine milk - histotroph

Question 48

what is the chorion and placental arrangement character of the horse?

Answer 48

◼ Equine – microcotyledonary – uterine milk - histotroph

Question 49

what is the chorion and placental arrangement character of the ruminant?

Answer 49

◼ Ruminant – cotyledonary - haemotroph

Question 50

what is the chorion and placental arrangement character of the carnivore?

Answer 50

◼ Carnivore – zonary - haemotroph

Question 51

what stuctures are in the umbilical cord and where do they travel to?

Answer 51

◼ 2 arteries – from iliac arteries
◼ 1 vein – to ductus venosis
◼ Urachus – from bladder to allantois

Question 52

does blood supply of fetal membranes come from the fetus or the mother?

Answer 52

the fetus! is in a totally sealed environment

Question 53

what is the purpose of villi, cotyledons, etc. in the placentae of the various species?

Answer 53

increase surface area for nutrient transfer

Question 54

remnants of the placenta that persist in the adult

Answer 54

◼ Meckels diverticulum – small intestine – yolk sac
◼ Yolk sac remnant in horse
◼ Persistent urachus
◼ Round ligaments of bladder (umbilical arteries)
◼ Falciform ligament (umbilical vein)