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imed3003 > Placenta > Flashcards

Placenta Flashcards

1
Q

What are the types of placentas seen in the animal kingdom?

A

Epitheliochorial: Maternal epithelium of the uterus comes in contact with the chorion. This is considered primitive.

Endotheliochorial: Maternal endometrial blood vessels are bare to their endothelium and these come in contact with the chorion. (dogs and cats)

Haemochorial: Placenta where the chorion comes in direct contact with maternal blood because blood vessels are open within the placenta. (human)

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2
Q

What are the shape-based classifications of placentas?

A

Discoid (humans/mice/rabbits)

Zonary

Cotyledonary

Diffuse

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3
Q

What are human placentas classified as?

A

Haemochorial and discoid.

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4
Q

When does implantation of blastocyst occur in humans?

A

Day 5-7 post fertilization it begins and completes by day 12

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5
Q

What kind of implantation occurs in humans?

A

Interstitial implantation (blastocyst penetrates endometrium completely)

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6
Q

What kind of nutrition does the early embryo rely on?

A

Histiotrophic nutrition (from endometrial glandular secretions) until about 10 weeks when maternal blood supply is established.

Some blood flow starts at 6 weeks gestation. (new study shows this however it isn’t complete)

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7
Q

What happens to oxygen tension in placenta at 10 - 12 weeks of pregnancy?

A

The oxygen tension in the placenta rises from <20mmHg to >50mmHg

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8
Q

Human embryos undergo interstitial implantation; what does this mean?

A

Blastocyst penetrates the endometrium completely

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9
Q

How does the blastocyst attach itself to the uterus during implantation?

A

Mucin layer is removed by dendritic cells to expose adhesion molecules.

Pro-inflammatory factors secreted by stromal and immune cells are required for adhesion and invasion.

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10
Q

Which part of the blastocyst becomes the placenta?

A

The trophoblast (chorion)

The amnion will enclose the amniotic cavity/fluid

The allantois becomes the umbilical cord

The yolk sac provides blood cells until the baby can make its own. This will eventually dissolve away.

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11
Q

What is the decidua?

A

Several layers surround the foetus. It is the most superficial layer of extraplacental membrane composed of cells from the mother.

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12
Q

What is the amnion and chorion?

A

Chorion is more superficial than the amnion and they are foetal tissue that meet with the decidua to form the mother-foetal interface.

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13
Q

Order of the extraplacental membranes:

A

Alphabetic order from most deep to most superficial (relative to the mother where deep means closest to the foetus)

Amnion Chorion Decidua

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14
Q

What are the chorionic and basal plates?

A

Chorionic plate is on the foetal side and is where foetal blood gets nutrients from maternal blood.

Basal plate is where maternal blood comes from allowing for exchange of nutrient and gases.

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15
Q

What are the stages of chorionic villi development?

A

Primary: Chorionic villi are at first small (anchoring) and non-vascular (intermediate villi). 13 - 15 days (cells are trophoblast only)

Secondary: The villi increase in size and ramify while the mesoderm grows into them. This happens at 16 - 21 days. (Cells are trophoblast and mesoderm)

Tertiary: Branches of the umbilical vessels grow into the mesoderm and in this way chorionic villi are vascularized to form stem villi and numerous terminal villi. From day 21 onwards (cells are trophoblast, mesoderm and blood vessels)

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16
Q

How do villous trophoblasts change from 1st to 3rd trimester?

A

Cytotrophoblasts and syncytiotrophoblast cells are more numerous and surround the inside cavity of first trimester trophoblasts but form a small number of cells in 3rd trimester trophoblast. (double ring structure in 1st trimester which thins into hardly any ring in 3rd trimester)

Foetal capillaries are more numerous in third trimester and the villi are thinner around them.

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17
Q

What is the maternal surface of the placenta composed of?

A

It is also called the basal plate, composed of 10 - 40 cotyledons subdivided by septa (grooves).

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18
Q

How heavy is the placenta when delivered?

A

500 - 700grams typically.

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19
Q

What kind of blood does the umbilical vein carry?

A

Freshly oxygenated blood

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20
Q

What are the types of trophoblasts? Why are they important?

A

Cytotrophoblasts

Extravillous trophoblasts

Endovascular trophoblasts (extravillous trophoblasts that end up in the vasculature)

Syncytiotrophoblasts (multinucleated cells that are the interface between maternal blood supply and foetal placental tissue)

They are specialized placental cells that facilitate invasion and implantation of the embryo. They are foetal in origin.

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21
Q

What is the function of cytoytophoblasts?

A

Progenitor stem cells from which all the other ones form

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22
Q

What is the function of Extravillous trophoblasts ?

A

Trophoblasts that are outside of the villi that invade and go into blood vessels and the chorionic membrane

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23
Q

What is the function of endovascular trophoblasts ?

A

They are extravillous trophoblasts that end up in the vasculature

24
Q

What are the properties of trophoblasts?

A

Invasion (and vascular remodelling)

Aggregation and fusion

Differentiation

Senescence and apoptosis

Shedding and exocytosis

Endocytosis and phagocytosis

Transport and metabolism

Endocrine production

25
Q

How does the villous trophoblast change over its lifecycle?

A

Starts as a stem cell which proliferates, then it differentiates and fuses to form a syncytium. Then the syncytium undergoes apoptosis to form a syncytial knot which can be shed.

This is all driven by a protein called syncytin which is a retroviral protein.

26
Q

How does trophoblast invasion resemble tumour growth?

A

Trophoblast invasion is facilitated by vascular remodelling however it differs because of it stopping randomly.

27
Q

How is the blood supply maintained to the placenta at all times?

A

Arteries are plugged by endovascular villi which replace smooth muscle cells making them incapable of contracting and ensuring a constant blood supply to the placenta.

Until 20 weeks the endothelium is clogged with trophoblasts until they go away and allow blood vessels to open fully. (leakage starts at 6 weeks)

28
Q

How does pregnancy with foetal growth restriction differ to normal pregnancy?

A

There is a high pressure of resistance to blood flow resulting in reduced blood flow through spiral artery to the placental villi.

29
Q

Where are the arteries and veins seen in the placenta?

A

Between the amnion and the chorion

30
Q

What is the purpose of the amnion?

A

It provides a buoyant environment that protects the embryo from physical trauma, ascending microorganisms and maintains constant temperature.

Important source of prostaglandins and cytokines that are important for labour onset.

31
Q

What is the function of the yolk sac?

A

It forms part of the gut, produces the earliest blood cells and blood vessels, and is a source of germ cells that migrate into the embryo to seed the gonads.

32
Q

What is the allantois and what is its function?

A

Allantois is an outpocketing of the yolk sac that is the structural base for the umbilical cord and becomes part of the urinary bladder.

33
Q

What does the umbilical cord do?

A

Contains umbilical arteries and vein, a core of embryonic connective tissue and is covered externally by the amniotic membrane.

34
Q

Where is the amniotic fluid derived from?

A

In early pregnancy it is initially derived from the maternal blood.

In late pregnancy after foetal renal development it is made up of foetal urine and foetal lung fluid.

Near term, the foetus swallows almost 400ml of amniotic fluid each day and then excretes it in the urine.

35
Q

What happens to amniotic fluid quality if foetal swallowing or kidney function is deficient?

A

It can dramatically change the quantity of amniotic fluid leading to polyhydramnios or oligohydramnios.

36
Q

At what rate does volume of amniotic fluid change?

A

It increases to about 1000ml by week 37 and decreases slowly until 40 weeks and then much more quickly if the baby is not born by the end of the 40th week.

37
Q

How do molecules get past the barrier created by the placenta?

A

Placenta serves an important barrier function protecting the foetus from exposure to maternal blood cells, microorganisms, and noxious chemicals.

Generally only small water soluble molecules are permeable across the placenta although many exceptions exist.

Transport across the placenta goes both ways.

Physical or chemical damage to the placenta reduces its barrier function.

38
Q

What are the 4 ways that substances can cross the placenta?

A

Passive diffusion

Facilitative transport

Active transport

Pinocytosis/Endocytosis

39
Q

What is the limit of size of molecules that can cross the placenta by passive transport?

A

500 - 600 Da

40
Q

How do proteins and nutrients get past the placenta?

A

Negligible/low transfer of polypeptides, however, there are receptors that allow for receptor-mediated transport of selected proteins.

41
Q

What can cross the placental membrane from mother to foetus?

A

Oxygen, CO2, CO, H2O, glucose, vitamins, elements

Amino acids, lactate, oxalate

Cholesterol and its esters

Long and short chain FAs

Steroid and thyroid hormones

Electrolytes

Maternal IgG (Fc)

Apolipoproteins and carrier proteins.

42
Q

What can cross the placental membrane from foetus to mother?

A

CO2, CO

Waste products (Urea, uric acid, bilirubin)

Xenobiotics and toxins

Steroid conjugates and metabolites.

43
Q

What are the blood flow factors that can limit foetal oxygenation, nutrition and metabolism?

A

Altered maternal perfusion

Altered foetoplacental transfusion

Reduced placental permeability

Increased placental metabolic needs.

44
Q

What hormones does the placenta produce?

A

Lots of progesterone (up to 1g a day)

Lots of estradiol + estrone

Estriol

45
Q

How are progesterone levels different between humans and other mammals prior to labour?

A

Progesterone levels drop right before labour in all mammals except humans.

46
Q

How does the placenta acquire maternal immune tolerance?

A

Trophoblasts secrete factors which promote formation of T regs and M2 macrophages with a unique phenotype in decidua.

Immune cell recruitment supports trophoblast invasion.

EVTs express non-classical MHC1 as they invade endometrium to induce uNK tolerance

Each phase of pregnancy requires different immunological conditions.

47
Q

What are the 3 immunological stages of pregnancy?

A

1st trimester: Implantation, inflammation

2nd trimester: Foetal growth, Th2 type response

3rd trimester: Inflammation, Th1 type response, and labour.

48
Q

What is placenta praevia?

A

Placenta overlies internal cervical os of uterus essentially covering the birth canal

49
Q

What is vasa praevia?

A

Foetal vessels lie within the membranes close too or crossing the inner cervical os

50
Q

What is placenta accreta, increta, and percreta?

A

Placental abnormal adhesion in which they penetrate the decidua (accreta), the uterine muscle (increta), or the uterine serosa (percreta).

51
Q

What is abruptio placenta?

A

Partial or complete separation with retroplacental blood clot formation and abnormal haemorrhage prior to delivery

52
Q

What is placental chorioangioma?

A

Benign haemangiomas associated with range of foetal problems if large.

53
Q

What are the major infective placental pathologies?

A

Placental villitis

Chorioamnionitis

Funisitis

54
Q

What is funisitis?

A

Inflammation of the umbilical cord

55
Q

What is choriamnionitis?

A

Inflammation of the foetal membranes

56
Q

What is placental villitis?

A

Inflammation of the placental villi (often viral but can also be bacterial and fungal)

57
Q

10 interesting reasons why the placenta is the most interesting organ in the body:

A

It invades maternal tissue like cancer but self limits expansion

It is bathed by maternal blood yet does not have an endothelial surface

Its key structure relies on cell fusion via captured retroviral proteins

It expresses a large proportion of the entire human genome

It expresses proteins that are not made up anywhere else in the body other than tumours

It acts like brain, liver, endothelium, and gut tissue

It avoids provokes maternal immune recognition but avoids attack despite being foetal tissue (50% male) expressing non-self antigens

It is a steroid hormone powerhouse more so than any other organ

It is both a barrier to transport and an active transporter depending on the substance concerned

It releases cellular fragments containing foetal genetic material to help communicate between mother and foetus.

It does all this for 9 months and then is discarded like a waste product.

imed3003 (48 decks)

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