Lecture 12: The Placenta and pregnancy (II)

Question 1

Describe the glandular “milk”

Answer 1

Secretions that enter the intervilli space.

Consumed as the major energy source in the first few weeks after implantation

Question 2

Describe the relationship between Premature blood flow and miscarriage

Answer 2

• Doppler ultrasound demonstrated an i_ncreased flow_ of maternal blood to the placenta in missed miscarriage at 7-9 or 10-11 weeks in missed miscarriages compared to normal controls
• There was no difference in blood flow at 12-13 weeks gestation between missed miscarriages and controls
• The premature maternal blood flow was distributed centrally and across the placenta whereas, in n_ormal pregnancies,_ the maternal blood flow was more likely to be observed at the periphery of the placenta.

Question 3

What is a missed miscarriage?

Answer 3

A missed miscarriage, also known as a missedabortion or a silent miscarriage, occurs when a fetus dies, but the body does not recognize the pregnancy loss or expel the pregnancy tissue.

As a result, the placenta may still continue to release hormones, so the woman may continue to experience signs of pregnancy.

Question 4

Define

Syncytiotrophoblast

Answer 4

surface layer of the placenta formed by fusion of VCTB.

STB does not replicate but is replaced by fusion of additional VCTB.

Question 5

Define Extravillous cytotrophoblast

Answer 5

differentiated cells that have migrated out of the villous placenta towards the maternal tissues

Question 6

What are some structural changes with gestational age in the placenta?

Answer 6

Structural Changes with gestational age

1. During early pregnancy stroma of the villi become more cellular and
   more vascularised
2. During the 2nd trimester v_illous cytotrophoblast thins down_
3. During the 3rd trimester v_illous cytotrophoblast is sparse_
4. Branching of v_illi increases_
5. Size of the p_lacenta increases_

Question 7

Describe the changes in size of the placenta with gestational age

Answer 7

Increases

Question 8

Placenta is mostly made up of ______ tissue

Answer 8

fetal tissue (not maternal tissue)

Question 9

Describe the Maternal contributions to the placenta

Answer 9

(most of the placenta is made up of fetal tissue)

• The decidua underlying the implantation site is called the decidua basalis.
• The decidua overlying the implantation site is called the decidua capsularis
• The decidua around the remainder of the uterus is call the decidua peritalis.

Question 10

•The decidua underlying the implantation site is called the ______

Answer 10

•The decidua underlying the implantation site is called the decidua basalis.

Question 11

•The decidua overlying the implantation site is called the ______

Answer 11

•The decidua overlying the implantation site is called the decidua capsularis

Question 12

•The decidua around the remainder of the uterus is call the ______

Answer 12

•The decidua around the remainder of the uterus is call the decidua peritalis.

Question 13

Describe the overall process of Placenta formation (youtube)

Answer 13

• Development of the placenta begins during implantation when the blastocyst adheres to the endometrial epithelium
• The _trophoblast cells differentiat_e into inner cytotrophoblast and outer syncytiotrophoblast layer
• As the cytotrophoblast layer differentiates, newly formed cells migrate to the synctiotrophoblast layer and lose their membranes, forming a rapidly growing, m_ulti-nucleated mass._
• The cytotrophoblast secretes proteolytic enzymes and the syncytiotrophoblast sends out finger like projects, allowing the blastocyst to embed into the endometrium
• Lacunae start to form in the syncytiotrophoblast. As the syncytiotrophoblast errodes the endometrial blood vessels and glands, the lacunae fills with maternal blood and glandular secretions.
• Isolated lacunae fuse to form a network where the blood flows, therefore establishing early utero placenta formation.
• Towards the 2nd week, small projections of the cytotrophoblast start to expand into the syncytiotrophoblast, forming primary chorionic villi
• In the 3rd week, extra embryonic mesoderm grows into these villi, forming a core of loose connective tissue. These structures are now known as the secondary chorionic villi
• By the end of the 3rd week, Blood vessles begin to form in the extra embryonic mesoderm, transforming them into tertiary chorionic villi.

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• Cytotrophoblast cells from the tertiary villi grow towards the decidua basalis, and spread across it to form a cytotrophoblastic shell.
• Villi that are connected to the decidua basalis through the cytotrophoblast plastic shell, are called Anchoring Villi
• Villi growing from the side are called the Branch villi
• These branch villi are surrounded by the intervillous space and serve as the main site of exchange between mother and fetus

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• By the 4th week, fetal blood flow is established. Poorly oxygenated blood is transported to the placenta from the fetus via the paried umbilical arteries. These arteries send branches into the chorionic villi and divide into capillary networks at the terminal ends.
• CO2 and wastes are removed into the fetal circulation across the placenta membrane into the maternal blood in the intervilli space.
• O2 and nutrients are transproted across the placental membrane in the maternal blood to the fetal capillairies.
• Oxygenated fetal blood travels through rain convergin to form a single umbilical vein that goes to the fetus.
• Blood returns to the maternal circulation through the endometrial veins or stopped by the incoming arterial blood.
• The placenta nourishes the fetus throughout development is delivered shortly after parturition.

Question 15

(Maternal contributions to the placenta)

As gestation progresses……

The _______ then fuses with the _______

Answer 15

•As gestation progresses the amniotic cavity enlarge_s o_bliterating the uterine cavity.

The d_ecidua capsularis_ then fuses with the decidua peritalis.

Question 17

_______ are invaded. _____ are never invaded.

Answer 17

Spiral arteries are invaded

Veins are never invaded

Question 18

In addition to the body of the placenta (chorion thrombosum), there is also the ______

3(2) ______ _____ are called ________

Answer 18

Placental membranes

1) Amnion (avascular covers cord and placenta)- closest to the baby
2) Chorion (fetal vessels)-
3) Decidua (derived from the decidua capsularis and peritalis- not fetal membrane)

Question 19

What is inside the umbilical cord?

Answer 19

• •2 arteries(carries oxygenated blood)
• •1 vein ​
  
  • •Formed from the y_olk sac and allantois_
  • •The vessels of the umbilical cord are derived from the allantois
• Whartons jelly
  
  • (sitting between the 3 vessles and underlaying the amnioic epithelium)
  • •Consists of a network of myofibroblasts
  • •Spaces are filled with mucopolysaccharides

Question 20

Why is the Wharton’s Jelly so important?

Answer 20

(sitting between the 3 vessles and underlaying the amnioic epithelium)

• Consists of a network of myofibroblasts
• Spaces are filled with mucopolysaccharides

A: False knot is a varicosity of the blood vessles. Nothing pathological about them

B: True knot: as the baby is moving around, the baby has tied the knot in the cord. The effect is: compress BV

The Wharton’s jelly _keeps the cord turgent (_cannot be tightened). So it prevents occlusion of the vessels.

Lack of Wharton’s jelly can be the cause of fetal demise.

Question 21

Describe the several adaptations of the villi to increase transport the placenta (4)

Answer 21

1) The villous structure is tortuous with a l_arge surface area_
2) The synctiotrophoblast has a microvillous surface (increased area for transfer)
3) In the 3rd trimester, most villi are small tertiary villi
4) In the 3rd trimester, the fetal capillaries are closely apposed to the syncytiotrophoblast.

Question 22

What are some placental adaptations?

What are its functions?

Answer 22

To increase transport the placenta has several adaptations.

1) The villous structure is tortuous with a large surface area
2) The synctiotrophoblast has a microvillous surface (increased area for transfer)
3) In the 3rd trimester, most villi are s_mall tertiary villi_
4) In the 3rd trimester, the fetal capillaries are closely apposed (side-by-side) to the syncytiotrophoblast.

Question 23

Fetal blood has ______affinity for oxygen due to _____

Answer 23

Fetal blood has greater affinity for oxygen due to Hbf

At pO2 30torr

Fetal blood is 80% saturated

Adult blood is 50% saturated

Question 24

Describe the differences between fetal and adult blood

Answer 24

1) Fetal blood has greater affinity for oxygen due to Hbf

At pO2 30torr

Fetal blood is 80% saturated

Adult blood is 50% saturated

2) Fetal blood has more haemoglobin and can carry more oxygen than maternal (adult blod)

Term fetal: 20-25ml/dl

Maternal: 15.3ml/dl

Question 25

2) Fetal blood has _____ haemoglobin and can carry ______oxygen than maternal (adult blod)

Answer 25

2) Fetal blood has more haemoglobin and can carry more oxygen than maternal (adult blod)

Term fetal: 20-25ml/dl

Maternal: 15.3ml/dl

Question 26

Describe the Bohr effect

Answer 26

As maternal blood picks up fetal metabolites, the pH lowers.

Thus, the affinity for O2 decreases and dissociation of O2 increases

The converse occurs of the fetal side- double Bohr effect

Question 27

Describe 3 features of gas transfer int he placenta

Answer 27

1) Fetal blood has greater affinity for oxygen due to Hbf

2) Fetal blood has more haemoglobin and can carry more oxygen than maternal (adult blod)

3) Bohr effect

• As maternal blood picks up fetal metabolites, the pH lowers.
• Thus, the lowered pH causes decrease in affinity for O2 and dissociation of O2 increases
• The converse occurs of the fetal side- double Bohr effect

4) Haldane effect

• The capacity of heamoglobin to bind CO2 is related to the amount of bound oxygen.
• Thus, if _oxygen is lost from the maternal blood t_he capacity of maternal blood for CO2 increases.
• The converse occurs of the fetal side –double Haldane effect.

Question 28

Describe the Haldane effect

Answer 28

• The capacity of heamoglobin to bind CO2 is related to the amount of bound oxygen.
• Thus, if oxygen is lost from the maternal blood the capacity of maternal blood for CO2 increases.
• The converse occurs of the fetal side –double Haldane effect.

Question 29

Describe the function of the amniotic fluid in the placenta (5)

Answer 29

1) buoyant medium allows symmetric growth
2) cushions the embryo/fetus
3) Prevents adhesions of the fetus with the membranes

4) allows the fetus to move –muscle development, movement of limb
5) D_evelopment of GI/respiratory tracts_ –breathing and swallowing.

Question 30

Describe the Origins of the Amniotic fluid

Answer 30

1) Initially ultra filtrate of maternal plasma
2) Major fetal contribution
3) 20+ weeks fetal urine and surface of placenta and cord.

Question 31

How is the volume of the amniotic fluid maintained?

Answer 31

Human fetal urine output is estimated at approx 500-1200 mls/day (indirect measurement)

Fluid leaves the amniotic cavity mainly by fetal swallowing (500-1000 mls/day)

Fluid can also move across the fetal skin (prior to keratinisation at 24 weeks)

Fluid can move across the fetal membranes into the maternal circulation (minor) or into the fetal vessels of the placenta and umbilical cord (larger)

Question 32

What is the name of the condition where there’s excessive accumulation of amniotic fluid

Answer 32

Polyhydramnios

• Excessive amniotic fluid possibly due to loss of swallowing
• Found in many cases of diabetic pregnancy

Question 33

What is a condition that involves lack of amniotic fluid called?

Answer 33

Oligohydramnios

Lack of amniotic fluid potentially due to kidney problems

Question 34

What are the names of 2 conditions with abnormal amount of amniotic fluid?

Answer 34

• Polyhydramnios
• Excessive amniotic fluid possibly due to loss of swallowing
• Found in many cases of diabetic pregnancy

Oligohydramnios
•L_ack of amniotic fluid_ potentially due to kidney problems

Question 35

What are 2 diagnostic tests that can be done by sampling the placenta?

Answer 35

1) Chorionic villi sampling
2) Amniocentesis (biopsi needle goes into the amniotic fluid transabdominally)

Question 36

In preganancy 3-6^ of cellf ree DNA in maternal blood is ______

Answer 36

Derived fromt he fetus- more specifically the placenta.

Non-invasive prenantal testing exploits this fetal cell-free DNA to screen for fetal genetic anomalies especially trisomy 21.

Question 37

The placenta forms a barrier to _____

Answer 37

Barrier to infection

Prevents (usually) transmission of…

1) Hep B
2) Rabies
3) Measles
4) Malaria- but malaria cuases “clogging of the placenta

Question 38

Is malaria transmitted across the placenta?

Answer 38

No

Malaria- but malaria cuases “clogging of the placenta

Question 39

What viruses can cross the placenta?

Answer 39

1) HIV
2) Small pox
3) Rubella
4) CMV
5) Toxoplasmosis

Question 40

A period of critical organogenesis is _______ days after the first day of the LMP

Answer 40

A period of critical organogenesis is 20-70 days after the first day of the LMP (1 week before the first missed menstruation)

Question 41

Describe 2 drugs that can cause serious damage if the fetus is exposed between 20-70 days?

Answer 41

• Eg thalidomide (originally given as a sedative) antiinflammatory and antiangiogenic –limb reduction defects (abnormal arm and leg development)
• Diethylstilbestrol (DES) causes cancer (Clear cell adenocarcinoma) in the vagina or cervix of adults after in uteroexposure to DES (1:1000 of those at risk).

Daughters developed cancer

Question 42

What drugs are given to the fetus via the mother?

Answer 42

Betamethasone

Glucocorticoid given to prevent Resp Distress Syndrome

Question 43

Does ethanol cross the placenta?

Answer 43

Yes- and may cause fetal alcohol syndrome,

Binge drinking can cause the risk of still birth

Question 44

Do recreational drugs cross the placenta?

Answer 44

Yes. recreational drugs may cause

1) intrauterine growth restriction
2) Developmental delay

Question 45

Does paracetamol and asprin cross the palcenta?

Answer 45

Yes but they’re safe

Question 46

Does heparin cross the placenta?

Answer 46

No

Question 47

Does wafarin cross the placenta?

Answer 47

Yes and can cause fetal malformations.