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Unit 7 > Physiology of the Placenta > Flashcards

Physiology of the Placenta Flashcards

1
Q

The placenta fulfills several critical roles as the interface between mother and fetus.
- Name 5 of these roles,

A

1- It prevents rejection of the fetal allograft
2- Enables respiratory gas exchange
3- Transports nutrients
4- Eliminates foetal waste products
5- Secretes peptide and steroid hormones that regulate both maternal metabolism and fetal growth and development.

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2
Q

1- Explain the maternal blood is supplied to the placenta?

2- How does maternal blood enter intervillous space?

3- Why is an adequate flow of maternal blood to the placenta vital?

A

1- Free-flowing lake that is not bounded by vessel walls

2- Reduced pressure

3- Vital to the growth and development of the fetus > Reduced maternal blood supply to the placenta leads to a small fetus.

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3
Q

Describe the transport of oxygen from the atmosphere to the foetal tissues. (6)

A
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4
Q

The Placenta plays the role of lungs as foetal lungs are NOT functional.

  • What type of blood does the left umbilical vein carry?
  • What type of blood does the right+left umbilical arteries carry?
  • Where do they carry blood to?
A
  • Like pulmonary veins, left umbilical vein carries highly oxygenated blood from placenta to heart.
  • Like pulmonary artery, right and left umbilical arteries bring deoxygenated blood to placenta.
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5
Q

1- Compare foetal haemoglobin affinity to that of adult haemoglobin.
2- How would this present on an oxygen dissociation curve?

A

1- Fetal hemoglobin’s affinity for oxygen is substantially greater than that of adult hemoglobin
- Enables HbF to extract oxygen from the HbA in the mother’s blood

2- Left shifted
P50 value is lower > Lower values indicate greater affinity

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6
Q

What 4 factors cause a left shit on oxygen dissociation curve?

A

*Note: 2,3-BPG is the same as 2,3-DPG

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7
Q

We need to balance the need to generate ATP for cell metabolism BUT also maintain appropriate oxygenation/deoxygenation status of haemoglobin.

1- How is this balance maintained?

A
  • Isomerisation of 1,3-BPG to 2,3-BPG which enhances the deoxygenation of hemoglobin.
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8
Q

What causes the ultimate increase in 2,3-BPG?

A
  • Low pH activates the activity of biphosphoglyceromutase and inhibits bisphosphoglyerate phosphatase
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9
Q

What is the structure of foetal haemoglobin?

A
  • Formed by 2 alpha subunits (top) and two gamma subunits (bottom), as well as their four heme groups.
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10
Q

1- How does O2/CO2 cross the placenta?
2- What is hydros fetalis?

A

1- Simple difffusion , no barrier across placenta unless it becomes separated or oedematous.

2- Abnormal accumulation of fluid in 2 or more fetal compartments.
- May also be associated with polyhydramnios (excess amniotic fluid) and placental edema.

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11
Q

1- The rate of transfer of gases is proportional to what? (2)

2- Why is umbilical venous PO2 (28mm Hg) of oxygen being relatively low important for survival in utero?

A

1- Difference in gas tension across the placenta and the surface area of the placenta.

2- High PO2 initiates physiologic adjustments (e.g., closure of the ductus arteriosus and vasodilation of the pulmonary vessels) that normally occur in the neonate but would be harmful in utero.

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12
Q

Oxygenation of a third-trimester fetus would define a state of severe hypoxia in postnatal life.

  • How is it possible, then, for the human and fetus to have an oxygen consumption rate per kilogram that is about twice the basal adult value
A
  • Output of the foetal heart, which is about 460 mLmin−1kg−1
  • Foetal cardiac output compensates for the low level of foetal oxygenation by maintaining a high ratio of blood flow to oxygen consumption through the circulation of individual fetal organs.
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13
Q

What is the Bohr effect?

A
  • CO2 helps the release of O2 from Haemoglobin = Bohr effect
  • CO2 concentration is high in the respiring cell > hemoglobin releases oxygen.
  • H+s bind to Hb, change its shape, and cause it to release more O2 to tissues at a given PO2
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14
Q

What is the double bohr effect? What does it help with?

A
  • Increase fetal oxygenation
  • The transfer of CO2 from fetal to maternal blood shifts the maternal oxyhaemoglobin curve to the right and the fetal curve to the left, facilitating the transfer of oxygen across the placenta from mother to fetus.

The double Bohr effect:
1. CO2 passes into maternal blood, decreases the affinity of maternal haemoglobin for oxygen, causes unloading of blood into the foetal blood. (first effect)
2. The decreasing PCO2in foetal blood increases itsaffinityfor oxygen (second effect)

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15
Q

What is the double Haldane effect?

A
  • As it becomes oxygenated, foetal haemoglobin releasesCO2(first effect)
  • As maternal haemoglobin becomes deoxygenated, it binds moreCO2(second effect)
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16
Q

How does Foetal blood compensates for low PO2? (2)

A

- High haematocrit (Hb~150-170g/L)
- At a lower PO2, the left-shifted foetal haemoglobin is more saturated than the adult haemoglobin would be

> As the consequence, the average oxygen content of foetal blood is greater than that of maternal blood

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17
Q

Compare where early nutrition with late nutrition comes from for the foetus.

A
  • Early nutrition is due to trophoblastic digestion and absorption of nutrients from the endometrial decidua.
  • Later nutrition results from diffusion through the placental membrane.
18
Q

1- What is the placenta highly permeable to?
2- How are amino acids transported across the placenta?
3- What type of vitamins are transferred from maternal to foetal circulation?

A

1- Glucose > main energy source for foetus.
(less permeable to fructose and other disaccharides)

2- Action of specific receptors

3- Water-soluble ones

19
Q

Why is maternal hyperglycaemia and ketosis reflected in fatal circulation?

A
  • Glucose, amino acids, and ketones move freely into the fetal circulation, whereas insulin, glucagon, and free fatty acids do not.
20
Q

The placenta is permeable to substances that can be damaging to the embryo.

  • Give 2 examples of this. And what effects these substances have on foetus.
A

1- Certain drugs can cause major birth defects if they reach the embryo during critical periods of development.

2- The placenta is highly permeable to alcohol, and excessive alcohol ingestion by the mother can produce fetal alcohol syndrome.

21
Q
  • Name a few of the factors that are associated with placental insufficiency and decreased delivery of nutrients to the developing foetus.
A

IUGR = Intrauterine Growth Restriction

22
Q

Net placental transport is determined by multiple factors… Name these.

A
  • Uteroplacental and umbilical blood flows,
  • Placental exchange area and metabolism,
  • Activity and expression of placental nutrient transporters
23
Q

The placenta is NOT innervated so how is communication enabled between the mother and the foetus?

A
  • Humoral agents
    > Signalling molecules secreted by the placenta can act locally through paracrine and autocrine regulation
24
Q

How does hCG regulation pregnancy in week 1?
> When is hCG detectable in woman’s blood?

A
  • hCG prevents the ovarian corpus luteum from degenerating so that it can continue to secrete oestrogen and progesterone
    → which act to maintain the endometrial lining.
  • Because the levels of progesterone and oestrogen are maintained, menstruation does not occur.

> hCG is detectable in a woman’s blood and urine about 8 days after fertilization.

25
Q

Human Chorionic gonadotropin (hCG) is one of the earliest products of cells forming the embryo.

1- What is the structure of hCG?
2- The alpha subunit is a glycoprotein of 92 amino acids stabilised by 5 disulphide linkages, what hormone is it identical to?
3- What factor differentiates the glycoprotein hormones?

A

1- hCG is a glycoprotein composed of two subunits, alpha and beta, held together by ionic and hydrophobic forces.

2- Identical to that of the pituitary glycoprotein hormones, luteinizing, follicle stimulating and thyroid stimulating hormones.

3- The beta subunit is a glycopeptide of 145 amino acids stabilized by six disulfide linkages.
> The beta subunits of the glycoprotein hormones are unique and give them their different biological characteristics

26
Q

1- What is the exponential rise of hCG after implantation characterised by?
> How do clinicians use this characteristic clinically?

A

1- Doubling time of 30.9 ± 3.7 hours.
> to differentiate normal from abnormal gestations e.g. ectopic

  • The inability to detect an intrauterine pregnancy by endovaginal ultrasound when serum hCG levels reach 1100 to 1500 mU/mL suggests an abnormal gestation or ectopic pregnancy.
  • Higher than normal hCG levels may indicate a molar pregnancy or multiple-gestational pregnancies.
27
Q

Syncytiotrophoblasts produce free β-hCG and Cytotrophoblasts produce α subunit.

  • Describe how the ratio production of these 2 subunits varies throughout pregnancy.
A
  • Initially, immature syncytiotrophoblast produces free β-hCG subunits, whereas the cytotrophoblast’s ability to produce the α subunit appears to lag by several days.
  • As the trophoblast matures, the ratio of α subunits to β subunits reaches 1 : 1, and a peak of approximately 100,000 mU/mL is reached by the 9th or 10th week of gestation
  • By 22 weeks’ gestation, the placenta produces more of the α subunit than β-hCG. At term gestation, the ratio of α subunit to hCG release is approximately 10 :1.
28
Q

Levels of hCG in combination of what 2 other tests are used as screening for detection of foetal anomalies?

A
  • maternal α-fetoprotein and unconjugated estriol
29
Q

hCG production early on is primarily by Corpus luteum hCG production peaks at about 8 weeks. What does this trigger the corpus luteum to do?

A
  • Corpus luteum to produce ever-increasing levels of oestrogen and progesterone.
    > These hormones act to maintain nutritional support for the embryo and fetus
30
Q

1- By the 9th week what becomes the primary source of oestrogen and progesterone?

2- After 4 months what hormones are responsible for maintaining pregnancy as hCG levels decrease significantly and stay low?

A

1- Placenta
- From the second trimester the placenta takes over the hormonal role of the ovaries and begins producing oestrogen and progesterone

2- Following the fourth month, rising levels of placental oestrogen and progesterone are sufficient to maintain pregnancy.

31
Q

from week 17-38 what is the primary source of Oestrogen
Progesterone
Relaxin
Human chorionic somatomammotropin
Corticotropin-releasing hormone

A
  • Placenta
32
Q

1- How does oestrogen maintain endometrium during pregnancy?

2- What hormones inhibit milk synthesis?

3- What hormone inhibits memorial contractions?

A

1- Increase uterine blood flow

2- High levels of oestrogen and progesterone

3- Progesterone, to prevent premature birth

33
Q

What is the major oestrogen formed in pregnancy?
> What do maternal serum levels of estriol increase to?

A
  • estriol
    (Estriolis not secreted by the ovary ofnonpregnantwomen)
    > between 12 and 20 ng/mL by term
34
Q

What is the function of progesterone in pregnancy?
> How does the foetus inactivate progesterone?

A

1- Prevents uterine contractions
2- Establishing an immune tolerance for the products of conception.
3- Suppresses gap junction formation, (needed for myometrial contraction)
4- Placental CRH expression,
5- Actions of oestrogen, cytokines, and prostaglandin.

> Transformation to corticosteroids or by hydroxylation or conjugation to inert excretory products.

35
Q

What is the foetal placental unit?

A
  • Main pathways of steroid hormone biosynthesis.
    > Adrenal DHEA is largely transported as its sulfate, DHEA-S, which can also be formed from steroid sulfates starting with cholesterol sulfate.
36
Q

1- During pregnancy when are relaxin levels at their highest? why?

2- What else can relaxin do? (2)

A

1- First trimester > promote implantation of the developing fetus into the wall of the uterus and the growth of the placenta.

2-
- Early in pregnancy, relaxin also inhibits contractions in the wall of the uterus, to prevent premature childbirth.
- Relaxin can regulate the mother’s cardiovascular and renal systems to help them adapt to the increase in demand for oxygen and nutrients for the fetus, and to process the resulting waste products.

37
Q

Towards the end of pregnancy what does relaxin promote?

A

1- Ruptureof the membranes surrounding the fetus and thegrowth,opening and softening of thecervixand vaginato aid the process of childbirth.

2- There is also evidence thatrelaxincan relaxtheligamentsat the front of the pelvis to ease deliveryof the baby.

3- It also initiates labor and facilitates delivery of the baby by dilating the cervix and increasing flexibility of ligaments and pubic bones.

38
Q

What is the function of Human chorionic somatomammotropin (hCS) ?

A
  • Ensure that the nutritional demands of the fetus are met, functioning as the “growth hormone” of pregnancy.
  • hCS increases maternal fatty acid use for ATP production, leaving more glucose available for the fetus.
  • hCS inhibits glucose uptake by maternal cells.
39
Q

1- Describe the levels of the following during pregnancy:
- maternal glucose levels
- plasma free fatty acids
- insulin secretion

2- Peripheral uptake of ….. is inhibited in the mother but …. crosses the placenta freely.

3- The placenta is permeable to insulin what does this mean for the foetus?

A

1- During pregnancy -
maternal plasma glucose levels are ↓,
plasma free fatty acids are ↑,
and insulin secretion is ↑ with resistance to endogenous insulin as a consequence of contra-insulin effects.

2- Peripheral glucose uptake is inhibited in the mother but glucose crosses the placenta freely.

3- Leaves even more blood glucose available to the fetus.

40
Q

Increased oestrogen act as a timer for birth and preparation for lactation.

1- How does this increase come about?

2- CRH stimulates the foetal anterior pituitary to secrete what hormone? What does this hormone trigger?

A

1- Placental CRH levels increase greatly toward the end of the pregnancy and stimulate the fetus and the placenta to produce more oestrogens.

2- Adrenocorticotropic hormone (ACTH).
ACTH ↑ fetal cortisol > triggers fetal lung maturationand surfactant production

41
Q

Increased oestrogen act as a timer for birth and preparation for lactation.

1- How does this increase come about?

2- CRH stimulates the foetal anterior pituitary to secrete what hormone? What does this hormone trigger?

A

1- Placental CRH levels increase greatly toward the end of the pregnancy and stimulate the fetus and the placenta to produce more oestrogens.

2- Adrenocorticotropic hormone (ACTH).
ACTH ↑ fetal cortisol > triggers fetal lung maturationand surfactant production

42
Q

Detailed appendix of hormones involved in pregnancy+ parturition

A

Unit 7 (16 decks)

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