Lecture 12; Normal pregnancy Flashcards
Describe the placental adaptations to increase transport:
- The villous structure is tortuous with a large surface area
- The syncytiotrophoblast has a microvillous surface (increased are for transfer)
- In the third trimester most villi are small tertiary villi
- In the third trimester the fetal capillaries are closely opposed to the syncytiotrophoblast
To make exchange efficient
Describe the structural chanes with gestational age in the placenta:
- During early pregnancy stroma of the villi become more cellular and more vascularised
- During the 2nd trimester villous cytotrophoblast thins down
- During 3rd trimester villous cytotrophoblast is sparse (to shorten diffusion, brings BV close)
- Branching of villi increases
- Size of the placenta increases
What does the term floating villi assist in flow dynamics:
Term floating villus slows blood flow by stopping pulsitile flow.
Describe the decidual reaction:
- The stromal cells of the decidua are swollen and store glycogen.
- Upon implantation this reaction is enhanced
Described the anatomy of the decidua:
- Decidua under the implantation site is called the decidua basalis
- Decidua over the implantation site is called the decidua capsularis
- The decidua around the remained of the uterus is called the decidua peritalis
What happens to amniotic cavity as gestation progresses?
- As gestation progresses the amniotic cavity enlarges obliterating the uterine cavity
- The decidua capsularis then fuses with the decidua peritalis
What are the placental membranes?
- Amnion; Avascular covers cord and placenta
- Chorion; Fetal vessels
Decidua, derived from the decidua capsularis and peritalis not a fetal membrane
Describe what the umbilical cord is formed from?: and its structure:
- Formed from the yolk sac and allantois (vessels)
- 2 art, 1 vein
- ## Whartons jelly (provides tugor, preventing compression)
Describe the whartons jelly of the umbilical cord:
- Consists of a network of myofibroblasts
- Spaces are filled with mucopolysaccharides
What are the functions of the amniotic fluid:
- Buoyant medium allows symmetric growth
- Cushions the embryo/fetus
- Prevents adhesions of the fetus with the membranes
- Allows the fetus to move - muscle development
- Development of GI/respiratory tracts - breathing and swallowing
What are the origins of the amniotic fluid:
- Initially ultra filtrate of maternal plasma
- Major fetal contributions
- 20+ weeks fetal urine and surface of placenta and cord.
Describe the movement of amniotic fluid:
- Fluid leaves the amniotic cavity mainly be fetal swallowing (500-1000mls/day)
- Fluid can also move across the fetal skin (prior to keritinisation at 24 weeks(
- Fluid can move across the fetal membranes inot the maternal circulation (minor) or into the fetal vessels of the placenta and umbilical cord (larger)
Describe polyhydramnios and oligohydramnios:
Polyhydramnios
- Excessive amniotic fluid possibly due to loss of swallowing
- Found in many cases of diabetic pregnancy
Oligohydramnios
- Lack of maniotic fluid potentially due to kidney problems
What is the amniocentesis?
Amnion and chorion fuse
What is amniocentesis sampling?
Occurs after fusion of two layers and samples the amniotic fluid
Samples the cell-free DNA for minimally invasive antenatal diagnostics
What does the placenta normally prevent transmission of?
Hep B
Rabies
Measels
Malaria - (but causes clogging of the placenta)
What does the placenta permits transmission of?
HIV CMV Small pox Rubella (german measles) Toxoplasmosis
When is the period of critical organogenesis?
20-70 days after the first day of LMP
Describe the potential damage of drug transport in the placenta:
Drugs transferred during the period of organogenesis may cause serious damage.
i. e Thalidomide -> Limb reduction defects
i. e Diethylstilbestrol -> causes cancer in the vagina or cervix of the daughter of the mother.
How can placental drug transport be beneficial?
Other drugs are given to the fetus via the mother
- i.e betamethasone i.e glucocorticoid given to prevent Resp. Distress Syndrome
What are some other drugs in pregnancy that are bad?
- Ethanol; Crosses the placenta and may cause fetal alcohol syndrome, inc. risk of still birth
- Recreastional drugs may cause IUGR
- Paracetamol and aspirin are safe
- Herapin does not cross placenta
- Warfarin crosses placenta causes fetal malformations
What is the function of P4 and E2 in the placenta?
- Progesterone maintains uterine quiescence and promotes development of the decidua
- Oestrogen upregulates progesterone receptors and progesterone down regulates oestrogen receptors.
Where in the placenta produces the progesterone?
- Synthesised mainly by the syncytiotrophoblast of the placenta
What happens to the cervix in pregnancy?
- Cervix softens and glands proliferate to occupy approx 1/2 of the mass of the cervix.
- A mucus plus is secreted into what has become a honeycomb-like structure in the cervix.
- Up to 80% of the non-pregnant cervix is collagen
What happens to the abdominal wall and skin in pregnancy?
- Blood flow to the skin is inc. in pregnancy i.e warm and clammy hands
- Flow to the hands is increased 6-7 fold
- Flow to feet is also increased.
= Generically indicates inc. flow to other skin regions
What happens to pigmentation in pregnancy? what causes it?
- There are pigmentation changes in some area of skin nipples and areola
- There is also development of a linea nigra.
- Chloasm may develop mainly in neck and face (lost or regress after pregnancy
These pigmentation changes are due to an increased secretion of melanocyte stimulation hormone which is markedly elevated from the second month of pregnancy.
What can happen to the skin in later pregnancy compared to beforementioned?
- 50% develop striae gravidarum (reddish streaks)
- Hair loss is reduced in pregnancy but the excess gained is lost in the puerperium
