6.1 Placental Function And Dysfunction Flashcards
When does the placental begin to develop?
Second week of development
What does the outer cell mass differentiate into in week 2?
Syncytiotrophoblast
Cytotrophoblast
What does the inner cell mass differentiate into in week 2?
The bilaminar disk
- Epiblast
- Hypoblast
What two cavities are within the embryo by end of week 2?
Yolk sac
Amniotic cavity
What is the embryo suspended in by end of week 2 and by what structure is it suspended?
Chorionic cavity
Suspended by a connecting stalk
What happens to the yolk sac?
Disappears
What happens to the amniotic sac and chorionic sac?
The amniotic sac enlarges
Chorionic cavity becomes occupied by the expanding amniotic cavity
What are primary villi?
Early finger-like projections of trophoblast
What are secondary villi?
Invasion of mesenchyme into core
What are tertiary villi?
Invasion of mesenchyme core by foetal vessels
Name three things that implantation achieves
Establishes a basic unit of exchange
Anchors the placenta
Establishes maternal blood flow in the placenta
Where does the conceptus implant?
Within the stroma (uterine epithelium is breached)
Implantation is interstitial, true or false?
True
What ultimately separates the maternal blood from the foetal capillary wall?
One layer of trophoblast
Why does the placental membrane become progressively thinner?
Needs of foetus increase
What is the placental a specialisation of?
The chorionic membrane
What are the two categories of implantation defect?
Implantation in wrong place
Incomplete invasion
What can implantation in the wrong place cause?
Ectopic pregnancy
Placenta previa
What can be caused by incomplete invasion?
Placental insufficiency
Pre-eclampsia
Define ectopic pregnancy
Implantation at site other than uterine body
Often Fallopian tubes
Can be ovarian or peritoneal
Endometrial areas normally provide modulation of the invasive force - doesnt happen in ectopic pregnancy
What is placenta previa?
Implantation in the lower uterine segment
Can cause haemorrhage
May need a C section
What happens to the endometrium in the presence of the conceptus?
Transforms into the decidua
What does the decidual reaction do?
Provides the balancing force for the invasive force of the trophoblast
What can be seen on the foetal aspect of the placenta (gross morphology)?
Umbilical cord -> Umbilical vessels -> Chorionic vessels
Amnion
What can be seen on the maternal aspect of the placenta?
Cotyledons
Describe the chorionic villus in the first trimester
Thicker barrier
Complete layer of cytotrophoblast
Acts as a stem cell layer for syncytiotrophoblast
Describe the third trimester chorionic villus
Barrier at optimal thickness
Occasional cytotrophoblast cell but they have mainly regressed
How many umbilical arteries are their and what do they do?
2
Deoxygenated blood from foetus to placenta
How many umbilical veins are there and what is the role of them?
One
Oxygenated blood from placenta to foetus
What two types of hormones does the placenta produce?
Protein
Steroid
What are the protein hormones of the placenta?
Human chorionic gonadotrophin
Human chorionic somatomammotrophin
Human chorionic thyrotrophin
Hyman chorionic corticotrophin
Which steroid hormones are produced by the placenta?
Oestrogen
Progesterone
When is hCG produced and what by?
During the first 2 months of pregnancy
By the syncytiotrophoblast
What is the role of hCG?
Supports the secretory function of the corpus luteum
Why can hCG easily be used as the basis for pregnancy testing?
Excreted in maternal urine
What is the function of placental steroid hormones?
Maintain the pregnant state
When does placental production of steroid hormones take over from the corpus luteum?
11th week
How do placental hormones influence maternal metabolism?
Progesterone
- Increased appetite
hCS, hPL
- Increase glucose availability to foetus
- Maternal insulin resistance
What are the two types of transport in the placenta?
Simple diffusion
Facilitated diffusion - glucose
Active transport
Why do we need an adequate uteroplacental circulation?
To maintain the oxygen gradient to the foetus
What active transporters are expressed and by what?
Syncytiotrophoblast
Amino acids, iron, vitamins
Which molecule is transferred in passive immunity and by what process?
IgG
Receptor mediated
What can Rhesus incompatibility of the mother and foetus cause?
Haemolytic disease
Name some harmful substances that can cross the placenta
Thalidomide, alcohol, therapeutic drugs (anti-epileptics, warfarin, ACE inhibitors), drugs of abuse
Why does thalidomide cause limb defects?
Crosses the placenta and destroys small blood vessels (in developing limbs)
What are the consequences of maternal smoking on the placenta?
Smaller placenta
Calcification
