Placenta Flashcards
Why does establishment of the placenta take precedence in early embryonic development?
To ensure support for the pregnancy
What is meant by haemomonochorial in relation to the placenta?
The placenta is haemomonochorial
One layer of trophoblast ultimately separates maternal blood from foetal capillary wall
Give some information on implantation in regards to the placenta.
Implantation is interstitial
- The uterine epithelium is breached and the conceptus
implants within the stroma
The placental membrane becomes progressively thinner as the needs of the fetus increase
What are the aims of implantation in regards to the placenta?
Establish the basic unit of exchange:
- Primary villi: early finger-like projections of trophoblast
- Secondary villi: invasion of mesenchyme into core
- Tertiary villi: invasion of mesenchyme core by fetal
vessels
Anchor the placenta:
- Establishment of the outermost cytotrophoblast shell
Establish maternal blood flow within the placenta
Give a reference of timing to the different stages of placenta development.
Day 13 - Primary
Day 15-16 - Secondary
Day 23 - Tertiary
Tell me a bit about implantation defects. (location)
Ectopic pregnancy
- Implantation at site other than uterine body (most
commonly fallopian tube.
- Can be peritoneal or ovarian
- Can very quickly become life-threatening emergency
Placenta praevia
- Implantation in the lower uterine segment
- Can cause haemorrhage in pregnancy
- Requires C-section delivery
How does the endometrium prepare for implantation in regards to the placenta?
“pre-decidual” cells
Elaboration of spiral arterial blood supply
Describe decidualisation.
The decidual reaction provides the balancing force for the invasive force of the trophoblast
- Ectopic pregnancy
- Conditions characterised by excessive invasion
Describe the remodelling of the spiral arteries.
Creation of low resistance vascular beds
Maintains the high flow required to meet fetal demand
- Particularly late in gestation
Tell me a bit about an implantation defect. (completion)
Incomplete invasion
- Placental insufficiency
- Pre-eclampsia (hypertension and high protein in urine)
Tell me about twinning and it’s relationship to the placenta.
The degree to which membranes are shared in monozygotic twins can vary
You can have:
- Two amnions & two chorions
- Two amnions but a shared connection
- Amnion and chorion are both shared
Describe the 1st trimester placenta.
Placenta established
Placental “barrier” is still relatively thick
Complete cytotrophoblast layer beneath syncytiotrophoblast
Describe the term placenta.
Surface area for exchange dramatically increased
Placental “barrier” is now thin
Cytotrophoblast layer beneath syncytiotrophoblast
Tell me about the umbilical cord vessels & the fetal circulation.
Two umbilical arteries
- Deoxygenated blood from fetus to placenta
One umbilical vein
- Oxygenated blood from placenta to fetus
What are the functions of the placenta?
Metabolism:
- Placental synthesis of:
- Glycogen
- Cholesterol
- Fatty acids
Endocrine:
- Hormones produced by the placenta are:
- Protein
- Human chorionic gonadotrophin (hCG)
- Human chorionic somatomammotrophin
- Human chorionic thyrotophin
- Human chorionic corticotrophin
- Steroid
- Progesterone
- Oestrogen
- Protein
Transport:
- Simple diffusion
- Molecules moving down a concentration gradient:
- Water
- Electrolytes
- Urea & uric acid
- Gases
- Facilitated diffusion
- Applies to glucose transport
- Molecules moving down a concentration gradient:
What is hCG?
Human chorionic gonadotrophin
Produced during the first 2 months of pregnancy
Supports the secretory function of the corpus luteum
Produced by syncytiotrophoblast therefore is pregnancy specific
Excreted in maternal urine therefore used as the basis for pregnancy testing
Trophoblast disease
- Molar pregnancy (hydatidiform mole)
- Choriocarcinoma
What are the placental steroid hormones and what is their purpose?
Progesterone and Oestrogen
Responsible for maintaining the pregnant state
Placental production takes over from corpus luteum by the 11th week
How do placental hormones influence maternal metabolism?
Progesterone
- Increased appetite
hCS/hPL
- Increases glucose availability to fetus
Describe gas exchange across the placental membrane?
Simple diffusion
Flow-limited but not diffusion-limited
Fetal O2 stores are small therefore maintenance of adequate flow essential
Describe active transport across the placenta.
Specific “transporters” expressed by the syncytiotrophoblast
- Amino acids
- Iron
- Vitamins
Explain passive immunity.
Fetal immune system is immature
Receptor-mediated proves, maturing as pregnancy progresses immunoglobulin class-specific
- IgG only
- IgG concentration in fetal plasma exceed those in maternal circulation
What are the consequences of the transport function of the placenta?
The placenta is not a true “barrier”
Teratogens access the fetus via the placenta
Unintentional outcomes from physiological process
What drugs are harmful in pregnancy?
Thalidomide Alcohol Therapeutic drugs Drugs of abuse Maternal smoking
What can go wrong with antibody transport in regards to the placenta and fetus?
Haemolytic disease of the newborn
- Rhesus blood group incompatibility of mother and fetus
- Now uncommon because of prophylactic treatment
What infectious agents are a risk in fetus’?
Varicella zoster Cytomegalovirus Treponema pallidum Toxoplasma gondii Rubella
