Session 8 - Preggers Flashcards
How long before blastocyst enters uterine cavity?
4-5 days
What does implantation involve, in terms of cell layers?
Interaction between trophoblast and epithelium of the uterus
What does trophoblast divide into?
Synctiotrophoblast and cytotrophoblast
What does haemomonochorial mean?
One layer of trophoblast separates maternal blood from foetal capillary wall
What happens to wall of placenta over time?
Placental membrane becomes progressively thinner as the needs of the foetus increase
What is the basic unit of exchange in a placenta?
Villi
Outline the development of the villi of the placenta overtime
o Primary villi
Early, finger-like projections of trophoblast
o Secondary villi
Invasion of mesenchyme into core
o Tertiary villi
Invasion of mesenchyme core by fetal vessels
What are the three main aims of implantation?
Establish the basic unit of exchange
Anchor the placenta
Establish maternal blood flow within the placenta
How is the placenta anchored?
By the establishment of outermost cytotrophoblast shell
What are the two main changes in the endometriun which allows placental development ?
o Decidualisation
o Remodelling of Spiral Arteries
What is decidualisation
Decidual cells develop under the influence of progesterone in the endometrium.
Provides balancing force for the invasive force of the trophoblast
What occurs in remodelling of spiral arteries, and why does this happen?
Creation of low resistance vascular bed
Maintains the high flow required to meet fetal demand, particularly late in gestation
Name three implantation defects
Ectopic pregnancy
Placenta praevia
Incomplete invasion
Outline what occurs in ectopic pregnancy
Implantation at site other than uterine body
Most commonly fallopian tube
Can be peritoneal or ovarian
Can very quickly become a life-threatening emergency
Outline placenta praevia
Implantation in the lower uterine segment
Can cause haemorrhage in pregnancy
Requires C-Section delivery
What occurs in incomplete invasion?
Placental insufficiency
Pre-Eclampsia
Outline the structure of the placenta (x4)
1. A fetal portion o Formed by the chorion frondsum o Bordered by the chorionic plate 2. A maternal portion o Formed by the decidua basalis o The decidual plate is most intimately incorporated into the placenta
What exists between chorionic and decidual platers?
The intervillous spaces
What forms in fourth and fifth months?
Decidual septa. which projects into the intervillous spaces but do not reach the chorionic plate
What do the decidual septa divida the placenta into?
Cotyledons, or compasrtments
Describe the first trimester placenta
o Placental ‘barrier’ to diffusion still relatively thick
o Complete cytotrophoblast layer beneath syncytiotrophoblast
Describe the placenta at full term
o Surface area for exchange dramatically increased
o Placental ‘barrier’ is now thin
o Cytotrophoblast layer beneath syncytiotrophoblast lost
What do the umbilical arteries and veins project into?
Tertiary villi
Outline foetal blood vessels
Two Umbilical Arteries
o Deoxygenated blood Fetus Placenta
One Umbilical Vein
o Oxygenated blood Placenta Fetus
How do cotyledons receive their blood?
80 – 100 spiral arteries that pierce the decidual plate
Describe the factors influencing the passive diffusion of substances across the placenta
o Concentration Gradient
The steeper the gradient, the more diffusion
o Barrier to diffusion
Placental membrane gradually thins throughout pregnancy as the demand of the fetus increases
o Diffusion distance
Haemomonochorial
What crosses the placenta via simple diffusion?
o Water o Electrolytes o Urea and uric acid o Gases Flow limited, not diffusion-limited Fetal O2 stores are small – maintenance of adequate flow is essential
What crosses the placenta via facilitated diffusion?
o Glucose
What crosses the placenta via active transport?
Specific transporters are expressed by the syncytiotrophoblast
o Amino acids
o Iron
o Vitamins
Name five teratogens which can damage foetus
o Thalidomide o Alcohol o Therapeutic drugs o Drugs of abuse o Maternal smoking
Name five pathogens which can cross the placenta
o Varicella zoster o Cytomegalovirus o Treponema Pallidum o Toxoplasma gondii o Rubella
What are the two types of hormones produced by placenta?
Protein hormones
Steroid hormones
Name four protein hormones produced by the placenta
o Human Chorionic Gonadotrophin (hCG)
o Human Chorionic Somatommotrophin (hCS)
o Human Chorionic Thyrotrophin
o Human Chorionic Cortiotrophin
Describe the production and role of hCG
Produced during the first two months of pregnancy
Supports the secretory function of the corpus luteum
Produced by syncytiotrophoblast, therefore is pregnancy specific
What is the role of hCS?
Influences maternal metabolism, increasing the availability of glucose to the fetus
What are the two steroid hormones produced by placenta?
Progesterone
Oestrogen
What is the main role of placenta produced progesterone
Placenta takes over production from the corpus luteum (Week 11)
Influences maternal metabolism by increasing appetite
Name three substances other than hormones synthesised by the placenta
Glycogen
Cholesterol
Fatty acids
Describe the hormonal basis of testing for pregnancy
o Produced during the first two months of pregnancy
o Supports the secretory function of the corpus luteum
o Produced by syncytiotrophoblast, therefore is pregnancy specific
o Excreted in maternal urine, therefore is used as the basis for Pregnancy Testing
What immunological component does the foetus produce by the end of the first trimester?
Complement
What is the immune defence of the foetus provided by?
IgG from the mother, which is transported from mother to foetus at approximately 14 weeks. IgG is transported via receptor mediated pinocytosis.
What is haemolytic disease of the newborn?
o Rhesus blood group incompatibility of mother and fetus
o Mother previously sensitised to rhesus antigen (e.g. previous pregnancy)
o IgG against rhesus crosses the placenta and attacked foetal RBCs
o Now uncommon because of prophylactic treatment
Rhesus –‘ve mothers pregnant with Rhesus +’ve fetus given Rhesus specific IgG throughout pregnancy, to prevent sensitisation in the event of exposure to the antigen (The given IgG will bind to antigen before the mother’s immune system can mount a response)
