16) Placenta Flashcards
What happens to placental membrane over the course of pregnancy?
Becomes progressively thinner
What are the aims of implantation?
Establish basic unit of exchange - chorionic villi
Anchor placenta - cytotrophoblast shell
Establish maternal blood flow in placenta
Describe the development of chorionic villi:
Primary - finger like projections of trophoblast
Secondary - invasion of mesenchyme into core
Tertiary - invasion of mesenchyme ore by fetal vessels
Give examples of implantation defects:
Ectopic pregnancy
Placenta praevia
What are pre-decidual/decidual cells?
Specialised cells of endometrium which control degree of implantation
What vascular modifications are required for endometrial vessels?
Creation of low resistance, high flow vascular bed by trophoblast invasion of spiral arteries
If there is inadequate modification of vessel walls, what can occur?
Pre-eclampsia
What can occur if invasion is incomplete?
Placental insufficiency
Describe the macrostructure of the placenta :
Covered in amniochorion
Organised into cotyledons
Describe the blood supply in the chorionic villi:
Two umbilical arteries - deoxygenated blood from fetus to placenta
Umbilical vein - oxygenated blood from placenta to fetus
What are anchoring villi?
Villi with cytotrophoblast cells that migrate to endometrial spiral arteries to develop uteroplacental circulation
What is the difference between placental barrier in 1st and 3rd trimester?
1st trimester - thick with complete layer of cytotrophoblast
3rd trimester - thin with scattered cytotrophoblast layer
What are the metabolic and endocrine functions of the placenta?
Synthesis of glycogen, cholesterol and fatty acids
Production of hormones
What steroid hormones does the placenta produce?
Progesterone and oestrogen
What protein hormones does the placenta produce?
hCG, hC somatomammotropin, hC thyrotropin, hC corticotropin
What is the function of hCG?
Maintain secretory function of corpus luteum
What can hCG be used for clinically?
Pregnancy testing - excreted in maternal urine
What can cause a large hCG in pregnancy?
Twins
Trophoblast disease: molar pregnancy (overgrowth of placental tissue) or choriocarcinoma
What is the function of human placental lactogen?
Increases glucose availability to fetus
How can substances be transported across the placenta? Give examples:
Simple diffusion - water, gases
Facilitated diffusion - glucose
Active transport - AAs, iron
Receptor mediated endocytosis - IgG
Why is it important for IgG to be transferred to the fetus?
Provides passive immunity as fetal immune system matures
What is transferred from fetus to mother across the placenta?
Waste products e.g. CO2, urea
Hormones
What is transferred from mother to fetus across the placenta?
Oxygen
Nutrients
Antibodies
Harmful substances
Give some examples of teratogens:
Drugs - thalidomide, alcohol
Infectious agents - varicella zoster, rubella
What is haemolytic disease of the newborn?
Where there is rhesus blood group incompatibility between mother and fetus so IgG transfer destroys fetal RBCs
