Fertilisation and physiology of pregnancy Flashcards
Where does fertilisation occur?
Ampulla of uterine tube
What happens during day 3-5 post fertilisation?
Blastocyst transports into uterus
What happens during day 5-8 post fertilisation?
Blastocyst implat in uterine wall
What do the inner cells and outer cells of the blastocyst develop into respectively?
Inner - becomes the embryo
Outer - burrows into uterine wall and becomes placenta
What is the first step of implantation of the blastocyst?
The free-floating blastocyst adheres to the endometrial lining, cords of trophoblastic cells begin to penetrate the endometrium
What is the second step of implantation of the blastocyst?
Advancing cords of trophoblastic cells tunnel deeper into endometrium, carving out a hole for the blastocyst. The boundaries between cells in the advancing trophoblastic tissue disintegrate
When does the blastocyst become completely buried in the uterine lining?
Day 12
What is decidua?
Decidua is the term for the uterine lining (endometrium) during a pregnancy
What tissues is the placenta derived from?
Decidual tissue
Trophoblastic tissue
What are trophoblasts?
Cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta
What happens to trophoblasts to create the placenta?
They differentiate into multinucleate cells (syncytiotrophoblasts) which invade decidua and break down capillaries to form cavities filled with maternal blood
Developing embryo sends capillaries into the syncytiotrophoblast projections to form “placental villi”
How does the structure of the placental villi ensure there is no direct contact between maternal and feotal blood?
Each villus contains foetal capillaries separated from maternal blood by a thin layer of tissue – no direct contact between foetal & maternal blood
When are the placenta and foetal heart functional?
Week 5 of pregnancy
How does the placenta work as an arteriovenous shunt?
More villi are produced as the placenta develops, increasing surfact contact area between uterus and placenta, allowing more exchange
Only a thin membrane separates the embryo’s blood in the villi from mother’s blood in the intervillous space (ie. no direct contact between foetal & maternal blood).
Circulation within the intervillous space acts partly as an arteriovenous shunt
What three factors mean that sufficient oxygenation of the fetus is possible?
- Fetal Hb (increased ability to carry O2)
- Higher Hb concentration in fetal blood - more than mother (see graph)
- Bohr effect (Fetal Hb can carry more oxygen in low pCO2 than in high pCO2)
How does water cross the placenta?
Goes from mother to fetus along osmotic gradient
How do electrolytes cross the placenta?
Follow water - use the same concentration gradient as water
What is the main source of energy for the fetus?
Glucose transported across the placenta by simplified transport
How do levels of human chorionic gonadotrophin (HCG) and human chronionic somatomammotrophin (HCS) change during pregnancy?
HCG - prevents involution of corpus luteum
HCS - begins production at week 5 of pregnancy, increases steadily
What is the purpose of Human Chorionic Somatomammotropin?
Growth hormone-like effects: protein tissue formation
Decreases insulin sensitivity in mother: more glucose for the fetus
Involved in breast development and possibly lactation
What role does progesterone play in pregnancy?
Development of decidual cells
Decreases uterus contractility
Preparation for lactation
What role does estrogen play in pregnancy?
Enlargement of uterus
Breast development
Relaxation of ligaments
What are estriol levels an indicator of?
Viability of fetus
What effects does the production of corticotrophin releasing hormone from the placenta have on the mother?
Activates ACTH:
aldosterone production can result in hypertension
glucocorticoid production can cause oedema, insulin resistance and gestational diabetes
