Flashcards in Physiology- Pregnancy and Lactation Deck (78)
Describe the process from fertilisation to implantation
How many days after fertilisation does the blastocyst transport into the uterus?
How many days after fertilisation does the blastocyst attach to the lining of the uterus?
What happens to the inner cells of the blastocyst?
Develop into the embryo
What happens to the outer cells of the blastocyst?
Burrow into uterine wall and become placenta
What happens when the blastocysts adheres to the endometrial lining?
Cords of trophoblastic cells begin to penetrate the endometrium
What is the trophoblast?
Surface layer of cells of the blastocyst
What do the cords of trophoblastic cells do after endometrium penetration?
Tunnel deeper, carving out a hole for the blastocyst. Boundaries between cells in the advancing trophoblastic tissue disintegrate
Where is the blastocyst when implantation is finished?
Completely buried in endometrium
By what day will the blastocyst be buried in the uterine lining?
What is the placenta derived from?
Trophoblast and decidual tissue
Describe how cavities filled with maternal blood are formed from trophoblast cells
Cells (chorion) differentiate into multinucleate cells (syncytiotrophoblasts) which invade decidua and break down capillaries to form cavities
Describe what happens to the broken down capillaries in the forming of cavities
Developing embryo sends capillaries into the syncytiotrophoblast projections to form placental villi
Describe a placental villus
Each contains foetal capillaries separated from maternal blood by a thin layer of tissue- no direct contact between foetal and maternal blood
What type of exchange exists between mother and foetus?
2 way exchange of resp gases, nutrients, metabolites etc-largely down diffusion gradient
When are the placenta and foetal heart functional by?
5th week of pregnancy
What provides early nutrition to the embryo?
Invasion of trophoblastic cells into decidua
What does HCG signal the corpus luteum to continue secreting?
Progesterone- stimulates decidual cells to concentrate glycogen, proteins and lipids
Where do placental villi extend into?
The uterine wall
What is the purpose of placental villi?
Increases contact area between uterus and placenta & more nutrients and waste materials can be exchanged
What does circulation within the intervillous space of the placenta act as?
An arteriovenous shunt
What plays the role of the foetal lungs?
What is contained within umbilical blood?
Mix of arterial and venous blood
What does the exchange of CO2 follow from mother to foetus?
Reversed gradient to oxygen
Partial pressure elevated in foetal blood
What does foetal, oxygen saturated blood return to the foetus via?
The umbilical vein
What does maternal, oxygen poor blood return to the mother via?
What 3 factors facilitate the supply of oxygen to the foetus?
Foetal Hb: increased ability to carry O2
Higher Hb concentration in foetal blood (50% more than adults)
Bohr effect: Foetal Hb can carry more oxygen in low pCO2 than higher pCO2
What transport mechanisms do the placental exchange processes occur via?
Passive transport (without energy consumption)
Describe water diffusion into placenta
Exchange increases during pregnancy up to 35th week (3.5l/day)