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Which hormone is responsible for maintaining the corpus luteum during early pregnancy?
What role does progesterone play during pregnancy?
In which timeframe can hCG typically be detected in maternal urine after implantation?
What is progesterone's relationship to estrogen during pregnancy?
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What effect does a progesterone receptor blocker, like Mifepristone, have during pregnancy?
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What marks the beginning of the establishment of fetal blood flow?
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What type of nutrition is characterized by the transport of materials from maternal endometrial fluids before implantation?
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What structure is formed by cytotrophoblast cells as they migrate into the maternal endometrium?
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What is the primary function of the placenta during pregnancy?
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Which hormone is initially responsible for sustaining the corpus luteum during early pregnancy?
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Which of the following is primarily responsible for converting maternal vessels into low pressure, high capacity circulation?
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What is the primary role of branching villi in the placenta?
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What does decidualization refer to in the context of implantation?
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Failure in the conversion of maternal vessels to low pressure circulation can lead to which of the following complications?
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Which of the following structures begins to form immediately after the fertilization of the ovum?
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Which week marks the completion of maternal blood flow development through the placenta?
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What is a consequence of a non-receptive endometrium during implantation?
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Where do the lacunae that pool maternal blood originate?
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What are the main components exchanged between maternal blood and fetal circulation?
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What embryonic structure develops after the morula stage but before the implantation?
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Which condition can lead to failed implantation or miscarriage according to known risks?
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Which hormone is primarily responsible for promoting uterine growth in conjunction with oestrogens during pregnancy?
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What is the effect of progesterone dominance in the context of pregnancy?
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Which molecule is transported via active transport mechanisms during pregnancy?
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What critical physiological role does hCG play shortly after implantation?
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Which characteristic of progesterone levels is essential for the continuation of pregnancy?
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What is the primary purpose of extravillous trophoblast cells during placental development?
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During which week does fetal blood flow begin to be established?
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What occurs during the decidualization response in implantation?
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What type of villi are primarily involved in nutrient exchange between maternal and fetal blood?
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Which of the following factors can contribute to a non-receptive endometrium?
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What potential complication is associated with inadequate conversion of maternal vessels to low pressure circulation?
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How does the trophoblast contribute to endometrial changes during implantation?
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What is a potential consequence of decreased levels of hCG in early pregnancy?
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Which of the following statements about the lacunae in the syncytiotrophoblast is accurate?
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What is the direct function of the placenta in relation to fetal waste?
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What is the effect of decidualization on uterine blood vessels?
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Which cellular structure forms as the trophoblast proliferates during implantation?
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Cytotrophoblast cells contribute to the formation of which structure necessary for placenta anchoring?
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What type of nutrition characterizes the supply of maternal endometrial fluids prior to implantation?
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What essential nutrient provided by the placenta is crucial for fetal energy needs?
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What does the presence of maternal blood pooling in the placenta indicate?
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What is the primary role of integrins on the trophoblast during implantation?
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What happens to the blastocyst if the endometrium is not mature during implantation?
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During implantation, which process involves syncytiotrophoblast cells invading endometrial cells?
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What is one of the main functions of the placenta regarding fetal development?
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What percentage of implanted embryos typically result in miscarriage?
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Which of the following hormones is produced by trophoblast cells to signal the corpus luteum?
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Which statement accurately describes the source of progesterone during the first 50 days of pregnancy?
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What is the consequence if progesterone levels fall or its receptor is blocked during pregnancy?
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In the context of the placenta, what function does the maternal blood pool serve?
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What is a common aetiology for implantation failure?
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Which mechanisms allow for the transport of glucose and lactate during pregnancy?
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What physiological changes are caused by the dominance of progesterone throughout gestation?
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What role does the cytotrophoblast play in the formation of the placenta?
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What is the primary function of extravillous trophoblast cells?
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Which type of molecules can diffuse through the placental barrier via simple diffusion?
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Which week marks the establishment of fetal blood flow?
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What is responsible for pooling maternal blood in the placenta?
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What complication is associated with failure in converting maternal vessels to low pressure circulation?
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What nutrition type is completed by Week 14 during placental development?
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Which type of chorionic villi are primarily responsible for nutrient exchange?
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What is a key characteristic of maternal and fetal blood circulation in relation to the placenta?
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Study Notes
Pre-Implantation
- Zygote is the first cell of a new organism
- Morula stage has 8-16 cells
- Blastocyst stage has 32-64 cells
- Trophoblast: outer layer of blastocyst
- Embryoblast: inner cell mass
Implantation and Embryonic Phase
- Implantation occurs 12 days after ovulation
- Blastocyst relies on secretions from the oviduct and endometrium
- Endometrium is receptive for a short window of 3 days due to maximum progesterone production by the corpus luteum
- Integrins on the trophoblast allow blastocyst to attach to receptors on the endometrium
- If the endometrium is not mature, the blastocyst can detach and implant later
Implantation Process
- Trophoblast with integrins adhere to the endometrium with receptors
- The trophoblast proliferates and becomes:
- Cytotrophoblast (inner layer)
- Syncytiotrophoblast (outer layer)
- Syncytiotrophoblast cells invade the endometrial cells until the blastocyst is buried
- Endometrial cells cover the blastocyst forming a seal
- Trophoblast initiates local changes in the endometrium:
- Change in matrix composition
- Change in stromal cell morphology
- Sprouting and ingrowth of capillaries
- Trophoblast cells produce human chorionic gonadotropin (hCG) which signals the corpus luteum to continue producing progesterone and estrogen until 8 weeks
Implantation issues
- Even with a healthy embryo, implantation failure rate is high:
- ⅔ blastocysts fail to implant
- ⅓ of implanted embryos miscarry
- Lack of hCG can lead to decreased estrogen and progesterone, causing sloughing of the endometrium
Etiology of Implantation Issues
- Scarring of the uterus: Pelvic inflammatory disease
- Hormonal imbalances: Polycystic Ovary Syndrome (PCOS)
- Non-receptive endometrium
- Ectopic pregnancy: implantation outside the uterus
- Placenta previa: blastocyst implants near the opening of the cervix
- The placenta covers the opening to the vagina
- Placenta can separate prematurely
Function of the Placenta
- Provides nutrients and removes fetal waste:
- Nutrients: glucose, lipids, minerals, oxygen
- Wastes: urea, heat, carbon dioxide
- Fetus is independent from fetal brain, lung, gut, kidneys
- Fetus depends on liver/spleen for:
- Hematopoiesis
- Cardiovascular system function
- Partial immunological barrier
- Synthesizes and secretes hormones required for pregnancy and fetal growth:
- Steroids: progesterone, estrogen
- Prostaglandins: PGE2, PGF2alpha
- hCG, hPL
- CRH, GH, ACTH, GnRH, TSH
- Relaxin
- Doppler ultrasound can test fetal growth and placental function
Maternal Blood Flow in the Placenta
- Maternal blood via spiral arteries pools in the maternal blood pool
- Fetal circulation passes through the umbilical cord and enters the chorionic villi where exchange occurs
Formation of the Placenta
- Syncytiotrophoblast cells form a multinucleated wall after implantation
- Decidualization response damages uterine blood vessels
- Blood from uterine spiral arteries pool in the lacunae of the syncytiotrophoblast containing maternal blood
- The lacunae merge
- Cytotrophoblast sends cells to anchor the placenta to the endometrium forming the 1˚ chorionic villi
- At week 3, fetal mesoderm layer expands to form 2˚ chorionic villi
- Blood vessels enter the villi forming 3˚ chorionic villi
- Cytotrophoblasts form the cytotrophoblastic shell
- Villi attached to this are called anchoring villi
- Villi branching off the sides are called branching villi (main site of exchange)
- Fetal blood flow is established by week 4
Formation of the Placenta: Conversion
- Second differentiation of the cytotrophoblast cells
- Matured maternal blood flow develops by weeks 10-12
- Forms the extravillous trophoblast cell:
- Cytotrophoblast cells detach from the villi and migrate into the maternal endometrium and myometrium
- Cells that migrate along maternal spiral arteries become endovascular extravillous trophoblast
- Function to convert maternal vessels into a low pressure, high capacity circulation by:
- Loss of smooth muscle, endothelial lining and vasoreactivity
- Failure associated with complications, such as high pressure breaking villi and causing poor diffusion:
- Preeclampsia
- Intrauterine growth restriction of the fetus
Maternal to Embryonic Nutrition
-
Histiotrophic nutrition: Before implantation and early implantation
- Endometrial fluids, mainly from uterine glands
- Materials pass through a thin layer of trophoblast and are distributed via diffusion
- As mesoderm develops, blood vessels develop and link up to form a network
-
Haemotrophic nutrition: Blood-borne via placenta. Complete by week 14
- Maternal and fetal circulation are separate:
- Uterine arteries and veins between mother and placenta
- Umbilical arteries and veins between fetus and placenta
- Arteries carry blood away from the heart towards the placenta
- Umbilical arteries are paired and umbilical veins are singular
- Maternal and fetal circulation are separate:
- Transport:
- Simple diffusion: Low molecular weight and non-polar molecules
- Facilitated diffusion: Glucose, lactate
- Active transport: Amino acids, iron, calcium, phosphorus, vitamins
- Permeable to alcohol, nicotine, and drugs
Hormones During Pregnancy
| Hormone | Produced By | Function |
|---|---|---|
| hCG | Blastocyst | Maintains the corpus luteum which secretes progesterone and estrogen, maintaining pregnancy. Found in maternal urine 2-3 days post-implantation |
| Progesterone (P4) | Corpus luteum (first 50 days) | Keeps the myometrium and uterine muscle inactive (antagonizes oestrogens). Promotes uterine growth with oestrogens. Relaxations of smooth muscle in genital, vascular, urinary and GI tracts. Extended secretion critical for initiation and maintenance of pregnancy. If levels fall or receptor is blocked, pregnancy fails. |
| Placental trophoblast |
Pre-Implantation
- Zygote is the first stage of development after the egg is fertilized by sperm.
- Morula is a solid ball of 8-16 cells formed by the division of the zygote
- Blastocyst is a hollow ball of 32-64 cells formed by the further division of the morula.
- Blastocyst has two main cell types: trophoblast and embryoblast.
- Trophoblast forms the outer layer of the blastocyst. It will eventually develop into the placenta.
- Embryoblast forms the inner cell mass of the blastocyst. This will develop into the embryo itself.
Implantation and Embryonic Phase
- Implantation occurs approximately 12 days after ovulation.
- The endometrium is the inner lining of the uterus. It becomes receptive for a short window of 3 days, coinciding with the maximum progesterone secretion from the corpus luteum.
- Integrins on the trophoblast help the blastocyst attach to the endometrium.
- If the endometrium is not ready, the blastocyst will detach and move to the lower part of the uterus to try again.
Implantation Process
- The trophoblast adheres to the endometrium.
- The trophoblast proliferates and forms two layers: cytotrophoblast (inner) and syncytiotrophoblast (outer).
- The syncytiotrophoblast invades the endometrial cells until the blastocyst is completely embedded.
- Endometrial cells cover the blastocyst, forming a seal.
- The trophoblast initiates local changes in the endometrium, including: - Changes in matrix composition. - Change in stromal cell morphology. - Sprouting and ingrowth of capillaries.
- The trophoblast cells produce human chorionic gonadotropin (hCG), which signals the corpus luteum to continue producing progesterone and estrogen until 8 weeks of pregnancy.
Implantation Issues
- Despite a healthy embryo, the implantation rate is low.
- Over two-thirds of blastocysts fail to implant.
- One-third of implanted embryos miscarry.
- Lack of hCG leads to a decrease in estrogen and progesterone, causing the endometrium to shed.
- The causes of implantation failure are largely unknown.
- Potential causes include:
- Scarring of the uterus from pelvic inflammatory disease.
- Hormonal imbalances from Polycystic Ovary Syndrome (PCOS).
- Non-receptive endometrium.
- Ectopic pregnancy (implantation outside of the uterus).
- Placenta previa (implantation near the opening of the cervix)
- Placenta can cover the opening to the vagina.
- Placenta may separate prematurely.
The Placenta
- Provides all nutrients and removes all fetal waste.
- Nutrients include: glucose, lipids, minerals, and oxygen.
- Waste products include: urea, heat, and carbon dioxide.
- The fetus is independent of fetal brain, lung, gut, and kidneys.
- The fetus is dependent on its liver and spleen for haematopoiesis, cardiovascular system, and the placenta.
- Acts as a partial immunological barrier, as the fetus is foreign to the mother.
- Synthesizes and secretes hormones needed for the maintenance of pregnancy and growth of the fetus.
- Steroids: progesterone and estrogen
- Prostaglandins: PGE2 and PGF2alpha
- hCG, hPL
- CRH, GH, ACTH, GnRH, TSH
- Relaxin (also produced by the corpus luteum)
- The Doppler Ultrasound can test the growth of the fetus and the function of the placenta.
The Placenta Circulation
- Maternal blood flows through spiral arteries and pools in the maternal blood pool.
- Fetal blood circulation passes through the umbilical cord and enters the chorionic villi, where the exchange occurs.
Formation of the Placenta
- After implantation, the syncytiotrophoblast cells form a multinucleated wall.
- The decidualization response damages uterine blood vessels.
- Blood from uterine spiral arteries pools in lacunae (spaces) of the syncytiotrophoblast. These spaces contain maternal blood.
- Lacunae merge.
- Cytotrophoblast extends cells to anchor the placenta to the endometrium, forming the primary chorionic villi.
- By week 3, the fetal mesoderm layer expands under the cytotrophoblast, forming the secondary chorionic villi.
- Blood vessels enter the villi to form the tertiary chorionic villi.
- Cytotrophoblasts form a cytotrophoblastic shell.
- Villi attached to the shell are called anchoring villi.
- Villi branching off the sides are called branching villi, which are the main site of exchange.
- Fetal blood flow is established by week 4.
Formation of the Placenta (Continued)
- The cytotrophoblast cells differentiate into a fully mature maternal blood flow by Week 10-12, forming the extravillous trophoblast cell.
- Cytotrophoblast cells detach from villi and migrate into the maternal endometrium and myometrium.
- Cells that migrate along maternal spiral arteries become endovascular extravillous trophoblast.
- The extravillous trophoblast converts maternal vessels into a low-pressure, high-capacity circulation by:
- Loss of smooth muscle, endothelial lining, and vasoreactivity.
- Failure can cause complications, as too much pressure breaks villi, leading to poor diffusion. This is linked to pre-eclampsia and intrauterine growth restriction of the fetus.
Maternal to Embryonic Nutrition
-
Histiotrophic nutrition occurs before implantation and in early implantation.
- Endometrial fluids, mainly from uterine glands, are consumed.
- Materials pass through a thin layer of trophoblast and are distributed by diffusion.
- As mesoderm develops, blood vessels form and connect to create a network.
-
Haemotrophic nutrition occurs via the placenta and is complete by week 14.
- This involves the utilization of blood-borne nutrients.
- Maternal and fetal circulation are separate.
- Uterine arteries/veins connect the mother and placenta.
- Umbilical arteries/veins connect the fetus and placenta.
- Arteries carry blood away from the heart towards the placenta.
- Umbilical arteries are paired, while the umbilical vein is singular.
-
Transport:
- Simple diffusion for low-molecular weight and non-polar molecules.
- Facilitated diffusion for glucose and lactate.
- Active transport for amino acids, iron, calcium, phosphorus, and vitamins.
- The placenta is permeable to alcohol, nicotine, and drugs.
Hormones During Pregnancy
-
hCG is produced by the blastocyst and can be found in maternal urine 2-3 days post-implantation.
- It maintains the corpus luteum, which continues to secrete progesterone and estrogen, sustaining the pregnancy.
-
Progesterone is produced by the corpus luteum for the first 50 days and by the placental trophoblast after that.
- This hormone maintains the myometrium (uterine muscle) and uterine lining inactive by antagonizing the effects of estrogen.
- Progesterone contributes to uterine growth with estrogen.
- Progesterone relaxes smooth muscle in the genital, vascular, urinary, and gastrointestinal tracts.
- Extended progesterone secretion is essential for the initiation and maintenance of pregnancy.
- If levels fall or the progesterone receptor is blocked, pregnancy fails. This is the mechanism of action of progesterone receptor blockers (Mifepristone) used for medical abortion of pregnancies.
Pre-Implantation
- Zygote: The first stage of development after fertilization, a single cell.
- Morula: A solid ball of 8-16 cells formed from the zygote.
-
Blastocyst: A hollow ball of 32-64 cells formed from the morula, containing the trophoblast and the embryoblast (inner cell mass).
- Trophoblast: The outer layer of cells that will develop into the placenta.
- Embryoblast: The inner cell mass that will develop into the embryo.
Implantation and Embryonic Phase
-
Day 12 after ovulation: The blastocyst implants in the endometrium, facilitated by the receptive state of the endometrium and the presence of integrins on the trophoblast.
- Receptive endometrium: Achieved by the window of 3D in conjunction with maximum progesterone release from the corpus luteum.
-
Process:
- Adherence: The trophoblast adheres to the endometrium.
- Trophoblast proliferation: The trophoblast divides and forms the cytotrophoblast and syncytiotrophoblast.
- Decidualization response: The syncytiotrophoblast cells invade the endometrial cells, burying the blastocyst.
- Endometrial seal: The endometrial cells cover the blastocyst, forming a seal.
-
Trophoblast-induced endometrial changes:
- Matrix composition alterations.
- Stromal cell morphology changes.
- Capillary sprouting and ingrowth.
- Human chorionic gonadotropin (hCG) production: hCG is produced by the trophoblast and signals to the corpus luteum to continue producing progesterone and estrogen for 8 weeks.
Implantation Issues
-
High failure rate: More than two-thirds of blastocysts fail to implant, and a third of implanted embryos miscarry.
- Lack of hCG: Leads to a decrease in estrogen and progesterone, causing the endometrium to slough off.
-
Aetiology:
- Uterine scarring: Pelvic inflammatory disease.
- Hormonal imbalances: Polycystic ovary syndrome (PCOS).
- Non-receptive endometrium.
- Ectopic pregnancy: Implantation outside the uterus.
-
Placenta previa: The blastocyst implants near the cervical opening.
- Placental coverage of the vaginal opening.
- Premature placental separation.
The Placenta
-
Function: Supports the fetus through:
- Nutrient delivery: Glucose, lipids, minerals, and oxygen.
- Waste removal: Urea heat, and CO2.
- Fetal independence: From the fetal brain, lungs, gut, and kidneys.
- Fetal dependence: On the liver and spleen for hematopoiesis, cardiovascular system function, and placental function.
- Immunological barrier: Partial barrier against the mother's immune system, ensuring the fetus is not rejected.
- Hormone production: Progesterone, estrogen, prostaglandins (PGE2, PGF2alpha), hCG, human placental lactogen (hPL), corticotropin-releasing hormone (CRH), growth hormone (GH), adrenocorticotropic hormone (ACTH), gonadotropin-releasing hormone (GnRH), thyroid-stimulating hormone (TSH), and relaxin.
- Fetal monitoring: Doppler ultrasound assesses fetal growth and placental function.
Placenta Formation
- Syncytiotrophoblast formation: Forms a multinucleated wall.
- Decidualization response: Damages uterine blood vessels.
- Maternal blood pooling: Maternal blood from uterine spiral arteries collects in the lacunae (spaces) of the syncytiotrophoblast, forming the maternal blood pool.
- Lacunae fusion: Lacunae merge.
-
Chorionic villi formation:
- 1° chorionic villi: Formed by cytotrophoblast cells anchoring the placenta to the endometrium.
- 2° chorionic villi: Developed by week 3, when the fetal mesoderm layer expands under the cytotrophoblast.
- 3° chorionic villi: Formed by blood vessel integration into the villi, becoming the main sites of exchange.
-
Cytotrophoblastic shell formation:
- Anchoring villi: Villi attached to the shell.
- Branching villi: Villi branching off the sides of the shell.
- Fetal blood flow establishment: Established by week 4.
Placental Conversion
- Cytotrophoblast differentiation: The second differentiation of cytotrophoblast cells into extravillous trophoblast cells.
- Mature maternal blood flow: Fully developed by week 10-12.
-
Extravillous trophoblast formation: Cytotrophoblast cells detach from villi and migrate into the maternal endometrium and myometrium, converting the maternal spiral arteries into low-pressure and high-capacity circulation.
- Endovascular extravillous trophoblast: Cytotrophoblast cells that migrate along the maternal spiral arteries.
-
Conversion mechanism:
- Vascular adaptations: Loss of smooth muscle, endothelial lining, and vasoreactivity.
- Failure complications: High pressure can break villi and hinder diffusion, leading to pre-eclampsia and intrauterine growth restriction of the fetus.
Maternal to Embryonic Nutrition
-
Histiotrophic nutrition: Occurs before and during early implantation, relying on endometrial fluids and diffusion through a thin layer of trophoblast.
- Uterine glands: Contribute to the endometrial fluids.
-
Haemotrophic nutrition: Occurs via the placenta from week 14 onwards.
-
Separate circulations: Maternal and fetal circulations are distinct.
- Maternal circulation: Uterine arteries and veins between the mother and placenta.
- Fetal circulation: Umbilical arteries and veins between the fetus and placenta.
-
Transport mechanisms:
- Simple diffusion: For low molecular weight and non-polar molecules.
- Facilitated diffusion: For glucose and lactate.
- Active transport: For amino acids, iron, calcium, phosphorus, and vitamins.
-
Separate circulations: Maternal and fetal circulations are distinct.
Hormones During Pregnancy
-
Human chorionic gonadotropin (hCG):
- Source: Blastocyst.
- Detection: Found in maternal urine 2-3 days after implantation.
- Function: Maintains the corpus luteum, ensuring progesterone and estrogen production to sustain the pregnancy.
-
Progesterone (P4):
- Source: Corpus luteum (first 50 days) and placental trophoblast.
-
Function:
- Relaxes the myometrium and uterine muscles, preventing premature contractions and labor.
- Promotes, with estrogen, uterine growth.
- Relaxes smooth muscles in the genital, vascular, urinary, and gastrointestinal tracts.
- Essential for the initiation and maintenance of pregnancy.
- Low levels or blocked receptors lead to pregnancy failure.
- Progesterone receptor blockers: Such as Mifepristone, are used for medical abortion.
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