8. implantation Flashcards
(22 cards)
What are the three distinct cell populations in a blastocyst?
- Trophectoderm
- Epiblast
- Hypoblast
These populations have specific functions in embryonic development and placentation.
What is the primary role of the trophectoderm?
Forms placental structures and extraembryonic membranes
The name ‘trophectoderm’ means ‘nutrient-seeking’.
What factors do epiblast cells express?
- Oct4
- Sox2
- Nanog
These factors are crucial for maintaining pluripotency.
What does the hypoblast contribute to?
Extraembryonic membranes (yolk sac)
Hypoblast cells are flattened epithelial cells with microvilli.
What is the window of implantation for humans?
Days 7-10/11 post-fertilization
This window is specific to the uterus.
Which hormones are required for implantation and decidualization?
- Estradiol
- Progesterone
Estradiol rises during the follicular phase and remains elevated during the luteal phase.
What changes occur in the uterus to prepare for implantation?
- Uterine glands enlarge under estrogen
- Progesterone stimulates secretions containing glucose and amino acids
- MUC1 glycoprotein coats uterine epithelium
MUC1 prevents blastocyst attachment until local removal occurs.
What is the initial attachment stage of implantation characterized by?
Lectin-glycan interactions and integrin-mediated adhesions
This attachment is relatively weak initially.
What occurs during the invasion stage of implantation?
- Trophoblast cells become invasive
- Secrete matrix metalloproteinases
- Degrade extracellular matrix of uterine wall
Invasion may also induce apoptosis in uterine epithelial cells.
Define decidualization.
Thickening of uterine wall in response to blastocyst presence
This process is dependent on progesterone.
What is the role of trophoblast cells in immune tolerance?
Express non-classical HLA-E, F, and G
This prevents recognition as foreign tissue by the maternal immune system.
How is the amniotic cavity formed in humans?
Cells in the center of epiblast form amnion
The separation creates the amniotic cavity.
What types of endodermal cells develop from the primary yolk sac?
- Visceral endoderm
- Parietal endoderm
Visceral endoderm is adjacent to the epiblast.
What does the term ‘primitive’ indicate in embryonic layers?
Layers become ‘embryonic’ as they mature
This terminology change indicates developmental progression.
What three embryonic germ layers are formed during gastrulation?
- Embryonic ectoderm
- Embryonic mesoderm
- Embryonic endoderm
Each layer has distinct developmental fates.
What type of cleavage occurs in mammals?
Holoblastic (complete) cleavage
Mammalian cleavage is characterized by a rotational pattern and asynchronous divisions.
What is unique about amphibian cleavage?
Holoblastic but unequal cleavage
Smaller cells form at the animal pole, while larger cells form at the vegetal pole.
What type of cleavage is seen in birds and reptiles?
Meroblastic (incomplete) cleavage
Only the blastodisc undergoes division, while the yolk remains intact.
What drives rapid divisions during cleavage?
Maternal Mitosis Promoting Factor (MPF)
MPF consists of Cyclin B and Cdc2 kinase.
What is the clinical application of hormonal contraceptives?
Provide high levels of estrogen/progesterone to prevent follicle development and ovulation
They act through negative feedback on FSH/LH release.
What is an ectopic pregnancy?
Implantation outside uterus
This can occur in locations such as the fallopian tube or abdomen.
What is a common cause of early pregnancy loss?
Complications during implantation and early post-implantation period
Many losses occur without recognition as pregnancies.
