L31 Pregnancy, Parturition and Lactation Flashcards
What is fertilisation?
The fusion of a sperm cell (male gamete) and an egg cell (female gamete)
Where are gametes transported to during fertilisation?
Gametes transported to ampulla of oviduct (the widest part of the fallopian tube)
What cells surround the oocytes?
Oocytes - immature egg cells
They are surrounded by granulosa cells
What makes a successful penetration?
- Capacitation (changes, prepaing them for ferilitsation) in female tract
- Cervical mucus channels - smooth muscle contractions in the cervix can help direct sperm towards uterus
What is sperm acrosomal reaction?
Penetration
What happens during the Oocyte ‘activation’ cortical reaction?
There is a calcium increase:
- Second meiotic division
- Prevents polyploidy
Polyploidy is a condition in which an organism possesses more than two complete sets of chromosomes
What is polyploidy?
Polyploidy is a condition in which an organism possesses more than two complete sets of chromosomes
What is Pre-implantation?
Pre-implantation refers to the period of time before an embryo implants in the uterine lining
Describe the process of pre-implantation (3)
1) Fertilisation: The fusion of sperm and an egg to create a zygote
2) Cleavage: The zygote undergoes a series of rapid cell divisions, known as cleavage. These divisions occurs without an increase in overall size, resulting in a cluster of cells called a morula
3) Blastocyte formation: The morula further develops into a blastocyte
What is the conceptus nourished by?
Conceptus - refers to the developing embryo
Conceptus nourished by oviduct secretions - 3 days
What is a blastocyst?
A blastocyst is a hollow ball of cells that forms early in pregnancy
How does a blastocyte form? (5)
1) Fertilization: The journey begins with fertilization, where a sperm cell successfully fuses with an egg cell.
2) Zygote Formation: This fusion creates a single cell called a zygote, which contains the complete set of chromosomes from both parents.
3) Cleavage: The zygote undergoes a series of rapid cell divisions called cleavage. These divisions occur without an increase in the overall size of the embryo, resulting in a cluster of cells.
4) Morula Stage: After several rounds of cleavage, the embryo reaches the morula stage. The morula is a solid ball of 16-32 cells.
5) Blastocyst forms
What happens during the cleavage stage of the preimplantation phase?
- Rapid cell division (zygote repeatedly divides)
- Overall size of embryo remains unchanged but the number of cells increase
- Ultimately producing blastoyst
What is implantation?
The process where the fertilised egg attaches itself to the lining of the uterus
When does implantation often occur?
6-12 days after ovulation
Why is the low oestradiol to progesterone ratio important for implantation?
It’s the result of the secretory phase
What is the oestradiol to progesterone ratio like in the endometrium reception of blastocyst?
Low Oestradiol to progesterone ratio
What does the Blastocyst promote during implantation?
It promotes endometrial stromal cells to undergo significant transformation which are crucial for supporting the developing embryo
This process is called predecidualisation (actually need to know)
Blastocyst promotes endometrial stromal cells to transform into what? What is the name of this process?
Transforms into decidua
Process is called predecidualisation
What are trophblast cells?
They are the outer layer of cells in the blastocyst
The trophoblast, the outer layer of cells in the blastocyst, further differentiates into two distinct layers. What are these layers?
- Cytotrophoblast (inner): single mitotic layer
- Synctiotrophoblast (outer): produces hormones (e.g. HCG)
What are the 4 stages of endometrial invasion? Explain each stage
1) Hatching - Blastocyst, still surrounded by the zona pellucide (a protective layer), needs to disintegrate to allow the ‘hatching’ of the blastocyst
2) Apposition: Trophoblastic + endometrial epithelium membranes meet
3) Adhesion: Inner cell mass and endometrial cells interact and glue together
4) Trophoblastic cell proliferation + differentiation to syncytiotrophoblast to penetrate endometrium
What is the main role of the placental development?
Acts as a life support system for developing fetus - around 120 maternal spiral arteries bring pulsatile blood
What adaptations does the placenta have to support the baby for 9 months? (3)
- Intervillous spaces reduces force + velocity for exchange
- Syncytiotrophoblast lacunae - merge + fill with maternal blood
- Villi extends into the uterine wall, maximising the contact area between maternal and fetal blood
How does the villi/microvilli projecting into the maternal blood form?
Cytotrophoblasts and synctriotrophoblasts starts to differentiate and proliferate into villis
Foetal + maternal blood in the mature placenta is separated by what 4 things?
- Foetal capillary endothelium
- Mesenchyme
- Cytotrophoblast
- Syncytiotrophoblast
How are maternal and foetal blood different?
- Foetal haemoglobin has a higher affinity for oxygen compared to maternal haemoglobin
Fetal hemoglobin is shifted to the left compared to tht of adult haemoglobin
What substances are transported from the maternal blood to the foetal blood?
- Glucose - facilitated diffusion
- Amino acids - secondary active transport
- Vitamins - active transport
What substances are transported from the foetal blood to the maternal blood?
Waste urea, creatinine via diffusion
Why does the foetal haemoglobin have a higher affinity compared to the maternal haemoglobin?
Competitive for the same oxygen so this difference allows the fetus to efficiently extract oxygen from the mother’s blood within the placenta
How are large molecules transported between the foetal and maternal blood?
Receptor mediated endocytosis
LDL, hormones, antibodies
What is HCG?
Human chorionic gonadotropin - hormone that maintains/rescues corpus luteum
What is the result of HCG rescuing corpus luteum?
Continues secretion oestrogen and progesterone to support endometrium
What are the hormonal changes during pregnancy ?
1) When corpus luteum is developing, the hormone HCG is produced exponentially
2) When placenta starts to develop the fall of HCG starts and an increase of progesterone, prolactin and estradiol begins
What is the importance of human placental lactogens (hPL)?
1) Coordinate fuel economy - increases blood sugar so glucose more readily available for fetus (energy source)
2) Development mammary glands
How is progesterone synthesised?
- Cholesterol undergoes a series of enzymatic reactions, converting it to pregenolone
- Pregenolone is transported to SER to form progesterone where it can be transported to the mother and fetus
How is estriol synthesised?
1) Starts off with cholesterol converting to pregnenolone by a series of enzymes
2) Fetal adrenal gland produces a precursor hormone called DHEA-S
3) This is then converted into 16-OH DHEA-S by a series on enzymes in the placenta
4) This undergoes aromatisatioin which makes estriol
Estriol is primarily synthesised in the placenta during pregnancy
What is Quiescence?
Refers to the state of uterine relaxation and insenstive to uterotonic hormones
This happens because progesterone suppresses myometrial contractions
Is Quiescence 95% of the gestation period?
Yes. Uterine relaxation and inactivity is throughout the majority of pregnancy
What 3 broad things happen during stage 1 of parturition?
(Prior to birth)
- Shifting hormonal balance
- Uterine muscle changes
- Cervical changes
Describe the shifting hormonal balance during parturition stage 1
- Foetal H-P Adrenal axis increases cortisol levels which ….
- Oestrogen: progesterone ratio increases = increased contractility
- Oestrogen stimulates prostaglandin (PG) release
What are the stages of Parturition? (4)
Parturition stage
- 0) Quiescence
- 1) Activation/transformation
- 2) Stimulation/labour/birth
- 3) Involution (recovery from birth)
What does Prostaglandin do during activation/ transformation?
- Promotes formation of gap junctions
- Softening, thinning + dilation of cervix
What kind of gene expression happens during parturition stage 1?
- Increased expression of contraction- associated genes (CAPs), e.g. uterine muscle receptors such as oxytocin and prostaglandin receptors are upregulated
- Cervical gene expression - enzymes to hydrolyse collagen matrix for softening/thinning/dilation of cervix
What is the positive feedback during the 2nd stage of parturition ?
Labour
1) As baby’s head presses aginst cervix, stretch receptors in the cervix are stimulated
2) This stimulation sends signals to the brain, which triggers the release of oxytocin from pituitary gland
3) Oxytocin stimulates stronger uterine contractions
4) Thos produces stronger contractions to further push the baby’s head against the cervix, stimulating the stretch receptors even more
What are the 3 stages of labour and delivery?
- Dilation (placental relaxin)
- Expulsion
- Placental (separation from decidua)
What is the 3rd stage of parturition ?
Involution - uterus returns to its normal size after childbirth
How does haemostasis work post birth?
Vasoconstriction of the spiral arteries helps to minimise blood loss from the placental site after delivery which will decrease haemorrhage
What are the effects of decreased placental oestrogen after birth?
- Sharp decline in oestrogen leads to myometrial atrophy - involution (returning of uterus)
- Regression uterine vasculature
Decribe the hormonal changes during pregnancy (breast milk)
- Estrogen + progesterone stimulate breast growth + development
- Estrogen stimulates anterior pituitary to produce prolactin (PRL) for further development but in pregnancy, est + prog inhibit PRL action on breast
Describe the hormonal changes during postpartum
- Estrogen increases cell proliferaion
- PRL - initiates milk production
- Oxytocin increases myoepithelial contraction which stimulates ejection
- PRL + cortisol maintain milk production
How does the neuronal and hormonal systems interact to enable lactation? (4)
- Prolactin from anterior pituitary
- Oxytocin from posterior pituitary
- Downregulates GnRH release to inhibit ovarian cycle
- Inhibits dopamine release from hyporhalamus (dop. inhibits AP release of PRL)
Describe the ‘let-down reflex’
- Suckling stimulus triggers the release of oxytocin from the pituitary gland - myoepithelial cells surrounding the alveoli, causing them to contract which squirts milk out of alveoli
- Suckling stimulus also triggers the release of prolactin from the pituitary gland to produce milk
