Pregnancy, parturition + lactation Flashcards
Semester 1 year 1
What are oocytes surrounded by?
Granulosa cells
What must happen to allow the sperm to penetrate the egg?
-sperm undergo physiological changes to their membrane + increase mobility in the vagina
-smooth muscle contractions in uterus + fallopian tubes to aid sperm trajectory
-cervical mucus made into channels to help sperm be propelled
How does fertilisation occur?
-sperm undergo acrosomal reaction that allows penetration
-acrosome contains enzymes that break down the egg
-a cortical reaction activated the oocyte - increase in Ca2+, causing 2nd meiotic division + prevents polyploidy
Describe what happens to the fertilised egg pre-implantation
-it’s nourished by oviduct secretions as it moves along it for 3 days
-when it reaches uterus, it floats freely for another 3 days
-then forms a blastocyst (becomes lined by trophoectoderm layer)
-after 6 days, blastocyst is implanted
Why does it take 3 days for the fertilised egg to move along the fallopian tube?
-impeded by contractions of isthmus stopping it from reaching uterus
-allows womb lining to generate for implantation
Describe the process of implantation of the fertilised egg
-blastocyst received into endometrium supported by secretory phase, where there’s a low oestradiol to progesterone ratio
-blastocyst promotes transition of endometrial stromal cells into decidua cells (predecidualisation)
-blastocyst trophoblast cells used to gain nourishment from endometrium
Describe inner and outer cytotrophoblasts
-inner = single mitotic layer that differentiates into:
-outer = produces hormones
What are the stages of endometrial invasion?
- hatching
- apposition
- adhesion
- invasion
Describe the hatching stage of endometrial invasion
The zona pellucida surrounding the blastocyst begins to disintegrate
Describe the apposition stage of endometrial invasion
-trophoblastic + endometrial epithelium membranes meet
-complete degradation of zona pellucida
Describe the adhesion stage of endometrial invasion
-adhesion between maternal + developing trophoblast cells
-have intracellular + extracellular integrins
Describe the invasion stage of endometrial invasion
-trophoblastic cell proliferation + differentiation to syncytiotrophoblast
-syncytiotrophoblast penetrates the endometrium
Describe the structure of the placenta
-maternal spinal arteries bring food
-intervillous space reduces force + velocity to allow for exchange
-syncytiotrophoblast lacunae merge + fill with maternal blood
-cytotrophoblast + syncytiotrophoblast form villi/microvilli projecting into maternal blood
In a mature placenta, what separates maternal and foetal blood?
-foetal capillary endothelium
-mesenchyme
-cytotrophoblasts
-syncytiotrophoblast
What substances are transported between maternal and foetal blood and how?
-from M to F: glucose (F. diffusion), amino acids (2 active transport), vitamins (active transport)
-from F to M: waste urea + creatinine
-large molecules move by receptor-mediated endocytosis
-oxygen exchange facilitated by higher oxygen affinity of foetal haemoglobin
What hormonal changes occur during trimester 1?
-in trophoblasts (then placenta), human chorionic gonadotropin (HCG) ‘rescues’ the corpus luteum
-as a result, corpus luteum continues secretion of oestrogen + progesterone to support the endometrium
What hormonal changes occur during trimester 2-3?
-placenta becomes primary hormone source, replacing corpus luteum
-human placental lactogens (group of hormones) are secreted
What do the human placental lactogens do?
-coordinate fuel economy (what’s given to foetus + what remains with mum)
-control development of mammary glands
What are the stages of partuition?
-stage 0 - quiescence
-stage 1 - activation/transformation
-stage 2 - stimulation/labour/birth
-stage 3 - involution recovery from birth
Describe stage 0 of parturition
-from conception to initiation of parturition
-uterus is relaxed + insensitive to uterotonic hormones
-progesterone suppresses myometrial contractions
Describe stage 1 of parturition
-preparation of birth
-foetal-hypothalamic pituitary adrenal axis increases cortisol production
-cortisol increases oestrogen-progesterone ratio to increase contractility
-oestrogen stimulates prostaglandin (PG) release
-gene expression of contraction-associated proteins (CAPs), receptors for OT + PG, enzyme PG synthesis
-cervical gene expression of enzymes to hydrolyse collagen matrix
What do prostaglandins (PG) do?
-promotes gap junction formation
-causes softening, thinning + dilation of cervix
Describe stage 2 of parturition
-increased PG levels cause myometrial contraction due to OT + cervical dilation
-increased myometrial connectivity due to gap junctions
-increased myometrial responsiveness due to PG + OT receptors
-+ive feedback leads to Ferguson reflex (neuroendocrine regulation of OT) + uterine contraction to stimulate PG
-stages of labour + delivery: dilation, expulsion, placental
Describe stage 3 of parturition
-haemostasis
-decreased placental oestrogen causes: myometrial atrophy (myometrium muscle starts to regress - involution) + regression of uterine vasculature
-cervix remodelling
-reestablishment of endometrial cycle after 3-5 months
What is haemostasis?
Vasoconstriction of spinal arteries to decrease risk of haemorrhage
Where does lactation occur and what makes up the area?
-secretory unit of breast
-made up of: alveoli surrounded by contractile myoepithelial cells + adipose tissue
Describe the hormonal effects of pregnancy on lactation
-oestrogen + progesterone stimulate breast growth + development
-oestrogen stimulates anterior pituitary gland to produce prolactin (PRL) for further development
-oestrogen + progesterone inhibit PRL lactogenic action on the breast
Describe the postpartum hormone action on lactation
-oestrogen increases cell proliferation
-PRL initiates milk production
-OT increases myoepithelial contraction for ejection
-PRL + cortisol maintain milk production
What must interact to enable lactation?
Neuronal + hormonal systems
Why is PRL essential for production of milk?
-inhibits dopamine released
-OT from posterior pituitary
-downregulates release of GnRH to inhibit ovarian cycle
