Endocrinology of Pregnancy Flashcards
Where is tubular fluid reabsorbed and what controls this process?
Rete testis
Early epididymis
This is under the control of oestrogen
Where do you find oestrogen within the male reproductive tract?
Tubular fluid produced by sertoli cells
What stimulates the release of nutrients and other molecules (e.g. glycoproteins) into the epididymal fluid?
Androgens
What are the roles of these secreted nutrients and molecules?
Provide energy for the impending journey
Coat the surface of the spermatozoon (to protect them from the hostile environment)
Within which part of the male reproductive tract is fluid reabsorbed and secretory products put in?
Epididymis
Why is the concentration of sperm in the vas deferens higher than further down the reproductive tract?
Further down the reproductive tract, other fluids and secretory products are added thus diluting the sperm.
Where is a vasectomy performed?
Lower end of the vas deferens
Which structures contribute to the seminal fluid?
Epididymis/testes (small contribution)
Seminal vesicle (2/3)
Prostate (1/3)
Why is there fibrinogen and fibrinolytic enzymes in the seminal fluid?
After ejaculation, the semen initially clots and then must be broken down
Describe the capability of the spermatozoa in the seminiferous tubule.
Quiescent and incapable of fertilising an ovum
Describe the capabilities of the spermatozoa in the vas deferens.
Capable of limited movement
Limited capability to fertilise an ovum
When do sperm achieve full activity and capability achieved and what is the name given to this process?
Capacitation
This occurs within the female reproductive tract
What 3 changes take place in capacitation?
Loss of glycoprotein coat
Change in surface membrane characteristics (leading to acrosome reaction when in close proximity to the ovum)
Whiplash movements of the tail
What are all these changes dependent on?
Oestrogen
Calcium
Describe the acrosome reaction.
Spermatozoon binds to ZP3 glycoprotein on the zona pellucida
Once bound to ZP3, progesterone stimulates calcium influx into the spermatozoon
This results in a calcium-dependent acrosome reaction
This enables an exposed spermatozoon recognition site to bind to ZP2
Once bound to ZP2, the acrosome releases its enzymes allowing penetration of the zona pellucida so that the head of the spermatozoon can enter the ovum
Where does fertilisation normally occur?
Fallopian tube
What does fertilisation result in the expulsion of?
Second polar body
The zonal reaction immediately follows fertilisation. Describe the zonal reaction.
Cortical granules release molecules that degrade the zona pellucida (including ZP3 and ZP2)
This prevents further binding of other sperm
This is also CALCIUM dependent
Describe how the conceptus receives nutrients before implantation.
Uterine secretions
How long is this free-living phase of the conceptus?
9-10 days
In what stage of the menstrual cycle is all of this occurring?
Luteal phase – oestrogen and progesterone are high
What does the conceptus compact to form?
8-16 cells morula
What are the two parts of the blastocyst?
Inner cell mass – becomes the embryo
Trophectoderm – becomes the chorion (which becomes the placenta)
What hormonal change facilitates the transfer of the conceptus to the uterus?
Increasing progesterone: oestrogen ratio
What is a decidua?
Thick layer of modified mucous membrane, which lines the uterus during pregnancy and is shed with afterbirth
What hormone environment is required for implantation?
Progesterone dominance in the presence of oestrogen
State 2 molecules that are of particular importance in implantation. Mention which cells produce these molecules.
Leukaemia inhibitory factor (LIF)
Produced by endometrial secretory glands
Stimulates adhesion (attachment) of blastocyst to endometrial cells
IL-11
Also released from endometrial cells and released into uterine fluid
When the trophoblast cells of the blastocyst invade the underlying uterine stromal tissue, you get a decidualisationreaction. What main changes take place in decidualisation?
Increased vascular permeability in the invasion region, associated with oedema of tissues
Localised changes in intracellular composition and progressive sprouting and growth of capillaries
Which chemical factors are involved in decidualisation?
Mainly IL-11
Histamine
Certain prostaglandins
TGF-beta = promotes angiogenesis
What is the role of hCG and when does it peak?
Peaks at 8 weeks and is particularly important in the first 6 weeks
It mimics LH by binding to LH receptors on the corpus luteum and stimulating the production of oestrogen and progesterone
NOTE: hCG is produced by trophoblast cells
What change takes place after about 5 weeks?
The role of hormone production is handed over from the corpus luteum to the placenta
Describe how oestrogen and progesterone levels change throughout pregnancy.
Oestrogen and progesterone levels continue to rise through pregnancy with progesterone always being the dominant influence
What is human placental lactogen? Describe its roles.
It is a growth hormone that has prolactin like effects
It is important for the growth and development of the foetus
After what point would oophorectomy have no effect on pregnancy and why?
After around 6 weeks (40 days)
By this point the placenta would have taken over the role of hormone production so the ovaries are no longer needed
Which steroid precursor tends to be provided by the mother for the foetus?
Pregnenolone
Which androgen is formed by the maternal and foetal adrenals?This is used as a precursor for oestrogen production.
Dehydroepiandrosterone Sulphate (DHEAS)
Which oestrogens are produced by the placenta using DHEAS from the mother and foetus?
Oestradiol
Oestrone
These two oestrogens aren’t a good measure of foetal health. Explain why.
These oestrogens are dependent on precursor production from the both the foetal AND maternal adrenals.
Therefore, it is not a good measure of foetal health.
What is the main oestrogen of pregnancy? Describe how it is produced.
OESTRIOL
DHEAS from the foetal adrenals is conjugated in the foetal liver to form 16-alpha-hydroxy DHEAS
16-alpha-hydroxy DHEAS is then de-conjugated in the placenta and used to produce oestriol
What can be measured to gage the health of the foetus?
Oestriol: oestradiol + oestrone levels
Oestriol: total oestrogens
Describe how maternal hormones change in pregnancy.
Most hormones increase in pregnancy (the pituitary gland becomes enlarged) Hormones that increase: Thyrotrophin Corticotrophin Prolactin Growth hormone Iodothyronines Adrenal steroids PTH Hormones that decrease: Gonadotrophins hGH (because placental hGH variant increases towards term) NOTE: hGH = human growth hormone
What biochemical change is required for contraction of the uterus during parturition?
Increase in intracellular calcium concentration
Describe how oestrogen increases the chance of contraction.
Oestrogen binds to oestrogen receptors and triggers the synthesis of prostaglandins within the endometrial cells.
Prostaglandins stimulate the release of calcium from intracellular stores.
So oestrogen tends to increase the chance of contraction
Describe how oxytocin increases the chance of contraction.
Oxytocin binds to its receptor on the endometrial cell and opens calcium channels, allowing calcium ions to move in from outside
Describe the effect of progesterone on this contraction process.
Progesterone keeps the effects of oestrogen under control
Progesterone inhibits oestrogen receptors
Progesterone inhibits the production of prostaglandins
What change occurs when the foetus reaches a particular size, which is crucial for contraction to take place?
There is a switch in steroid synthesis from progesterone synthesis to oestrogen synthesis
This leads to oestrogen dominance –> prostaglandin production –> calcium release from intracellular stores –> promotion of muscle contraction
What 2 hormones are involved in milk production and milk ejection?
Prolactin – milk production
Oxytocin – milk ejection
These both have a similar neuroendocrine reflex arc stimulated by suckling
