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 (converted from testosterone by aromatase)
What stimulates the release of nutrients (e.g. fructose) and other molecules (e.g. glycoproteins) into the epididymal fluid?
Androgens
State the components of semen and where they come from
Spermatozoa
Seminal fluid
- small contribution from epididymis/testis
- seminal vesicles
- prostate
- bulbourethral glands
Leucocytes
What are the roles of these secreted nutrients and molecules?
- Energy for the journey
- Coat the surface of the spermatozoon (to protect them from the hostile environment)
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
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 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
- Whiplash movements of the tail
What are all these changes dependent on?
Oestrogen
Ca2+
Describe the acrosome reaction
- Spermatozoon binds to ZP3 glycoprotein (receptor of zona pellucida/glycoprotein layer)
- G-protein mediated Ca2+ influx into sperm (stimulated by progesterone)
- Release of hyaluronidase & proteolytic enzymes from acrosome
- Spermatozoon penetrates the Zona Pellucida
Where does fertilisation normally occur?
Fallopian tube
What does fertilisation result in the expulsion of?
Second polar body (after secondary oocyte completes meiosis 2)
What reaction immediately follows fertilisation? Describe it
Zonal reaction
Cortical granules release molecules that degrade the zona pellucida (including ZP3 and ZP2) => prevents further sperm binding as no receptors
- Also CALCIUM dependent
Describe the development of the conceptus after fertilisation
- Continues to divide as it moves down Fallopian tube to uterus (3-4 days) => morula
- Receives nutrients from uterine secretions
- Becomes a blastocyst (consisting of an inner cell mass, blastocyst cavity and surrounding layer of cells called the trophoblast)
How long can the free-living phase (prior to implantation) last for?
Approx. 9-10 days
Implantation can be describes by two phases, name and briefly describe them
Attachment phase = outer trophoblast cells contact uterine surface epithelium
THEN
Decidualisation phase = changes in underlying uterine stromal tissue (within a few hours)
What factor is secreted from endometrial secretory glands to stimulate the adhesion of the blastocyst to the endometrial cells?
Leukaemia inhibitory factor (LIF)
What other molecule(s) may be involved in the implantation process?
Interleukin-11 (IL11) (released into uterine fluid by endometrial cells)
HB-EGF
What hormone is required for the decidualisation phase to occur, and what factors are involved?
Progesterone (in the presence of oestrogen)
Interleukin-11 (IL11), histamine, certain prostaglandins & TGFb (TGFb promotes angiogenesis)
State the four endometrial changes due to progesterone?
- Glandular epithelial secretion
- Glycogen accumulation in stromal cell cytoplasm
- Growth of capillaries
- Increased vascular permeability (→oedema)
What is the role of hCG, when does it peak, and what is it produced by?
- It mimics LH by binding to LH receptors on the corpus luteum and stimulating the production of oestrogen and progesterone
- Peaks at 8 weeks and is particularly important in the first 6 weeks
- Produced by trophoblast cells
What change takes place after about 5/6 weeks? State its significance regarding an oophorectomy.
The role of hormone production is handed over from the corpus luteum to the placenta
After this point, the oophorectomy would have no effect on pregnancy since the ovaries are no longer needed
Describe how oestrogen and progesterone levels change throughout pregnancy.
Oestrogen (mainly oestriol) and progesterone levels continue to rise through pregnancy with progesterone always being the dominant influence
In the first 40 days;
- Essential for developing fetoplacental unit
- Inhibits maternal LH & FSH (-ve feedback)
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
Which steroid precursor tends to be provided by the mother for the foetus?
Pregnenolone
Which androgen is formed by the maternal and foetal adrenals?
Dehydroepiandrosterone Sulphate (DHEAS)
Which oestrogens are produced by the placenta using DHEAS from the mother and foetus? Why aren’t they a good measure of foetal health?
Oestradiol
Oestrone
These oestrogens are dependent on precursor production from the both the foetal AND maternal adrenals.
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
Describe how maternal hormones change in pregnancy.
INCREASE:
- ACTH
- Adrenal steroids
- Prolactin
- IGF1 (stimulated by placental GH-variant)
- Iodothyronines
- PTH related peptides
DECREASE
- Gonadotrophins
- Pituitary GH
- TSH
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 oxytocin receptors) and induces phospholipase A2 activation => mediates the synthesis of the prostaglandin PGF2a from arachidonic acid within the endometrial/myometrial cells.
Prostaglandins stimulate the release of calcium from intracellular stores.
Describe how oxytocin increases the chance of contraction.
Oxytocin binds to its receptor on the endometrial/myometrial cell and opens calcium channels, allowing Ca2+ influx
Describe the effect of progesterone on this contraction process.
Progesterone regulates oestrogen function
by inhibiting oestrogen receptors and hence 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
What is one other function of oxytocin?
Cervical dilation
