Endocrinology of pregnancy

Question 1

Where is tubular fluid reabsorbed and what controls this process?

Answer 1

Rete testis/Early epididymis

This is under the control of oestrogen

Question 2

Where do you find oestrogen within the male reproductive tract?

Answer 2

Tubular fluid produced by sertoli cells (converted from testosterone by aromatase)

Question 3

What stimulates the release of nutrients (e.g. fructose) and other molecules (e.g. glycoproteins) into the epididymal fluid?

Answer 3

Androgens

Question 4

State the components of semen and where they come from

Answer 4

Spermatozoa

Seminal fluid

• small contribution from epididymis/testis
• seminal vesicles
• prostate
• bulbourethral glands

Leucocytes

Question 5

What are the roles of these secreted nutrients and molecules?

Answer 5

• Energy for the journey

- Coat the surface of the spermatozoon (to protect them from the hostile environment)

Question 6

Why is the concentration of sperm in the vas deferens higher than further down the reproductive tract?

Answer 6

Further down the reproductive tract, other fluids and secretory products are added thus diluting the sperm.

Question 7

Where is a vasectomy performed?

Answer 7

Lower end of the vas deferens

Question 8

Describe the capability of the spermatozoa in the seminiferous tubule

Answer 8

Quiescent and incapable of fertilising an ovum

Question 9

Describe the capabilities of the spermatozoa in the vas deferens.

Answer 9

Capable of limited movement

Limited capability to fertilise an ovum

Question 10

When do sperm achieve full activity and capability and what is the name given to this process?

Answer 10

Capacitation

This occurs within the female reproductive tract

Question 11

What 3 changes take place in capacitation?

Answer 11

1. Loss of glycoprotein coat
2. Change in surface membrane characteristics
3. Whiplash movements of the tail

Question 12

What are all these changes dependent on?

Answer 12

Oestrogen

Ca2+

Question 13

Describe the acrosome reaction

Answer 13

• 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

Question 14

Where does fertilisation normally occur?

Answer 14

Fallopian tube

Question 15

What does fertilisation result in the expulsion of?

Answer 15

Second polar body (after secondary oocyte completes meiosis 2)

Question 16

What reaction immediately follows fertilisation? Describe it

Answer 16

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

Question 17

Describe the development of the conceptus after fertilisation

Answer 17

• 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)

Question 18

How long can the free-living phase (prior to implantation) last for?

Answer 18

Approx. 9-10 days

Question 19

Implantation can be describes by two phases, name and briefly describe them

Answer 19

Attachment phase = outer trophoblast cells contact uterine surface epithelium

THEN

Decidualisation phase = changes in underlying uterine stromal tissue (within a few hours)

Question 20

What factor is secreted from endometrial secretory glands to stimulate the adhesion of the blastocyst to the endometrial cells?

Answer 20

Leukaemia inhibitory factor (LIF)

Question 21

What other molecule(s) may be involved in the implantation process?

Answer 21

Interleukin-11 (IL11) (released into uterine fluid by endometrial cells)

HB-EGF

Question 22

What hormone is required for the decidualisation phase to occur, and what factors are involved?

Answer 22

Progesterone (in the presence of oestrogen)

Interleukin-11 (IL11), histamine, certain prostaglandins & TGFb (TGFb promotes angiogenesis)

Question 23

State the four endometrial changes due to progesterone?

Answer 23

1. Glandular epithelial secretion
2. Glycogen accumulation in stromal cell cytoplasm
3. Growth of capillaries
4. Increased vascular permeability (→oedema)

Question 24

What is the role of hCG, when does it peak, and what is it produced by?

Answer 24

• 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

Question 25

What change takes place after about 5/6 weeks? State its significance regarding an oophorectomy.

Answer 25

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

Question 26

Describe how oestrogen and progesterone levels change throughout pregnancy.

Answer 26

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)

Question 27

What is human placental lactogen? Describe its roles.

Answer 27

It is a growth hormone that has prolactin like effects | It is important for the growth and development of the foetus

Question 28

Which steroid precursor tends to be provided by the mother for the foetus?

Answer 28

Pregnenolone

Question 29

Which androgen is formed by the maternal and foetal adrenals?

Answer 29

Dehydroepiandrosterone Sulphate (DHEAS)

Question 30

Which oestrogens are produced by the placenta using DHEAS from the mother and foetus? Why aren’t they a good measure of foetal health?

Answer 30

Oestradiol Oestrone These oestrogens are dependent on precursor production from the both the foetal AND maternal adrenals.

Question 31

What is the main oestrogen of pregnancy? Describe how it is produced.

Answer 31

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

Question 32

Describe how maternal hormones change in pregnancy.

Answer 32

INCREASE: - ACTH - Adrenal steroids - Prolactin - IGF1 (stimulated by placental GH-variant) - Iodothyronines - PTH related peptides DECREASE - Gonadotrophins - Pituitary GH - TSH

Question 33

What biochemical change is required for contraction of the uterus during parturition?

Answer 33

Increase in intracellular calcium concentration

Question 34

Describe how oestrogen increases the chance of contraction.

Answer 34

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.

Question 35

Describe how oxytocin increases the chance of contraction.

Answer 35

Oxytocin binds to its receptor on the endometrial/myometrial cell and opens calcium channels, allowing Ca2+ influx

Question 36

Describe the effect of progesterone on this contraction process.

Answer 36

Progesterone regulates oestrogen function | by inhibiting oestrogen receptors and hence the production of prostaglandins

Question 37

What change occurs when the foetus reaches a particular size, which is crucial for contraction to take place?

Answer 37

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)

Question 38

What 2 hormones are involved in milk production and milk ejection?

Answer 38

Prolactin – milk production Oxytocin – milk ejection These both have a similar neuroendocrine reflex arc stimulated by suckling

Question 39

What is one other function of oxytocin?

Answer 39

Cervical dilation