Pregnancy

Question 1

What happens to the tubular fluid within the male reproductive tract?

Answer 1

1. Fluid reabsorption within rete testis + early epididymis induced by luminal oestrogens
2. Glycoproteins + fructose vital for maturation process secreted into epididymal fluid induced by androgens - provide energy + coat surface of spermatozoon (to protect from hostile environment)

Question 2

Explain fertilisation

Answer 2

• In fallopian tube
• Results in expulsion of 2nd polar body
• Leads immediately to zonal reaction: cortical granules release molecules which degrade zona pellucida (ZP2, ZP3); prevents further binding of other sperm; Ca dependent
• Once diploidy established, zygote begins dividing to form initial 2-cell conceptus

Question 3

Explain implantation

Answer 3

• Invasive
• Requires progesterone domination in presence of oestrogen

1. Initial attachment phase:
   - Outer trophoblast cells make contact w/uterine surface epithelium
   - Leukaemia inhibitory factor (LIF) from endometrial secretory glands + blastocyst stimulates adhesion of blastocyst to endometrial cells
   - IL-11 released from endometrial cells into uterine fluid - trophoblast migration, decidualisation
   - Many other molecules involved that stimulates these 2 important molecules
2. Decidualisation of underlying uterine tissue within a few hours

Question 4

What happens during decidualisation?

Answer 4

• Within a few hours of implantation
• Invasion of underlying uterine stromal tissue by trophoblast cells of blastocyst
• Requires progesterone domination in presence of oestrogen
• IL-11, histamine, some prostaglandins, TGFB (angiogenesis) all involved

Within hours:

• Increased vascular permeability in invasion region, associated w/tissue oedema
• Localised changes in IC composition + progressive sprouting + capillary growth
• Glandular epithelial secretion
• Glycogen accumulation in stromal cell cytoplasm

Question 5

How do circulating hormone concentrations change throughout pregnancy?

Answer 5

• hCG surge, peaks at 8 weeks
• Oestrogen and progesterone increase thr/o pregnancy
• Progesterone remains dominant influence right until the end
• Human placental lactogen - also increases in line w/oestrogen

Question 6

What does semen consist of?

Answer 6

• Spermatozoa
• Seminal fluid
• Leucocytes
• Potentially, viruses, e.g. HBV, HIV

Question 7

What does seminal fluid consist of?

Answer 7

Lots of molecules to provide energy, and environment for spermatozoa to work properly:

• Fructose
• Fibrinogen
• Citric acid
• Acid phopshatase
• Fibrinogenase + fibrinolytic enzyme

Question 8

What percentage of spermatozoa in ejaculate enter the cervix?

Answer 8

1%

Question 9

How do spermatazoa from different parts of the male reproductive tract differ?

Answer 9

• Spermatozoa from seminiferous tubule are quiescent + incapable of fertilising ovum
• Spermatozoa from vas deferens are capable of limited movement (whiplash activity) + limited capability of fertilising ovum
• Full activity + fertilising capability only achieved once within female reproductive tract - CAPACITATION

Question 10

How are spermatozoa activated?

Answer 10

CAPACITATION

• Loss of glycoprotein coat
• Change in surface membrane characteristics (leading to acrosome reaction when in close proximity to ovum)
• Whiplash movements of tail
• Takes place in ionic + proteolytic environment of oviduct - OESTROGEN-DEPENDENT + CALCIUM-DEPENDENT
• Ca + oestrogen in fluid of female RT

Question 11

What happens as the sperm approaches the ovum?

Answer 11

• Changes in membrane
• Spermatozoon binds to ZP3 glycoprotein on zona pellucida
• Progesterone stimulates Ca influx into spermatozoon
• Results in Ca-dependent acrosome reaction
• Enables exposed spermatozoon recognition site to bind to 2nd glycoprotein (ZP2)
• Once ZP2 bound, acrosome release its enzymes (hyaluronidase)allowing penetration of zona pellucida so head of spermatozoon can enter ovum

Question 12

How does the conceptus develop?

Answer 12

• Conceptus continues to divide as it moves down fallopian tube to uterus (3-4 days)
• Until implantation, developing conceptus receives nutrients from uterine secretions
• Ball of cells w/outside cells getting nutrients + inner cells less and less nutrients
• Free-living phase lasts 9-10 days
• Woman is in luteal phase (high oestrogen, high progesterone)
• Conceptus first compacts to 8-16 cells morula
• Then becomes blastocyst w/inner cell mass (becomes embryo) + trophoectoderm (becomes chorion –> placenta)
• Transfer to uterus facilitated by increasing progesterone:oestrogen ratio (in luteal phase)
• Implantation leads to establishment of physical + nutritional contact w/maternal tissues

Question 13

Why is implantation vital?

Answer 13

To establish system for getting nutrients from mother to embryo