Wk9 pregnancy recognition and foetal development Flashcards
- Recall species timing of implantation in relation to blastocyst hatching (days)
- In order to pregnancy to keep going, we need maternal recognition of pregnancy…
- Mare = 16-18 days NOT 36-38**
- Cow = 18-22 for implantation
- ewe = 15-18
- sow = 14-18
- bitch = 18-20
1) Describe the process of maternal recognition of pregnancy in different species and how this ensures ongoing pregnancy
- Luteolysis usually occurs which ends luteal phase and starts a new follicular phase
- But if pregnancy, pregnancy interrupts the normal oestrous cycle by preventing luteolysis (the default)
- Progesterone levels remain high as a result
- For pregnancy to proceed, embryo must biochemically signal to the maternal environment prior to luteolysis - molecular interaction known as maternal recognition of pregnancy.
2) Recall gestation length across species
- Horses pregnant for almost a year
- Pigs have weird amount (3.8months)
- Dog and cat 2 month
- We can see that many early processes happen at the same time between species, regardless of total gestation length: e.g heartbeat present occurs on 25 day approximately for all species
- Body systems are differentiated by about half way through gestation.
Signalling hormones vary for animals:
- Ruminants
- Mare
- Sow
Bitch/queen
- Ruminants: IFNt
- Mare: mechanical? PGF2a inhibition
- Sow: estradiol
Bitch/queen: no signal (default is no luteolysis)
Pregnancy recognition - ruminants
IFNt role
- Critical time = d13-14 (ewe) or d15-16 (cow)
- Conceptus secretes interferon tau (IFNt) aka trophoblast protein 1
- It just prevents luteolysis*
IFNt also promotes uterine gland secretion to support developing conceptus, and can influence maternal immune response
- It just prevents luteolysis*
Pregnancy recognition - horses
We don’t know molecular signal, but describe physical migration of conceptus in mares
- Critical time: d12-14
- Conceptus: stays spherical, we don’t get elongation in mares
- So we get physical migration of the conceptus through the uterus is required - which substitutes for elongation that occurs in other species
Eventually though, PGF2a concentrations are decreased - so we escape luteolysis
Pregnancy recognition - pigs (sow)
- Critical time
Recognition cascade of pigs (in relation to PGF2a and E2)
- Critical time: d11-12
- Recognition cascade:
- Conceptus secretes estradiol E2
- PGF2a is still produced in response to oxytocin from PP and CL and endometrium
- E2 causing rerouting of PGF2a into uterine lumen (Exocrine) instead of uterine vein (endocrine)
- PGF2a breaks down in lumen
- No signal for luteolysis = CL maintained
NOTE: minimum of 2 conceptuses in each horn is required to generate enough local signal to prevent luteolysis in the sow
Pregnancy recognition - carnivores
- No specific signal required for maternal recognition of pregnancy
CL last for length of gestation, whether there is a pregnancy or not..
Maintaining P4 throughout pregnancy
- Maternal recognition of pregnancy prevents luteolysis which has one critical outcome:
- Maintaining high concentrations of progesterone
Note: important for insemination as if you miss this time period, the body will resort back to follicular phase
- Maintaining high concentrations of progesterone
What would happen if we gave recombinant IFNT to a cycling (non-pregnant) ewe?
- Prevent luteolysis from occurring
We don’t use this in practice though.
Foetal size/growth rate through pregnancy
- Most relevant in cattle - use foetal size to estimate gestational age by rectal palpation for pregnancy diagnosis
Stage of pregnancy relevant to the size
Sexual differentiation during foetal development
- Male and female chromosomes
What does the Y chromosome contain
- Mammals: X and Y chromosomes
- Male: XY and female XX
- Only males can carry Y, so offspring sex is determined by sperm
- Y chromosomes contains SRY gene (sex determining region)
Produces the testis determining factor protein
Migration of primordial germ cells (PGC’s)
The yolk sac - why is this important feature?
- Yolk sac: this is the source of the primordial germ cells *
- PGCs develop in the hindgut
- Migrate to genital (gonadal) ridge and undergo MASSIVE mitosis - building up reservoir of stem cells
Gonadal ridge forms a bipotential gonad (can develop into a testis or ovary)
Sexual differentiation during foetal development:
The 2 duct systems that form alongside intermediate and final kidneys are..
- Paramesonephric duct (aka Mullerian duct)
Mesonephric duct (aka Wolffian duct)
Why are the 2 duct systems that form alongside the kidneys important for sex development?
At this stage embryo is phenotypically sexually indifferent - due to effects of SRY (sex determining region)
- Male = regression of paramesonephric duct due to anti-mullerian hormone (AMH)
Female = regression of mesonephric duct
T or F
Comparing a pregnant sow (3.8months gestation) and mare (11 months gestation), foetal heartbeat would not be detectable until much later in an equine foetus?
FALSE
The early development processes happen at roughly the same time in species, regardless of total gestation length.
Descibe the hormonal profile during week prior to parturition (before parturition)
- P4 to E2 conversion before birth (this drops 24-48hrs prior to birth).
□ E2 increases myometrial contractions, increased uterine pressure, increased stimulation of cervix, increased secretion (cervix and vagina) - Rising LH from uterine crowding
- PGF2a (prostaglandin) - luteolysis. Also dilates cervix and increase contractions. Can be used to induce labour, also abortion at early stages for uterine evacuation.
Descibe hormonal profile during parturition?
- Oxytocin: stimulates contractions + increases prostaglandin = further contractions initiated.
- Relaxin = relaxes cervix and pelvic ligaments for birth
