Pregnancy and Development

what are cleavage divisions

early mitotic divisions producing blastomeres; asynchronous in mammals

What is the pre-implantation period

Development from fertilization until implantation/attachment

What is cavitation

formation of fluid-filled cavity (blastocoel) → blastocyst

what drives cavitation

Na⁺/K⁺-ATPase creating osmotic gradient for fluid influx

What are the two main blastocyst cell types?

• Inner Cell Mass (ICM) → embryo

• Trophectoderm → extra-embryonic tissues

What is hatching

blastocyst escapes zona pellucida via proteases

why is hatching important

allows implantation and dependence of uterine environment

What is pre-attachment development

embryo develops freely in uterus before implantation

what is implantation

adhesion of trophoblast to uterine epithelium

what is embryonic elongation

blastocyst becomes tubular/filamentous (ruminants, pigs)

Why is elongation important

maximizes surfaces area for maternal contact

Which animals do NOT elongate

horses, carnivores, primates (remain spherical)

What is histotrophe

nutrient-rich secretions from uterine glands

functions of histotrophe

nourishes embryo before (and sometimes after) implantation

Why is MRP necessary

To prevent luteolysis and maintain progesterone production

What happens if luteolysis occurs

pregnancy fails (CL regresses)

Two types of MRP

• luteotrophic (support CL)

• anti-luteolytic (block PGF2α)

What is the MRP signal in cows/sheep/goats

Interferon tau

What is the signal in pigs

estradiol

What is the MRP signal in humans

hCG

Which species don’t require MRP signals

Dogs and Cats

What happens in Phase 1 of implantation

Zona pellucida shedding

What is happens in Phase 2

pre-contact migration/orientation

What happens in Phase 3

Weak attachment (apposition)

What happens in Phase 4

Strong adhesion

What happens in Phase 5

invasive implantation (species-dependent)

What is the placenta

Interface between maternal and fetal tissues

What is the placenta

interface between maternal and fetal tissues

main fetal components

Chorion + allantois (chorioallantoic placenta)

Diffuse placenta

villi spread across uterus (pig, horse)

Cotyledonary placenta

discrete placentomes (ruminants)

Zonary placenta

Band around fetus (dog, cat)

discoid placenta

disc-shaped (primates, rodents)

what are the main functions of the placenta

• gas exchange

• nutrient transfer

• waste removal

• hormone production

• immune roles

What does progesterone do during pregnancy

• maintains endometrium

• Inhibits contractions (progesterone block)

What does estrogen do late in pregnancy

• promotes labor

• Increases uterine contractility

what is the role of fetal cortisol

• triggers organ maturation

• initiates parturition

• Increases prostaglandins

parturition - phase 0

uterine quiescence

Parturition - Phase 1

Activation (cervix softens, uterus prepares

Parturition - Phase 2

Delivery of fetus (strong contractions)

Parturition - Phase 3

Expulsion of placenta + uterine recovery

what is Ferguson’s reflex

positive feedback loop: cervical stretch → oxytocin → stronger contractions

What does oxytocin do

Stimulates uterine contractions

main pregnancy diagnostic methods

• palpation

• hormones

• ultrasound (most accurate)