chapter 28:pregnancy

Conceptus (embryo or fetus)

Pregnant persons developing offspring

Pregnancy

State of carrying a developing concepus

Gestation period

Time during which the development of the conceptus occurs. Lasts from the last menstrual period until birth. 280 days.

Embryonic period or embryo

fertilization through week 8

Fetal period

Week 9 through birth

When can fertilization occur

two days before ovulation and no later than 24 hours after

Acrosomal reaction

Release of acrosomal enzymes to penetrate oocyte

Blocks of polyspermy

Prevent further sperm entry, ensuring only two copies of each chromosome are present in the fertilized ovum

Two mechanisms of monospermy

Oocyte membrane block and cortical reaction

Cortical reaction

Ca increase triggering exocytosis of cortical granules to harden zona pellucida and destroys sperm binding receptors

steps of sperm penetration

Approach corona radiata

Acrosomal reaction

Binding

Fusion

Blocks of polyspermy

Steps in fertilization

Secondary oocyte, meiosis 2, forming ovum and second polar body

Sperm and ovum swell forming pronuclei

DNA in pronuclei replicate and form mitotic spindle fibers

Chromosomes mix and zygote is ready for division

Cleavage

Period of rapid mitotic division of the zygote without intervening growth

Zygote to blastocyst

Zygote

4-cell stage (day 2)

Morula (day 3) ball of cells

Early blastocyst (day 4) hollows out and fills with fluid

Implanting blastocyst with trophoblast cells and eccentric cells

Eccentric cells

Embryoblast

Cytotrophoblast

Forms innermost layer of cells

Syncytiotrophoblast

Outermost layer and eventually the placenta

Syncytium

Cells fused together form a single multinuclear cytoplasmic mass. Invade endometrium and rapidly digest the uterine cells it contacts

How long does implantation last

5 days but complete at day 12

Syncytiotrophoblast secrete?

Human chorionic gonadotroin (hCG) to act like luteinizing hormone but bypass hypothalamus pituitary ovarian controls to still produce estrogen and progesterone

What does hCG prevent

Immune system from rejecting the implanted embryo

What produces hCG

Trophoblast cells