1

From Egg to Embryo

Pregnancy –

Conceptus –

Gestation period –

Preembryo –

Embryo –

Fetus –

2

Relative Size of Human Conceptus

Figure 28.1

3

Accomplishing Fertilization

The oocyte is viable for 12 to 24 hours

Sperm is viable 24 to 72 hours

For fertilization to occur, coitus must occur no more

than:

Three days before ovulation

24 hours after ovulation

Fertilization – when a sperm fuses with an egg to

form a zygote

4

Blocks to Polyspermy

Only one sperm is allowed to penetrate the oocyte

Two mechanisms ensure monospermy

Fast block to polyspermy -

Slow block to polyspermy – zonal inhibiting

proteins (ZIPs):

5

Events Immediately Following Sperm Penetration

Figure 28.3

6

Cleavage: From Zygote to Blastocyst

Figure 28.4

7

Implantation of the Blastocyst

Figure 28.5a

8

Implantation of the Blastocyst

Figure 28.5b

9

Placentation

Figure 28.7a-c

10

Placentation

Figure 28.7d

11

Placentation

Figure 28.7f

12

Ectopic Pregnancy

When embryonic mass implants someplace other

than endometrium

Most often is tubular

In abdominal cavity must be delivered by cesarean

section

13

Maternal Serum Screen and Amniocentesis

Done after 16 – 17 weeks to detect fetal

chromosomal abnormalities

Serum screen – looks for protein markers

Amniocentesis – more invasive

14

Hormonal Changes During Pregnancy

Figure 28.6

15

Parturition: Initiation of Labor

Estrogen reaches a peak during the last weeks of pregnancy

causing myometrial weakness and irritability

Weak Braxton Hicks contractions may take place

As birth nears, oxytocin and prostaglandins cause uterine

contractions

Emotional and physical stress:

Activates the hypothalamus

Sets up a positive feedback mechanism, releasing more

oxytocin

16

Parturition

Fetus becomes too large for uterus, triggers fetus

anterior pituitary to release ACTH

ACTH acts on fetus adrenal cortex to produce

cortisol,

Cortisol targets placenta

Inhibits its production of progesterone

Stimulates production of estrogen

Increases release of prostaglandins

17

Parturition: Initiation of Labor

Figure 28.16