Outline-4, BIO 2320, Pregnancy and Development


A. Fertilization

1. Oviduct is site

2. Capacitation

Enables sperm to fertilize ovum

3. Diploid; Zygote

4. Sex determination

5. Twins

a. Dizygotic (fraternal)

b. Monozygotic (identical)

B. Cleavage (30hrs.-4days); Morula

Mitosis divisions as embryo travels along oviduct towards uterus

C. Blastocyst Stage (day 5)

Rearrangement of cells, embryo is in the uterus

1. Trophoblast cells

Outermost cells destined to become placenta

2. Inner cell mass

Group of cells destined to become fetus

3. Implantation (Day 7-8)

Embryo burrows into endometrium

D. Gastrulation & Germ Layers (2nd week)

1. Ectoderm

Outer germ layer destined to become nervous tissue and skin

2. Mesoderm

Middle layer destined to become skeleton, muscles, heart, vessels….

3. Endoderm

Inner layer destined to become lungs and GI organs

E. Neurulation (3rd week; embryo is 2 mm long)

1. Neural grove

2. Neural tube

Results in brain and spinal cord

F. Organogenesis (4th week; 5mm long)

1. All major organs, arm/leg buds, have begun their formation

2. Thalidomide ; German measles can adversely affect organogenesis

G. Embryo vs Fetus– by end of 3rd mo., all major organs

established [25 mm, 1 gram], all left is growth for 2nd & 3rd trimester

H. Maintenance of endometrium

1. Estrogen & Progesterone

Quite important in maintaining endometrium, from corpus luteum in early pregnancy, from placenta later in pregnancy

2. Birth control pills

Most are a combination of estrogen and progesterone, what does this do to ovulation?

3. HCG (2-12 wks)

Human Chorionic Gondotropin, made by embryo, maintains corpus luteum

I. Placental development (begins at 4 wks, mostly functional by 12 wks)

1. Overall function

Nutrients, Waste, Estrogen & Progesterone production

2. Maternal tissue

– Decidua basalis

Of endometrium

3. Fetal tissue

a. Trophoblast cells become the…

b. Chorion

c. Villi

d. Umbilical Artery & Vein form capillary beds in villi, which become surrounded by maternal blood

e. Umbilicus

Arteries and vein

f. Amnion, Amniotic fluid

Sac surrounding fetus, filled with fluid for protection, movement, and temperature constancy

J. Gestation (280 days)

K. Parturition

1. Labor (contractions every 30 min)

2. Amniotic fluid released

3. Positive feedback

As labor increases, Oxytocin increases

a. Increased estrogen which increases

uterine contractility towards end of pregnancy, then levels drop

b. Decreased progesterone

c. Prostaglandin

Made by placenta, causes uterine smooth muscle contraction

d. Oxytocin (Increased # receptors)

Causes strong uterine contractions

e. Head as a wedge

f. Relaxin, made by placenta

helps to dilate cervix, relax symphysis pubis

Hormones of childbirth, relying on a positive feedback loop increasing oxytocin levels

4. Afterbirth [10-45 min later]


Ovulation and Implantation video