Development of the Fetus

How does implantation occur?

The blastocyst attaches to the endometrium 6-8 days post fertilization

How does the trophoblast help with implantation?

The trophoblast produces enzymes to aid penetration of the endometrium

How do the extra layers of the blastocyst form?

The inner cell mass forms the embryo, while the trophoblast forms the supporting membranes

What is the outermost embryonic germ layer?

Ectoderm

• Consists of skin, central and peripheral nervous systems

What is the middle embryonic germ layer?

Mesoderm

• Consists of muscle, bone, heart, blood vessels and connective tissue

What is the innermost embryonic germ layer?

Endoderm

• Consists of epithelium of GIT, gall bladder, trachea and lungs

Define the terms zygote, embryo, and fetus

Zygote = fertilized egg

Embryo = 8 weeks development

Fetus = 9 weeks to childbirth

How does estrogen and progesterone affect pregnancy?

Estrogen stimulates uterine contractions, while progesterone inhibits uterine contractions

Describe how estrogen, progesterone and oxytocin affect labour

Estrogen

• Prepares for contractions at the start of labor

Progesterone

• Levels fall dramatically before labor

Oxytocin

• Initiates forceful uterine contractions

Describe how the hormones estrogen, progesterone, oxytocin and prolactin affect lactation

Estrogen

• Develops the breast

Progesterone

• Develops the glandular tissue

Oxytocin

• Causes the milk ejection reflex

Prolactin

• Produces the milk

Fetal Circulation

What is the inefficiency of fetal circulation?

The mixing of oxygenated and deoxygenated blood due to the ductus venosus

How does the body compensate for this inefficiency?

It makes fetal hemoglobin bind to oxygen more

How do newborn blood cells differ from adult blood cells?

Higher RBC & WBC count and Hb concentration

Where does erythropoeisis occur in fetuses?

In the liver, spleen, bone marrow and lymph nodes

What are fetal lungs filled with in the womb?

They are filled with fluid

What is the pulmonary surfactant and when is it produced?

The pulmonary surfactant is phospholipoprotein and it is produced between week 26-28

Why do fetuses need pulmonary surfactant?

They need pulmonary surfactant to prevent their lungs from collapsing and to transition from having their lungs filled with fluid to breathing air