Animal Reproduction

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Slide 66

Placental circulation

Placenta

Uterus

Umbilical cord

Chorionic villus, containing fetal capillaries

Maternal blood pools

Maternal arteries

Maternal veins

Maternal portion of placenta

Fetal arteriole

Fetal venule

Umbilical cord

Fetal portion of placenta (chorion)

Umbilical arteries

Umbilical vein

Slide 67

Splitting of the embryo during the first month of development results in genetically identical twins. Release and fertilization of two eggs results in fraternal and genetically distinct twins.

The first trimester is the main period of organogenesis = development of the body organs.

All the major structures are present by 8 weeks, and the embryo is called a fetus.

Slide 68

Changes occur in the mother:

Growth of the placenta

Cessation of ovulation and the menstrual cycle

Breast enlargement

Nausea is also very common.

Slide 69

Human fetal development

(a) 5 weeks

(b) 14 weeks

(c) 20 weeks

Slide 70

(a) 5 weeks

Slide 71

(b) 14 weeks

Slide 72

(c) 20 weeks

Slide 73

Second Trimester

During the second trimester:

The fetus grows and is very active

The mother may feel fetal movements

The uterus grows enough for the pregnancy to become obvious.

Slide 74

Third Trimester

During the third trimester, the fetus grows and fills the space within the embryonic membranes.

A complex interplay of local regulators and hormones induces and regulates labor, the process by which childbirth occurs.

Slide 75

Labor

Estradiol

Oxytocin

from ovaries

Induces oxytocin receptors on uterus

from fetus and mother’s posterior pituitary

Stimulates uterus to contract

Stimulates placenta to make

Prostaglandins

Stimulate more contractions of uterus

Positive feedback

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Slide 76

The three stages of labor

Placenta

Umbilical cord

Uterus

Cervix

Dilation of the cervix