Gestation and Birth

Viv Rolfe

Lecture Outline

• To investigate the major events of gestation and parturition.

• What is implantation?

• 3 stages of gestation (germinal, embryogenic and foetal phases).

• Structure and function of the placenta and umbilical cord.

• 3 stages of parturition.

Gestation and Partition(Pregnancy and birth)

(280 days/9 months)

Development of the zygote / embryo / foetusin the female reproductive tract,

and delivery from the female.

Gestation Week 1

Fertilization

ImplantationEmbryonicGrowth

FoetalGrowth

Birth

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Fertilization

Implantation

The ZYGOTE rapidly divides into a mass of cells called the MORULA.

The cells DIFFERENTIATE (change type) forming the BLASTOCYST: Trophoblast – large fluid-filled sphere (foetal placenta)

Inner cell mass (embryo)

Cellular Changes

Blastocystcavity

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Implantation

6-8 days after fertilization the blastocyst implants into the uterine wall.

The endometrial glands start to enlarge and becomes more vascularised.

Implantation

What is the word for the implantation and

development of the embryo outside of the uterine cavity?

Ectopic pregnancy.

Inutero-development

Chorionic villi (Placenta)

Body Stalk (Umbilical cord)

Yolk sacEarly source of nutrients

Ectoderm

Mesoderm

Endoderm

(GERM LAYERS)

Gestation

Fertilization

ImplantationEmbryonicGrowth

FoetalGrowth

Birth

Weeks 1-8.

A time of rapid cell differentiation and growth.

All the body tissues and organs develop from the PRIMARY GERM LAYERS.

The placenta also begins to develop.

Embryonic Period

Ectoderm Nervous system

Epidermis of the skin

Eye, ear

Endoderm Mucosal surfaces

Glands

Mesoderm Skeletal, smooth and cardiac muscle.

Cartilage, bone, blood, lymphoid tissue.

Germ layers

Gestation

Fertilization

ImplantationEmbryonicGrowth

FoetalGrowth

Birth

Foetal Period

• Weeks 12-38.• The embryo is referred to as a

FOETUS.• It has a human appearance.• It now rapidly grows (from a few

cm to up to 50 cm), occupying all of the abdominal space.

Placentaand umbilicalcord are fully developed(2-3 months)

Forms a barrier between mother and embryoto deliver NUTRIENTS and OXYGEN.

Removes WASTE from embryonic blood.

Becomes an endocrine organ by producing HORMONES (oestrogen, progesterone) to control pregnancy

Placenta

• 1st trimester (first 3 months)• Embryonic period - development of body organs

• Baby’s heart starts beating about 4 weeks.

Summary of the Stages of Pregnancy

• 3rd trimester – (months 7-9).

•2nd trimester (months 4-6)

•Foetal period – rapid growth and much activity.

Effects on the mother

Enlargements of the uterus

Gastrointestinal symptoms

Morning sickness is due to elevated progesterone

Heartburn due to organ crowding by the fetus

Constipation is caused by declining motility

Urinary System

Kidneys have additional burden and produce more urine

The uterus compresses the bladder

Effects on the mother

Cardiovascular system

Body water levels rise

Blood volume increases by 25 to 40 percent

Blood pressure and pulse increase

Varicose veins are common

Gestation/pregnancy(280 days/9 months)

Fertilization

ImplantationEmbryonicGrowth

FoetalGrowth

Birth

Labour – the series of events that expel the infant from the uterus

Initiation of labor Estrogen levels rise

Prostaglandin starts uterine contractions

Birth - parturition

Dilation Cervix becomes dilated

Uterine contractions begin and increase

The amnion ruptures

Expulsion Infant passes through the cervix and vagina

Normal delivery is head first

Placental stage Delivery of the placenta

Labour

Effects of birth on the foetus

• The baby undergoes amazing physiological changes at birth.

• What happens?

Oxygen and nutrients no longer supplied by the mother.

Carbon dioxide and other wastes aren't eliminated by her.

Loss of protection from the uterus.

Temperature drop.

Exposed to microbes!

Rapid Changes in the Lungs

• Change from being fluid filled and collapsed in the uterus, to filled with air.

• Blood CO2 is high at birth stimulating the respiratory centre in the brain.

• The baby draws its first breath.

Rapid Changes in the Heart

• Closure of the foramen ovale in the heart (which doesn’t close in “hole in the heart baby’s”).

• This diverts de-oxygenated blood to the LUNGS and not to the PLACENTA.

• The umbilical artery and vein close down.

• There is rapid red and white blood cell production at birth.