Development

Embryo to Fetus to Birth1-3 Trimesters

Day 28

2-3.5 mm

Neurula

Amniotic Sac • Originally forms around the embryo

• Eventually fills with liquid provided by the mother’s cells

• Later, formed by the fetal kidneys

• Circulates when the baby drinks the liquid and excretes it out

Amniotic Sac• Some babies

are born inside the amniotic sac• 1 in 80,000

births

Umbilical cordPlacenta

• Placenta: holds baby to the mother

• Diffusion of food, oxygen, carbon dioxide and waste takes place

• Umbilical cord contains an artery and a vein

• One carries things to the baby

• One carries things away from the baby

4 weeks

• Brain is formed• Heart is beating• Eye, legs,arms

begin• 1/6 inch

6 weeks

• ½ inch• Circulation begins• Toes and fingers

forming

8 Weeks Eyes, nose, lips, tongue, ears and teeth are forming

Gonad formation begins

Functioning heart

Now considered FETUS

1.2 inches

12 Weeks2.5 – 3 inches and .5 – 1 oz.

• Sex of the baby can be determined

• Nails and earlobes develop• Eyes almost fully

developed• All parts present, now

major GROWTH and DEVELOPMENT

2nd Trimester

• Placenta fully developed

• Fetus can hear mother

• Vernix forms – creamy white substance that protects thin skin

Week 13 to Week 27

2nd Trimester• Skin is reddish and forms lanugo

(downy hair)• Reflexes: swallow, suckling, jumping

end of 2nd trimester: 15 inches long 2.5 pounds

• Sleep – wakefulness cycles

• Fat forms

• lungs are beginning to exhale amniotic fluid

(practice for breathing)

• circulatory system working

3rd Trimester• Fetus has sight and

hearing• Soft skeleton• Laguno disappears –

skin begins pigmentation

• Circulatory and Respiratory systems mature

Week 28 to Week 40

• Mother’s antibodies pass to fetus

• Digestive organs expel wastes- meconium

• Baby moves downward towards birth canal

Parturition (Birth)

• Expel fetus from uterus = LABOR• Last few weeks of pregnancy, estrogen levels

peak: – myometrium forms oxytocin receptors– Interupts progesterone, allows small uterine

contractions (false labor, Braxton Hicks)• Oxytocin production causes placenta to

release prostaglandins = more powerful contractions

Positive Feedback Loop• Hypothalamus activated by increasing pressure levels on

the cervix• Activates pituitary to release more OXYTOCIN…

Three Stages of Labor: DIALATION• True contractions dilates

cervix 1 to 10 cm• Contractions – Increase from weak to

vigorous– Regular– Upper uterus downwards to

birth canal– Soften cervix: effaces– 6-12 hours

Three Stages of Labor: EXPULSION

• Delivery of infant out of vagina• Mother’s response is to push• Infant is facing downwards:

vertex, if butt down: breech• Mucus is suctioned before full

delivery – baby begins to breathe

• Complications (dropping oxygen levels or heart rate in infant) overcome by forceps, vacuum or Cesarean section

Three Stages of Labor: PLACENTAL• Uterine contractions

compresses blood vessels• Placenta detaches• Afterbirth = placenta, fetal

membranes and umbilical cord

• Need to remove all tissues – could cause excess bleeding

Thank your mother…• Uterus stretches to occupy most abdominal cavity• Estrogen/progesterone surge (morning sickness)• Ribs flare (shortness of breath, but vital capacity increases)• Lordosis – lumbar curvature (back aches)• Relaxin causes pelvic ligaments and pubis to widen/relax

(duck walk)• Organ displacement = pressure on esphogus, stomach, and

intestines (heartburn, small meals, constipation)• Excess waste from fetus and limited room (frequent

urination…uncontrollable)• Blood volume increases up to 40% , blood pressure and

pulse rate increases (swelling = edema)