Fetal development

1. FETAL DEVELOPMENT
Introduction
 Embryology is the study of development from the
fertilized egg through the 8 weeks
 Fetal period begins 9 to till birth during these time
developing human is called fetus.
Intrauterine Development
Two main phases are:
 1. Cellular multiplication
 2. Implantation
Cellular Multiplication
 The fertilized zygote begins its travel through the
fallopian tube toward the uterus.
 Cell / mitotic division (cleavage) occurs
 Morula eventually forms a fluid filled cavity within the
cell mass.
 Inner solid cell mass is called Blastocyst
 Outer cell mass that surrounds the cavity is the
Trophoblast
Development
Stage 1 – Pre-embryonic/Ovular period
 Weeks 1 - 2
Stage 2 -- Embryonic
 Weeks 3 - 8
STAGE 3 -- FETAL
 Weeks 9 - 40
Pre-embryonic Period
Weeks 1-2
 Traveling in the fallopian tube where rapid cellular
multiplication and differentiation occurs.
 The establishment of the embryonic membranes and the
germ layers (germinal period).
 Groove formed along middle of the back for the neural
tube.
Embryonic Period
Weeks 3-8
 Anterior end of neural tube closes
 to form the brain and the posterior
 end closes to form the spinal cord
 Heart begins to beat
 Eyes appear
 Limb Buds for arms
 and legs
 CR = 4 mm
Week 5
 Head grows larger
 Primitive heart tube is forming. Vasculature begins to
develop in embryonic disc.
 A notochord forms in the center of the embryonic disk
 Hand and feet plates develop
 Facial features begin to develop
 CR = 8 mm.
Week 6
 Fetal circulation is established
 Chambers form in the heart
 Upper lip and palate start fusing
 Eyes move to front of face
 Fingers are webbed
 External ear develops
Week 7
 Eyelids start to form
 Fingers develop; elbows visible
 Diaphragm separates
 abdomen from chest
 Bronchi develop
 Arms and legs move
Week 8
 Fingers and toes distinct
 Skeletal ossification begins
 Testes and ovaries are
 distinguishable
 Heart has four chambers
 Circulation through
 umbilical cord occurs
 *** ALL essential external and internal structures are
present and now will continue to grow
The Zygote—Month 1
 Fertilized egg reaches the uterus and attaches itself to
the uterus.
 Cell multiplication begins
 Internal organs and circulatory system begins to form.
 Cell Division takes place and at the end of two weeks
the zygote is the size of a pin-head
 Heart begins to beat
 Small bumps show the beginnings of arms and legs
The Embryo—Month 2
 At 5 weeks the embryo is ¼ inch long
 All major organ systems develop
 The placenta and Umbilical Cord develop
 Placenta- The tissue that connects the sac around the
unborn baby to the mother’s uterus
 Umbilical Cord- Tube that connects the baby to the
placenta
 Brings the baby nourishment and oxygen from the
mother’s blood
 Takes away waster products
 Amniotic Fluid surrounds the baby
 Face, and limbs take shape
The Fetus—Month 3
 The fetus is about 1 inch long
 Nostrils, mouth, lips, teeth buds, and eyelids form
 Fingers and toes are almost complete
 Arms, legs, fingers, and toes have developed
 All internal organs are present—but aren’t ready to
function
 The genital organs can be recognized as male or female
Weeks 9-12- 3rd
month
 Head size increases
 Nails appear
 Eyelids appear and close and fuse shut
 Kidneys excrete urine
 Intestines are forming; peristalsis begins
 Heartbeat can be heard via ultrasound
The Fetus—Month

2.  Fetus is 3 inches long and weights 5 oz.
 Baby is covered with a layer of thick, downy hair called
lanugo.
 Heartbeat can be heard clearly.
 The baby can such thumb, swallow and hiccup.
Weeks 13-16- 4th
month
 Lips form, facial contour develops
 Ossification of bone begins
 Meconium begins to form in the intestines
 Hair present on scalp
 Sex can be determined visually
The Fetus-Month 5
 The Fetus is about 6 inches long and weighs 4-5 oz.
 A protective coating called vernix begins to form on
baby's skin.
 Hair eyelashes and eyebrows appear
 Organs keep maturing
 Fetus is very active
 The eyes can open and blink
Weeks 17-20 -5th
month
 Hair abundant on head
 Lanugo covers the body
 Myelination of spinal cord begins
 Suck and swallow begin
 Quickening occurs ~ 18 weeks
The Fetus—Month 6
 The fetus is 8-10 inches long and weighs 4-5 oz.
 Your baby's lungs are filled with amniotic fluid, and he
has started breathing motions.
 If you talk or sing, he can hear you.
 Fat is starting to deposit under the skin
Weeks 21-24- 6th
month
 Respiratory movement with air sacs formed
 Surfactant production begins ~ 24 weeks
 Brain appears mature
 Eyebrows and eyelashes
 can be seen
 Reacts to sudden noise
 with active movement
The Fetus—Month 7
 Fetus is 10-12 inches long and weighs about 1-2
pounds.
 Fetus is active and then rests.
 The baby now uses the four senses of vision, hearing,
taste and touch
Weeks 25 – 28- 7th
month
 Eyelids open and close
 Capillaries proliferate around the lungs’ alveoli making
gas exchange possible
 Skin has wrinkled red appearance
 Rapid brain development
The Fetus—Month 8
 The fetus is 14-16 inches long and weighs 2-3 pounds
 Layers of fat are piling on.
 Fetus has probably turned head-down in preparation for
birth.
 Fetus may react to noises with a jerking action
Weeks 29- 32- 8th
month
 Subcutaneous fat forms
 Testes start descending
 Fingernails and toenails are complete
 Bones are fully developed, but still soft and pliable
The Fetus—Month 9
 Fetus is about 17-18 inches long and weighs 5-6 pounds
 Skin is smooth because of the fat
 Baby’s movement slows down due to lack of room
 “Lightening” occurs when the baby drops in the pelvis
 Disease fighting antibodies are taken from the mother’s
blood
Weeks 33-36- 9th
month
 Lanugo begins to disappear.
 Fingernails reach the end of the fingertips.
 A baby born at 36 weeks has a high chance of survival,
but may require medical interventions.
Weeks 37 to 40
 The fetus is considered full-term at the end of the 39th
week of gestational age.
 It may be 48 to 53 cm (19 to 21 inches) in length.
 The lanugo is gone except on the upper arms and
shoulders.
 Fingernails extend beyond fingertips.
 Small breast buds are present on both sexes.
 Head hair is now coarse and thickest.
The development is continued postnatally with
adaptation to extrauterine life and child
development stages
Nutrition
The fetus passes through 3 phases of acquisition of nutrition
from mother:
 Absorption phase: Zygote is nourished by cellular
cytoplasm and secretions in fallopian tubes and uterine
cavity.
 Histoplasmic transfer: After nidation and before
establishment of uteroplacental circulation, fetus
nutrition is derived from decidual cells and maternal
blood pools that open up as a result of eroding activity
of trophoblasts.
 Hematotrophic phase: After third week of gestation,
substances are transported passively via intervillous
space.
Functions of the Placenta
 Fetal Respirations
 Fetal Nutrition
 Endocrine Functions
 Elimination of Wastes
 Barrier against certain substances