Transcript Conception and Fetal Development

CONCEPTION AND FETAL
DEVELOPMENT
Revised Spring 2011
HOW DOES THE FEMALE
BODY PREPARE FOR
CONCEPTION?
Describe the process of maturation of an ovum
Menstrual Cycle
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Varies every 28 - 35 days
The time between ovulation and menstruation is
relatively constant (14 days). Follicular phase.
The variable is from menses to ovulation. It can
not be predicted, the luteal phase.
Affected by various physical and emotional
factors
Maturation of the Ovum
Ovarian Cycle
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Follicular Phase- Development of the graafian
follicle
Ovulatory Phase- Ovulation
Luteal Phase- Formation of corpus luteum
HOW WILL THE PATIENT
KNOW THAT SHE IS
OVULATING?
Signs and Symptoms of Ovulation
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1. Body temperature increase
2. Mittelshmerz
3. Cervical mucus changes
 Increase
in amount
 Becomes thin, watery, and clear
 Ferning
 Stretchable: spinnbarkheit
 Alkaline
WHAT HAPPENS TO THE
CORPUS LETEUM OF I DO
NOT GET PREGNANT?
WHAT HAPPENS TO THE
CORPUS LUTEUM IF I BECOME
PREGNANT?
Endometrial Cycle
The uterine endometrium repsonds to ovarian
hormones and goes through the phases in building
up the lining of the uterus in preparation for
implantation
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Hormonal Cycle
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FSH- Follicle stimulating hormone
 Begins
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LH- Luteinizing hormone
 Assists
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growth and maturation of the graafian follicle
in continued growth of the graafian follicle
Estrogen
 Responsible
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for proliferation of endometrium
Progesterone
 “Pro
gestation”. The corpus luteum produces
progesterone so the endometrium won’t slough off
Conception

Maturation of ovum and sperm cells
 Pregnancy
comes about from the union of a female
germ cell, ovum with a male germ cell, the
spermatozoon
 Conception
One ovum per month
is discharged from the
ovary. It is
transported into the
fallopian tube where
it begins its journey
through the tube in
search of the sperm.
Viable for 12-24
hours
Fertalization
When intercourse
occurs, millions of
sperm travel in
search of an ova.
During travel
through the female
reproductive
system,
capacitation
occurs
Fertilization
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As the sperm swarm around the ova, the
Acromosome caps of sperm release zona digesting
enzymes
WHY IS THE NUMBER OF SPERM SO
IMPORTANT IF ONLY ONE SPERM
ENTERS THE EGG?
Fertilization
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Distal portion of the
fallopian tube
Only one sperm
penetrates ova
Each contributes 23
chromosomes
Sex of baby
determined at this time
PRE-EMBRYONIC
DEVELOPMENT
Fertilized ovum begins its travel to the
uterus
Cellular Multiplication
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Morula eventually
forms a fluid filled
cavity within the cell
mass.
 Inner
solid cell mass is
called the blastocyst
 Outer cell mass that
surrounds the cavity is
called the trophobast
Trophoblast
Outer layer of cells
Blastocyst
Inner cell mass
Placenta
Chorion
Fetus
Amnion
Implantation
Germ Layers
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Ectoderm
Mesoderm
Endoderm
Development Periods

Stage 1 – pre-embryonic
 weeks

1-2
Stage 2 -- embryonic
 weeks
3-8
 period of ORGANOGENESIS
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Stage 3 -- fetal
 weeks
9 - 40
Embryonic Period
Weeks 4-8
Week 4

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
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and legs
 CR = 4 mm
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Week 5
 Head
grows larger
 Hand and feet plates develop
 Facial features begin to develop
 CR = 8 mm.
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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
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Week 7
Eyelids start to form
 Fingers develop; elbows visible
 Diaphragm separates
abdomen from chest
 Bronchi develop
 Arms and legs move
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Week 8
Fingers and toes distinct
 Skeletal ossification begins
 Testes and ovaries are
distinguishable
 Heart has four chambers
 Circulation through
umbilical cord occurs
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*** ALL essential external and internal structures are present
and now will continue to grow
The patient tells the nurse that she is worried that
the baby may have some defect because she was
on antibiotics and other cold medication during the
first week after intercourse/conception

What is happening during the first week after
conception that would assist the nurse in answering
her question?
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Fetal Period
Weeks 9-40
Weeks 9-12
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Head size increases
Face is well formed
Nails appear
Eyelids appear and close and fuse shut
Kidneys excrete urine
Intestines are forming; peristalsis begins
Heartbeat can be heard via ultrasound
Tooth buds appear for the baby teeth
Weeks 13-16
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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
Weeks 17-20
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Hair abundant on head
Lanugo covers the body
Vernix begins to form
Myelination of spinal cord begins
Suck and swallow begin
Quickening occurs ~ 18 weeks
Weeks 21-24
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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
Weeks 25-28
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Eyelids open and close
Capillaries proliferate around the lungs’ alveoli
making gas exchange possible
Skin has wrinkled red appearance
Rapid brain development
Weeks 29-32
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Subcutaneous fat forms
Testes start descending
Fingernails and toenails are complete
Bones are fully developed, but still soft and pliable
Weeks 33-40
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Limbs start to flex
Muscle tone is developed
Lanugo disappears
Body begins to store fat
Maternal antibodies transfer to the fetus
Exhibits sleep and awake patterns
Ask Yourself????
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The thickened endometrium in which the fertilized
embryo implants is called the:
a.
b.
c.
d.
Endoderm
Decidua
Amnion
chorion
Answer this……
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The fetal nervous system is formed by the germ
layer known as the:
a. ectoderm
b. mesoderm
c. entoderm
d. endoderm
AUXILLARY STRUCTURES
Placenta
Fetal Membranes
Functions of the Placenta

Fetal Respirations
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Fetal Nutrition
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Endocrine Functions
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Elimination of Wastes

Barrier against certain substances
Amnion
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Smooth, glistening membrane known as the Amnion
is the lining of a fluid filled space that develops
around the embryo
Functions of Amniotic Fluid
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Keeps the fetus at an even temperature
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Cushions the fetus against possible injury
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Provides place for the fetus to move easily and
grow symmetrically
Fetus drinks the fluid
Chorion
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Thick membrane with finger-like projections called
chorionic villi.
Chorionic villi contain blood vessels that are main
connection with mother.
Chorionic villi produce human chorionic
gonadotropin (HCG)
Merges with the decidua basalis to form the
PLACENTA.
Umbilical Cord
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Body stalk that attaches the embryo to the yolk sac
Contains blood vessels that extend into the chorionic
villi
Protected by wharton’s jelly
Teratogens
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Risk factors such as environmental substances
 Smoking
 Alcohol
 Drugs
 Viruses
 Occupational
hazards
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During what period of time is the baby most
susceptible to damage from teratogens?
Review
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Describe the components of the process of
fertilization.
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Ovum released into fallopian tube—viable for 24 hr.
Sperm deposited into vagina—viable for 48 to 72 hr
(highly fertile for 24 hr).
Sperm must undergo capacitation and acrosomal
reaction.
Sperm penetration causes a chemical reaction that
blocks more sperm penetration.
Fertilization occurs in the distal end of the fallopian
tube.
Sperm enters ovum. The nuclei of the ovum and sperm
unite and become a diploid zygote.
Review
How can knowledge of the normal fertilization process
assist in helping couples conceive?
Review
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How can knowing the gestational age of the fetus
help in assessment for the potential effects of a
teratogen?