fertilization: the reproductive systems process of ... · germinal stage: first two weeks day 1 to...

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Janet Belsky’s

Experiencing the Lifespan, 2e

Chapter 2:

Prenatal Development,

Pregnancy, and Birth

Meredyth Fellows, West Chester University of PA

Fertilization:

The Reproductive Systems

Female Reproductive

Structures

�Uterus

�Endometrium

�Cervix (neck of uterus)

�Fallopian tubes

�Ovaries

�Ovareside here

�Ova contain mother’s

genetic material

Reproductive Systems

Male Reproductive

Structures

�Testes

(continually

manufacture

sperm)

�Penis

Process of Fertilization: Union

of Sperm and Egg

�Ovulationoccurs:

�ovum expelled from

ovary

�suctioned into fallopian

tube

�Millions of sperm travel up

fallopian tube to ovum

�Alive for 7 days

�Fertilization

�One sperm penetrates

the ovum

�Nuclei (genetic material)

of the male and female

cells combine

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Genetics: Chromosomes, DNA,

Genes

�23 chromosome pairs

contain DNA (genetic

material)

�23 single strandseach

from mother and father

�Sex chromosome=1

chromosome pair (XX

female, XY male)

�Genes

�Located on chromosomes

�Contain chemical blueprint for

manufacture of proteins

Principles of Prenatal

Development

�Proximodistal

�Growth from middle to outside

�Cephalocaudal

�Growth from head to tail (feet)

�Mass to Specific

�Large structures appear before finer details

�Large movements appear before finer

movements

Stages of Prenatal Development

�Germinal

�First 14 days

�Period of Zygote

�Embryonic

�Week 3 to 8

�Period of Embryo

�Fetal

�Week 9 to Birth

�Period of Fetus

Germinal Stage: First two weeks

�Day 1 to 14, time from fertilizationto implantation

of blastocyst

�Zygotedivides once in the first 36 hours

�Every 12 -15 hours, divides again

�3 day trip down fallopian tube

�Once in the uterus, differentiates into

layers

�Zygote now called a blastocystand has

about 100 cells

�Blastocystimplants into the upper part of

the uterus

�Blood vessels proliferate to form the

placenta

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Recap: Events of the Germinal

Stage

Embryonic Stage: Weeks 3 to 8

�Fast paced forming of major organs and

body structures

�3rdweek after fertilization, circulatory

system forms and heart beats

�Neural tube forms—begins to

differentiate into the brain and spinal cord

�Arm and leg buds appear and elongate,

the heart begins to pump

�Outlines of eyes and ears appear

�Feet, elbows, wrists and fingers begin to

appear

�By week 8, the embryo is 1.5 inches long.

�The internal organs are in place and

embryo begins to look human.

Weeks 3, 4, and 9 of

Embryonic Stage

�Note proximodistaland cephalocaudal

trends

Fetal Stage: Week 9 to Birth

�Baby grows dramatically;

body structures are

refined; building blocks of

the brain are fully

assembled

�Neurons ascend to the top

of the tube, reach their

staging area and begin to

differentiate ( see

illustration)

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Fetal Stage

�Age of viability22 weeks (earliest date for

survival)

�Vital that baby’s lungs are mature enough to

breathe in oxygen and expel carbon dioxide.

�By the 25thweek, viability is above 50% if

acute care is available.

�Birth weight important to health of baby

�Baby needs as much time in womb as possible

�During last two months fetus gains 5 pounds

Poised to be Born!

�Illustration shows

fetus inside the

womb late in

pregnancy.

�Notice the placenta,

amniotic sac, and

umbilical cord

Pregnancy

�Gestation Period: period of pregnancy, 267-277 days

�Divided into Trimesters (about 3 months each)

�Important! Each woman may vary in her experience

(physical and emotional) of pregnancy.

�First Trimester

�Following implantation of blastocyst into uterus,

flood of hormones mayproduce fainting,

headaches, fatigue, tender breasts and morning

sickness

�Miscarriages (spontaneous abortions) are more

prevalent at this time

�Roughly 1 in 10 pregnancies ends in miscarriage

�Women in their late 30’s, miscarriage rate increases to 1 in 5

Pregnancy: Second Trimester

�Physically may feel much better

�Need for maternity clothes

�Quickeningoccurs (first indication of

the fetus moving)

�Feelings of attachmentmay begin

�A strong sense of attachment predicts

positive bonding after birth (although

attachment can happen at any time!)

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Pregnancy: Third Trimester

�Physical Symptoms and Emotional

States

�Leg cramps, backaches, anxiety, numbness in

lower limbs, heartburn, insomnia

�Irregular uterine contractions as baby sinks into

the birth canal

�Anxiety may begin as the focus shifts while

awaiting birth

Exploring the Pregnant Brain

�Recent research suggests:

�Pregnant women, no matter what the initial stress

levels, may experience less anxietyduring late

pregnancy.

�Research suggests that a woman’s physiology may

become biologically less reactive to stress prior to the

birth.

�Women whose stress levels remained high were more

likely to have premature births.

“Baby Brain”

�“Baby Brain”

�An expectant mother may feel as if she is

experiencing mental fog; thinking processes may

become hazy.

�Research with rats who have given birth shows:

�Aftergiving birth, pre-birth cognitive deficits more

than reverse.

�Changes seem to permanently pump up the

neurons in the memory centers of the brain.

�Better performance on memory and learning

tasks

�Research needed to show similar changes in humans

Pregnancy Is Not A Solo Act

�What forces turn the experience of pregnancy

into a period of distress?

�Low SESplaces women at risk of feeling

demoralized and depressed

�Low SES contributes to lack of access to prenatal

care, proper foods, and often, social support

�“Being loved” is the main force predicting

happy pregnancy. (social support)

�Dads also may experience strong emotions.

�They too may feel worried about this life change.

�Social support necessary

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Threats to the Developing

Baby: Category 1: Teratogens

�Teratogens: substances that may

cross the placenta to harm the

developing embryo or fetus

�Examples:

�Medications –Thalidomide

�Diseases –Rubella

�Social Drugs -Alcohol,

Nicotine, Cocaine

�Environment-Pesticides,

Radiation

�Stress –hormones and

effects on unborn baby

Basic Teratogenic Principles

�Teratogens do most damage during sensitive periods.

�Four Principles

�Most likely to cause structural damage during

embryonic period

�Can affect developing brain throughout pregnancy

�2ndand 3rdtrimester: risk of developmental

disorders

�Operate in a dose-response fashion (threshold level)

�Exert damage unpredictably

�Teratogens may also exert influence long after exposure

(e.g. DES, diethylstilbestrol)

Teratogens: Nicotine and

Alcohol

�Nicotine:

�Constricts blood vessels

�Increases risk of smaller

than normal and less

healthy newborn

�Alcohol:

�Excessive consumption

contributes to chance of

Fetal Alcohol Syndrome

Measurement Issues: How

much is too much?

�Researchers experience difficulty

defining exact amounts of exposure

that may cause harm to the developing

organism.

�Self-report questionnaires may be

unreliable.

�Rule of thumb: don’t smoke, drink, take

drugs, and avoid exposure to teratogens

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Threats from Within:

Chromosomal Disorders

�Chromosomes: human

complement is 46 (23 pairs)

�If developing baby is missing

or has an extra

chromosome, embryo may

miscarry

�When an extra chromosome

does occur:

�Down syndrome –

trisomy 21 (extra

chromosome or piece

copy to adhere to

chromosome 21)

Chromosomal Disorders:

Down Syndrome_Trisomy 21

�Risk factors: advanced maternal and paternal age (in

women, ova may have chromosomal faults)

�Women over 40, 1 in 100

�Women over 45, 1 in 25

�Symptoms: distinctive physical characteristics

�Flat facial profile

�Upward slant to eyes

�Stocky appearance

�Enlarged tongue

Down Syndrome continued

�At risk for heart defects and childhood

leukemia

�Mild to moderate mental retardation

�Shortened life-span

�Average life expectancy, 58!

Genetic Disorders: Single-

Gene Disorders

�Genes come in pairs –one on each

chromosome –and determine specific traits

�While most traits are dependent on many genes,

single genedisordersoccur due to a flaw in a

particular gene.

�Three modes of inheritance:

�Dominant

�Recessive

�Sex-Linked

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Genetic Disorders

�Dominantdisorders

�A person who inherits one copy of

the gene alwaysgets the disease.

�If oneparent has the genetic

disease, each child has a 50/50

chanceof inheriting the disease.

�Recessive

�Child gets illness by inheriting two

copies of the abnormal gene that

causes the disorder

�Odds of baby born to two carriers

having the illness are 1 in 4.

Genetic Disorders: Sex-linked

single-gene disorders

�Sex-Linked single-

gene disorder

�Illness carried on the

mother’s X

chromosome

�Typically leaves the

female offspring

unaffected but has a

50/50 chance of

striking each male

child

Interventions: Sorting Out the

Options

�First Step: Genetic Counselor

�Counsels couples about their own or their

children’s risk of developing genetic disorders

�Advice about available treatments

�Goal: permit couples to make mutual decision

�Genetic Testing

�Blood test: determines whether a person carries

the gene for a genetic disorder

Prenatal Tests

�Ultrasound

�Commonly used to date the

pregnancy and chart the fetus’s

growth, but it can also reveal

structural abnormalities.

�Chorionic Villus Sampling

�During 1sttrimester, remove

piece of developing placenta

�Test for genetic and

chromosomal conditions.

�Risks:

�5% risk of miscarriage

�Chance of limb

impairment

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Prenatal Testing

�Amniocentesis

�2ndtrimester procedure, typically week 14

�Remove cells from amniotic fluid and test

for genetic and chromosomal conditions

�Risk

�Miscarriage

Infertility

�The inability to conceive

after a year of

unprotected sex.

(Includes inability to

carry a child to term.)

�Infertility rates higher at

older ages

�Male and female

problems involved

�Emotional

consequences

�Anxiety, guilt, jealousy

Interventions: Assisted

Reproductive Technology

�ART: treatment in which the egg is fertilized

outside of the womb

�In Vitro Fertilization

�After woman has been given fertility drugs, eggs

are harvested

�put into petri dish along with partner’s sperm

�Developing cell mass is inserted into the woman’s

uterus with the hope of implantation into uterine

wall

Birth!

�Stage 1:Dilation

and Effacement

�Stage 2:Birth

�Stage 3:The

Expulsion of the

Placenta

Some threats during birth

include: baby inbreech

position, cervix not fully

dilating, difficult position

of umbilical cord

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Birth Options

�Birth options and Providers:

�Natural childbirth

�Deliver without medication with the help of midwife

or doula.

�Lamaze(pain management)

�Bradley(natural, non-medicated childbirth)

�Sometimes, medical intervention is needed.

�Cesarean

�Procedure common in some countries

�Used in the U.S. if complications occur

Medical Interventions

�Episiotomy

�Epidural

�Electronic Fetal Monitor

�Cesarean Section (C-Section)

�Remove fetus manually by making incision

into abdominal wall and uterus

�Used when complications occur

The Newborn

�Apgar Scale: first test immediately after birth

�Rated 0 to 2 for each category at one minute and

five minutes after birth

�Color

�Muscle Tone

�Respiration

�Heart Rate

�Reflex Response

�Score over 7 healthy

�Under 7, must be monitored or resuscitated and may go

to NICU

Threats to Development

�Low Birth Weight (LBW)

�Body weight of less than 5 ½ lbs.

�Arrived too early or did not grow in womb

�Very low birth weight

�Body weight of less than 3 ¼ lbs.

�Often very premature and rushed to NICU

(neonatal intensive care unit)

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Infant Mortality

�Infant mortality is an overall

barometer of a nation’s status.

�Countries vary greatly in their

infant mortality rates—with

developing countries doing far

worse.

�The U.S. ranks a humiliating 41st

in the world.

�One reason is our nation’s high

income inequalities, and

inadequate access to good

prenatal care

�SOCIOECONOMIC STATUS AFFECTS

OUR LIFESPAN JOURNEY FROM the

FIRST MOMENTS OF LIFE.