Physiology of Physiology of Pregnancy and Pregnancy and Prenatal DevelopmentPrenatal DevelopmentNP03L001 / Version 1.4

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Terminal Learning Terminal Learning ObjectiveObjective Given a scenario of a developing

fetus and the five elements of the nursing care process, determine approaches for patient care, by correctly responding to written, oral, and experiential assessment measures.

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Enabling Learning Enabling Learning ObjectivesObjectives A: Describe the process of

gametogenesis.

B: Relate ovulation and ejaculation to the process of human conception.

C: Explain implantation and nourishment of the embryo before development of the placenta.

D: Describe normal prenatal development from conception through birth.

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ELOs Con’tELOs Con’tE: Identify the structure and

functions of the placenta, amniotic sac, umbilical cord, and fetal membranes.

F: Compare fetal circulation to neonatal circulation.

G: Explain the similarities and differences in the two types of twins.

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GametogenesisGametogenesisGametogenesis: the

development of ova in the woman and sperm in the man.

Gametes:◦Oogenesis: formation of female gamete. ◦Spermatogenesis: formation of male

gamete. ◦Meiosis: the process in which cells divide

to form gametes.

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Check On LearningCheck On LearningQUESTION: What is female

gametogenesis called?

ANSWER: Oogenesis.

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Ovulation and EjaculationOvulation and EjaculationConception: human fertilization

occurs when the sperm penetrates an ovum and unites it.

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Preparation for Conception in the Preparation for Conception in the FemaleFemaleRelease of the ovum:

◦Ovulation occurs approximately 14 days before a woman’s next menstrual cycle would begin.

◦Is estimated to survive no longer than 24 hrs after its release at ovulation.

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Conception in the Female Conception in the Female Con’tCon’tOvum transportation:

◦Mature ovum is released on the surface of the ovary where it is picked up by the fallopian tube and transported through the tube and awaits fertilization.

◦The ovum fertilized or not, enters the uterus approximately 3 days after its release from the ovary.

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Preparation for Conception in Preparation for Conception in the Malethe MaleEjaculation: most sperm survive no

longer than 24 hours in the female reproductive tract, but a few may remain fertile for up to 5 days.

Transport of sperm in the female reproductive tract:◦Only sperm cells enter the cervix. ◦Most are lost along the way and fewer

than 200 reach the fallopian tube.

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Conception in the Male Conception in the Male Con’tCon’t  Preparation of sperm for

fertilization:◦Sperm are not immediately ready to

fertilize the ovum. ◦During the trip to the ovum, they

undergo changes that enable one of them to penetrate the protective layers surrounding the ovum, a process called capacitation.

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FertilizationFertilization

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© Copyright 1999-2001 by M. Terwilliger for the Westside PRC

FertilizationFertilizationOccurs when one spermatozoon enters the

ovum and the two nuclei containing the parents’ chromosomes merge.

 Sperm entrance into ovum: ovum is

fertilized in the distal third of the fallopian tube near the ovary.

Fusion of the nuclei of sperm and ovum:◦ The 23 chromosomes from the sperm unite

with the 23 from the ovum restoring the total number to 46.

◦ Fertilization is complete and cell division can begin when the nuclei of the sperm and ovum unit.

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Check on LearningCheck on LearningQUESTION What is Conception?

ANSWER: Human fertilization occurs when the sperm penetrates an ovum and unites it.

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ImplantationImplantation

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Pre-embryonic PeriodPre-embryonic Period

Consists of the first 2 weeks after conception.

 Around the 4th day after conception, the fertilized ovum, now called a zygote, enters the uterus.

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Initiation of Cell DivisionThe zygote divides until it reaches

16 cells at which time it is called a morula because it resemble a mulberry.

 The outer cells of the morula secrete fluid, forming a blastocyst a sac of cells with an inner cell mass placed off center within the sac.

The inner cell mass develops in the fetus.

 Part of the outer layer of cells develops as the placenta and fetal membranes.

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Entry of the Zygote into the Entry of the Zygote into the UterusUterusWhen the blastocyst contains

approximately 100 cells, it enters the uterus.

It lingers in the uterus another 2 to 4 days before beginning implantations.

The endometrium, now called the decidua, secretes rich fluids to nourish the zygote before placental circulation is established.

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Implantation in the Implantation in the DeciduaDeciduaImplantation at the proper time

and location in the uterus is critical for continued development.

 It occurs between the 6th and

10th days after conception.

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Maintaining the DeciduaMaintaining the DeciduaImplantation and survival of the

zygote the deciduas in the secretory phase.

The zygote secretes HCG to signal the woman’s require a continuing supply of estrogen and progesterone to maintain body that a pregnancy has begun.

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Location of ImplantationLocation of ImplantationSite of implantation is important

because that is where the placenta develops.

 Normal implantation occurs in

the upper uterus, slightly more often on the posterior wall than the anterior wall.

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Mechanism of Mechanism of ImplantationImplantationPrimary chorionic villi form that nourish the

zygote by diffusion because the circulatory system is not yet established.

 The villi will eventually form the fetal side

of the placenta.  The zygote is fully embedded within the

uterus by 10 days.  As it implants, usually near the time of the

next menstrual period, a small amount of bleeding may be confused with the normal period.

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Check On LearningCheck On LearningQuestion: What is the Pre-

embryonic Period?

Answer: The first 2 weeks after conception.

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Normal Prenatal Normal Prenatal DevelopmentDevelopment

Embryonic Period: extends from the beginning of the 3rd week through the 8th week after conception.

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Differentiation of CellsDifferentiation of CellsBy the end of the 8th week, all

major organ systems are in place and many are functioning, although in a simple way.

 Structures are vulnerable to damage

from teratogens (drugs, viruses, radiation, and infectious agents) because they are developing rapidly.

 Unfortunately, a woman may not

realize she is pregnant at this time.

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Weekly Embryonic Weekly Embryonic DevelopmentsDevelopmentsTerms:

◦Zygote: cell formed by union of sperm and ovum.

◦Embryo: 3rd week to 8th week of development.

◦Fetus: 9th week until birth.

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Zygotic StageZygotic StageAmniotic cavity.Yolk Sac.Mesoderm.Trilaminar embryonic disk. Week 2: occurs simultaneously

in all organ systems and proceeds in a cephalocaudal and central-to-peripheral direction.

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Embryonic StageEmbryonic Stage3 primary cell layers differentiate:

◦Ectoderm◦Mesoderm◦Endoderm

Growth is RAPID!!

Embryo develops ‘human’ appearance.

Teratogenic agents can seriously harm embryo.

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Prenatal Development Prenatal Development Week Week 33The first body segments appear:

◦Neural tube forms.

◦Primitive brain.

◦Primitive spinal cord.

◦A primitive or tubular heart begins beating at 22 to 23 days.

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Prenatal Development Prenatal Development Week Week 44

The embryo is now 1/5th inch long, and the head is a third of its total length. ◦ Embryos shape changes

resembling a “C” shape with a tail and a head.

◦  Neural tube closes.◦  Face and upper

respiratory tract begin.◦  Ears and eyes are

apparent.◦  Upper extremities

appear as buds.◦  Partitioning of the heart

into 4 chambers begins.◦  Esophagus and trachea

separate.33

Prenatal Development Prenatal Development Week Week 55Heart is beating and continuing

to develop 4 chambers.  Limbs continue to form. Head is large due to rapid brain

growth.

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Prenatal Development Prenatal Development Week 6Week 6

Heart has 4 chambers.

Facial development begins with eyes, ears, and nasal pits.

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Prenatal Development Prenatal Development Week 7Week 7

Development is proceeding rapidly.◦Face is more

human looking.

◦Eyelids begin to form.

 ◦Fast intestinal

growth.  36

Prenatal Development Week Prenatal Development Week 88The embryo is

now a little more than 1 inch long.

Fingers and toes are formed.

Purposeful movements occur but mother can't feel these yet.

Heart beats at 40-80 beats/minute.

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Fetal PeriodFetal PeriodLongest part of prenatal

development.

Begins 9 weeks after conception and ends with birth.

Teratogens may damage already formed structures but are less likely to cause major structural alterations.

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Weeks 9 through 12Weeks 9 through 12Head is half the total length of the fetus

at the start of this period.

First fetal movements begin but are too slight for the mother to detect.

 Eyes close at 9 weeks and reopen at 26

weeks.  Urine production begins. End of 12th week, fetal gender can be

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Fetus at 12 WeeksFetus at 12 Weeks

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Weeks 13 through 16Weeks 13 through 16

Grows rapidly in length.

Quickening (fetal movement) occurs.

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Weeks 17 through 20Weeks 17 through 20Vernix covers skin.

Lanugo is present. Eyebrows and

head hair appear.  Brown fat (special

heat-producing fat that helps newborn maintain temperature stability after birth) is deposited.

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Fetus at 18 weeks.

Fetus at 20 WeeksFetus at 20 Weeks

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Weeks 21 through 24Weeks 21 through 24Fetus appears thin due to minimal

fat. Skin is translucent and red. Lungs begin to produce surfactant

although alveoli immature. Most systems still extremely

immature and fetal survival is not likely.

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Fetus at 24 WeeksFetus at 24 Weeks

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Weeks 25 through 28Weeks 25 through 28

Fetuses more likely to survive if born as lungs and CNS have matured.

Fetus assumes head down position.

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Weeks 29 through 32Weeks 29 through 32Toenails and

fingernails are present.

 Subcutaneous

fat increases. Skin is

pigmented and smooth.

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Weeks 33 through 38Weeks 33 through 38Rate of growth slows, mainly

gaining weight.

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Check On LearningCheck On LearningQUESTION: What is an example

of teratogenic agent?

ANSWER: Any drug, virus or irradiation that the mother is exposed to can cause malformation of the fetus. An example is the virus Rubella.

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QUESTION: What is formed by the union of the sperm and ovum?

ANSWER: Zygote.

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Check on LearningCheck on Learning

Structure and Functions of Structure and Functions of Placenta, Umbilical Cord and Placenta, Umbilical Cord and Amniotic FluidAmniotic Fluid

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PlacentaPlacentaPlacenta: disk-like organ made up of

about 15-20 segments (cotyledons) that are present only during pregnancy.

Produces four hormones:◦Progesterone.◦Estrogen.◦Human chorionic gonadotropin

(hCG).◦Human placental lactogen (hPL).

The site of exchange of nutrients, oxygen and waste products.

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PlacentaPlacenta

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Placenta CirculationPlacenta Circulation

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Placenta Con’tPlacenta Con’tThe maternal side of the placenta has a

"beefy" red appearance due to the large number of arterioles and venules. Often referred to as “Dirty Duncan”.

The amniotic fetal membrane of the placenta has a grayish, shiny appearance at term. Often referred to as “Shiny Schultz”.

The placenta has no use after pregnancy and is expelled through the vagina after birth.

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Placenta Maternal SidePlacenta Maternal Side

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Placenta Fetal SidePlacenta Fetal Side

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Fetal MembranesFetal MembranesThe two fetal

membranes are the amnion (inner membrane) and the chorion (outer membrane).

The two membranes are so close as to be one (the “bag of waters”), but they can be separated.

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Amniotic SacAmniotic Sac

A sac made up of the chorion and the amnion that contains the fetus and amniotic fluid.

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Amniotic FluidAmniotic Fluid

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Amniotic Fluid FunctionAmniotic Fluid FunctionProtects the growing fetus and promotes

normal prenatal development. ◦Cushioning against impacts to the maternal

abdomen.◦Maintaining a stable temperature.◦Allowing symmetric development as the

major body surfaces fold toward the midline.◦Preventing the membranes from adhering to

developing fetal parts.◦Allowing room and buoyancy for fetal

movement.

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Amniotic Fluid CompoundsAmniotic Fluid CompoundsAlbumin.Urea.Bilirubin.Vernix.Lanugo.Fructose.Fat.

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Amniotic FluidAmniotic FluidThis fluid may be tested to

determine the health and development of the fetus during the later stages of pregnancy but may be tested as early as 8 weeks.

Volume: is approximately 700-800 ml at 40 weeks.

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Umbilical CordUmbilical CordJoins the embryo to the placenta.Contains 2 arteries and one vein:

◦The vein carries freshly oxygenated and nutrient-laden blood to the fetus.

◦The arteries carry deoxygenated blood back and waste products away from the fetus to the placenta.

Vessels of the umbilical cord are protected from compression by Wharton's jelly.

It has no pain receptors.

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Umbilical CordUmbilical Cord

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Check on LearningCheck on LearningQUESTION: What is the Amniotic

Sac?

ANSWER: A sac made up of the chorion and the amnion that contains the fetus and amniotic fluid.

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Check on Learning Check on Learning 

QUESTION: Which hormone provides for the expansion needed during pregnancy of the uterus, breast and breast glandular tissues? It also plays a role in increasing vascularity and vasodilatation of the villous capillaries of the placenta.

ANSWER: Estrogen.67

  Check On LearningCheck On Learning

QUESTION: Identify 3 parts of the umbilical cord.

 ANSWER: Two arteries, one vein,

and Wharton's jelly.

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Fetal vs. Neonatal Fetal vs. Neonatal CirculationCirculation

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Fetal CirculationFetal CirculationOxygenated blood is brought to the

fetus by the umbilical vein and enters the fetal liver, where it branches.

The first branch (portal sinus). The second branch (ductus venosus). Blood entering the heart from the

vena cava is directed across the right atrium through the foramen ovale to the left atrium.

Blood is then ejected from the left ventricle into the aorta and further circulated to the coronary arteries, brain, and upper extremities.

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Fetal Circulation Con’tFetal Circulation Con’tVenous blood returning from this

region returns to the right atrium through the superior vena cava and is directed downward through the tricuspid valve into the right ventricle.

It is then pumped into the pulmonary artery, where the majority of the blood is shunted to the descending aorta through the ductus arteriosus and perfuses the lower body.

Only a small amount of blood enters the fetal lungs as a result of high pulmonary resistance.

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Changes in Circulation After Changes in Circulation After Birth Birth

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Circulation Changes at Circulation Changes at BirthBirth

With the first breath, the newborn's lungs expand and the fluid within them is absorbed into the pulmonary circulation.

With that first breath, pulmonary and right heart pressures fall and systemic pressures begin to rise with the removal of the placenta.

The foramen ovale closes as the pressure in the left atrium exceeds the pressure in the right atrium.

The ductus arteriosus closes with the increased oxygen content of the newborn's blood.

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Multifetal PregnancyMultifetal Pregnancy

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Monozygotic Dizygotic

TwinsTwinsTwins are classified as monozygotic or

dizygotic.Monozygotic twins: 

◦ The twins carry the same genetic code and are the same sex.

◦ They share a placenta, but each has a separate umbilical cord.

Dizygotic twins: ◦ These twins have a separate placenta, and

the sex and genetic makeup can vary.◦ Dizygotic twins are no more closely related

than siblings born at different times.

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Multifetal Pregnancy Multifetal Pregnancy ComplicationsComplications

Complications with the Mother:◦ Spontaneous abortions.◦ Prematurity.◦ Uterine over distension that can cause

preterm labor.◦ Maternal anemia.◦ Pregnancy Induced Hypertension (PIH).◦ Placenta Previa.◦ Abruptio Placentae.◦ Polyhydramnios.

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Complications with Fetal Complications with Fetal TwinsTwinsCongenital anomalies.

Problems with entangled cords.

Growth problems.

Birth defects are more common in twins.

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Review of Main PointsReview of Main PointsGametogenesisFetal development and

maturation of body systemsFunctions of placenta, umbilical

cord and amniotic fluidFetal and neonatal circulationTwins

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Questions???