Fertilization and Fetal Development

8/2/2019 Fertilization and Fetal Development

1/50

Chapter 4: FERTILIZATION AND FETALDEVELOPMENT

I. FERTILIZATION

A. Fertilization is the union

of mature egg cell (ovum)and sperm cell happening in

the ampulla (outer third) of

the fallopian tube resulting

in a fertilized ovum known

as the zygote.


2/50

B. It is also termed

conception, fecundation, and

impregnation.

C. The movement of the

sperms caused by flagellar

action is believed to maintainthe sperms in suspension and

to maintain the sperms in

suspension and to facilitate

transport.


3/50

D. Each sperm reaches the site of

fertilization in the ampulla of the

fallopian tube shortly after

ejaculation, often only within 5

minutes. But on average, a time of 4to 6 hours seems more reasonable.

E. Sperms must be in the genital

tract 4 to 6 hours before they are ableto fertilize an egg, It is during this

period when the enzyme needed to

dissolve the cement substance

(hyaluronic acid) that holds together

the cells covering the ovum isactivated. This enzymes is called

hyaluronidase.


4/50

F. The sperm must undergo 2 processes before fertilization:

1. Sperm capacitation: the process by which the sperm becomes

hypermobli and there is a breakdown of the plasma membrane and

exposes the acrosomal membrane/ covering of the sperm head

allowing the sperm to bind with the zona pellucida of the ovum.

2. Acrosomal Reaction: follows capacitation; the acrosomal covering of

the head of the sperm contains hyaluronidase. So as millions of spermssurrounds the ovum, they deposit minute amounts of hyaluronidase in

the corona radiata, the outer layer of the ovum, which allows the

sperm head to penetrate the ovum


5/50

G. As soon as the sperm penetrates the zona

pellucida and makes contact with the vitelline

membrane of the ovum, a cellular change

occurs in the ovum that inhibits other spermsto penetrate. This cellular change is mediated

by release of material from the cortical

granules, organelles found just below the egg

surface


6/50

H. Fertilization occurs

when the male

pronucleus, thus the

chromosome diploidnumber (46) is restored

and a new cell, the

zygote, is created with

a new combination ofgenetic material which

creates a unique

individual different

from the parents and

anyone else.


7/50

II. CLEAVAGE/MITOSIS

A. Zygote: the cell that resultsfrom the fertilization of the

ovum by a spermatozoan. This

cell undergoes mitosis which is

the process of cell replication

where each chromosome splits

longitudinally to form a

double-stranded structure.


8/50

B. Cleavage: series of

mitotic cell division by

the zygote

C. Blastomeres:

daughter cells arising

from the mitotic cell

division of the zygote

92-cell, 4-cell, 8-cellblastomeres)


9/50

D. Morula: solid ball of

cells produced by 16 or so

blastomeres; called the

traveling form because itis ion this form when it

migrates thru the fallopian

tube and reaches the

uterine cavity about 3 to 4after ovulation.


10/50

E. Blastocyst: a fluid-filled cavity that

reaches the uterine cavity

Over the next 3 to 4 days of development,

a differentiation of cells as to their specific

potencies occurs. The reorganization ofthe morula follows forming a blastocyst.

This is the stage when there is already a

cavity in the morula called the blastocoels,

and when it enters the uterine cavity. The

cavity enlarges and pushes the morulacells into an outer layer of cells called the

trophoblast. Along with this is an inner

cells mass attached to one side of the

blastocyst. The divisions and the

reorganization have already consumed

energy stores available in the zygote, such

that it becomes necessary for the

blastocyst to embed or implant in the

uterine wall. This is necessary for it to

obtain nourishment for its further

development.


11/50

III. IMPLANTATION

A. Also called Nidation

B. Time: 6 to 9 days after

fertilization

C. Site: upper fundal portion or

upper one-third of the uterus; canbe anterior 9towards the mothers

front) or posterior. Abnormal

implantation sites are the fallopian

tubes which leads to ectopic

pregnancy and the lower uterinesegment which causes placenta

previa.


12/50

IV. THE PLACENTA

A. Dimension

1. Discoid: 15 to 20 cm in diameter and 2 to 3 cm thickness

2. Location: in the uterus, anteriorly or posteriroly near the

fundus.


13/50

3. Fetal Side: covered with

amnion; beneath it the fetal

vessels course with the

arteries passing over the

veins. Amnion: 0.02 to 0.05mm in thickness; a sac that

engulfs the growing fetus.

Amniotic fluid: clear fluid

that collects within theamniotic cavity


14/50

4. Maternal Side; divided into

irregular lobes; consist of

fibrous tissue with sparse

vessels confined mainly to thebase

5. Average weight at term 500

gm

6. Feto-placental weight ratio atterm - 6:1


15/50

B. Placenta is formed by the union of the pregnancy; thickens in pregnancy w/ depth of 5 to 10

mm.

1. Decidua Basalis: portion of deciduas directly beneath the site of implantation, under the

imbedded ovum.

2. Decidua Capsularis: the portion overlying the developing ovum; separates ovum from the rest of

the uterine cavity; most prominent by 2nd month.


16/50

3. Decidua vera/ Desidua

Parietalis: lines the remainder

of the uterus

Initially, the decidua capsularisand deciduas vera are

separated by a space because

the gestational sac does not fill

the entire uterine cavity; by the

fourth month, the growing sac

fills uterine cavity.


17/50

4. Layers of deciduas Basalis and Decidua

Vera

a. Zona Compacta: uppermost/surface

layer made up of compact cells.

b. Zona Spongiosum: middle, spongy

layer with glands and small blood vessels.

c. Zona Basalis: lowest most/ basal layer

* The zona basalis and zona spongiosumtogether form the functional layer zona

functionales). Implantation is up to the

level of spongiosum.

* The zona basalis remains after

delivery/ placental separation


18/50

5. Decidua Aging: Nitabuchs layer, a zone of

fibrinoid degeneration, is where invading

trophoblast meets the deciduas whenever the

deciduas is defective.


19/50

C. PLACENTAL MATURITY: 12 weeks or 3

months; functions most effectively through 40

to 41 weeks; may be dysfunctional beyond 42

weeks.


20/50

D. PLACENTAL FUNCTIONS: Varied

1. Nutritive: transport nutrients and

water soluble vitamins to fetus

a. Fluid/gas transport

* Diffusion: oxygen, carbon dioxide,

water and electrolytes move from greater

to lesser concentration

* Facilitated transport: glucose

* Active transport: amino acids,

calcium, iron

* Pinocytosis: fat, gamma globulin,

albumin

* Leakage allows fetal and maternal

blood to mix slightly because of placental

defect; normally there is no mixture of

fetal blood.


21/50

2. Excretory with the amniotic fluid as

the medium of excretion

3. Respiratory organ of the fetus.

4. The placental as a protective barriers

to some substance and organism like

heparin and bacteria; ineffective for

virus, alcohol, nicotine, antibiotics,

depressants and stimulants.


22/50

5. Endocrine: secretes hormones estrogen, progesterone, human

chorionic gonadotropin (HCG), and human placental lactogen (HPL),

also called chorionic somatomammotropin (HCS)

a. Estrogen and progeterones major source of production after the first2 months is the placenta.

b Human chorionic gonadotropin (HCG)


23/50

b. Human chorionic gonadotropin (HCG)

* Secreted as early as 8 to 10 days after fertilization; detected in serum

as early as the time of implantation by the most sensitive pregnancy test,

the radioimmunoassay (RIA); and detected in urine by simple pregnancy

test.

* Functionc: prolong the life of the corpus luteum; serves as basis for

pregnancy tests.

* The hormone found elevated in excessive vomiting

*Normal value: 400,00 I.U./24 hours


24/50

c. Human chorionic somatomammotropin (HCS) or Human Placental

Lactogen (HPL)

* Secreted by third week after ovulation

* Influences somatic cellular growth of the fetus; resembles thegrowth hormone

* The principal diabetogenic factor as it is the major insulin

antagonist, or glucose sparing hormone


25/50

V. THE UMBILICAL CORD/FUNIS

A. Length: 55cm, 1 inch across at term

B. Parts:

1. One left umbilical vein: carries oxygenated

blood to the fetus

2. Two umbilical arteries (left and right) carry

deoxygenated blood from fetus to placenta


26/50

3. Whartons jelly, gelatinous

substance

a. Whartons Jelly: Specialized

connective tissue, an extension of theamnion; surrounds the umbilical

cord to prevent cord compression.

b. The blood volume in the cord also

helps prevent cord compression.


27/50

C. The cord extends from the fetal surface of the placental to the fetal

umbilicus.

D. Function: to transport oxygen and nutrients to the fetus and to returnmetabolic wastes including carbon dioxide from the fetus to the placenta.


28/50

VI. THE AMNIOTIC FLUID

A. Clear, straw-colored fluid in w/c the fetus floats.

B. Origin: Both fetal and maternal: amniotic epithelium maternal serum and in later

part (10th week), fetal urine; constantly being replaced so there is no dry labor inpremature rupture of the bag of water.


29/50

C. Amount: 500 to 1,000 mL at term; polyhydramnios

excessive amount of amniotic, greater than 1,000 to 1,500

mL; oligohydramniosamount less than 300 to 500 mL.

D. Reaction: neutral to alkaline (pH 7 to 7.25)


30/50

E. Abnormal Fluid Functions

1. Serves as a protective

cushion/shock absorber

2. Separates fetus from

membranes allowing

symmetrical growth and free

movement.

3. Acts as a medium of excretion

4. Serves as fetal drinks


31/50

5. Serves as a specimen forperiodic diagnostic exams todetermine fetal wellbeing orits absence.

6. Maintains fetaltemperature

7. Equalizes uterine pressure

and prevents markedinterference with placentalcirculation during labor.


32/50

VII. STAGES OF INTRAUTERINE DEVELOPMENT

A. The Ovum

1. From fertilization to 2 weeks

2. The period of pre-differentiation of organs.


33/50

3. When the ovum is exposed to a teratogen, the all or none

law applies, meaning the ovum is damaged and is out in

spontaneous abortion or it is not affected at all and continues

to grow normally.


34/50

B. The Embryo

1. From 2 weeks to 2 months

2. The period of organ differentiation (organogenesis)

3. Most Dangerous Period: A teratogen introduced at this stage may result

in severe organ malformation and dysfunction.


35/50

C. The Fetus

1. From 8 weeks to birth

2. The period of post-

differentiation of organs

3. When exposed to a

teratogen, a malformation is

least likely to occur. If ever

the fetus is affected, the

effects will most likely be

alteration in size or function

but not in for.


36/50

VIII. THE EMBRYONIC

GERM LAYERS

A. Ectoderm: the outer layer;

develops into:

1. Nervous system.

2. Hair Hair, nails, skin

epidermis, sebaceous and sweat

glands

3. Salivary glands, mucous

membrane of mouth

4. Epithelium of nasal oral

passage


37/50

B. Mesoderm: the middle l;ayer,

develops into:

1. Dermis

2. Cardiovascular system

3. Reproductive system system

4. Musculo-skeletal system

5. Urogenital system system, except the

bladder


38/50

C. Endoderm/Entoderm: the

inner layer develops into:

1. Linings of gastrointestinaltract from pharynx to rectum]

2. Liver, pancreas thyroid,

parathyroid

3. Respiratory tract

4. Bladder, thyroid, thymus (for

immunity building)

IX FETAL CIRCULATION


39/50

IX. FETAL CIRCULATION

A. Oxygenated blood from the

placenta passes to the passes to the

umbilical vein (1 left that contains

the most amount of oxygenated

blood at its entry into the liver);

closes at birth with cord clamping

and becomes ligamentum teres.

From the umbilical vein, a smallamount of blood goes to the liver

to nourish the liver. Most of the

blood in the umbilical vein goes to

the inferior vena cava thru the

ductus which closes at birth w/cord clamping and becomes

ligamementum venosum.


40/50

B. From the inferior vena

cava, blood goes to the right

auricle and is shunted to the

left auricle by way of the

foramen ovale, thus bypassing the lungs. It

functionally closes with

establishment of respiration

about 1 to 3 days and

anatomically closes a\in afew months.


41/50

C. From the left auricle, blood goes to the left ventricle to the

aorta and to the lower parts of the body.

D. From the hypogastric arteries, the right and left umbilicalarteries receive unoxygenated blood w/c is directed back to the

placenbta for oxygenation and purification. The umbilical

arteries close at birth with cord clamping and later become

umbilical ligament.


42/50

E. Blood form the upper of thebody enters the heart by way ofthe superior vena cava (SVC).

From the SVC, it goes to theright auricle, then to the rightventricle and to the pulmonaryartery.


43/50

F. From the pulmonary artery, asmall amount of blood goes to thelungs to nourish the lungs, butmost of the blood is shunted to

the aorta by way of the ductusarteriosus. The ductus arteriosus,like the foramen ovale functionallycloses with establishment ofrespiration about 1 to 3 days and

anatomically closes in a fewmonths about 2 to 3 monthsbecoming ligamentum arteriosum.If ductuc arteriosus fails to close,it will become an acyanotic heartdisease patent ductus arteriosus(PDA) - with machinery likemurmurs as an important sign.


44/50

X. INTRAUTERINE GROWTH AND DEVELOPMENT

Age Development4 weeks All systems in the rudimentary form. Beginning formation of

eyes, nose, GIT, Heart chambers formed; heart beating (14days) With arm and leg buds.

8 weeks Head large in proportion to the body, Neuromusculardevelopment some movements, Rapid brain development,

External genitalia appear12 weeks Placenta fully formed and functionging, Kidneys develop;

secrete urine, Centers of ossification in most bones, With

sucking and swallowing, Sex distinguishable, FHT detected

by ultrasound16 weeks

More human appearance, Quickening - mulltigravida,Meconium in bowels, External genitalia obvious, Scalp hair

develops, Formed eyes, nose, ears, FHT by fetoscope20 weeks With vermix casecsa and downy lanugo, Quickening

stronger, felt by primigrivida, FHT audible using

stethoscope, Bones hardening


45/50

24 weeks Body-well proportioned, skin red and wrinkled, hearingestablished, eyebrows, eyelashes recognizable, When

born, may breathe, but usually doesnt.28 weeks Viable; immature if born at this time, Surfactantproduction begins, Body is less wrinkled, With iron

storage, Nails appear, Pupillary membrane has just

disappeared from the eyes32 weeks Subcutaneous fats begins to deposit, Skin is smooth

and pink, More reflexes present, With iron and calcium

storage, Good chances of survival if delivered36 weeks Lecithin/ sphyngomyelin ration 2:1 (L/S), nails firm,

With definite sleep/ wake pattern, Lanugo

disappearing, Survival same as term40 weeks Fulterm with good muscle tone and reflexes, Little

lanugo, If male, testes in scrotum, the age at time of

EDC, With other characteristics features of the

newborn.

S C A CO C


46/50

XI. SPECIAL CONCERN:

TERATOGENIC

A. Teratogenesis: the dysgenesis of

fetal organs as evidenced either

structurally or functionally

B. Manifestation: The typical

manifestation of teratogenesis arerestricted growth or death of the

fetus, carcinogenesis, and

malformation, defined as defects in

organ structure or function. These

abnormalities vary in severity and

major malformations may be life-threatening, or may have cosmetic

functional effects and require

major surgery.

C S f Ri k B di i i k i


47/50

C. Safety Risk: Because any medication can present risks in

pregnancy, and because not all risks are known, the safest

pregnancy-related pharmacy is as little pharmacy as possible.

Prescribing drugs for women during the antenatal and postnatal

period is a balancing act and that no risk-free alternatives exist.Each drug should be assessed, and its risks and benefits should be

weighed.

D P l E


48/50

D. Paternal Exposure:

Exposure to medications

may alter the quality, size,

shape performance, and

production of sperm. Thisobservation suggests that

drug exposure in the male

may put the fetus at risk.

Animal studies have shown

that maternal teratogenicexposure may lead to

pregnancy loss or failure of

the embryo to develop, but

no evidence shows that

paternal exposure directly

increases the risk of birth

defects

E Safety Guides Pregnancy


49/50

E. Safety Guides Pregnancy

1. For any ailments seek medical attention. Take only prescribed drugs.

2. D not self-medicate

3. Do not take over-the-counter drugs including vitamins and minerals.

4. Do not take alcohol no matter how slight. The US Federal Drug

Administration (FDA), the government agency that oversees the sfatey of

drugs, provides the most widely used system to grade the teratogenic effectsof medications. It assigns a safety category for medications using a 5-letter

system: A, B, C, D and X.

Drugs with Proven Terarogenic Effects


50/50

Drugs with Proven Terarogenic Effects

Drugs Teratogenic EffectsAnticholinergic drugs Neonatal meconium ileusAntithyroid drugs (Prophylthiouracil, methimazole) Fetal & neonatal goiter, hypothyroidismCyclophosphamide CNS malformation, secondary cancerDiethylstilbestrol Vaginal cancer, other genitourinary defects in male

or male offspringHypoglycemic drugs Neonatal hypoglycemiaMethotrexate

CNS & limb malformation

NSAIDs Constriction of ductus arteriosus, necrotizing

enterocolitisPhenytoin Growth retardation, CNS defectsPsychoactive drugs (barbiturates, opiods,

benzodiazepines)Neonatal withdrawal syndrome when given in late

pregnancyTetracycline Teeth staining/ defects, bone defectsThalidomide Limb defects/ shortening, internal organ defectsWarfarin (Coumadin) Skeleton & CNS defects **Heparin is the

anticoagulant of choice in pregnancy; does not

Date post:	05-Apr-2018
Category:	Documents
Upload:	mark-ludwig-labastida
View:	229 times
Download:	1 times

Fertilization and Fetal Development

Documents