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Unit 1: Antepartal Period
Genetics, Conception, Fetal Development
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Genetics
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Genetics: examine the functioning and composition of
the single gene. The study of heredity
Genes: Genes or combinations of genes contain coded
information that determines an individual’s unique
characteristics.
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Genomics Address the functions and interactions of all
the genes in an organism. It is the study of the entire
DNA structure.
- Genomic are providing better methods for:
■ preventing diseases and abnormalities,
■ diagnosing diseases,
■ predicting health risks, and
■ personalizing treatment plans.
- Genetic information includes personal data as well as
information about blood relatives.
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Genetic Counseling Services.
- Goal of screening is to detect or define risk for
disease in low risk populations and identify those for
whom diagnostic testing may be appropriate.
- A nurse can obtain a genetics history using a
questionnaire or checklist.
- Genetic counseling may occur in the office, or
referral to a geneticist.
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Who should be offered prenatal diagnosis?
• Maternal age 35years or more
• Previous history of chromosomal abnormalities
• Family history of metabolic or structural autosomal
recessive or dominant disorder.
• Couples who have a previous personal or family
history of first or second-degree relative of a neural
tube defect.
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Ethical Considerations
- Most genetic testing is offered prenatally in order to
identify genetic disorders in fetuses. When an
affected fetus is identified, termination of the
pregnancy is an option.
- Preimplantation genetic diagnosis (PGD). In this
procedure, embryos are tested before implantation by
in vitro fertilization (IVF)
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Potential impact of genetic
diseases to family and community
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Financial cost to family
Loss of family integrity
Social Isolation
Lifestyle alteration
Disruption of husband-wife relationship
Threatened family self concept
Psychological damage
Physical health problems
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Genetic testing
Prenatal testing : tests used to identify the genetic status
of a pregnancy at risk for a genetic condition.
Current prenatal testing option include:
Maternal serum screening
Alpha-fetoprotein (AFP) is a glycoprotein produced by the
fetal liver that reaches a peak in maternal serum between
the 14 to 34 weeks of pregnancy.
Most pregnant women have an MSAFP test done routinely
between 15 and 22 weeks of pregnancy (16 to 18 weeks
being ideal).
The level is elevated with fetal spinal cord disease and is
decreased in a fetal chromosomal disorder such as
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trisomy 21.
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Chorionic Villi sampling (CVS)
Analysis of chorionic villi from the growing placenta
for chromosome or DNA analysis. It may be done as
early as week 5 of pregnancy, it is more commonly
done at 8 to 10 weeks.
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Amniocentesis. Amniocentesis is the withdrawal of
amniotic fluid through the abdominal wall for
analysis at the 14th to 16th week of pregnancy
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Percutaneous Umbilical Blood Sampling. PUBS, or
cordocentesis, is the removal of blood from the fetal
umbilical cord at about 17 weeks using an
amniocentesis technique.
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Genes and chromosomes
The hereditary material carried in the nucleus of each
body cell determines an individual’s physical
characteristics. This material –DNA- forms threadlike
strands known as chromosomes.
Each chromosome is composed of many smaller
segments of DNA referred as genes.
Combinations of genes contain coded information
that determines an individual’s unique characteristics.
Genes never act in isolation, they always interact with
other genes and the environment.
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- Analysis of the number, form, and size of an
individual’s chromosomes is termed the karyotype.
- All normal human somatic cells contain 46
chromosomes arranged as 23 pairs of homologous
(matched) chromosomes.
- There are 22 homologous pairs of chromosomes and
one pair of sex chromosomes (XX or XY).
- The large female chromosome is called the X, the tiny
male chromosome is the Y. When one X chromosome
and one Y chromosome are present the embryo develops
as male. When two X chromosomes are present, the
embryo develops as a female.
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- Any change in gene structure or location leads to a
mutation, which may alter the type and amount of
protein produced.
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Dominant and Recessive Inheritance
 Genes are either dominant or recessive. When there is
both a dominant and a recessive gene in the pair, the
traits of the dominant gene are present.
 The traits of the recessive gene are present when both
genes of the pair are recessive.
 A person who has only one recessive gene for a
disorder is known as a carrier and does not present
with the disorder.
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Common types of genetic
disorders that follow the
autosomal recessive
inheritance pattern include
cystic fibrosis,
phenylketonuria, and sicklecell disease.
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Common types of genetic
disorders that follow the
autosomal dominant pattern
of inheritance include
neurofibromatosis,
, polycystic kidney disease.
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Sex-Linked Inheritance
■ Also referred to as X-linked
inheritance or traits .
■ These are genes or traits that
are located only on the
X chromosome. These genes
can be either recessive or
dominant.
X-linked dominant disorders
are rare. The most common is
hypophosphatemic (vitamin
D–resistant) rickets.
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Common types of genetic
disorders that follow X-linked
recessive inheritance patterns
include hemophilia, color
blindness.
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Causes of chromosomal abnormalities
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Radiation
Drugs
Viruses
Toxins
Chemicals
Women whose age is 35 years or more are at risk to
get Down syndrome. This group of women must be
referred to genetic counseling.
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■ Birth defects can occur from genetic disorders or be the
result of teratogen exposure.
Not all congenital disorders are inherited.
■ Teratogens are defined as any drugs, viruses,
infections, or other exposures that can cause
embryonic/fetal developmental abnormality.
■ The degree or types of malformation vary based on
length of exposure, amount of exposure, and when it
occurs during human development.
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The developing human is most vulnerable to the effects
of teratogens during the period of organogenesis, the
first 8 weeks of gestation.
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Malnutrition during pregnancy produce low birth
weight, newborns who are susceptible to infection,
also affects brain development during the latter half
of gestation and may result in learning disabilities in
the child.
Inadequate folic acid is associated with neural tube
defect.
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Female Reproductive System
The female reproductive system, has both external and
internal components.
Female External Structures
The structures that form the female external genitalia
are termed the vulva (from the Latin word for
“covering”).
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Mons pubis: is a fatty pad that lies over the anterior
surface of the symphysis pubis.
• Labia majora: are two rounded folds of fatty tissue
covered with skin that extend downward and
backward from the mons pubis.
- Highly vascular structures that develop covered by
pubic hair
- Protect the inner vulvar structures.
- They are fused anteriorly but separated posteriorly.
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Labia minora: are two flat, reddish folds of tissue
visible when the labia majora are separated.
Anteriorly, the labia minora fuse to form the prepuce
(hoodlike covering of the clitoris) . Labia minora
join to form a thin flat tissue called fourchette
underneath the vaginal opening at midline.
Clitoris is located underneath the prepuce, small
structure composed of erectile tissue with numerous
sensory nerve ending (plays an important part in
sexual excitement in females).
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Vaginal vestibule: almond ‫ لوز‬shaped area is the flattened,
smooth surface enclosed by the labia minora that
contains openings to the urethra, Skene glands, vagina,
and Bartholin glands.
Urethra: is not a reproductive organ but is considered
here due to its location. (approx. 2.5cm below clitoris.
Two Skene glands (paraurethral glands) : located on
each side of the urethra and produce mucus, which aids
in lubrication of the vagina.
Vaginal opening: in the lower portion of the vestibule and
varies in shape and size.
Hymen: connective tissue membrane, surrounds the
vaginal opening.
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Bartholin glands (vulvovaginal glands) : located
posteriorly on the sides of the vaginal opening.
During sexual arousal the glands secrete a clear
mucus to lubricate the vaginal introitus.
Perineum: area between fourchette and the anus, which
is a skin – covered muscular area that covers the
pelvic structures.
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Female Internal Structures
Female internal reproductive organs are the
ovaries, the fallopian tubes, the uterus, and the vagina.
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Vagina:
■ A muscular tube approximately 4 inches in length that
extends from the cervix to the perineum.
During the productive years the mucosal lining is
arranged in transverse folds called rugae. This rugae
allow the vagina to expand during childbirth.
Functions
■ Receive sperm during sexual intercourse
■ Provide exit for menstrual blood flow
■ Birth canal during second stage of labor
Vaginal secretions are slightly acidic (pH 4 to 5).
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Cervix: projects into a blind vault at the upper end of
the vagina. Anterior, posterior, and lateral pockets
called fornices surround the cervix.
Uterus:
■ Muscular organ shaped like an upside-down pear. Sits
midline in the pelvic cavity between the bladder and
rectum above the vagina.
■ It is approximately 3 inches long; 2 inches wide; 1
inch deep.
■ Four pairs of ligaments support the uterus: the
cardinal, uterosacral, round, and broad. Single anterior
and posterior ligaments also support the uterus.
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Uterus divided into two major parts: upper triangular
portion called the corpus and a lower cylindric
portion called the cervix.
Fundus : dome shaped top of the uterus and is the site
where the uterine tubes enter the uterus. Isthmus
(lower uterine segment) is a short constricted portion
that separates the corpus from the cervix.
Functions of uterus:
1. Reception, implantation, retention, and nutrition of
the fertilized ovum and later the fetus during
pregnancy.
2. Expulsion of the fetus during childbirth
3. Cyclic menstruation
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Uterine wall consists of three layers:
The uterine wall consists of three separate coats or
layers of tissue: an inner one of mucous membrane
(the endometrium), a middle one of muscle fibers (the
myometrium), and an outer one of connective tissue
(the perimetrium).
- Endometrium
Highly vascular lining made up of 3 layers, the outer 2
layer shed during menstruation.
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- Myometrium
Made up of layers of smooth muscles that extend in
3 different directions ( longitudinal, transverse, and
oblique). Longitudinal fibers of the outer
myometrium layer are found mostly in the funds
.This arrangement assists in expelling the fetus during
the birth process.
The middle layer contains fibers from all three
directions, which form a figure – eight encircling
large blood vessels …. This arrangement assists in
constricting blood vessels after childbirth and control
blood loss.
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Most of the circular fibers of the inner myometrial
layer are around the site where the uterine tubes enter
the uterus and around the internal cervical os
(opening). The fibers help keep the cervix closed
during pregnancy and prevent menstrual blood from
flowing back into the uterine tubes during
menstruation.
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Cervix: made up of fibrous connective tissues and
elastic tissue ….. For possible to stretch during
vaginal childbirth.
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Opening between the uterine cavity and the canal that
connects the uterine cavity to the vagina
(endocervical canal) is the internal os.
Narrowed opening between the endocervix and the
vagina is the external os.
Cx. Feels firm (like the end of a nose) with a dimple in
the center.
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Outer cervix: covered with a layer of squamous
epithelium. Mucosa of cervical canal is covered with
columnar epithelium, contains numerous glands that
secrete mucus in response to ovarian hormones. 2
types of cells meet inside the cervical os this called
squamocolumnar junction. And is the most
common site for neoplastic changes; cells from this
site are scraped for the Pap test.
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Uterine tubes (fallopian tubes): attach to the uterine
fundus. The tubes are supported by the broad
ligaments, range from 8 to 14 cm in length. Uterine
tubes provide a passage for ova from ovaries to
uterus.
Ovaries: almond shape organs located on each side of
the uterus below and behind the uterine tubes. They
are grayish white. During the reproductive years they
are approx. 3 cm long, 2 cm wide, and 1cm thick.
Functions of ovaries:
1. Ovulation
2. Production of estrogen, progesterone, and androgen
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Bony Pelvis
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The bony pelvis serves 3 primary purposes:
- Protection of the pelvic structures
- Accommodation of the growing fetus during
pregnancy
- Anchorage ‫ مالذ‬of the pelvic support structures.
2 innominate (hip) bones (consisting of ilium, ischium,
and pubis), the sacrum, and the coccyx make up the
four bones of the pelvis.
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The pelvis is divided into two parts:
1- False pelvis
Is the upper portion above the pelvic brim or inlet
2- True pelvis
Is the lower curved bony canal, which includes the inlet,
the cavity, and the outlet through which the fetus
passes during vaginal birth.
The dimensions of the true pelvis of a women are very
important because they must be large enough to allow
the infant’s head to pass during childbirth.
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Characteristics that differ in
the pelvis of the man and
woman:
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- The female inlet is larger and more circular
- The female sacrum is shorter and less curved
- The female ischial spines are shorter and farther
apart, thus the outlet is larger
- The female pubic arch is more rounded because the
angle of the pubic arch is greater.
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Breasts
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- Paired mammary glands located between 2nd and 6th
ribs.
- The breast are attached to the muscles by connective
tissue called fascia.
- The contour should be smooth with no retractions,
dimpling, or masses.
- Estrogen stimulates growth of breast, and the growth
of the extensive ductile system.
- Also increase the vascularity of breast tissue.
- Progesterone increase in puberty causes maturation
of mammary gland tissue.
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Nipple: The nipple is made up of epithelial,
glandular, erectile, and nervous tissue.
Areolar tissue: surrounds the nipple and is
recognized as the darker, smooth skin between the
nipple and the breast.
Montgomery’s tubercles ‫درنات‬: The small bumps or
projections on the areolar surface known as
sebaceous glands that keep the nipple area soft and
elastic
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- Each mammary gland is made 15 to 20 lobes, which
are divided into lobules.
The route of descent of milk and other breast secretions
is from alveoli to duct, to intralobar duct, to
lactiferous duct and reservoir, to nipple.
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Menstruation
Puberty is a broad term that denote the entire
transitional stage between childhood and sexual
maturity.
Menarche: first menstruation.
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A menstrual cycle (a female reproductive cycle) is
episodic uterine bleeding in response to cyclic
hormonal changes.
The menstrual cycle prepares the uterus for pregnancy.
When pregnancy does not occur, menstruation
follows.
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Menstruation: is the periodic uterine bleeding that
begins approximately 14 days after ovulation.
• The average length of a menstrual cycle is 28 days,
but variations are normal.
• The first day of bleeding is designated as day 1 of the
menses.
• The average duration of menstrual flow is 5 days (
range of 3 to 6 days)
• The average blood loss is 50ml (range of 20 to 80 ml)
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Menstrual Cycle
A woman’s menstrual cycle is influenced by the ovarian
cycle and endometrial cycle.
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Hypothalamic-Pituitary Cycle
Low blood levels of ovarian hormones stimulate the
hypothalamus to secrete gonadotropin releasing
hormone (GnRH). GnRH stimulates anterior pituitary
secretion of follicle-stimulating hormone (FSH) and
luteinizing hormone (LH).
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Ovarian Cycle
The ovarian cycle pertains to the maturation of ova and
consists of three phases:
1. The follicular phase begins the first day of
menstruation and last 12–14 days. During this phase,
the graafian follicle is maturing under the influence of
two pituitary hormones:
luteinizing hormone (LH) and follicle-stimulating
hormone (FSH). The maturing graafian follicle
produces estrogen.
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2. The ovulatory phase begins when estrogen levels
peak and ends with the release of the oocyte (egg) from
the mature graafian follicle. The release of the oocyte is
referred to as ovulation.
■ There is a surge in LH levels 12–36 hours before
ovulation.
■ There is a decrease in estrogen levels and an increase
in progesterone levels before the LH surge.
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3. The luteal phase begins after ovulation and lasts
approximately 14 days. During this phase, the cells of
the empty follicle undergo changes and form into the
corpus luteum.
■ The corpus luteum produces high levels of
progesterone along with low levels of estrogen.
■ If pregnancy occurs, the corpus luteum continues to
release progesterone and estrogen until the placenta
matures and assumes this function.
■ If pregnancy does not occur, the corpus luteum
degenerates and results in a decrease in progesterone
and the beginning of menstruation.
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Endometrial Cycle
The endometrial cycle pertains to the changes in the
endometrium of the uterus in responses to the hormonal
changes that occur during the ovarian cycle. This cycle
consists of three phases:
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■ The proliferative phase occurs following
menstruation and ends with ovulation. During this
phase, the endometrium is preparing for implantation by
becoming thicker and more vascular. These changes are
in response to the increasing levels of estrogen
produced by the graafian follicle.
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■ The secretory phase begins after ovulation and ends
with the onset of menstruation. During this phase, the
endometrium continues to thicken. The primary
hormone during this phase is progesterone, which is
secreted from the corpus luteum.
■ If pregnancy occurs, the endometrium continues to
develop and begins to secrete glycogen.
■ If pregnancy does not occur, the corpus luteum begins
to degenerate and the endometrial tissue degenerates.
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■ The menstrual phase occurs in response to hormonal
changes and results in the sloughing off of the
endometrial tissue.
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Other cyclic changes
- Before ovulation the woman’s basal body temperature
(BBT) is often below 37˚C; after ovulation with
rising progesterone levels, her BBT rises.
- Changes in the cervix and cervical mucus.
Preovulatory and postovulatory mucus is viscous, so
sperm penetration is discouraged. At the time of
ovulation, cervical mucus is thin and clear. It looks,
feels, and stretches like egg white. This stretchable
quality is termed spinnbarkeit. Some women
experience localized lower abdominal pain, termed
mittelschmerz ‫ الم االباضة‬, that coincides with
ovulation.
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Spinnbarkeit is the property of cervical
mucus to stretch a distance before breaking.
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Oogenesis
Oogenesis is the formation of a mature ovum (egg).
■ Oogenesis is regulated by two primary hormones.
■ Follicle-stimulating hormone (FSH) secreted from
the anterior pituitary gland stimulates growth of the
ovarian follicles and stimulates the follicles to secrete
estrogen.
■ Estrogen secreted from the follicle cells promotes the
maturation of the ovum.
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■ Process of oogenesis
- FSH stimulates the growth of ovarian follicle which
contains an oogonium (stem cell).
■ Through the process of mitosis ‫االنقسام الخيطي‬, the
oogonium within the ovary forms into two daughter
cells: the primary oocyte and a new stem cell.
■ Mitosis is the process by which a cell divides and
forms two genetically identical cells (daughter cells)
each containing the diploid number of chromosomes.
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■ Through the process of meiosis, the primary oocyte forms
into the secondary oocyte and a polar body. The polar body
forms into two polar bodies. The secondary oocyte forms
into a polar body and a mature ovum.
■ Meiosis ‫االنقسام المنصف او االختزالي‬is a process of two
successive cell divisions that produces cells that contain
half the number of chromosomes .
All the cells that may undergo meiosis in a woman’s
lifetime are contained in her ovaries at birth. The majority
of the estimated 2 million primary oocytes degenerate
spontaneously . Only 400 to 500 ova will mature during the
approximately 35 years of a woman’s reproductive life.
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Spermatogenesis is the formation of mature
spermatozoa (sperm).
■ Process of spermatogenesis :
- Through the process of mitosis, the spermatogonium
(stem cell) within the seminiferous tubules of the testis
forms into two daughter cells: a new spermatogonia and
a spermatogonium.
■ The spermatogonium differentiates and is referred to
as the primary spermatocyte.
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■ Through the process of meiosis, the primary
spermatocyte forms into two secondary spermatocytes
and each secondary spermatocyte forms into two
spermatids and contain the haploid number of
chromosomes.
■ Spermatids mature and are referred to as spermatozoa.
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Conception
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Conception, also known as fertilization, occurs when a
sperm nucleus enters the nucleus of the oocyte.
■ Fertilization normally occurs in the outer third of the
fallopian tube.
■ The fertilized oocyte is called a zygote and contains
the diploid number of chromosomes (46).
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Union of a single egg and sperm, marks the beginning
of a pregnancy. Conception occurs in a sequential
process. This process includes gamete (egg and
sperm) formation, ovulation (release of the egg),
union of the gametes (which results in an embryo),
and implantation in the uterus.
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The three stages of fetal development during pregnancy
are:
1. Preembryonic stage: fertilization through the second
week
2. Embryonic stage: end of the second week through
the eighth week
3. Fetal stage: end of the eighth week until birth
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Terms Used to Denote Fetal Growth
Name
• Ovum
• Zygote
to
• Embryo
• Fetus
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Time Period
From ovulation to fertilization
From fertilization
implantation
From implantation to 5–8 weeks
From 5–8 weeks until term
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Ovum
At ovulation the ovum is released from the ruptured
ovarian follicle. High estrogen levels increase the motility
of the uterine tubes so that their cilia are able to capture
the ovum and propel it through the tube toward the uterine
cavity . 2 protective layers surround the ovum. The inner
layer is a thick, cellular layer called the zona pellucida.
The outer layer called the corona radiata, is composed
of elongated cells. Ova are considered fertile for about 24
hours after ovulation.
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Sperm
Ejaculation normally
propel almost a teaspoon of
semen containing as many
as 200 to 500 million sperm
into the vagina. The sperm
swim by flagellar
movement of their tails.
Some sperm can reach site
of fertilization within 5
min., but average transit
time is 4 to 6 hours. Sperm
remain viable within the
woman’s reproductive
system for an average of 2
to
3 days.
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As sperm travel through the female reproductive tract,
enzymes( hyaluronidase) are produced to aid in their
capacitation (is physiologic change that removes the
protective coating from the heads of the sperm).
These enzymes are necessary for the sperm to
penetrate the protective layers of the ovum before
fertilization.
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Fertilization
Fertilization takes place in the ampulla ( the outer
third) of the uterine tube. When a sperm successfully
penetrates the membrane surrounding the ovum, both
sperm and ovum are enclosed within the membrane,
and the membrane becomes impenetrable to other
sperm; this process is termed the zona reaction.
The nuclei from sperm and egg fuse and the
chromosomes combine, restoring the diploid number
(46).
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Pregnancy lasts approximately 10 lunar months, 9
calendar months, 40 weeks, or 280 days. Length of
pregnancy is computed from the first day of the last
menstrual period (LMP) until the day of birth.
Conception occurs approx. 2 weeks after the day of the
LMP.
Intrauterine development is divided into three stages:
ovum or preembryonic, embryo, and fetus.
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Cell Division
■ The single-cell zygote undergoes mitotic cell division
known as cleavage.
■ Three days after fertilization, the zygote forms into a
16-cell, solid sphere that is called a morula.
■ Mitosis continues, and around day 5 the developing
human is known as the blastocyst and enters the uterus.
■ The blastocyst is composed of an inner cell mass
known as the embryoblast, which will develop into the
embryo, and an outer cell mass known as the
trophoblast, which will assist in implantation and
become part of the placenta.
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Ovulation, fertilization, and implantation. The blastocyst is differentiated into
three germ layers (ectoderm, mesoderm, and endoderm). Cells at the
periphery are trophoblast cells that mature into the placenta.
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Inner cell mass
Degenerating
zona pellucida
Blastocyst cavity
Blastocyst
cavity
(a) Zygote
(fertilized egg
(b) 4-cell stage (c) Morula
2 days
3 days
(a)
Fertilization
(sperm meets
egg)
(d) Early blastocyst
4 days
(b)
(e) Implanting
blastocyst
6 days
(c)
Ovary
Uterine
tube
Oocyte
(egg)
Trophoblast
(d)
Uterus
Ovulation
(e)
Endometrium
Cavity of uterus
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■ Multiple gestation refers to more than one developing
embryo such as twins and triplets.
Twins can be either monozygotic or dizygotic.
■ Monozygotic twins, also referred to as identical twins,
are the result of one fertilized ovum splitting during the
early stages of cell division and forming two identical
embryos.
These developing fetuses are genetically the same.
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If division occurs very late, cleavage may not be
complete, and conjoined or “ Siamese” twins could
result.
Monozygotic twinning rate is between 3.5 and per
1000 births. No association with race, heredity,
maternal age, or parity has been found. Use of
fertility drugs increases the incidence of monozygotic
twinning.
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Dizygotic twins, also referred to as fraternal twins, are
the result of two separate ova being fertilized by two
separate sperm.
These developing fetuses are not genetically the same.
The results of dizygotic twins (two amnions, two
chorions, and two placentas.
These dizygotic twins may be the same sex or different
sexes and are genetically no more alike than siblings
born at different times.
Dizygotic twinning increases in frequency with maternal
age up to 35 years, with parity, and with the use of
fertility drugs.
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Two Examples of Twinning
A. Identical Twins Fetuses are of the same sex and share one
placenta. One outer membrane envelops both amniotic sacs .
B .Fraternal Twins Fetuses may be of different sex. There are two
placentas and two separate amniotic sacs, each with its own
membrane
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Other multifetal pregnancies
The occurrence of multifetal pregnancies with three or
more fetuses has increased with the use of fertility
drugs and IVF.
Triplets occur in approx. 1 of 1341 pregnancies. They
can occur from the division of one zygote into two,
with one of the two dividing again, producing
identical triplets. Triplets can also be produced from
two zygotes, one dividing into a set of identical twins
and the second zygote a single fraternal sibling, or
from three zygotes. Quadruplets, quintuplets,
sextuplets have similar possible derivations.
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Implantation
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Implantation, the embedding of the blastocyst into
the endometrium of the uterus, begins around day 5 or
6.
Progesterone stimulates the endometrium of the uterus,
which becomes thicker and more vascular in preparation
for implantation.
■ Enzymes secreted by the trophoblast digest the
surface of the endometrium in preparation for
implantation of the blastocyst.
■ Implantation normally occurs in the upper part of the
posterior wall of the uterus.
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Some women experience slight implantation bleeding
(slight spotting and bleeding during the time of the first
missed menstrual period).
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Embryo And Fetal Development
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Embryo
The developing human is referred to as an embryo from
the time of implantation through 8 weeks of gestation.
Organogenesis, the formation and development of body
organs, occurs during this critical time of human
development.
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■ Primary germ layers begin to develop around day 14.
■ These germ layers, known as the ectoderm, mesoderm,
and endoderm, form the different organs, tissues, and
body structure of the developing human.
■ The ectoderm is the outer germ layer.
■ The mesoderm is the middle germ layer.
■ The endoderm is the inner germ layer.
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■ The heart forms during the 3rd gestational week and
begins to beat and circulate blood during the 4th
gestational week.
■ By the end of the 8th gestational week the developing
human has transformed from the primary germ layers to
a clearly defined human that is 3 cm in length with all
organ systems formed.
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Fetus
The developing human is referred to as a fetus from
week 9 to birth. During this stage of development, organ
systems are growing and maturing
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Fetal circulatory system
The cardiovascular system is the first organ system to
function in the developing human. Blood vessel and
blood cell formation begins in the third week and
supplies the embyro with oxygen and nutrients from
mother.
- During the fourth and fifth weeks the heart develops
into a four chambered organ.
- By the end of the embryonic stage, the heart is
developmentally complete.
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Three shunts are present in fetal life:
1. Ductus venosus: connects the umbilical vein to the
inferior vena cava
2. Ductus arteriosus: connects the main pulmonary
artery to the aorta
3. Foramen ovale: anatomic opening between the right
and left atrium.
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Unique features of fetal circulation are :
■ High levels of oxygenated blood enter the fetal
circulatory system from the placenta via the umbilical
vein.
■ The ductus venosus connects the umbilical vein to
the inferior vena cava. This allows the majority of the
high levels of oxygenated blood to enter the right
atrium.
■ The foramen ovale is an opening between the right
and left atria. Blood high in oxygen is shunted to the left
atrium via the foramen ovale. After delivery, the
foramen ovale closes in response to increased blood
returning to the left atrium. It may take up to 3 months
for full closure.
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■ The ductus arteriosus connects the pulmonary artery
with the descending aorta. The majority of the
oxygenated blood is shunted to the aorta via the ductus
arteriosus with smaller amounts going to the lungs.
After delivery, the ductus arteriosus constricts in
response to the higher blood oxygen levels and
prostaglandins.
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Fetal maturation
The stage of the fetus lasts from 9 weeks ( when the
embryo becomes recognizable as human being) until
the pregnancy ends. The fetus is less vulnerable to
teratogens, except for those that affect central nervous
system functioning.
Viability ‫ القابلية‬refers to the capability of the fetus to
survive outside the uterus. In the past the earliest age
at which fetal survival could be expected was 28
weeks after conception. Modern technology and
advances in maternal and neonatal care, viability is
now possible approx. 20 weeks after conception (22
weeks since LMP, fetal weight of 500g or more).
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Respiratory system
- the development of the respiratory tract begins in
week 4 and continues through week 17 with
formation of the larynx, trachea, bronchi, and lung
buds.
- Between 24 weeks and term birth, more alveoli form
- Specialized alveolar cells, type 1 and type 2 cells,
secrete pulmonary surfactants.
- After 32 weeks, sufficient surfactant is present to
provide infants with good chance of survival.
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Pulmonary surfactants (surface active phospholipids)
the detection of the presence of pulmonary
surfactant in amniotic fluid has been used to
determine the degree of fetal lung maturity. Lecithin
is the most critical alveolar surfactant required for
postnatal lung expansion. It is detectable at approx.
21 weeks and increases in amount after week 24.
Another pulmonary phospholipid, sphingomyelin,
remains constant in amount.
L/S ratio reaches 2:1 the lung are considered to be
mature, which occurs at approx. 35 weeks of
gestation.
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- Gestational diabetes and chronic glomerulonephritis
can retard fetal lung maturity.
- Fetal respiratory movements have been seen on U/S
as early as the 11 week. These movements may aid in
development of the chest wall muscles and regulate
lung fluid volume. The fetal lungs produce fluid that
expands the air spaces in the lungs. The fluid drains
into the amniotic fluid or is swallowed by the fetus.
- Before birth, secretion of lung fluid decreases. The
normal birth process squeezes out approx. one third
of the fluid. (C/S …..?). The fluid remaining in the
lungs at birth is usually reabsorbed into the infant’s
blood stream within 2 hours of birth.
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Hepatic system
- hematopoiesis begins during the sixth week and requires
that the liver be large.
- The embryonic liver is prominent , occupying most of
the abdominal cavity.
- Glycogen is stored in the fetal liver beginning at week 9
or 10. at term stores are twice those of the adult.
- Glycogen is the major source of energy for the fetus and
for the neonate stressed by in utero hypoxia, extrauterine
loss of maternal glucose supply, the work of breathing,
or cold stress.
- Iron is stored in the fetal liver. If maternal intake is
sufficient, the fetus can store enough iron to last for 5
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Gastrointestinal system
- fetus swallows amniotic fluid beginning in the fifth
month. Gastric emptying and intestinal peristalsis occur.
as the fetus near term, fetal waste products accumulate
in the intestines as dark green to black, tarry meconium.
Normally newborn pass meconium within 24 hours of
birth. Sometimes, with a breech presentation or fetal
hypoxia, meconium is passed in utero into the amniotic
fluid.
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- The gastrointestinal system is mature by 36 weeks.
- Digestive enzymes (except pancreatic amylase and
lipase) are present in sufficient quantity to facilitate
digestion.
Renal system
- kidneys form during the fifth week and begin to
function approx. 4 weeks later.
- Urine is excreted into the amniotic fluid and form a
major part of the amniotic fluid volume.
- At term fetus has fully developed kidneys.
- GFR is low, and the kidneys lack the ability to
concentrate urine, so this make newborn susceptible
to both overhydration
and
dehydration.
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- Most newborn void within 24 hours of birth.
Neurologic system
- The fetus can suck his or her thumb, swim in the
amniotic fluid pool ( result knot in umbilical cord)
- 16 and 20 weeks mother feel “ the baby moving”
quickening
- Fetuses respond to sound by 24 weeks.
- The fetus is able to distinguish taste.
- Fetus reacts to temperature changes.
- Fetus can see
- At term the fetal brain is approx. one fourth the size
of an adult brain.
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Endocrine system
- Thyroid gland develops along with structures in the
head and neck during the third and fourth weeks. The
secretion of thyroxine begins during the eighth week.
Maternal thyroxin does not readily cross the placenta,
therefore the fetus that does not produce thyroid
hormones will be born with congenital
hypothyroidism. If untreated, hypothyroidism can
result in severe mental retardation (so PKU screening
is important after birth).
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- Adrenal cortex is formed during the sixth week and
produces hormones by the eighth or ninth week. As
term approaches, the fetus produces more cortisol. This
hormone is believed to aid in initiation of labor by
decreasing the maternal progesterone and stimulating
production of prostaglandins.
- The islets of langerhans develop during the 12 week.
- Insulin is produced by the twentieth week. In infants
of mothers with uncontrolled diabetes, maternal
hyperglycemia produces fetal hyperglycemia,
stimulating hyperinsulinemia and islet cell hyperplasia.
This results in a macrosomic fetus.
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The hyperinsulinemia also blocks lung maturation,
placing the neonate at risk for respiratory distress and
hypoglycemia when the maternal glucose source is
lost at birth.
Reproductive system
- Sex differentiation begins in the embryo during the
seventh week.
- Distinguishing characteristics appear around the
ninth week and are fully differentiated by the twelfth
week.
- Fetal endometrium responds to maternal hormones,
and withdrawal bleeding or vaginal discharge
(pseudomenstruation) may occur at birth when these
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- The high level of maternal estrogen also stimulates
mammary engorgement and secretion of fluid
( witch’s milk) in newborn infants of both sexes.
Musculoskeletal system
- At birth, connective tissue sutures exist where the
bones of the skull meet (called fontanels) are
especially prominent. The sutures and fontanels allow
the bones of the skull to mold, or move during birth,
enabling the head to pass through the birth canal.
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Integumentary system
- By the seventh week, two layers of cells have formed.
The cells of the superficial layer are sloughed and
become mixed with the sebaceous gland secretions to
form the white, cheesy vernix caseosa, the material
that protects the skin of the fetus.
- Lanugo very fine hairs appear first at 12 weeks on
the eyebrows and upper lip.
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Immunologic system
- During the third trimester, albumin and globulin are
present in the fetus. The only immunological (Ig)
that crosses the placenta, IgG, provides passive
acquired immunity to specific bacterial toxins.
- Fetus produces IgM immunoglobulins by the end of
the first trimester. (produced in response to blood
group antigens, gram- negative enteric organisms,
and some viruses)
- IgA immunoglobulins are not produced by the fetus,
however, colostrum contains large amounts of IgA
and can provide passive immunity to the neonate who
is breastfed.
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Placenta
The placenta is formed from both fetal and maternal
tissue .
■ The chorionic membrane that develops from the
trophoblast along with the chorionic villi form the fetal
side of the placenta.
The chorionic villi are projections from the chorion
that embed into the decidua basalis and later form the
fetal blood vessels of the placenta.
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■ The endometrium is referred to as the decidua and
consists of three layers: decidua basalis, decidua
capsularis, and decidua vera.
The decidua basalis, the portion directly beneath the
blastocyst, forms the maternal portion of the
placenta.
■ The maternal side of the placenta is divided into
compartments or lobes known as cotyledons.
■ The placental membrane separates the maternal and
fetal blood and prevents fetal blood mixing with
maternal blood, but allows for the exchange of gases,
nutrients, and electrolytes.
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Function of the Placenta
■ Metabolic and gas exchange: In the placenta, fetal
waste products and CO2 are transferred from the fetal
blood into the maternal blood sinuses by diffusion.
■ Nutrients, such as glucose and amino acids, and O2
are transferred from the maternal blood sinuses to the
fetal blood through the mechanisms of diffuse and
active transport.
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■ Hormone production: The major hormones the
placenta produces are progesterone, estrogen, human
chorionic gonadotropin (hCG), and human placental
lactogen (hPL), also known as human chorionic
somatomammotropin.
■ Progesterone facilitates implantation and decreases
uterine contractility.
■ Estrogen stimulates the enlargement of the breasts
and uterus.
■ hCG stimulates the corpus luteum so that it will
continue to secrete estrogen and progesterone until the
placenta is mature enough to secrete these hormones.
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This is the hormone assessed in pregnancy tests. hCG
rises rapidly during the first trimester and then has a
rapid decline.
■ hPL:
- Promotes fetal growth by regulating glucose available
to the developing human.
- Stimulates breast development in preparation for
lactation.
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■ Viruses, such as rubella and cytomegalovirus, can cross
the placental membrane and enter the fetal system and
cause fetal death or defects.
■ Drugs can cross the placental membrane. Women
should consult with their health care provider before
taking any medication/drugs.
■ Caffeine, alcohol, nicotine, carbon monoxide, cocaine
readily cross the placenta.
■ The placenta becomes fully functional between the 8th
and 10th weeks of gestation.
■ By the 9th month, the placenta is between 15 and 25 cm
in diameter, 3 cm thick, and weighs approximately 600
grams.
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Embryonic Membranes
■ Two membranes (amnion and chorion) form the
amniotic sac (also referred to as the bag of waters).
■ The chorionic membrane (outer membrane) develops
from the trophoblast.
■ The amniotic membrane (inner membrane) develops
from the embryoblast.
■ The embryo and amniotic fluid are contained within
the amniotic sac.
■ The membranes stretch to accommodate the growth of
the developing fetus and the increase of amniotic fluid.
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Amniotic Fluid
■ Amniotic fluid is the fluid contained within the
amniotic sac.
■ Amniotic fluid is clear and is mainly composed of
water.
It also contains lecithin, sphingomyelin, carbohydrates,
lipids, electrolytes, fetal cells, lanugo, and vernix
caseosa.
■ Amniotic fluid during the first trimester is produced
from the amniotic membrane.
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During the second, the fluid is produced by the fetal
kidneys.
- The fetus urinates (11week) into the fluid, greatly
increasing its volume.
- The fetus swallow fluid, and fluid flows into and out of the
fetal lungs.
■ Amniotic fluid increases during pregnancy and peaks
around 34 weeks at 800–1,200 mL and then decreases to
500–600 mL at term.
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- Less than 500ml (oligohydramnios) is associated
with fetal renal abnormalities.
- More than 1,500–2,000 mL (Polyhydramnios or
hydramnios) is associated with gastrointestinal and
other malformations.
Newborns of mothers who experienced polyhydramnios
have an increased incidence of chromosomal disorders
and gastrointestinal, cardiac, and/or neural tube
disorders.
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Function of Amniotic Fluid
■ Acts as a cushion for the fetus when there are sudden
maternal movements
■ Prevents adherence of the developing human to the
amniotic membranes
■ Allows freedom of fetal movement, which aids in
symmetrical musculoskeletal development
■ Provides a consistent thermal environment
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Study of fetal cells in amniotic fluid through
amniocentesis yields much information about the
fetus:• Genetic studies (karyotyping) provide knowledge
about the sex of the fetus and the number and the
structure of chromosomes.
• (L/S) lecithin / sphingomyelin ratio determine
maturity of the fetus.
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Umbilical Cord
■ Connects the fetus to the placenta
■ Consist of two umbilical arteries and one umbilical
vein
■ Arteries carry deoxygenated blood.
■ The vein carries oxygenated blood.
■ ■ Usually inserted in the center of the placenta.
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- Approx. 1% of umbilical cords contain only two
vessels (associated with congenital malformation).
The cord rapidly increases in length. At term the cord is
2cm in diameter and ranges from 30 to 90 cm in
length (with an average of 55cm).
- True knot is rare.
- False knot occur as fold or Kinks in the cord .
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The vessels are surrounded by Wharton’s jelly, a
collagenous substance, which protects the vessels
from compression and ensures continued nourishment
of the embryo and fetus.
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When the cord is wrapped around the fetal neck, it is
called a nuchal cord.
- Umbilical cord is usually located centrally.
A peripheral location is less common and is known as a
battledore placenta.
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Thanks
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