Development and
Inheritance
Embryo

The first two months following
fertilization
Fetus

From week nine until birth
Pregnancy

Lasts about 40 weeks from the first
day of the last menstrual period
Fertilization

The genetic material from a haploid
sperm cell and a haploid secondary
oocyte merges into a single diploid
nucleus
Fertilization

Occurs in the fallopian tube
Fertilization

Occurs within 12-24 hours after
ovulation
Fertilization

There is a total of 3 days per month
during which coitus may result in
pregnancy.
Fertilization

Two days before ovulation and one
day after
Fertilization

Peristaltic contractions and cilia
transport the oocyte through the
uterine tube
Fertilization

Sperm swim up the uterus and
uterine tube by movements of their
tails and muscular contractions of the
uterus
Fertilization

Only 200 of the 300 million
spermatozoa reach the oocyte
Fertilization

Capacitation – the functional changes
that sperm undergo in the female
that allow them to fertilize an oocyte
Fertilization

A sperm must penetrate the corona
radiata and zona pellucida
Fertilization

Acrosomal enzymes digest a path
through the zona pelucida
Fertilization

The spermatozoa that penetrates the
oocyte loses its tail
Fertilization

Polyspermy is prevented by chemical
changes that penetrate a second
sperm from entering the oocyte
Fertilization

Once a sperm enters a secondary
oocyte, the oocyte completes meiosis
Fraternal Twins

Produced from the independent
release of two ova and the
subsequent fertilization of each by
different spermatozoa
Monozygotic twins

Derived from a single fertilized ovum
that splits at an early stage in
development
Formation of the Morula

Cleavage – early rapid mitotic cell
division of a zygote
Formation of the Morula

Blastomeres - The cells produced by
cleavage
Formation of the Morula

Morula – A solid mass of 16-32 cells
Development of the Blastocyst

The morula moves down the ciliated
uterine tube and into the uterine
cavity
Development of the Blastocyst

The morula develops into a
blastocyst
Development of the Blastocyst

1.
2.
3.
Blastocyst – a hollow ball of cells
that is differentiated into a
Trophoblast
Inner cell mass
blastocele
Development of the Blastocyst

Implantation – The attachment of a
blastocyst to the endometrium seven
to eight days after fertilization
Development of the Blastocyst

The trophoblast secretes human
chorionic gonadotropin
Development of the Blastocyst

hCG – rescues the corpus luteum
from degeneration and sustains its
function
Development of the Blastocyst

Trophoblast becomes the chorion
Development of the Blastocyst

Chorion – a membrane outside the
amniotic sac that has villi which
project into the placenta
Beginnings of Organ Systems

Gastrulation – inner cell mass of the
blastocyst differentiates into three
primary germ layers
Development of the Blastocyst

1.
2.
3.
Three primary germ layers
Ectoderm
Mesoderm
Endoderm
Embryonic Membranes

Lie outside the embryo and protect
and nourish the embryo and later,
the fetus
Embryonic Membranes
1.
2.
3.
4.
Yolk sac
Amnion
Chorion
allantois
Yolk Sac

It gives rise to cells that migrate to
the gonads to become
spermatogonia and oogonia (ICM)
Amnion

Surrounds the embryo creating a
cavity filled with amniotic fluid (ICM)
Chorion

Derived from the trophoblast
Chorion

Surrounds the embryo and later, the
fetus
Chorion

Embryonic part of the placenta
Allantois

Small vascularized membrane (ICM)
Allantois

Umbilical cord
Umbilical cord

Vascular connection between mother
and fetus
Umbilical Cord

Consists of two umbilical arteries
carrying dexoygenated fetal blood to
the placenta and one umbilical vein
that carries oxygenated blood from
the placenta into the fetus
Placenta

Developed by the third month of
pregnancy
Placenta

1.
2.
Formed by the
Chorion (embryonic portion)
Decidua basalis (maternal portion)
Placenta

All exchanges to and from the
embryo occur here
Placenta

Stores nutrients and released into
fetal circulation as required
Hormones of Pregnancy

During the first 3-4 months of
pregnancy, the corpus luteum
secretes progesterone and estrogen
Hormones of Pregnancy

Progesterone and estrogens maintain
the uterine lining and prepare the
mammary glands to secrete milk
Hormones of Pregnancy

After the third, the placenta secretes
estrogen and progesterone
Hormones of Pregnancy

Estrogen inhibits prolactin, so
lactation does not occur
Hormones of Pregnancy

Estrogen increases the number of
oxytocin receptors in the uterus
Hormones of Pregnancy

Relaxin – softens the cervix and
relaxes the pubic symphysis to
facilitate delivery
Hormones of Pregnancy

Corticotropin-releasing hormone –
the clock that establishes the timing
of birth
Anatomical and Physiological
Changes During Pregnancy

CO, HR, and SV increases
Anatomical and Physiological
Changes During Pregnancy

Breast enlargement
Anatomical and Physiological
Changes During Pregnancy

Increase in appetite
Anatomical and Physiological
Changes During Pregnancy

Increase in tidal volume and total
body oxygen consumption
Anatomical and Physiological
Changes During Pregnancy

Increase in GFR
Anatomical and Physiological
Changes During Pregnancy

Increase in frequency of urination
Anatomical and Physiological
Changes During Pregnancy

Some women experience elevated
blood pressure