BIOB33H3 Lecture Notes - Lecture 3: Dermis, Thyroid, Umbilical Cord
1
Lecture 3
The Reproductive System: Embryology and Human Development
(based on Chapter 28)
Introduction
•Development involves:
o Differentiation of cells
oReorganization of cells
•Development can be characterized by different
periods of time
oPrenatal development –
fertilization/conception to delivery
§Involves Embryology – prenatal
development focussing on the first
two months after fertilization
oPostnatal development – development from
birth to maturity
Fertilization
•Fertilization is the joining of two haploid cells to create a diploid cell
•Function of the haploid cells:
•Spermatozoon (see chapter 27)
o Delivers the paternal chromosomes to the ovum
o sperm has head, midsection and tail
o head has an acrosome and a nucleus containing 22 haploid chromosomes and one X or
Y chromosome)
o midsection has mitochondria to provide energy to move flagellum
oflagellum (tail) moves to allow sperm to swim
•Ovum (egg, only about 1)
oOutermost layer has loosely defined cells
called corona radiata (protective layer)
oDeep to corona radiata is another protective
layer the jelly-like zona pellucida
p o Contains a polar body which is a non-
functioning cell that eventually degrades (has no
role in fertilization)
o Provides the maternal chromosomes
(secondary oocyte that has pronucleus of 23
haploid chromosomes, 22 autosomes and a
second X chromosome, suspended in
metaphase of meiosis II)
o Ovum provides nourishment for embryonic
development
Fertilization
•An ovum is produced in one of the
ovaries once a month and travels along
the uterine tube to the uterus (cilia in
the tube move the egg along and it
takes about 4-5 days for the egg to get
to the uterus)
•Fertilization usually occurs in the
ampulla of the uterine tube
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•200 million sperm cells enter the vaginal
canal
•Only about 10,000 make it to the uterine
tubes
•Less than 100 actually contact the egg
•Only one will fertilize the egg
egg will be fertilized somewhere laong that path
zygote embeds into that thick wall of the uterus
called the endometrium (developing baby is
inside the wall of the uterus and then
eventually out grows that)
•Fertilization details
← - oocyte is what will provide nourishment to the
cell
oOocyte at Ovulation: Ovulation
releases a secondary oocyte and the first polar body; both
are surrounded by the corona radiata, which protects the
egg. The oocyte is suspended in metaphase of meiosis II
oFertilization and Oocyte Activation: Acrosomal reaction:
acrosomal enzymes (hyaluronidase) from multiple sperm create
gaps in the corona radiata. A single sperm then makes contact
with the oocyte membrane, and membrane fusion occurs,
triggering oocyte activation and completion of meiosis, (a
single sperm breaks down the corona radiate and zona
pollucia to other sperm
-Cortical Reaction: cortical granules from inside the oocyte dissolve into
the cytoplasm changing the permeability of the egg and make it
impermeable to other sperm ( as soon as one sperm breaks through,
there is a cortical reaction that prevents other sperms from entering the cell
-so: acrosome reaction is done by the sperm to break down the CR, then
cortical reaction is done to change permeability of egg to prevent other sperm from entering
-head (w/ genetic material enters)
-once cortical reaction happens, a pronucleus forms and the sperm is absorbed in to the egg)
o Pronucleus Formation Begins: The sperm is absorbed into the cytoplasm, the female
pronucleus develops.
o Spindle Formation and Cleavage Preparation: The male pronucleus develops, and
spindle fibers appear in preparation for the first cleavage division.
o Amphimixis: (fusion of the male and female pronuclei, 23 male
and female hploid chromosomes match up = 46 chromosomes
diploid) occurs and Cleavage Begins:
metaphase of first cleavage division
o Cytokinesis: (division and separation of cytoplasm of two daughter
cella). The first
cleavage divison nears completion roughly 30 hours after fertilization
Amphimixis first, then cytokinesis
oOnce fertilized called a zygote (merging of two gametes, creating
a single diploid cell (fertized egg)
Prenatal Development
•Prenatal development is gestation period (9 months)
•Prenatal development is divided into trimesters
o First trimester (rudiments of all organs
appear)
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o Second trimester (fetus looks like a
human)
o Third trimester (organs become
functional, rapid growth)
The First Trimester - 1 to 12 weeks (really just
a ball of stem cells these stem cells can become any type
of cell; totipotent stem cells)
•Four events within the first trimester
o Cleavage (sequence of cell
reproduction)
o Implantation (implantation into
endometrial lining)
o Placentation (formation of the placenta)
o Embryogenesis (development of the embryo)
•Cleavage and Blastocyst Formation
•Cell division results in the formation of
blastomeres (blast – precursor) –
identical daughter cells, get smaller
with each subsequent division (each
individual cell is called a blastomere;
entire structure is called a blastocyst,
blastocyst stage takes about a week)
•A solid ball of cells eventually develops
– this is a morula (morus – mulberry,
tightly packed)
o
o
o
o
o
solid ball of cell some signal happens that push all the cells in
that ball to be pushed to one side; now have essentially an
empty ball called blastocoel)
• Entire structure stays the same
•Some cells migrate to one “edge” of the morula creating a
mass of cells and a hollow cavity (w/ some fluid) called the
blastocoele
-The ball of cells is now called the blastocyst (Is
floating in the uterus while the light blue cells are called the
embryoblast and only those cells will become the embryo)
•The outer layer of the blastocyst consists of cells called the
trophoblast (tropho – food, blast – precursor, these cells will
provide food/nutrients to the developing embryo)
•The inner cell mass (embryoblast – will become the
embryo) consists of stem cells that will develop into all the
cells and cell types in the body (note: stem cells that are used
for cloning are from the blastocyst stage, these cells are pleuri
(multi) potent (power) and can differentiate into any cell or
tissue type in the body) *these are the controversial “stem
cells” you hear about
•Implantation ( embryoblast side goes in first)
•Upon contact with the endometrial lining, the trophoblast cells
divide rapidly create a large multi nucleated cell called the
syncytial trophoblast
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
The reproductive system: embryology and human development (based on chapter 28) Development involves: differentiation of cells, reorganization of cells. Development can be characterized by different periods of time: prenatal development fertilization/conception to delivery. Involves embryology prenatal development focussing on the first two months after fertilization: postnatal development development from birth to maturity. Fertilization is the joining of two haploid cells to create a diploid cell. Spermatozoon (see chapter 27: delivers the paternal chromosomes to the ovum o o sperm has head, midsection and tail head has an acrosome and a nucleus containing 22 haploid chromosomes and one x or. Fertilization usually occurs in the ampulla of the uterine tube. 200 million sperm cells enter the vaginal canal: only about 10,000 make it to the uterine tubes. Less than 100 actually contact the egg: only one will fertilize the egg. Egg will be fertilized somewhere laong that path.
