Male and female reproductive systems
Where does meiosis occur
in the male?
What are the products of
meiosis?
Male reproductive system
Meiosis in seminiferous tubules produces sperm cells
Haploid nuclei, mitochondria, tail for mobility
When does meiosis occur in
the male?
How are male gametes
nourished and activated?
Where does meiosis occur
in the female?
What are the products of
meiosis?
When does meiosis occur
in the female?
Where does fertilization
occur?
Where does the embryo
develop?
Female reproductive system
Female reproductive system
Meiosis in ovaries produces egg cells
Each meiosis produces a single egg cell
About 1,000,000 cells begin meiosis before birth
Other daughter cells form small polar bodies
Meiosis stops in prophase I
About 400,000 oocytes remain at puberty
Each month, a few oocytes proceed to metaphase II
Hormones trigger release of one oocyte (ovulation)
If sperm penetrates membrane, meiosis finishes
Fertilization
Embryo development
Fertilization usually occurs in fallopian tube
Implantation: blastocyst embeds in lining of uterus
Sperm penetrates oocyte membrane, triggers chemical changes
Inner cell mass develops into embryo
Sperm and egg nuclei fuse within 12 hours zygote
Outer cells produce hCG hormone, preventing menstruation
Cleavage: rapid mitosis following fertilization
Hollow ball of cells (blastocyst) forms in about 4 days
blastocyst
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Development
Embryo development
Fertilized egg is:
Within two weeks:
Undifferentiated (not specialized)
Fluid-filled amniotic cavity surrounds ICM
Undetermined (fate is not set)
ICM flattens into embryonic disc
Totipotent (can produce any cell type)
Three tissue layers form:
Ectoderm skin, nerves and glands
As embryo develops:
Cells’ fate first becomes determined
Later, cells differentiate (specialize)
Mesoderm muscle, bone, blood vessels
Endoderm internal organs
Chorionic villi extend into mother’s circulation
Totipotent Pleuripotent Specialized
Cells become specialized by
Activating some sets of genes
Inactivating other sets of genes
Specialization is generally irreversible in humans
Stem cell research
Stem cell research
Why are researchers interested in embryonic or fetal
cells?
Where can we find stem cells?
ICM – totipotent
Not specialized: totipotent or pleuripotent
Early embryo – pluripotent
Able to divide many more times than adult cells
Umbilical cord – multipotent blood cells
Can be transplanted without rejection
A few specific tissues in adult (multipotent)
What is a stem cell?
Undifferentiated cell
Pleuripotent or totipotent
Divides to produce:
A more specialized cell
How do we obtain stem cells?
Totipotent and pleuripotent cells must be obtained from an
embryo
Umbilical and placental tissue after birth
Adult stem cells from cadaver brains, donor marrow, etc.
Another stem cell
Stem cell research
How are stem cells used now?
Stem cell research
What is stem cell cloning?
Umbilical stem cells to treat anemia and blood disorders
Not production of carbon-copy humans!
Bone marrow stem cells to replace cells lost in cancer treatment
Fuse a human cell (e.g., skin) with enucleated cow oocyte
Develop to blastocyst stage
How might stem cells be used in the future?
“Cell therapy” for damaged tissues
Harvest ICM cells
Advantage: stem cells genetically identical to patient’s own
Testing of new drugs on specific cell types
Research on development and developmental genes
Production of organs for transplant?
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