Transcript Development

Development
Ejaculation
the release of semen
-Approximately 2 teaspoons (10 mL)
-280 million sperm
-Most die in the vagina within minutes after
ejaculation
-Once they move through the cervix into the
uterus, they can survive longer, up to 5 days.
-Outside the body sperm will die within minutes.
SPERM STRUCTURE
•Head
•contains nucleus
•an organelle “cap” called an Acrosome (contains digestive
enzymes)
•Tail
•flagellum – whipping motion provides motility.
•Base of tail contains a coiled mitochondrion to provide power
for movement.
Capacitation: readying the sperm
• Sperms cannot fertilize oocytes when they are
newly ejaculated.
• The acrosome is not active
• Chemicals in the uterus cause the acrosome to
become active
OvulationSecondary oocyte (nuclues contains 1/2 the chromosomes)
Folicle cells (make up the corona radiata)
Zona pellucida (protects the “egg”)
At the cervix
• Helping the sperm:
– At ovulation, the muscus that normally covers the
opening of the cervix thins out
– This allows sperm to pass through the cervical
opening.
– It is also thought to help guide the sperm
Stage 1 of fertilization:
• Sperm come in contact with the follicle
cells of the corona radiata
• Enzyme action from multiple acrosomes
help sperm pass through
• Flagella action also aids corona radiata
penetration
Stage 2 of fertilization:
• Penetration of the zona pellucida around the oocyte:
– Acrosomal enzymes: cause lysis of the zona pellucida
• Once sperm penetrates zona pellucida, the zona reaction
occurs:
– This reaction makes the zona pellucida impermeable to other
sperms.
– Zona pellucida begins to harden
– When more than one sperm manages to enter the ovum
(dispermy = 2; triploidy = 3), the fetus nearly always aborts.
Corona radiata
Figure 7.8
Stages 3 of fertilization:
• Fusion of plasma membranes of oocyte and sperm
– Causes action potential of the seconadary oocyte
membrane
• 2nd meiotic division of oocyte is completed
– The secondary oocyte was previously arrested in
metaphase of the 2nd meiotic division, and now forms the
mature ovum and another polar body.
– https://www.youtube.com/watch?v=_5OvgQW6FG4
Twins: still 1 sperm per egg
• Monozygotic (monoovular):
– A fertilized, single egg splits into two developing
zygotes at a very early stage.
– Identical twins; same sex.
• Dizygotic (polyovular):
– Result from the fertilization by two sperm of two
separate ova that have reached maturation at the
same time.
– Not identical twins; can be different sexes
– Incidence increases with age of the mother
Day
2-3
• Cleavage begins
Cleavage is cell splitting
• The cells continue
“splitting” by mitosis
• The size of the embryo does
not change, but the number
of cells does
• This is all occurring in the
oviduct
• Zona pellucida is hard
MORULA
• Cleavage stage ends
• now called a morula (Latin
for raspberry)
• It is a solid ball of cells
(about the size of the tip of
your pen)
• It will continue to be called
a morula as long as it is a
“solid ball”
Day 4 - 5
Blastocyst
• The Morula hollows
out as cells move
outward.
• The inside fills with
liquid (the liquid is
produced by the cells)
• Cells are too many and
too small to be seen at
this point
• This is now a
blastocyst
Inside the Blastocyst
Parts of the blastocyst:
• Inner Cell mass:
will become
develop into the
child
• Blastocoel: empty
space of liquid is
inside (-coel means
empty space)
• Trophoblast: outer
layer of cells which
will become
membranes
Human Hatching
The blastocyst will
“hatch” from the
hardened
zona
pellucida
.1 - .2 mm
Implantation
embryo attaches to uterine lining
• Embryo produces
pregnancy
hormone (hCG)
(human chorionic
gonadotropin )
– Found in blood
and urine
Approximately 6-8 days after
fertilization
Hormonal Control of Pregnancy
• Initially the trophoblast cells secrete Human
Chorionic Gonadotrophin (HCG)
• Functions of HCG:
– Prevents the degeneration of the corpus luteum
– Stimulates the growth of the CL.
• Increase secretion of both estrogen and progesterone
• Prevents mestruation
Small chorionic villa (finger-like
projections) grab on to the
endometrium
These projections make contact with the maternal
blood supply, becoming the pipeline through which
the fetus derives nutrients and oxygen, and rids itself
of carbon dioxide and wastes. The placenta has not
formed yet.
The process of: Gastrulation
• A hole forms at the top of the
blastocyst near the inner cell mass
– This hole is called the blastopore
• Cells begin to migrate inward forming
layers (forming shape- morph)
• The blastocyst is now becoming a
gastrula
• Cell to cell
interaction lines up
the cells properly
• 3 layers are formed
Ectoderm
Mesoderm
Endoderm
Differentiation
• Cells are now committed
• Each layer will only become what
it has been programmed to become
(by your DNA)
At 19 dys – photo
about 25 dys: 2.5 mm
Neurulation
• Brain and spinal
cord are forming
• The skull will not
completely close
until months after
birth
• WHY?
• What do we call
these spots?
•Brain regions can be
found
Neurula
•Neural groove, which
will become the spinal
column
•Heart begins to develop
•Hematopoiesis begins
•https://www.youtube.com
/watch?v=M5NzACjICpE
Day 28
2-3.5 mm