4. Chemotactants, secreted by the ovary,
attract sperm and interact with receptors
in the sperm membrane.
cGMP, formed by such activators of
guanylyl cyclase as atrial natriuretic
peptide (ANP) and nitric oxide ,
mediates an increase in the velocity and
directionality of sperm movement, and it
stimulates the acrosome reaction.
6. Once sperm are very close to the zona pellucida of the ovum,
they undergo the acrosomal reaction.
As a result of Ca2+ stimulation, as well as protein kinase C
(PKC) and protein kinase A (PKA) activation, the acrosomal cap
releases a corona-dispersing enzyme, a trypsin-like enzyme
(known as acrosin), a neuraminidase, and hyaluronidases.
Together, these enzymes disperse and digest the granulosa
cells of the cumulus oophorus, and they permit attachment of
sperm to the zona pellucida.
The acrosomal reaction is stimulated by, and penetration of
the zona is facilitated by, species-specific zona receptors.
These receptors have oligosaccharide-binding sites for sperm
membrane proteins, in particular one receptor that is termed
ZP3
9. Fusion sets off a reduction in the
membrane potential of the ovum that
prevents polyspermy, the fertilization of
the ovum by more than one sperm.
This transient potential change is followed
by a structural change in the zona pellucida
that provides protection against
polyspermy on a more long-term basis.
11. Implantation ordinarily occurs on about the fifth to
seventh day after ovulation
Implantation results from the action of trophoblast
cells that develop over the surface of the blastocyst
These cells secrete proteolytic enzymes that digest
and liquefy the adjacent cells of the uterine
endometrium
Progesterone helps in implantation by upregulating
Synthesis of attachment molecule- integrin and
osteopontin
Implantation
12. A, Floating blastocyst.
B, Attachment to the uterine epithelium and initial invasion of the
syncytiotrophoblast cells.
14. The fully implanted embryo invades the maternal vasculature and
the uterine epithelium grows over the implantation site and undergoes the
decidualization
15. Failure to Reject the "Fetal Graft"
placental trophoblast does not express the
polymorphic class I and class II MHCgenes and instead
expresses HLA-G, a nonpolymorphic gene.
Fas ligand on the surface of the placenta, and this
bonds to T cells, causing them to undergo apoptosis
17. Pregnancy is marked by the development of a unique
organ, the placenta, which has a limited lifespan.
This organ has diverse functions. It serves
(1) as the fetal gut in supplying nutrients,
(2) as the fetal lung in exchanging oxygen and carbon
dioxide,
(3) as the fetal kidney in regulating fluid volumes and
disposing of waste metabolites, and
(4) as a versatile endocrine gland that synthesizes
many steroid and protein hormones that affect
both maternal and fetal metabolism.
Placenta
20. Foetus
Mother uterus Placenta
The MOTHER, PLACENTA, and FETUS acts as a
unit to provide the optimal environment for
fetal development
Feto-placental unit
Fetoplacental unit
23. During pregnancy, the extreme quantities of estrogens
cause (1) enlargement of the mother’s uterus, (2)
enlargement of the mother’s breasts and growth of the
breast ductal structure, and (3) enlargement of the
mother’s female external genitalia.
The estrogens also relax the pelvic ligaments
of the mother, so that the sacroiliac joints become
relatively limber and the symphysis pubis becomes
elastic.These changes allow easier passage of the fetus
through the birth canal. There is much reason to
believe that estrogens also affect many general aspects
of fetal development during pregnancy, for example,
by affecting the rate of cell reproduction in the early
embryo
24. 2. Progesterone decreases the contractility
of the pregnant uterus, thus preventing uterine
contractions from causing spontaneous
abortion.
3. Progesterone contributes to the development of
the conceptus even before implantation, because
it specifically increases the secretions of the
mother’s fallopian tubes and uterus to provide
appropriate nutritive matter for the developing
morula and blastocyst. There is also reason to
believe that progesterone affects cell cleavage in
the early developing embryo.
4. The progesterone secreted during pregnancy helps
the estrogen prepare the mother’s breasts for
lactation,
