Hormonal control of pregnancy

Nitin Pandey

Fertilization & Implantation

Fertilization occurs at ampulla of the uterine tube

Steps of fertilization1. Sperm are attracted to the ovum

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.

Steps of fertilization2. Sperm bind to the zona pellucida

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

Steps of fertilization3. Release acrosomal enzymes

Steps of fertilization4. Fusion of membranes and entry of male pronucleus into ovum

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.

Fertilization of ovum

Implantation ordinarily occurs on about the fifth toseventh day after ovulation

Implantation results from the action of trophoblastcells 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 upregulatingSynthesis of attachment molecule- integrin and osteopontin

Implantation

A, Floating blastocyst. B, Attachment to the uterine epithelium and initial invasion of thesyncytiotrophoblast cells.

The blastocyst penetrates deeper into the uterine stroma and develops an amniotic cavity.

The fully implanted embryo invades the maternal vasculature andthe uterine epithelium grows over the implantation site and undergoes the decidualization

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

Development and structure an of human placenta

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

hCG and Human chorionic somatotropin

Foetus

Mother uterus PlacentaThe MOTHER, PLACENTA, and FETUS acts as a unit to provide the optimal environment for fetal development

Feto-placental unit

Fetoplacental unit

Fetoplacental unit

urinary estriol excretion of the mother can be monitored as an index of the state of the fetus.

Thank you

During pregnancy, the extreme quantities of estrogenscause (1) enlargement of the mother’s uterus, (2)enlargement of the mother’s breasts and growth of thebreast ductal structure, and (3) enlargement of themother’s female external genitalia.The estrogens also relax the pelvic ligamentsof the mother, so that the sacroiliac joints becomerelatively limber and the symphysis pubis becomeselastic.These changes allow easier passage of the fetusthrough the birth canal. There is much reason tobelieve that estrogens also affect many general aspectsof fetal development during pregnancy, for example,by affecting the rate of cell reproduction in the earlyembryo

2. Progesterone decreases the contractilityof the pregnant uterus, thus preventing uterinecontractions from causing spontaneousabortion.3. Progesterone contributes to the development ofthe conceptus even before implantation, becauseit specifically increases the secretions of themother’s fallopian tubes and uterus to provideappropriate nutritive matter for the developingmorula and blastocyst. There is also reason tobelieve that progesterone affects cell cleavage inthe early developing embryo.4. The progesterone secreted during pregnancy helpsthe estrogen prepare the mother’s breasts forlactation,