1-Fertilization

Definition:It is the process by

which the sperm of the male & ovum of the female meet and fuse.

Site: In the ampullary

part of the uterine tube, for 2 reasons: It is close to the

ovary. It is the widest part of

the uterine tube.

It is small (with a length ofabout 50µ, and highly motile. Itconsists of head, neck and amotile tail. The head containsthe nucleus that is covered byThe acrosome (an organellecontaining enzymes). There

aretwo types of sperms accordingto the chromosomal contentsi.e. the Y- bearing sperm(having 22 autosomes + Y)And the X bearing sperm(having 22 autosomes +X).

It has large size, immotile, covered by zona pellucida and corona radiate. Its cytoplasm is abundant (containing yolk granules for nutrition of the embryo during the first week of development). Its nucleus contains 22 chromosomes + one X chromosome.

How the sperms reach

the site of fertilization?

1. By movement of their tail.

2. By the movement of uterine cilia.

3. By chemo attraction.

How the oocyte reaches

the site of fertilization?

1. By the movement fimbria of the uterine tube.

2. By peristaltic movement of the uterine tube.

Capacitation: the glycoproteincoat is removed from the

surfaceof the sperm's acrosome. It

takesabout 7 hours. Only thecapacitated sperms canpenetrate the corona radiata.Acrosome reaction: It occursafter capacitation whereproteolytic enzymes as acrosin,esterases, hyaluronidase, andneuraminidase are liberated inorder to penetrate the zonapellucida.

1. Passage of sperm through the corona radiate.

2. Penetration of the zona pellucida.

3. Fusion of the oocyte and sperm cell membranes to form the zygote (the unicellular embryo).

Once a sperm penetrates the zona pellucida, a zona reaction (a change in the properties of the zona pellucida) occurs that makes it impermeable to other sperms.

- This zona reaction is caused by the action of lysosomal enzymes released by cortical granules near the plasma membrane of the oocyte.

1. Restoration of the diploid number of chromosomes (46 chromosomes).

2. Determination of the embryo's chromosomal sex (the female is 46,XX and the male is 46,XY).

3. Stimulation of cleavage (mitotic cell divisions of the zygote).

This method is used in cases of infertility where the ovaries are stimulated by high doses of hormones to produce many ova in the same ovarian cycle (ovarian stimulation). Then several ova are withdrawn from the Graffian follicles of the ovary of the wife before ovulation. They are then placed with the husband's sperms in a petri-dish containing nutrient medium. So fertilization occurs outside the mother's uterine tube (in vitro). Two or three of the resulting zygotes are placed back in the uterus (embryo transfer ) after 3 days of fertilization.

Intracytoplasmic sperm injection (ICSI)

It is the method of choice in cases of infertility due to the male factor (severe oligospermia). It implies the same process as IVF except that the best sperm is selected and injected into the ovum cytoplasm.

Definition: It is the repeated mitotic divisions of the zygote, resulting into a rapid increase in the number of cells that are called blastomeres.

Site: The uterine tube medial to the ampula.

a- Morula:It has 16 cells(blastomeres). Ithas mulberryappearance. It issurrounded byZona pellucida.It enters theuterus nearly 3Days afterfertilization.

b- Blastocyst formation:

As morula reaches the uterine

cavity, fluid from the uterine cavity

penetrates the zona pellucida and

accumulates in the inter-cellular

spaces of the inner cell mass .

-A single cavity is formed and called

blastocele .

-The morula after the formation of

blastocele is called blastocyst.

-The blastocyst consists of inner cell

mass (it will form the future embryo;

so it is called embryoblasts) and

outer cell mass (future trophoblast &

placenta). The zona pellucida

disappears allowing for implantation.

Definition: Penetration of the blastocyst into the superficial (compact) layer of the endometrium.

Time: Implantation occurs at the 6th day after fertilization and is completed about the 11th day.

Site: The normal site is the endometrium of the posterior wall of the fundus of the uterus in or near the middle line. The endometrium after implantation is called decidua.

Definition: It is the compact layer of the endometrium after implantation of the blastocyst.

1. Decidua basalis (part of endometrium between the blastocyst & the myometrium ).

2. Decidua paritalis (endometrium covers the wall of the uterus).

3. Deciduas capsularis (endometrium between the blastocyst & uterine cavity).

4. Decidua marginalis (endometrium surrounding the site of implantation).

1. Uterine ectopic pregnancy: a. At the cornu of the uterus

(the site of attachment of the uterine tube) leading to early abortion.

b. At the lower uterine segment leading to placenta previa.

c. Cervix, leading to cervical pregnancy and early abortion.

2. Extra uterine ectopic pregnancy:

a. The commonest site is in the Fallopian tube leading to tubal pregnancy that leads to early abortion or tubal rupture with severe internal haemorrhage.

b. Ovary (ovarian pregnancy), broad ligament or omentum (rare).

c. Peritoneum of Douglas pouch (abdominal pregnancy).

mesentry

tubeovary

Internal os

It is also called ectopic pregnancy. It might result in death of the embryo or early abortion with severe internal hemorrhage.

1,A2,C

1,C1,B

2,A2,B

Definition: Implantation of the blastocyst in the lower segment of the uterus close to the internal os. Thus the placenta will precede the fetus at delivery (normally, the fetus is the lowermost and fills the lower segment). Previa = at the front of the fetus.

Types of placenta previa: 1. Placenta previa parietalis: The placenta lies in the lower segment away from the internal os of the cervical canal.2. Placenta previa marginalis: The placenta covers partially the internal os. During labour, it is shifted upwards away from the internal os .3. Placenta previa centralis: it lies in the lower segment and completely covers the internal os. During labour, it leads to ante-partum Hge. It may lead to malposition of foetus.

Prof.: Dr. Wafaa Abdel-Rahman