Gamete transport and capacitation
After ejaculation, spermatozoa enter the vagina where some perish, while the rest are propelled through cervical mucus under the influence of prostaglandins. In the upper regions of the tract, they undergo capacitation, acquiring hyperactive motility and the ability to penetrate the membranes. A mature oocyte, surrounded by the corona radiata and zona pellucida (zona pellucida), is captured by the fimbriae and moved into the uterine tube via fluid flow and peristaltic contractions.
Cleavage and pre-implantation period
The fused cells form a zygote, which begins mitotic division — cleavage, resulting in the formation of blastomeres. This process follows the "all-or-none" principle: with partial damage, blastomeres regenerate; with massive damage, the embryo dies. After 4 days, the embryo at the morula stage reaches the uterine cavity, transforming into a blastocyst consisting of an embryoblast and a trophoblast.
Implantation and decidual transformation
The implantation of the blastocyst into the secretory-phase endometrium takes about two days and requires strict synchrony. The endometrium transforms into the decidua, which is divided into parietal, capsular, and basal parts. The syncytiotrophoblast erodes blood vessels, forming lacunae and the intervillous space into which maternal blood pours.
Chorionic development and placenta
During the 2nd and 3rd weeks, primary, secondary, and tertiary chorionic villi develop. Vascularization results in the formation of a hemochorial placenta. The villi differentiate into the chorion laeve and chorion frondosum. Free villi provide metabolic exchange, while anchoring villi fix the placenta to the uterine wall.
Five to six days before nidation: first the morula in the tube, then the blastocyst in the uterus.
Class and exam questions
Where does fertilization take place?
The process of sperm-egg fusion is localized in the ampullary region of the uterine tube.
What role does the zona pellucida play after fertilization?
Immediately after fusion with a single spermatozoon, the zona pellucida becomes impermeable, establishing a block to polyspermy.
What is capacitation?
This is the process of removing the glycoprotein coat from the sperm head, accompanied by hyperactive motility and increased penetrating ability.
What else to study on this topic
- Spermatogenesis and the role of the Y chromosome in sex determination
- Hormonal regulation of uterine tube contractility
- Anatomical division of the decidual membranes
- First and second waves of trophoblast invasion
- Structure of cotyledons and mature chorionic villi
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