Embryology and Oocyte Development

Embryology

• Embryo development hinges upon uterine tissue function
• Uterine tissue structure changes throughout the menstrual cycle (25-28 days)
• Women are born with a finite number of oocytes (primary oocytes) arrested in prophase of the first meiotic division

Oocyte Development

• At puberty, a monthly selection of primary oocytes begins development
• Primordial follicles are formed by a single layer of granulosa cells surrounding primary oocytes
• Primary follicles transform into secondary follicles as they grow, increasing the layers of granulosa cells and containing an antrum (fluid-filled cavity)
• A single dominant follicle (Graafian follicle) matures, producing increased estrogen to thicken the uterine lining in preparation for potential implantation
• A surge in luteinizing hormone (LH) triggers ovulation, releasing the secondary oocyte into the fallopian tube
• The remnants of the Graafian follicle transform into the corpus luteum.
• Progesterone secreted by the corpus luteum prepares the endometrium for implantation.

Implantation

• Implantation starts at the beginning of week 6 at the ampulla of the uterus.
• Fertilized egg (zygote forms an embryo), growing and dividing during one week's travel to the uterus, forms a blastocyst
• Implantation requires a receptive uterine lining. It is facilitated by hormones, particularly progesterone, ensuring its receptiveness
• Successful implantation can only occur if the uterus has reached a receptive phase
• Embryo attaches to the endometrium and destroys some tissue to access nutrients during implantation which lasts for one week

Pregnancy

• Pregnancy lasts 38 weeks (266 days) from fertilization
• First 8 weeks form embryonic period.
• Embryo→ Zygote→ morula→ Blastocyst stages of early development.
• At the 8-cell stage, cells are totipotent.
• These stages establish the components of the placenta (chorionic, amniotic, yolk sacs).
• During the third week, gastrulation creates the three primary germ layers (ectoderm, mesoderm, and endoderm).

Explore the intricate processes of embryonic development and the stages of oocyte maturation. This quiz covers key concepts including uterine tissue function, the menstrual cycle, and follicle transformation essential for ovulation. Test your knowledge on how these processes prepare the body for potential pregnancy.