Embryology Basics Quiz

Introduction to Embryology and the First Week of Human Development

• Embryology is the study of the development of a genetically unique organism.
• The zygote is a diploid (half genes from mother and half from father).
• The zygote does not encode its own genome (maternal effect).
• Identical twins result from an early separation of the zygote into two separate cell masses.
• Fraternal twins result from the formation of two separate zygotes.
• The process of fertilization results in the formation of the zygote.
• The first stage of development in a genetically unique organism.

Stages of Embryonic Development

• Germinal period (weeks 1-2): Involves fertilization and the early divisions of the zygote within the fallopian tube.
• Embryonic period (weeks 3-8): Significant development of the major organs and body systems.
• Fetal period (weeks 9-birth): Continued growth and maturation of the body systems.
• Stages from fertilization to implantation and development.
• Early development stages - zygote, 2-cell, 4-cell, 8-cell stage, morula, blastocyst.

Oogenesis

• Oogonia (germ cells): One to two million formed during development per ovary.
• Primary oocytes: 60,000 - 80,000 remain in each ovary by puberty.
• Secondary oocytes (follicles): About 20 proceed to maturation every month.
• 1-2 develop and proceed to ovulation each month. The process of forming female gametes.

Spermatogenesis

• Spermatogonium (germ cell): Start of spermatogenesis.
• Formation of the male gametes. Development of sperm cells, from spermatogonium to maturation.

Fertilization

• Process where a male and female gamete fuse.
• Occurs in the ampullary region of the uterine tube.
• Only 1% of sperm enter the cervix.
• The trip to the fallopian (oviduct) can take 30 mins to 6 days.

Capacitation

• This happens in fallopian tube. Interactions between sperm and fallopian tube surface.
• Destabilization of acrosomal sperm head membrane.
• Increased motility.

Acrosome Reaction

• The reaction occurs in the acrosome of the sperm.
• Allows sperm to break into the zona pellucida of the egg.
• Involves release of acrosin and trypsin-like enzymes.

Fertilization Stages

• Phase 1: Penetration of the corona radiata.
• Phase 2: Penetration of the zona pellucida.
• Phase 3: Fusion of the sperm and oocyte membranes.
• The egg responds in three ways to protect itself from polyspermy; altering the membrane structure, completing the second meiotic division and formation of the female pronucleus, metabolic reactivation for early embryogenesis.

Blastocyst Formation

• Morula enters the uterus; fluid goes through the zona pellucida into the intercellular space.
• Forming the blastocoel (blastocyst).
• Inner cell mass (embryoblast) and outer cell mass (trophoblast) formation.
• Zona pellucida ruptures to allow implantation.

Blastocyst Implantation

• Trophoblast cells secrete enzymes to penetrate between epithelial cells of the uterine wall (endometrium).
• Immune systems are modulated to accept the "foreign" embryo.
• Implantation occurs in specific uterine areas. The lining (enodometrium) undergoes changes that support implantation and the embryo's early growth.

The uterine wall

• It consists of three layers: Endometrium, Myometrium, Perimetrium.
• Endometrium, the innermost layer, undergoes cyclical changes during the menstrual cycle.
• Changes in the endometrium during the menstrual cycle.

Menstrual Cycle

• Cycle Regulated by hormones released by the ovaries.
• The different phases (Follicular, Secretory, menstrual, gravid).
• The endometrium undergoes cyclical changes from puberty to menopause.

Ectopic Pregnancy

• Occurs when the blastocyst implants outside the uterus (usually the fallopian tubes).
• Most often the embryo dies during the second month of gestation.
• A life-threatening pregnancy if not terminated.
• This occurs with approximately 2% of all pregnancies.

Assisted Reproductive Technology (ART)

• Includes medical procedures to address infertility.
• About 15-30% of couples encounter infertility problems.
• 1% of births from ART procedures have significant complications.
• IVF uses in-vitro (test tube) fertilizations.
• ART risks include: increased prematurity, low birth weight, increased risk of birth defects, childhood malignancies.

Embryonic Stem Cells

• Embryonic stem cells (ESCs) can be isolated from human embryos and cultured indefinitely.
• ESCs are pluripotent, meaning they can differentiate into any type of cell in the body.
• ESCs can be used for stem cell therapy.

Chromosomal Abnormalities

• Numerical chromosomal abnormalities (e.g., trisomies, monosomies).
• Trisomy 21 (Down syndrome), Trisomy 18 (Edwards syndrome), Trisomy 13 (Patau syndrome).
• Sex chromosome trisomies (e.g., Klinefelter syndrome (XXY), Trisomy X (XXX), Jacob's syndrome (XYY).
• Sex chromosome monosomy (e.g., Turner syndrome (45,X)).
• Risk of aneuploidy increases with maternal age.

Test your knowledge on the fundamental concepts of embryology, including human development stages, importance of the study, and birth defects. This quiz covers key topics regarding gamete formation and prenatal development periods. Perfect for students in biology or health sciences.