Summary of "FECUNDACIÓN Y DESARROLLO EMBRIONARIO/PSU BIOLOGÍA/CLASE Nº14"
Summary of "FECUNDACIÓN Y DESARROLLO EMBRIONARIO/PSU BIOLOGÍA/CLASE Nº14"
This video is a detailed educational lecture on fertilization, embryonic development, and pregnancy hormones, aimed at biology students preparing for the PSU (university entrance exam) in Chile. The class is presented by a professor from Universidad Mayor and covers the biological processes from gamete formation through early embryogenesis and hormonal regulation during pregnancy.
Main Ideas and Concepts
1. Fertilization Process
- Fertilization is the union of two haploid gametes (sperm and oocyte) to form a diploid zygote.
- Occurs primarily in the first third of the oviduct (fallopian tube).
- The sperm must travel from the vaginal canal through the uterus to reach the oocyte.
- Stages of fertilization include:
- Penetration of the corona radiata: The sperm uses enzymes like hyaluronidase to pass this outer layer.
- Species recognition and adhesion: Sperm and oocyte membranes recognize each other via species-specific receptors.
- Acrosome reaction: Release of enzymes (acrosin, hyaluronidase) from the sperm’s acrosome to penetrate the zona pellucida.
- Penetration of the zona pellucida: Enzymatic digestion allows sperm entry.
- Membrane fusion: Only the sperm nucleus enters the oocyte cytoplasm.
- Block to polyspermy: Cortical granules release enzymes that harden the zona pellucida to prevent multiple sperm entry.
- Activation of meiosis II: The oocyte resumes and completes meiosis, ejecting the second polar body, becoming an ovum.
- Formation of male and female pronuclei: Chromosomes condense and prepare for syngamy.
- Syngamy: Homologous chromosomes pair.
- Amphimixis: Formation of a common metaphase plate leading to the first mitotic division.
- Consequences of fertilization:
- Restoration of diploidy.
- Determination of genetic sex (XX or XY).
- Initiation of mitotic divisions leading to embryo formation.
2. Embryonic Development
- After fertilization, the zygote undergoes segmentation (cleavage) — a series of mitotic divisions producing a Blastocyst.
- The Blastocyst has a polarized cell mass:
- Inner cell mass → embryo.
- Outer cells → embryonic annexes (support structures).
- Implantation occurs in the uterine endometrium about 7–8 days post-fertilization, where the trophoblast invades the uterine lining.
- Gastrulation:
- Formation of three germ layers: ectoderm, mesoderm, and endoderm.
- Ectoderm → nervous system, skin.
- Mesoderm → muscles, skeleton, reproductive and urinary systems.
- Endoderm → respiratory and digestive systems, liver, endocrine glands.
- The embryo forms a tube-like structure; certain physical marks (e.g., linea alba, philtrum) are remnants of this stage.
- Organogenesis:
- Formation of organs and body structures.
- Embryo has a tail and resembles other vertebrate embryos in early stages.
- Embryonic annexes include yolk sac, umbilical cord, chorion, amniotic cavity, and fluid.
- At about 12 weeks, the embryo is considered a fetus, with fully formed organs that grow and mature during the fetal period.
- Embryonic annexes support fetal development and maintain pregnancy.
3. Pregnancy Hormones
- Human Chorionic Gonadotropin (hCG):
- Produced by the chorion of the embryo.
- Maintains the corpus luteum (gluteal body) in the ovary.
- Keeps Progesterone and estrogen levels high during the first trimester.
- Detected by pregnancy tests.
- Progesterone:
- Known as the "pregnancy hormone."
- Maintains the uterine endometrium to support implantation.
- Produced by the corpus luteum during the first 3 months, then by the Placenta.
- Levels drop sharply at delivery to allow labor.
- Estrogens:
- Increase throughout pregnancy.
- Prepare mammary glands for lactation.
- Promote uterine muscle (myometrium) growth for childbirth.
- Placenta:
- Functions as an endocrine organ producing hormones like Progesterone and placental lactogen.
- Modifies maternal metabolism to support fetal growth.
- Takes over hormone production after the first trimester.
Methodology / Instructional Content (Quiz Questions and Answers)
Fertilization requirements:
Category
Educational
