✅ INTRODUCCIÓN A LA EMBRIOLOGÍA HUMANA | Conceptos Básicos 📚
Introduction to Human Embryology
What is Embryology?
- Embryology is defined as the study of the embryo, encompassing all changes from fertilization to birth.
- It includes the examination of the placenta and extraembryonic structures such as amnion, yolk sac, chorion, allantois, and umbilical cord.
Stages of Prenatal Development
- Prenatal development is divided into three periods: pre-embryonic, embryonic, and fetal stages.
- The process begins on day 0 with fertilization, forming a zygote from the union of sperm and oocyte in the distal third of the fallopian tube.
Early Development Phases
- During the first week post-fertilization, the zygote becomes a blastocyst; this stage involves segmentation occurring in the fallopian tube.
- In week two, implantation occurs as the bilaminar embryo forms; this continues within the pre-embryonic period.
Transition to Organ Formation
- By week three, a trilaminar embryo emerges through gastrulation; this marks the end of the pre-embryonic phase.
- From weeks four to eight (the embryonic period), organogenesis takes place where initial organ structures develop.
Fetal Development and Susceptibility Period
- After week nine until birth is termed fetal development; functional growth of organs occurs during this time.
- The embryonic period has critical susceptibility phases where external factors can lead to significant malformations due to high cell division rates.
Genetic and Epigenetic Regulation
- Normal development relies on genetic regulation (DNA blueprint influence) and epigenetic regulation (external factor impact).
Morphogenetic Mechanisms
- Five key morphogenetic mechanisms are crucial for embryonic shape formation: induction, cellular differentiation, growth, migration, and programmed cell death (apoptosis).
Detailed Mechanisms:
- Induction: A tissue prompts another tissue to undergo change.
- Cellular Differentiation: Leads to diverse cell types through increased morphological complexity.
- Growth: Refers to size increase in various parts/organs of an embryo.
- Migration: Involves cells moving from their origin site to new locations within developing tissues.
- Programmed Cell Death (Apoptosis): A regulated process leading to cellular destruction with structural changes at a microscopic level.
Understanding Body Structure Orientation
- Knowledge about relative body structure positions is essential in embryology for understanding developmental changes.
Positional Terminology:
- Sagittal Plane: Divides body into right and left halves.
- Coronal Plane: Separates body into ventral (front) and dorsal (back).