Primeros estadios embrionarios humanos

Welcome and Introduction

In this section, Stella Maris Roma introduces the topic of early embryonic stages and provides a historical context for the lecture.

Definition of Embryology

• Stella Maris Roma discusses the definition of embryology and its significance for medical professionals.

• Embryology encompasses morphological changes from zygote formation to birth.

Recommended Bibliography

• Stella Maris Roma highlights recommended literature for studying embryological topics.

• Carlos Spitzer's "Gusano de los Libros" is mentioned as a valuable resource in histology and embryology studies.

Gamete Formation: Meiosis

This part delves into the process of gamete formation through meiosis, emphasizing its importance in genetic variability.

Meiosis Process

• Explanation of gamete formation in males (spermatozoa) and females (ovocytes).

• Description of meiosis as a unique cell division leading to haploid cells with 23 chromosomes each.

Significance of Meiosis

• Meiosis introduces genetic variability by generating genetically distinct cells from the parent cell.

• Importance of meiosis in ensuring genetic diversity within species while maintaining familial similarities.

Ovogenesis Process

Focuses on ovogenesis, detailing the intricate process leading to functional ova production in females.

Ovogenesis Steps

• Ovogenesis initiates during intrauterine stages, halts at meiosis I, resumes post-puberty, and completes only upon ovulation.

Proceso de Ovogénesis y Espermatogénesis

This section delves into the processes of ovogenesis in females and spermatogenesis in males, detailing the formation of ova and spermatozoa.

Ovogenesis

• Ovogenesis initiates in intrauterine life, undergoing multiple pauses and stages within the ovaries.

• Follicles containing oocytes arrested in meiosis 1 mature under follicle-stimulating hormone influence, with only one follicle reaching maturity per cycle.

• Mature follicles consist of an ovum surrounded by a basal membrane (zona pellucida), granulosa cells forming an antro folicular space filled with fluid, and concentric layers including theca interna and externa.

Spermatogenesis

• Spermatogenesis occurs in testicular seminiferous tubules, where meiosis progresses continuously post-puberty to produce spermatozoa every 72 days.

• Spermatozoa possess a hydrodynamic design for movement through the female genital tract, comprising a head with 23 chromosomes, an intermediate piece, and a flagellum for propulsion.

Understanding Progesterone-Induced Changes in Female Reproductive System

In this section, the focus is on the changes induced by progesterone in the female reproductive system, particularly in the endometrium and stromal cells.

Progesterone-Induced Changes

• Progesterone induces changes in the endometrium, leading to thin-walled vessels called capillaries.

• Stromal cells in the endometrium enlarge and become laden with material under progesterone stimulation.

Impact of Progesterone on Embryo Implantation

This part discusses how progesterone-induced changes affect embryo implantation and potential outcomes if the endometrium is not adequately prepared.

Embryo Implantation

• The changes induced by progesterone are crucial for embryo implantation, known as residualization.

• If the endometrium is not adequately prepared due to these changes, it can lead to failed embryo implantation and potentially result in a spontaneous abortion.

Interactions for Successful Fertilization

This segment emphasizes the importance of interactions between gametes for successful fertilization within the female genital tract.

Gamete Interactions

• Besides a receptive endometrium, successful fertilization requires interactions between gametes within the female genital tract.

• These interactions involve specific components like oocytes, corona radiata cells, and follicular fluid moving towards the ampulla tubaria for fertilization.

Sperm Journey Towards Fertilization

Detailing the journey of sperm from deposition to reaching and capacitating near an oocyte for fertilization.

Sperm Movement

• Sperm deposited in the vagina must ascend through various parts of the female reproductive tract towards an oocyte for fertilization.

Embryonic Development Overview

In this section, the speaker discusses the process of fertilization and the subsequent stages of embryonic development.

Fertilization Process

• The fusion of gametes restores the species' chromosomal number.

Early Embryonic Stages

• The outer membrane of the acrosome fuses with the plasma membrane, releasing lytic enzymes for tunnel formation in the zona pellucida.

Importance of Understanding Developmental Stages

• Knowledge of embryonic stages is crucial for promoting reproductive health and preventing potential diseases in both embryos/fetuses and mothers.

Stages of Intrauterine Development

This part delves into the three main stages of intrauterine development: pre-embryonic, embryonic, and fetal periods.

Pre-Embryonic Period

• Spans the first to third week, involving the formation of ectoderm, mesoderm, and endoderm layers.

Embryonic Period

• Lasting from the fourth to ninth week, characterized by organ system development and vulnerability to teratogens.

Fetal Period

• Extends from the ninth week until birth, focusing on organ maturation and functional preparation post-birth.

Development of the Blastocyst

In this section, the development of the blastocyst is discussed, focusing on key stages and structures involved in early embryonic development.

Formation of Blastula

• The zygote undergoes segmentation to form 24, 8, or 16 cells initially. Due to the presence of the zona pellucida, cell separation is prevented.

Morula Formation

• Morula formation occurs through mitotic division leading to an increase in cell number but a decrease in cell size. Ciliary cell movement aids morula advancement.

Blastocyst Structure

• The blastocyst consists of an outer zona pellucida and internal cellular structures.

• Cells outside the blastocyst are designated as the external cellular mass while those inside form the internal cellular mass or embryoblast.

Cell Differentiation

• Cells in the external mass contribute to placental and extraembryonic structures, while cells in the internal mass differentiate into embryonic body and organs.

Implantation Process

• The blastocyst cannot implant until enzymes from trophoblast cells create a hole in the zona pellucida for hatching.

• Once hatched, it can adhere to endometrial epithelium for implantation initiation.

Early Embryonic Development

This section delves into events during early embryonic development including implantation processes and structural changes.

Implantation Initiation

• By day five and a half post-fertilization, the blastocyst reaches the uterus after losing its zona pellucida enzymatically. This loss enables endometrial implantation.

Second Week Development

• Transitioning into week two involves observing changes post-endometrial contact for implantation initiation.

• Distinct layers form within the trophoblast: syncytiotrophoblast (yellow) and cytotrophoblast (pink).

Trophoblast Differentiation

• Cytotrophoblast cells initially divide extensively before fusing together. Fused cells secrete lytic enzymes that aid tissue degradation for nutrient acquisition.

Nutrient Acquisition Mechanism

• Tissue destruction by trophoblastic cells aims at obtaining nutrients from maternal tissues like glands and stroma via enzymatic breakdown facilitating embryo growth and progression.

Formation of Cavities

• Trophoblastic differentiation leads to syncytiotrophoblast (blue) responsible for erosion activities and cytotrophoblast (yellow). Two cavities emerge: amniotic cavity and yolk sac cavity aiding nutrient procurement.

Semana del Desarrollo Embrionario - Segunda y Tercera Semana

In this section, the development of the embryo during the second and third weeks is discussed, focusing on key structures and processes such as the extraembryonic mesoderm, cavities formation, and cell differentiation.

Mesoderm Formation in Second Week

• During the second week of development, an exception to the rule occurs with the appearance of the extraembryonic mesoderm outside the embryo.

• The extraembryonic mesoderm divides into two layers: visceral (or parietal) layer and somatic (or ectoplacental) layer, forming a chorionic cavity.

• The implantation process involves trophoblast cells proliferating to form finger-like projections called villi for increased surface area.

Villi Structure and Function

• Villi structures aid in nutrient exchange by increasing surface area within a confined space.

• Villi are categorized as primary or secondary based on their cellular composition and function in enhancing nutrient exchange.

Hormonal Regulation and Implantation

• The trophoblast produces human chorionic gonadotropin hormone that enters maternal blood circulation to support pregnancy maintenance.

• Human chorionic gonadotropin stimulates progesterone production by the corpus luteum, crucial for maintaining endometrial changes necessary for implantation.

Castration Process in Third Week

The third week marks significant developments including gastrulation characterized by cell movements leading to germ layer formation.

Linea Primitiva Formation

• A primitive streak appears during gastrulation marking a critical stage in embryonic development.

• Cells undergo invagination at the primitive streak forming distinct layers: epiblast, hypoblast, and primitive node.

Cell Differentiation at Primitive Streak

• Cells at the primitive streak lose intercellular connections leading to their migration towards specific regions for further differentiation.

Desarrollo Embrionario Temprano

In this section, the speaker discusses the early embryonic development focusing on the establishment of body axes and the formation of different cell layers.

Establishment of Body Axes

• The primitive streak marks the establishment of the anteroposterior axis in the embryo.

• Cells from the primitive streak give rise to waves of cells, including those forming the notochord or primitive vertebral column.

• Differentiation occurs with some cells moving cephalically to form structures like the notochord while others remain in specific regions due to an area of intimate union called buccopharyngeal membrane.

Formation of Mesoderm Layers

This part delves into how cells from the primitive streak differentiate into mesoderm layers that play crucial roles in embryonic development.

Mesoderm Differentiation

• Cells from the primitive streak form mesodermal cell masses around the notochord known as paraxial mesoderm.

• Another group, termed intermediate mesoderm, locates beside paraxial mesoderm.

• Lateral plate mesoderm forms lateral to these layers and will contribute to structures like diaphragm and heart later in development.

Neurulation Process

The neurulation process induced by notochord is discussed here, highlighting its significance in forming neural structures essential for nervous system development.

Neurulation Induction

• Notochord induces neurulation leading to formation of neural plate, neural groove, and eventually neural tube.

• Neural crest cells at edges of neural groove migrate away during tubular closure.

New Section

In this section, the discussion revolves around the formation of shields or barriers in a synthetic context and their impact on implantation processes.

Formation of Shields and Impact on Implantation

• The presence of shields or barriers around the synthetic material can hinder the action of enzymes, such as lysis enzymes, affecting shield formation and potentially impeding implantation.

• The mesoderm from the extraembryonic layer integrates into structures like villi, contributing to shield formation and trophoblastic proliferation, influencing implantation dynamics.

• Vellosities in the third week exhibit trophoblastic characteristics with three layers within the extraembryonic mesoderm, leading to capillary vessel development for fetal blood circulation.

New Section

This segment delves into secondary villi development with three layers in the extraembryonic mesoderm and subsequent capillary vessel formation for fetal blood circulation.

Development of Secondary Villi and Capillary Vessels

• Secondary villi form with three layers within the extraembryonic mesoderm, facilitating capillary vessel growth for fetal blood flow circulation within lacunae spaces.

• The emergence of fetal capillaries marks tertiary villi development while maintaining three layers characteristic of third-week structures, emphasizing key events during embryonic week three.

New Section

This part highlights crucial events during embryonic week three, including neural tube formation, appearance of three germ layers, secondary and tertiary villi structure with triple-layered composition.

Key Events in Embryonic Week Three

• Notable occurrences include neural tube establishment, differentiation into three germ layers (ectoderm, endoderm, mesoderm), secondary and tertiary villi formation featuring triple-layered composition essential for nutrient exchange.

• By week four's conclusion, significant changes occur as the embryo transitions from a flat structure to a cylindrical form resembling early human development stages.

New Section

This section explores cylindrical body transformation during week four due to neural tube growth impacting closure mechanisms along longitudinal planes.

Cylindrical Body Transformation

• Neural tube expansion drives body shape transition from flat to cylindrical through longitudinal folding processes influenced by cephalic-caudal growth discrepancies.

Embryology Development Overview

In this section, the speaker discusses the development of the embryo in detail, focusing on key structures and processes during the fourth week.

Embryonic Structures and Proliferation

• The primitive umbilical cord and our body are within the amniotic cavity. Surrounding this is the chorionic cavity with villi that proliferate significantly in the fourth week.

• Proliferation leads to a fluffy appearance, denser around the embryo (chorion frondosum) and less dense at the opposite pole (chorion laeve), which eventually disappears.

Fourth Week Summary

• The fourth week marks embryonic period initiation, organogenesis stage including nervous system and heart formation. Nutrient absorption occurs as implantation into the endometrium takes place.

Conclusion and Gratitude

• The speaker metaphorically transitions from day to night, expressing gratitude for attention during this fascinating developmental stage. Encourages further exploration via their Instagram for more insights.

• Expresses thanks for engagement in understanding this miraculous phase of life's journey.