✅ CAMBIOS EXTERNOS EN EL EMBRIÓN | PERIODO EMBRIONARIO 📚 EMBARAZO 👶 EMBRIOLOGÍA

Introduction and Overview

In this video, the speaker introduces the topic of the embryonic period and discusses the external morphological changes that occur during this stage.

Embryonic Stage and Age Measurement

• The age of the embryo is initially expressed based on somites.

• Later, age is determined by the cephalocaudal length of the embryo, measured in millimeters.

• The cephalocaudal length is the measurement between the vertex of the skull and the midpoint between the apices of the embryo's buttocks.

External Changes in Early Embryonic Stage

• At around day 20-21, first three pairs of somites appear, and the embryo acquires its final tubular shape (1.5 to 3 mm in length).

• The dorsal surface shows a neural groove limited by neural folds.

• By day 22-23, there are 4 to 12 pairs of somites (2 to 3.5 mm in length), and the embryo begins to curve due to growth at its cephalic and caudal ends.

• Pharyngeal arches start appearing, with stomodeum located between them.

• By day 24-25, there are 12 to 20 pairs of somites (2.5 to 4.5 mm in length). Optic vesicles and otic placodes become visible.

Further Development in Late Embryonic Stage

• Around day 26-27, there are already 21 to 29 pairs of somites (3 to 5 mm in length).

• The embryo adopts a "C" shape due to cerebral vesicle development.

• Rostral neuropore closes; optic vesicles become evident; oropharyngeal membrane starts perforating; third pharyngeal arch appears; otic plates sink and become otic fossae; buds of upper limbs appear.

• During the fifth week (day 28-30), the embryo grows considerably (4 to 6 mm in length).

• Optic vesicles form lens plates, otic fossae deepen into otic vesicles, olfactory plates are visible, fourth pharyngeal arches appear, upper limbs resemble paddles, and buds of lower limbs appear.

Late Stage Development

• By day 31-32, somites continue to form but no longer protrude from the surface. Length is 5 to 7 mm.

• Head is flexed on the trunk; cervical curvature is observed; optic vesicles become optic cups; lens plates unite to form lens vesicles; olfactory plates become olfactory pits; upper limbs resemble paddles or oars; lower limbs resemble fins.

Final Stages of Embryonic Period

• Between days 33 and 36, the embryo measures between 7 and 9 mm in length.

• Primary brain vesicles transform into secondary brain vesicles; lens vesicles separate from ectodermal surface.

The summary has been created based on the provided transcript.

Desarrollo embrionario - Semana 6 a 8 New Section

This section provides an overview of the embryonic development from week 6 to week 8.

Development of Upper and Lower Limbs

• The second pharyngeal arch contributes to the growth of upper limbs, which take on the shape of fins.

• The embryo measures between 13 and 17 millimeters in length, and the buds for lower limbs appear.

Facial Features and Ear Development

• Eyelid primordia form, and the caudal neuropore closes.

• Auricular prominences fuse to form rudimentary earlobes, while the caudal end starts to taper off.

Cervical Sinus Closure and Somite Formation

• The cervical sinus is obliterated between days 31 and 32 due to fusion with the lateral neck wall.

• Somites continue forming but no longer protrude on the surface.

Visible Nipples and Digital Rays

• Nipples become visible on the ventral chest wall, making it difficult to count them.

• Digital rays in hand plates become apparent as well. The embryo's length is around 5 to 7 millimeters.

Head Flexion, Curvature, and Optic Vesicles

• Notches appear on the free edge of hand plates as head flexes over the trunk with cervical curvature observed.

• Digital radiations are observed in foot plates, while optic vesicles transform into optic cups around days 47 and 48.

Lens Vesicle Formation and Olfactory Fossa Development

• Lens placodes unite to form lens vesicles, and olfactory placodes transform into olfactory fossae.

• The embryo's cephalocaudal length is around 16 to 18 millimeters.

Limb Growth and Hand Plate Liberation

• Trunk region elongates and straightens, while upper limbs take on the shape of a paddle or oar.

• Upper and lower limbs increase in length, with fingers starting to separate.

Intestinal Loop Development and Optic Cup Formation

• Intestinal loops become prominent within the umbilical cord base, visible through transparency.

• Primary brain vesicles develop further, along with pontine curvature.

Embryo Length and Facial Changes

• The embryo reaches a length of 18 to 22 millimeters between days 49 and 51.

• Head rounding occurs, neck straightens and elongates between days 37 to 40. The embryo measures around 8 to 11 millimeters in length.

Facial Features Differentiation and Intestinal Visibility

• Hands show fully separated fingers, auricular prominences appear at the edges of the first pharyngeal groove.

• Foot digits are identifiable but remain fused, while eyes exhibit dark pigmentation due to retina pigmentation.

Elbow and Wrist Formation

• Elbow and wrist primordia can be distinguished in upper limbs around days 54 and 55. The embryo's length ranges from 23 to 28 millimeters.

Neck Region Development and Eyelid Coverage

• Neck region forms between days 41 and 43, with well-developed eyelids covering most of the eyes. The embryo measures around 11 to 14 millimeters in length.

Conclusion of Embryonic Stage and Foot Plate Formation

• By week 8, the embryonic stage concludes with hand plate formation on days 52 and 53. Lower limbs take on the shape of a paddle or oar. The embryo reaches a length of approximately 22 to 24 millimeters.

New Section

The transcript mentions the liberation of the toes.

Liberation of Toes

• The transcript states that "los dedos de los pies se encuentran liberados" (the toes are liberated).