✅ PERIODO EMBRIONARIO | DE LA TERCERA A LA OCTAVA SEMANA 📚 ORGANOGÉNESIS | CAPAS GERMINALES

From the Third to the Eighth Week: Embryonic Period

The video discusses the embryonic period, focusing on key developmental processes and structures from the third to the eighth week of human embryology.

Germ Layer Derivatives and Prenatal Development

• Gastrulation leads to the formation of germ layers, giving rise to various organs and tissues.

• The embryonic period spans from the third to eighth week, varying based on different literature sources.

• The embryonic period involves organogenesis where ectoderm, mesoderm, and endoderm form tissues and organs.

Neurulation and Neural Tube Formation

• Neurulation begins with notochord development inducing neural plate thickening.

• Neurulation progresses as neural plate grows cephalo-caudally, forming neural folds and groove.

• Fusion of neural folds forms the neural tube which gives rise to the central nervous system.

Ectodermal Derivatives and Neural Crest Cells

• Ectoderm differentiates into neuroectodermal cells within the neural tube.

Neural Crest Development

This section delves into the differentiation of neural crest cells and their contributions to various structures in the body.

Differentiation of Neural Crest Cells

• Neural crest cells differentiate into various tissues and organs, including connective tissue, bone of the face and skull, ganglia of cranial nerves, thyroid gland C cells, heart's conal septum, dermis of face and neck, dorsal roots of spinal ganglia, sympathetic chain ganglia, adrenal medulla, parasympathetic ganglion of gastrointestinal tract.

Contributions to Organ Formation

• Neural crest cells contribute to the formation of melanocytes, odontoblasts, smooth muscle cells in blood vessels of face and forebrain.

Formation of Optic Vesicles and Lens

• The otic placodes form optic vesicles for hearing and balance structures while lens placodes form lens vesicles contributing to eye development.

Mesodermal Germ Layer Derivatives

This section explores the derivatives of the mesodermal germ layer during embryonic development.

Mesoderm Differentiation

• Mesoderm gives rise to epidermis, hair, nails, skin glands, mammary glands, adenohypophysis (anterior pituitary), tooth enamel.

Paraxial Mesoderm Formation

• Paraxial mesoderm thickens near notochord forming a plate called Paraxial Mesoderm which later organizes into somitomeres contributing to head mesenchyme.

Somite Development

• Somites are organized segments derived from somitomeres; they form in craniocaudal direction with each pair appearing at a rate until around week five when there are 42 to 44 pairs.

Embryonic Development Overview

This section delves into the importance of specific spaces during embryonic folding and the formation of body cavities.

Importance of Body Cavities Formation

• The space created during the embryo's folding is crucial as it gives rise to three types of body cavities: pericardial, pleural, and peritoneal cavities.

Development of Heart and Blood Vessels

Focuses on the initiation of heart, blood vessels, and blood cells development in the third week.

Initiation of Cardiovascular System Development

• In the third week, development commences for the heart, blood vessels, and blood cells within an 18-day-old embryo.

Formation of Heart Cells and Blood Vessels

Discusses how heart cells and blood vessels originate from specific mesodermal regions.

Origin of Heart Cells and Blood Vessels

• Heart cells derive from splanchnic or visceral mesoderm located cranially to oropharyngeal membrane.

• Primary Cardiogenic Field forms an inverted U shape where heart development occurs.

• Blood cells and vessels also stem from mesoderm.

Blood Cell Formation Process

Explores the process through which blood cells are formed in embryos.

Process of Blood Cell Formation

• Hemangioblasts differentiate from extra-embryonic splanchnic mesoderm surrounding yolk sac.

• Hemoangioblasts group into islets known as Wolf and Pander islets or blood islets.

• Islets emit buds through budding process to form a network of small vessels.

Primitive Blood Cell Development

Details the emergence and fate of primitive blood cells in early embryonic stages.

Primitive Blood Cell Generation

• Central cells within islets become precursors for blood cells while peripheral ones form endothelial lining for developing vessels.

Yolk Sac Hematopoiesis

Highlights the significance of yolk sac as an initial hematopoietic organ in embryonic development.

Yolk Sac Functionality

• Yolk sac serves as first hematopoietic organ producing primitive blood cells that enter circulation around day 22.

• These primitive blood cells undergo programmed cell death later replaced by fetal-originated ones.