✅ EMBRIOLOGÍA de las CAVIDADES CORPORALES y el DIAFRAGMA 🫁📚

Cavidades Corporales y su Desarrollo

Introducción a las Cavidades Corporales

• Las cavidades corporales son espacios confinados dentro del cuerpo que albergan órganos internos, proporcionando protección, separación y soporte.

Clasificación de las Cavidades

• Se dividen en dos cavidades principales: dorsal (que incluye la cráneo y el conducto vertebral) y ventral (subdividida en torácica y abdominal pélvica).

• La cavidad torácica contiene el corazón y los pulmones; la abdominal pélvica alberga órganos digestivos, urinarios y reproductores.

Formación del Celoma Intrambronario

• El desarrollo del celoma intrambronario comienza en la tercera semana de gestación, tras la gastroelación en el mesodermo lateral.

• Durante esta etapa inicial, pequeñas cavidades se desarrollan en el mesodermo, con una delaminación que forma capas parietal osomática y visceral o esplácnica.

Estructura de las Capas Mesodérmicas

• La capa parietal osomática está adyacente al ectodermo superficial; mientras que la visceral o esplácnica se adosa al endodermo.

• Estas capas darán origen a la soma topleura (pared lateral del cuerpo) y a la esplácnopleura (recubre vísceras).

Evolución de las Cavidades Corporales

• Al inicio de la cuarta semana, el celoma intrambronario se convierte en la cavidad corporal primitiva.

• Esta cavidad representa futuras estructuras como la pericárdica, pleural y peritoneal.

Comunicación entre Porciones del Celoma

• Hasta finales de la cuarta semana, las porciones del celoma permanecen comunicadas con revestimientos viscerales y parietales.

Desarrollo de Membranas Serosas

• La capa parietal osomática formará membranas serosas como el pericardio fibroso; mientras que la visceral formará el epicardio.

Plegamiento Embrionario

• A finales de la tercera semana ocurre un plegamiento embrionario que transforma al embrión de una forma plana a tubular.

Formación de Pliegues Laterales

• Este proceso involucra cuatro pliegues: cefálico, caudal y dos laterales.

Reubicación durante el Plegado Cefálico

• Durante este plegado, el corazón se reubica caudalmente frente al intestino anterior.

Estructuras Derivadas del Mesenterio

• Los mesenterios surgen post plegamiento desde hojas somáticas y viscerales del mesodermo lateral.

Tipos de Mesenterios

• Se discuten dos tipos: ventral (conectando intestino anterior hasta duodeno cercano con hígado), dorsal (desde intestino anterior hasta posterior).

Importancia Estructural

Formation of Body Cavities and the Diaphragm Development

Division of the Coelom

• The division of the intramural coelom into pericardial cavity, pleural cavities, and abdominal cavity occurs with the formation of pleuropericardial membranes, pleuroperitoneal membranes, and the diaphragm.

Development of Membranes

• The separation between pleural cavities and the pericardial cavity happens as lungs grow towards pericardioperitoneal canals.

• Membranous ridges appear on each canal's lateral wall: a pleuropericardial membrane located cranially above developing lungs and a pleuroperitoneal membrane situated caudally below them.

Expansion and Fusion of Membranes

• Pleuropericardial membranes contain common cardinal veins and phrenic nerves; they expand ventrally around the heart as lungs grow, dividing mesenchyme into an outer layer (future thoracic wall) and an inner layer (future fibrous pericardium).

• These membranes grow laterally and eventually fuse at midline with ventral esophageal mesenchyme, separating pericardial from pleural cavities.

Separation of Pleural and Peritoneal Cavities

• Pleuroperitoneal membranes project into pericardioperitoneal canals, fusing with dorsal mesentery of esophagus during week six to separate pleural from peritoneal cavities.

Structure and Function of the Diaphragm

• The diaphragm is a dome-shaped muscular structure that separates thoracic from abdominal cavities.

• Its development involves several embryonic components including dorsal esophageal structures.

Mesodermal Contributions to Diaphragm Formation

• The transverse septum appears in week three as a mass of mesoderm tissue forming a thick connective partition that grows dorsally from ventrolateral embryo body creating a semi-circular division between heart and liver.

Dorsal Mesentery Interaction

• Dorsal mesentery extends sagittally from dorsal thorax to esophagus; it fuses with transverse septum after surrounding esophagus.

Growth Dynamics in Embryonic Development

• Pleuroperitoneal membranes arise from dorsolateral body walls projecting towards pericardioperitoneal canals adjacent to esophagus.

• Some embryology texts state these canals disappear when transverse septum expands; however, Lachman suggests they continue growing until fusion covers transverse septum completely.

Muscle Cell Origin for Diaphragm

• Muscle cells in body wall originate from somites C3-C5 levels penetrating into pleuroperitoneal membranes to form diaphragm musculature.

Expansion Effects on Body Walls

• As lungs grow, their caudal tips open additional space in lateral body walls causing tissue layers to split into two: an outer layer contributing to definitive abdominal wall and an inner layer aiding peripheral diaphragm portions outside those derived from pleuroperitoneal membranes.

Sinuous Configuration Creation

• Further lung expansion leads to costodiaphragmatic recesses forming characteristic dome shape of diaphragm.

Central Tendon Origins Debate

• According to Mur & Artiaga, central tendon originates from transverse septum; Lagman attributes it to central portion of pleuroperitoneal membranes.

Pillars Formation

• Dorsal mesentery generates pillars for diaphragm while remaining contributes to muscular portion.

Changes in Positioning and Innervation

Septum Location During Development

• In week four, transverse septum is positioned anteriorly relative to cervical somites C3-C5.

Myoblast Migration

• By week five, myoblast migration occurs towards developing diaphragm carrying nerve fibers along.

Phrenic Nerve Origin

• Phrenic nerves providing motor innervation originate from ventral branches of cervical spinal nerves C3-C5.

Apparent Descent Explanation

• Rapid growth at dorsal end causes apparent descent of diaphragm during development stages.

Final Positioning by Week Eight

• By week six, developing diaphragm aligns with thoracic somites; by early eighth week its dorsal part reaches first lumbar vertebra level.

Lengthening Phrenic Nerves

• This descent explains long trajectory (approximately 30 cm in adults).

Conclusion on Body Cavities Formation