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DEVELOPMENT OF THE DIAPHRAGM

INTRODUCTION

- The diaphragm is a muscular partition

btw the thoracic and abdominal cavities.

- It has a central tendinous and peripheral

muscular part.

- Its development is intimately related to d

development of the pericardial and

pleural cavities (both lying above d

diaphragm) and the peritoneal cavity

(lying below d diaphragm).

FORMATION OF THE DIAPHRAGM

- The diaphragm develops from 4

structures:

o The septum transversum (the

cranial part),

o Pleuroperitoneal membranes

o Mesentery of the oesophagus

o Mesoderm of the body wall

- The septum transversum originates

from the mesoderm of the cervical

somites C3, C4 and C5 on day 22 of I.U.

life. Its cranial part gives rise to

diaphragm; its caudal part gives rise to

the liver and ventral mesentery of the

foregut.

o By the time it develops, it only

partially separates the future

thoracic cavity from the future

abdominal cavity; the

pleuroperitoneal membrane later

completes the separation.

- The pleuroperitoneal membranes

develop btw 5th and 7th week arising

from the posterolateral part of the

pericardioperitoneal canals. They grow

towards the septum transversum a

mesentery of the oesphagus and fu

with them by d 7th week.

- MESENTERY OF THE OESPHAGUS: T

dorsal mesentery of the oesophag

is derived by the 5th

week(or at the EOF THE 4th week) from the visceral

splachnic mesoderm after d completion

the lateral folding. The vent

mesentery of the oesophagus

derived from the septum transversum.

- The muscle of the diaphragm

derived from the myoblasts, from t

cervical myotomes (C3, C4 and C5) thmigrate into the septum. From t

septum, the myoblast invades the rest

the structures that form the diaphrag

except the central portion. This cent

portion is a part of the sept

transversum which later become t

central tendon, enclosing the infer

vena cava.

- The crura of the diaphragm are form

from myoblast that grow in the dor

mesentery of the oesphagus.

- The peripheral part of the diaphrag

derived from the mesoderm of the bo

wall (thoracic body wall).

- Phrenic nerves supplying both senso

and motor innervation to the muscle

derived from the

C3, C4, C5 cervical somites, same as

septum transversum. The low

intercostal (thoracic) nerve, supply

sensory innervation to the peripheral p

of d diaphragm, is derived from t

mesoderm of the body wall.

REPOSITIONING OF THE DIAPHRAGM

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- Initially the developing diaphragm lies in

d cervical region (i.e. at d level of the

cervical somites) during the 4th week.

- By d 6th week, d developing diaphragm is

at the thoracic region (level of thoracic

somites) and has carried along with it itsphrenic nerve which passes thru d fibrous

pericardium of the heart..

- This repositioning is caused by rapid

growth of the dorsal part of d embryo

(vertebral column) compared with d

growth of the ventral part.

- By end of the 8th week (beginning of 3rd

month), some of the dorsal part of d

diaphragm originate at d level of the 1stlumbar vertebra.

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