Embryo Syst 1. Dev of Muscle and Cavities Mb2

Embryology Systemic
Part 1
V Tchokonte-Nana, Ph.D.
For
MB2, Universite des Montagnes, School of Medicine,
Cameroon
Muscular System
 As with the skeletal system most of

the muscular system also develops
from the mesodermal germ layer
 Smooth muscle develops from
splanchnic mesoderm which
surrounds gut /derivatives.
 • Cardiac muscle develops from
splanchnic mesoderm which
surrounds the heart tube.
1
TRUNK MUSCULATURE
 Skeletal muscle of the

trunk develops from
 paraxial mesoderm (which forms somites &
somitomeres)
 • Somites differentiate
 Somites differentiate
 into:-
 1. Sclerotome → Axial skeleton &
 2. Dermomyotome →
 a.Dermatome dermis and subcut tissues &
 b.Myotome segmental muscles (& takes with it its own
segmental nerve).
2
FATE OF MYOTOME CELLS
 Myotome cells split off, move to

their definitive locations, &
become elongated & spindle
shaped (called myoblasts)
 Many myoblasts fuse to
become Multinucleated muscle
fibres.
3
 Myofibrils appear in
cytoplasm.
 By 12/52 cross striations
typical for skeletal muscle
appear.
 Somites: form body wall musculature

 It forms a dorsal epimere & a ventral hypomere.
 The epimere forms the vertebral extensors;
 while the hypomere forms the muscles of the body wall and limbs.
 Note the different innervation viz. dorsal and ventral primary rami
 same process in head and neck region i.e. form myoblasts which will
form extra ocular eye muscles, face, larynx, tongue etc
4
5
Head Musculature
Head Musculature
6
Limb Musculature
 Condensation of mesenchyme near the base of limb buds (7th week)

 Mesenchyme is derived from dorsolateral cells of somites
 Migrate into limb bud to form the muscles
 Connective tissue dictates the pattern of muscle formation
 Upper limb buds lie opposite the lower five cervical and upper two
thoracic segments
Limb Musculature
 Lower limb buds lie opposite

lower four lumbar and
upper two sacral segments
 Upper limb rotates 90°
laterally, while lower limb
rotates 90° medially
 Thus, the upper and lower
limbs are 180 degrees out of
phase.[There is a 180°
medial rotation of the lower
limb compared to
developing upper limb
(angle of flexion differs)].
7
Cardiac Muscle
 Develops from splanchnic mesoderm surrounding the endothelial

heart tube
 Myoblasts adhere to one another by intercalated discs
 Myofibrils develop as in skeletal muscle but do not fuse
 Few special bundles become visible (Purkinje fibers)
8
Smooth Muscle
Clinical Correlations
9
Systemic Embryology
Part 1
V Tchokonte-Nana, Ph.D.
For
MB2, Universite des Montagnes, School of Medicine,
Cameroon
10
INTRAEMBRYONIC COELOM
11
 Appears as isolated spaces in the lateral mesoderm

 In the 4th week, the spaces fuse to form a single horseshoe-shaped (U-
shaped) cavity
 The coelom divides the lateral mesoderm into:
1. Somatic (parietal) layer: under ectoderm
2. Splanchnic (visceral) layer: over endoderm
 Somatopleure = somatic mesoderm + overlying

ectoderm
 Splanchnopleure = splanchnic mesoderm +
underlying endoderm
12
 DERIVATIVES: It gives rise to three body cavities:

1. A pericardial cavity: the curve of U
2. Two pericardioperitoneal canals (future pleural
cavities): the proximal parts of the limbs of U
3. Two peritoneal cavities: the distal parts of the
limbs of U
 Each cavity has a parietal layer (derived from
somatic mesoderm) & a visceral layer (derived
from visceral mesoderm)
 FUNCTION: It provides space for the organs to
develop & move
13
DEVELOPMENT OF PERITONEAL
CAVITY
 Major part of intraembryonic coelom

 Develop from the distal parts of the limbs of the U-
shaped cavity
 Originally, it is connected with extraembryonic
coelom (midgut herniates to the outside through this
connection)
 At 10th week, it looses its connection with
extraembryonic ceolom (when midgut returns to
abdomen)
DEVELOPMENT OF PERITONEAL
CAVITY
 Originally, there were 2 peritoneal cavities

 After lateral folding of embryo, the peritoneum
becomes a single cavity
HOW?
14
15
MESENTERIES
 A MESENTERY is a double layer of peritoneum that

begins as an extension of the visceral peritoneum
covering an organ
 The mesentery connects the organ to the body wall
and transmits vessels and nerves to it
 Transiently, the dorsal & ventral mesenteries divide
the peritoneal cavity into right & left halves
 The ventral mesentery disappears EXCEPT where
stomach develops
 (WHY?)
16
PERICARDIAL CAVITY
 Develops from the curve of the U-shaped cavity

 During formation of head fold, the heart &
pericardial cavity move ventrocaudally & become
anterior to the foregut (esophagus)
 It is bounded by an outer somatic & an inner visceral
layer, forming the serous pericardium
PERICARDIAL CAVITY
 Originally, it is connected with the 2

pericardioperitoneal canals
 Later on, it become separated from the 2
pericardioperitoneal canals
HOW?
17
PERICARDIAL CAVITY
 Originally, the bronchial buds are small relative to

the heart
 Bronchial buds grow laterally into
pericardioperitoneal canals (future pleural
cavities)
 Pleural cavities expand ventrally around heart &
splits mesoderm into:
1. Outer layer: forms thoracic wall
2. Inner layer: pleuropericardial membrane
18
PLEUROPERICARDIAL
MEMBRANES
 THE PARTS SURROUNDING THE SEROUS PERICARDIUM:

form the fibrous pericardium
 THE PARTS BEHIND THE HEART: fuse with the ventral
mesentery of the esophagus (at 7th week), forming
the mediastinum & separating pericardial from
pleural cavities
 N.B.: The right pleural cavity separates from
pericardial cavity earlier than left
PLEURAL CAVITIES
 Develop from the 2 pericardiperitoneal canals

 Originally, they are connected with pericardial &
peritoneal cavities
 Later on, they become separated from:
1. Pericardial cavity
2. Peritoneal cavity (HOW?)
19
PLEUROPERITONEAL
MEMBRANES
 Produced when developing lungs & pleural cavities

expand into the body wall
 During 6th week, they fuse with dorsal mesentery of
esophagus & septum transversum, separating
pleural cavities from peritoneal cavity
 N.B.: The right pleural cavity separates from
peritoneal cavity earlier than left
20
DEVELOPMENT OF DIAPHRAGM
DEVELOPMENT OF DIAPHRAGM
 The diaphragm develops from:

1. Septum transversum: forms the central tendon
2. Dorsal mesentery of esophagus: forms the right &
left crus
3. Muscular ingrowth from lateral body wall:
posterolateral part (costal part)
4. Pleuroperitoneal membranes: small portion of
diaphragm
21
SEPTUM TRANSVERSUM
 At 3rd week, it is in the form of mass of mesodermal

tissue in the cranial part of embryo (opposite the 3rd,
4th & 5th cervical somites)
 At 4th week (during formation of head fold), it moves
ventrocaudally forming a thick incomplete partition
between thoracic & abdominal cavities
 At 6th week, it expands & fuse with dorsal mesentery
of esophagus & pleuroperitoneal membranes to
form the diaphragm
INNERVATION OF DIAPHRAGM
 Myoblasts from 3rd, 4th & 5th cervical somites

migrate into diaphragm & bring their nerve fibers
from them
 Nerve fibers derived from ventral rami of 3rd, 4th &
5th cervical nerves fuse to form phrenic nerve that
elongate to follow the descent of diaphragm
1. Both motor & sensory supply of the diaphragm is
derived from phrenic nerve
2. The part of diaphragm derived from lateral body
wall receives sensory fibers from lower intercostal
nerves
22
ANOMALIES OF DIAPHRAGM
1. CONGENITAL DIAPHRAGMATIC HERNIA

2. EVENTRATION OF DIAPHRAGM
3. CONGENITAL HIATAL HERNIA
CONGENITAL DIAPHRAGMATIC
HERNIA
23
CONGENITAL DIAPHRAGMATIC
HERNIA
 A posterolateral defect of diaphragm

 Cause: defective formation and/or fusion of
pleuroperitoneal membrane with other parts of
diaphragm
 Effects:
1. Herniation of abdominal contents into thoracic
cavity
2. Peritoneal & pleural cavities are connected with
one another
 The defect usually occurs in the left side (WHY?)
24
EVENTRATION OF DIAPHRAGM
EVENTRATION OF DIAPHRAGM
 Cause: failure of muscular tissue from body wall to

extend into pleuroperitoneal membrane on one side
 Effects: superior displacement of abdominal viscera
(surrounded by a part of diaphragm forming a
pocket)
25
CONGENITAL HIATAL HERNIA
 Herniation of part of the stomach through a large

esophageal hiatus (opening)
26

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Embryology Systemic

 As with the skeletal system most of

 Skeletal muscle of the

 Myotome cells split off, move to

 Somites: form body wall musculature

 Condensation of mesenchyme near the base of limb buds (7th week)

 Lower limb buds lie opposite

 Develops from splanchnic mesoderm surrounding the endothelial

 Appears as isolated spaces in the lateral mesoderm

 Somatopleure = somatic mesoderm + overlying

 DERIVATIVES: It gives rise to three body cavities:

 Major part of intraembryonic coelom

 Originally, there were 2 peritoneal cavities

 A MESENTERY is a double layer of peritoneum that

 Develops from the curve of the U-shaped cavity

 Originally, it is connected with the 2

 Originally, the bronchial buds are small relative to

 THE PARTS SURROUNDING THE SEROUS PERICARDIUM:

 Develop from the 2 pericardiperitoneal canals

 Produced when developing lungs & pleural cavities

 The diaphragm develops from:

 At 3rd week, it is in the form of mass of mesodermal

 Myoblasts from 3rd, 4th & 5th cervical somites

1. CONGENITAL DIAPHRAGMATIC HERNIA

 A posterolateral defect of diaphragm

 Cause: failure of muscular tissue from body wall to

 Herniation of part of the stomach through a large

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