PROF DRBRIG (R) LIAQAT ALI MINHAS

Neural groove

Ventral Somite wall

Notochord

Mesoderm cells become epithelial and are arranged around a small lumen

Ventrolateral Muscle cells

Dermatome

Dorsomedial Muscle cells

Neural tube

Lateral somitic frontier

Intra embryonic cavity

sclerotome Dorsal aortaCells in the ventral and medial walls of the somite lose their epithelial characteristics and migrate around the neural tube and notochord, and some move into the parietal layer of lateral plate mesoderm. Collectively, these cells constitute the sclerotome. Cells at the dorsomedial (DML) and ventrolateral (VLL) region of the somite from muscles cell precursors. Cells from both regions migrate ventral to the dermatome to form the dermomyotome. VLL cells also migrate into the parietal layer of lateral plate mesoderm across the lateral somitic frontier (green line). In combination, somitic cells and leteral plate mesoderm cells constitue the abaxial mesodermal domain, while the primaxial mesodermal domain only contains somitic cells (paraxial mesoderm)

Dermatome

Sclerotome

Togather, dermatome cells and the muscle cells that associate with them from the dermomytome.

Neural tube

Sclerotome

Dermatome

Myotome

The dermomyotome begins to differentiate, myotome cells contribute to primaxial muscles, and dermatome cellsform the dermis of the back.

Dorsal primary ramus

Hypaxial muscles

Extensor muscle of limb

Body wall muscles

Flexor muscleOf limb

Back (epaxial )Muscle

Ventral primary ramus

Cross section through half the embryo showing innervation to developing musculature. Epaxial (true back muscle) are innervated by dorsal (posterior) primary rami. Hypaxial muscle (limb and body wall ) are innervated by ventral (anterior) primary rami.

Poland sequence. The pectoralis minor and part of the pectoralis major muscles are missing on the patient’s left side. Note displacement of the nipple and areola.

Posterior view

Forelimbs with their dermatome segments indicated. (From Moore, KL and Dalley,AF. Clinically Oriented Anatomy,5th ed.

Pharyngeal arch muscles

Eye muscles

EyeLimb axis epithelial ridgeMesenchymal

CondensationOf limb bud

Occipital myotomes

Cervical myotomes

Thoracic myotomes

Musclature in the head and neck derived from somitomeres and myotomes that form from the occipital region caudally in a 7- week embryo.

Intermediate mesoderm

Lateral plate

Paraxial mesoderm

Intercellular clefts

Endoderm

Transverse section through an embryo of approximately 19 days. Intercellular clefts are visible in the lateral plate mesoderm.

Wall of amniotic cavityParietal mesoderm layer

Embryonic body cavity

Wall of yolk sac

ViseralMesoderm

layer

Section through an embryo of approximately 20 days. The lateral plate is divided into somatic and visceral mesoderm layers that line the intraembryonic cavity. Tissue bordering the intraembryonic cavity differentiates into membranes.

Parietal mesoderm

Yolk sac

Viseral mesoderm

Amniotic cavity

The intraembryonic cavity is in open communication with the extraembryonic cavity

Amniotic cavity Surface ectoderm

Embryonic body cavityConnection between gut and yolk sac

The intraembryonic cavity is about to lose contact with the extraembryonic cavity.

Parietal mesoderm

Dorsal mesentery

Embryonic body cavity

Surface ectoderm

Gut

Viseral mesoderm

At the end of the fourth week, splanchnic mesoderm layers are continuous with somatic layers as a double-layered membrane, the dorsal mesentery. Dorsal mesentery extends from the caudal limit of the foregut to the end of the hindgut.

Angiogenic cell membrane

Amniotic cavity

Cloacal membrane

Connecting stalk

allantois

Endoderm

Oropharyngeal membrane

Ectoderm

Midsagittal sections of embryos at various stages of development showing cephalocaudal folding and its effects upon position of the heart, septum transversum, yolk sac, and amnion. Note that, as folding progresses, the open ing of the gut tube into the yolk sac narrows until it forms a thin connection, the vitelline (yolk sac)duct, between the midgut and the yolk sac

17 days

foregut

Hindgut

Heart tube

Pericardial cavity

22 days.

Oropharyngeal membrane Cloacal membrane

Heart tube

Septum transversum

24 days

Lung bud

Remnant of the Oropharyngeal

membrane

Septum transversum

Vitelline duct

Liver bud

Midgut

Allantois

Yolk sac

28 days, arrows; head and tail folds.

Liver

Pharyngeal gut

Stomodeum

Lung bud

Stomach

Hindgut

Pancreas

Cloaca

AllantoisPrimitive Intestinal

loop

Vitelline duct

Gallbladder

Pharyngeal pouches, epithelial lining of the lung buds and trachea, liver, gallbladder, and pancreas.

Heart bulge

Urinary bladder

Cloacal membrane

Pharyngeal Pouches

The urinary bladder is derived from the cloaca and, at this stage of development, is in open connection with the allantois.

Ectopia cordis. The heart lies outside the thorax, and there is cleft in the thoracic.

Gastroschisis. Intestine have herniated through the abdominal wall to the right of the umbilicus, the most common location for this defect.

Bladder exstrophy. Cloure in the pelvic region has failed. In males, the defect usually a split in the dorsum of the penis, a defect called epispadius.

Blandder

Penis with epispadius

Scrotum

Cloacal exstrophy. A larger closure defect in which most of the pelvic region has failed to close, leaving the bladder, part of the rectum, and the anal canal expesed.

Amnion Abdominal wall

Intestinal loops

Umbilical cord

Example of omphaloceles, a defect that occurs when loops of bowel, that normally herniate into the umbilical cord during the 6th to 10th week of gestation (physiological umbilical herniation), fail to return to the bodycavity.

A. Drawing showing loops of herniated bowel within the umbilical cord that have failed to return to the abdominal cavity. The bowel is covered by amnion because this membrane normally reflects onto umbilical cord

Infant with an omphalocele. The defect is associated with other major malformations and chromosome abnormalities.

Intraembryonic body cavity

Septum transversum

Closing cranial neural fold

Primitive pericardial cavity

Anterior intestinal portal

Lateral body wall fold

Posterior intestinal portal

Hindgut

Drawing showing the ventral view of an embryo at 24 days gestation. The gut tube is closing, the anterior and posterior intestinal portals are visible, and the heart lies in the primitive pleuropericardial cavity, which is partially separated from the abdominal cavity by the septum transversum.

Vitelline duct

Septum transversum

Allantois

Sinus venosus

Liver cords

Cloaca

Body wall

Pericardio peritoneal

canals

Foregut

Portion of an embryo at approximately 5 weeks with parts of the body wall and septum transversum removed to show the pericardioperitoneal canals. Note the size and thickness of the septum transversum and liver cords penetrating the septum

Lung bud

Pleuropericardial

Phrenic nerve

Common cardinal vein

Heart

Growth of the lung buds into the pericardioperitoneal canals. Note the pleuropericardial folds.

Pleuro pericardial membrane

Primitive pleural cavity

Lung

Visceral pleura

Pericardial cavity

Parietal pleura

Fibrous Pericardium

SuperiorVena cava

Parietalplerua

Pleural cavity

Phrenicnerve

A. Transformation of the pericardioperitoneal canals into the pleural cavities and formation of the pleuropericardial membrane. Note the pleuropericardial folds containing the common cardinal vein and phrenic nerve. Mesenchyme of the body wall splits into the pleuropericardial membrane and definitive body wall.

B. The thorax after fusion of the pleuropericardial folds with each other and with the root of the lungs. Note the position of the phrenic nerve, now in the fibrous pericardium. The right common cardinal vein has developed into the superior vena cave.

Pleuroperitoneal fold

Septum Transversum

Pericardioperitoneal

Development of DiaphragmPleuroperitoneal folds appear at the beginning of the fifth week.

AortaEsophagusmesentery

Esophagus

Pleuroperitoneal folds fuse with the septum transversum and mesentery of the esophagus in the seventh week, separating the thoracic cavity from the abdominal cavity.

Septum transversum

Inferior vena cava

Pleuroperitoneal membrane

Muscular ingrowth from

body wall

Transverse section at the fourth month of development. An additional rim derived from the body wall forms the most peripheral part of the diaphragm.

Inferior vena cava

Aortic hiatus

Central tendon

Opening between sternal and costal heads

Absence of pleuroperitoneal

membrane

Opening of Esophagus

Abdominal surface of the diaphragm showing a large defect of the pleuroperitoneal membrane

Left lung

Colon

StomachDiaphragm

Hernia of the intestinal loops and part of the stomach into the left pleural cavity. The heart and mediastinum are frequently pushed to the right, and the left lung is compressed.

Radiograph of a newborn with a large defect in the left side of the diaphragm. Abdominal viscera have entered the thorax through the defect.