BODY CAVITIES

Slidelearn Team

FORMATION OF BODY CAVITY END OF 3RD WEEK At the end of third week

there is differentiation of Intraembryonic mesoderm changes into Paraxial mesoderm Intermediate

mesoderm Lateral plate

mesoderm

FORMATION OF BODY CAVITY Lateral plate mesoderm Intracellular clefts appears in the

lateral plate mesoderm at 3rd week and divides it into Parietal/somatic layer Visceral/splanchnic layer Primitive body cavity

Somatic mesoderm later forms the parietal layer of serous membrane lining outside the pericardial, peritoneal and pleural cavities

Splanchnic mesoderm form the viseral layer that cover the lungs, abdominal organs and the heart

FORMATION OF (intraembryonic coelom) BODY CAVITY

Intraembryonic mesoderm give rise to three cavities

Pericardial cavity Large Peritoneal cavity Two pericardioperitoneal

cavities

Lateral body folds: Parietal layer of LPM Overlying ectoderm Cells of adjacent somites

Endoderm: folds & closes Gut tube

End of 4th week Closure of gut tube

Midgut connection to yolk sac Vitelline duct Incorporate in umbilical cord Degenerate in 2nd - 3rd

months

Closure of ventral body wall Head and tail folds Embryo curve in fetal position Gap in area of connecting

stalk

SEROUS MEMBRANES

Parietal layer Serous layer of serous membranes Lining peritoneal, pleural &

pericardial cavities Visceral layer

Visceral layer of serous membrane Covering abdominal organs, heart

and lungs

SEROUS MEMBRANES

Parietal and visceral layers Become mesothelial continuous at junction of gut

& posterior abdominal wall Form Dorsal mesentery Extent; foregut to hind gut

Ventral mesentary Caudal foregut to upper

duodenum Thinning of septum

transversum

CLINICAL APPLICATIONS

Ventral body defectsThorax, abdomen, pelvisFailure of closure of ventral body wallMainly involve lateral body folds

Ectopic cordis Gastroschisis Bladder & cloacal exstrophy

Ectopic cordis

Failure in thoracic region Heart outside body cavity Cantrell Pentalogy

Secondary to body wall closure defect

Defect from sternum to upper abdomen

Ectopia cordis Defect in diaphragm Absence of diaphragm Omphalocele Gastroschisis

Gastroscisis Defect in abdominal region Intestinal loop herniate in

amniotic cavity Incidence increasing Common in mothers; lean &

below 20yrs Detected by

Ultrasound Alpha fetoprotein Affected loops; ulcerate,

volvulus, compromised blood supply

Bladder & cloacal exstrophy

Pelvic region defect Minor defect: only

bladder involved Major defect :bladder

and rectum exposed

Omphalocele

Failure of gut tube to return to abdominal cavity

Loops of intestine and liver outside

Covered by amnion 2-5/10,000 15% cases have chromosomal

abnormality Elevated alpha fetoprotein

THORACIC CAVITY

Septum Transversum Thick plate of

mesoderm B/w thoracic cavity

and yolk sac stalk Incomplete “Pericardioperitoneal

canals” on each side of gut

Lung bud

grow within pericardioperitoneal canals

Expand dorsally, ventrally and laterally

Canals become small Lungs grow in

mesenchyme of body wall

THORACIC CAVITY

Pleuropericardial folds Small ridges Projecting in primitive thoracic

cavity Become membranes Contain

Common cardinal veins Phrenic nerves

Fuse with each other & lung root

Dividing thoracic cavity Adult “fibrous pericardium”

DIAPHRAGM

Pleural cavity communicate with peritoneal by pericardioperitoneal canals

Crescent shaped pleuroperitoneal folds Extends medially and ventrally 7th week fuse with

Mesentary of esophagus Septum transversum

Addition of peripheral rim Myoblasts from somites C3-5

penetrate membrane

DIAPHRAGM

Derived from Septum transversum –

central tendon Pleuroperitoneal

membranes—membranous part

Somites C3-5 -- Muscular component

Mesentary of esophagus -- crura

DESCENT OF DIAPHRAGM

Initially septum transversum---opposite cervical somites Nerve supply from C-3,4,5 Forming phrenic nerves (sensory and motor) Pass through pleuropericardial folds Sensory fibers from thoracic intercostal nerves as most

peripheral part derived from thoracic wall mesenchyme

6th week – level of thoracic somites 3rd month - Lower thoracic & first lumbar vertebra

CLINICAL APPLICATIONS

Congenital diaphragmatic hernia 1/2000 Failure of pleuroperitoneal

membranes Pleural and peritoneal

cavities communicate Abdominal viscera enter

pleural cavity 85-90 % left side heart pushed anteriorly Lungs hypoplastic 75% death

Clinical Anomalies

Parasternal herniaMuscular fibers failureDiscover at several years of ageSmall peritoneal sac with intestinal loop

Esophageal herniaShortness of esophagusUpper part of stomach in thoraxStomach constricted at diaphragm