Download anatomy 6: formation of body cavities and diaphragm

ANATOMY 6: FORMATION OF BODY CAVITIES AND DIAPHRAGM
Review of Folding of Embryo:
 4th week: transition from flat disc to hollow tubular structure
 faster proliferation of cells on upper surface of embryonic disk than lower surface bending/folding
 cranio-caudal: growth of nervous system
 lateral: growth of somites
 http://www.indiana.edu/~anat550/cvanim/index.html
Review: Cranial Folding
 structures cranial to developing brain: oropharyngeal membrane, cardiogenic region, septum transversum
 folding causes cardiogenic region and septum transversum to be caudal to oropharyngeal membrane and located in
the chest region
 septum transversum- most cranial; furthest from primitive streak diaphragm; connects cardiac field to amnion
 *think of envelop example*
 Day 27: formed primitive heart tube, starting to develop dorsal aorta, neural tube fusing
 Endoderm: epithelium internal organs and GI tract
 Ectoderm: epidermis, cutaneous glands, internal ear, lens, CNS, cells of PNS
Review: Mesoderm Derivatives
 paraxial mesoderm: somites (next to notochord)
 intermediate mesoderm: urinary and reproductive tracts
 lateral mesoderm:
o splits into 2 layers- upper continuous with amnion (parietal); and lower continuous with yolk sac (visceral)
o parietal dermis of back, abdominal wall, outer linings of body cavities
o visceral muscular layers and blood vessels of gut, circulatory system, external covering of internal organs
Body Cavities
 pericardial cavity: around heart
 pleural cavities: one cavity around each lung
 peritoneal cavity: abdominal cavity; around abdominal viscera
Formation of Intraembryonic Coelom (Early Body Cavity)
 formed from space created when lateral mesoderm splits into parietal and visceral layers
 forms as U shape around cranial embryonic disk
 continuous with chorionic cavity (extraembryonic coelom)
 embryo folds craniall- traps coelomic space between upper and lower layers
 embryo folds laterally- wraps around space to enclose space within body
Divisions of Intraembryonic Coelom
 folds of tissue form and grow across coelomic space to separate regions
 pleuropericardial folds: between pericardial cavity and pericardioperitoneal canals
 pleuroperitoneal folds: separate the peritoneal cavity from the pericardioperitoneal canals
Pleuropericardial folds
 form in intraembryonic coelom between developing heart and lungs
 grows medially separating 2 dorsolateral pleural cavities from single ventromedial pericardial cavity
 fuse with mediastinal meso around foregut to form pleuropericardial membrane
Pleuroperitoneal folds
 form in dorsal aspec
 grow ventrally
 thin as they grow pleuroperitoneal membranes
 septum transversum: thick band of meso that translocates caudal to heart after folding
 pleuroperitoneal membranes- join septum transversum to separate pleural and peritoneal cavities
Pericardial Cavity
 heart enlarges and pushes up into space of newly formed pericardial cavity
 fist into balloon analogy
 gives visceral and parietal pericardium
Pericardium
 serous pericardium—from serosa (lining of early embryonic cavity – intraembryonic coelom)
 visceral pericardium- derived from visceral lateral mesoderm (floor of intraembryonic coelom)
 parietal pericardium- derived from parietal lateral mesoderm (roof of intraembryonic coelom)
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ANATOMY 6: FORMATION OF BODY CAVITIES AND DIAPHRAGM
 parietal pericardium fuses with pleuropericardial folds (which become fibrous pericardium)
 separated by pericardial cavity
Pleural Cavities
 dorsolateral to pericardial cavity
 lung buds form off developing trachea and push into pleural cavities
 as lungs grow- cavities expand lateral and ventral on either side of heart
 visceral pleura- derived from visceral lateral mesoderm
 parietal pleura- derived from parietal lateral mesoderm
 pleural cavity between
Abdominal cavity
 parietal mesoderm lines elongating body wall
 visceral mesoderm adjacent to yok sac
 yolk sac shrinks visceral meso wraps around developing gut tube trapping b/n two visceral meso layers
 pleuroperitoneal folds form and join with septum transversum to separate pleural and peritoneal cavities
 2 cavities fuse to form single cavity
 all GI structures develop in-between the 2 layers of visceral mesoderm membranes (intestines, spleen, pancreas,
part of liver
Peritoneum and Mesenteries
 parietal peritoneum: lines body wall
 visceral peritoneum: covers GI organs
 dorsal and ventral mesenteries- fused double layer of visceral peritoneum suspending and supporting developing
gut tubes
 most of ventral mesentery breaks down single cavity
 gut suspended by dorsal mesentery
 coelom lined with epi derived from somatic mesoderm parietal pleura / pericardium / peritoneum
 organs in coelom covered with epi from splanchnic meso visceral pleura / pericardium / peritoneum
 where peritoneum reflects from body wall to gut tube bilayered mesenteries (important for innervation and
vasculature)
Formation of Diaphragm
 4 embryonic components of diaphragm
o septum transversum- forms central tendon
 grows dorsally to form pleuroperitoneal membranes (which are growing ventrally)
o pleuroperitoneal membranes- form 2 small areas on either side of diaphragm
o myoblasts- invade esophageal mesentery which elongates to form crura of diaphragm
o muscle ingrowths- body wall musculature
 openings esophagus, aorta, vena cava
 pleuroperitoneal membranes- only small part of developed diaphragm
 greatest contribution: ingrowth of mm from body wall and central tendon
 innervation: when in cervical region, adjacent to 3-5th somites
 myoblasts and associated nerve fibers (3-5th spinal nn) from somites invade septum tranasversum phrenic n
 as diaphragm moves to thoracic position- brings cervical nn with it
 periphery innervated by thoracic nn because periphery is from ingrowth of muscles in body wall
Malformation of Diaphragm
 congenital diaphragmatic hernia
o pleuroperitoneal folds fail to form
o pleuroperitoneal membrane fails to fuse with other components
o mostly on L side
o intestines, stomach, and liver may be found in thoracic cavity; respiratory distress
 Eventration- muscle of diaphragm not functional- intestine pushes upward but is not in thoracic cavity
Major Developments Wk. 4:
 NT begins closing (rostral- day 26; caudal- day 28)
 Pharyngeal arches begin to form- primordia of many structures in face and neck
 Upper limb buds, otic pits, lens placodes, lower limb buds
 Heart pumps blood
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ANATOMY 6: FORMATION OF BODY CAVITIES AND DIAPHRAGM
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