LEC 17: Body Cavities/Diaphragm - 08.28.14 Flashcards
intraembryonic coelom
- primordium of embryonic body cavities
- formation of intraembryonic coelom begins early in the 4th week
- spaces in the lateral mesoderm coalesce to form horseshoe shaped coelomic cavity
- communicates with extraembryonic coelom
- provides space for organs to develop/move
extraembryonic coelom
primordium of chorionic cavity
intraembryonic coelom vs. extraembryonic coelom
intraembryonic coelom = primodium of embryonic body cavities
extraembryonic coelom = primordium of chorionic cavity
2 types of folding that lead to cylindrical appearance of body cavity (mouth to anus)
- head-tail fold (cranial-caudal fold)
- lateral folds
cranial-caudal fold
rapid grwoth of brain with respect to rest of embryo causes head and tail to fold together
lateral folds
embryo folds laterally due to rapid growth of amniotic cavity (accumulates fluid) and somites beside notochord grow rapidly and push things laterally
embryonic body cavity
forms the following structures:
- pericardial cavity
- (2) pericardial-peritoneal canals
- peritoneal cavity
What lines the embryonic body cavity
- parietal layer (somatic mesoderm)
* covers body wall - visceral layer (splanchnic mesoderm)
* covers guts
mesentery
a double layer of peritoneum that connects an organ to the body wall; blood vessels and nerves travel in the mesentery
dorsal mesentary
suspends caudal foregut, midgut, and hindgut in the peritoneal cavity
ventral mesentary
disappears except in the proximal foregut (stomach and proximal duodenum)
What is the arterial supply to the primitive gut
- celiac (foregut)
- superior mesenteric (midgut)
- inferior mesenteric (hindgut)
arteries, nerves, and veins all pass through dorsal mesentary
communication between intraembryonic coelom and extraembryonic coelom
- provides space for “physiologic herniation” of the midgut
- closes around 10 weeks after intestines have returned to abdomen
pleuropericardial folds
- divides embryonic body cavity for heart/lung
- pleuropericardial membranes contain common cardiac veins and phrenic nerves
- fuse with mesenchyme ventral to esophagus in midline to separate pericardial and pleural cavities
4 embryonic components of the diaphragm
- septum transversum
- pleuroperitoneal membranes
- dorsal mesentary of the esophagus
- muscular in-growth from lateral body walls
septum transversum
- primordium (mesoderm) of central tendon of the diaphragm
- begins cranial to the developing heart
- “migrates” via cranio-caudal folding of embryo to separate heart from liver
pleuroperitoneal membranes
- pleural/peritoneal cavities
- grow in from lateral body walls
- fuse with dorsal mesentary of esophagus and septum transversum
- myoblasts migrate into pleuroperitoneal membrane to close the pleuroperitoneal openings
pleuroperitoneal membranes in fetal vs. adult diaphragm
pleuroperitoneal membranes form a large part of the fetal diaphragm but a small part of adult diaphragm
dorsal mesentary of esophagus
- forms median portion of diaphragm
- crura of diaphragm (pair of muscle bundles) form from myoblasts that have migrated into dorsal mesentary
muscular ingrowth of lateral body wall
- expanding pleural cavities divide body wall into:
- external layer = definitive body wall
- internal layer = peripheral diaphragm
- expansion forms costodiaphragmatic recesses (costophrenic angles)
innervation of diaphragm
- septum transversum intially opposite 3rd/4th/5th cervical spinal nerves
- spinal nerves migrate with septum transversum
- fibers fuse to form two (2) phrenic nerves (motor and sensory)
- intercostal nerves in body wall (sensory)
- diaphragm appears to descend as embryo folds
- phrenic nerves ~30cm long in adults
What nerves innervate the diaphragm
Cervical 3, 4, 5 keep the diaphragm alive
Congenital Diaphragmatic Hernia (CDH)
- 1 in 2,200 newborns
- left-sided defects predominated (right closes before left)
- abdominal viscera (stomach, spleen, intestines) herniate from abdomen into chest
