LEC 17: Body Cavities/Diaphragm - 08.28.14

Question 1

intraembryonic coelom

Answer 1

• 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

Question 2

extraembryonic coelom

Answer 2

primordium of chorionic cavity

Question 3

intraembryonic coelom vs. extraembryonic coelom

Answer 3

intraembryonic coelom = primodium of embryonic body cavities

extraembryonic coelom = primordium of chorionic cavity

Question 4

2 types of folding that lead to cylindrical appearance of body cavity (mouth to anus)

Answer 4

1. head-tail fold (cranial-caudal fold)
2. lateral folds

Question 5

cranial-caudal fold

Answer 5

rapid grwoth of brain with respect to rest of embryo causes head and tail to fold together

Question 6

lateral folds

Answer 6

embryo folds laterally due to rapid growth of amniotic cavity (accumulates fluid) and somites beside notochord grow rapidly and push things laterally

Question 7

embryonic body cavity

Answer 7

forms the following structures:

• pericardial cavity
• (2) pericardial-peritoneal canals
• peritoneal cavity

Question 8

What lines the embryonic body cavity

Answer 8

1. parietal layer (somatic mesoderm)
   * covers body wall
2. visceral layer (splanchnic mesoderm)
   * covers guts

Question 9

mesentery

Answer 9

a double layer of peritoneum that connects an organ to the body wall; blood vessels and nerves travel in the mesentery

Question 10

dorsal mesentary

Answer 10

suspends caudal foregut, midgut, and hindgut in the peritoneal cavity

Question 11

ventral mesentary

Answer 11

disappears except in the proximal foregut (stomach and proximal duodenum)

Question 12

What is the arterial supply to the primitive gut

Answer 12

1. celiac (foregut)
2. superior mesenteric (midgut)
3. inferior mesenteric (hindgut)

arteries, nerves, and veins all pass through dorsal mesentary

Question 13

communication between intraembryonic coelom and extraembryonic coelom

Answer 13

• provides space for “physiologic herniation” of the midgut
• closes around 10 weeks after intestines have returned to abdomen

Question 14

pleuropericardial folds

Answer 14

• 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

Question 15

4 embryonic components of the diaphragm

Answer 15

1. septum transversum
2. pleuroperitoneal membranes
3. dorsal mesentary of the esophagus
4. muscular in-growth from lateral body walls

Question 16

septum transversum

Answer 16

1. primordium (mesoderm) of central tendon of the diaphragm
2. begins cranial to the developing heart
3. “migrates” via cranio-caudal folding of embryo to separate heart from liver

Question 17

pleuroperitoneal membranes

Answer 17

• 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

Question 18

pleuroperitoneal membranes in fetal vs. adult diaphragm

Answer 18

pleuroperitoneal membranes form a large part of the fetal diaphragm but a small part of adult diaphragm

Question 19

dorsal mesentary of esophagus

Answer 19

• forms median portion of diaphragm
• crura of diaphragm (pair of muscle bundles) form from myoblasts that have migrated into dorsal mesentary

Question 20

muscular ingrowth of lateral body wall

Answer 20

• expanding pleural cavities divide body wall into:
  
  • external layer = definitive body wall
  • internal layer = peripheral diaphragm
• expansion forms costodiaphragmatic recesses (costophrenic angles)

Question 21

innervation of diaphragm

Answer 21

• 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

Question 22

What nerves innervate the diaphragm

Answer 22

Cervical 3, 4, 5 keep the diaphragm alive

Question 23

Congenital Diaphragmatic Hernia (CDH)

Answer 23

• 1 in 2,200 newborns
• left-sided defects predominated (right closes before left)
• abdominal viscera (stomach, spleen, intestines) herniate from abdomen into chest