Body Cavity Development

Question 1

Deuterostomes?

Answer 1

• second mouth
• we from a tube with ectoderm on outside
• endoderm inside
• mesoderm in between

Question 2

Coelom? what forms it?

Answer 2

• body cavity

- forms within mesoderm

Question 3

What layer controls what we bring in?

Answer 3

Endoderm

-nutrients, air

Question 4

Oropharyngeal membrane?

Answer 4

• cranial end where ectoderm and endoderm come in contact

- will become mouth

Question 5

Cloacal membrane?

Answer 5

• caudal end where ectoderm and endoderm come in contact

- will become anus

Question 6

What axes do the three layers fold in?

Answer 6

• lateral

- cranial-caudal

Question 7

Lateral folding starts when?

Answer 7

3rd week

Question 8

Early formation of Coelom (day 19)?

Answer 8

-lateral plate mesoderm forms small openings called intercellular clefts

Question 9

Splitting of lateral plate mesoderm (day 20)?

Answer 9

• intercellular clefts separate the somatic (parietal) mesoderm from splanchnic (visceral) mesoderm
• this space is called intraembryonic coelom or embryonic body cavity

Question 10

Mushroom stage (day 21)?

Answer 10

• amniotic sac begins to surround embryo
• yolk sac begins to narrow
• intraembryonic and extra embryonic coeloms still connected

Question 11

Isolation of embryonic coelom (day 24)?

Answer 11

• somatic mesoderm encompasses intraembryonic coelom
• splanchnic mesoderm surrounds nascent gut tube to form dorsal and ventral mesenteries
• gut tube still connected to yolk sac

Question 12

Body cavity closure (end of 4th week)?

Answer 12

• fusion of somatic (parietal) mesoderm to form ventral body wall
• splanchnic (visceral) mesoderm of ventral mesentery breaks down to form continuous left and right intraembryonic coelom
• gut contained within splanchnic mesoderm and is connected to dorsal body wall by dorsal mesentery

Question 13

Allantois?

Answer 13

• forms part of urogenital system

- hindgut

Question 14

Angiogenic cell cluster?

Answer 14

• future heart

- more cranial and distal to oropharyngeal membrane

Question 15

Cranial caudal folding (day 22)?

Answer 15

• folding of endoderm at cranial and caudal ends
• foregut
• hindgut forms
• pericardial cavity forms under cranial portion
• septum transversum adjacent to heart and gut tube

Question 16

Site of lung bud formation?

Answer 16

foregut

Question 17

Liver bud forms where?

Answer 17

• midgut

- forms in the septum transversum (expands toward foregut)

Question 18

Pleuropericardial folds (5th week)?

Answer 18

• expands dorsomedially to separate pleural and pericardial cavities
• each contain phrenic nerve
• forms fibrous pericardium

Question 19

Pleuroperitoneal folds?

Answer 19

• expands ventrally to fuse with septum transversum and foregut mesentery
• separates pleural and peritoneal cavities

Question 20

Formation of diaphragm (7th week)?

Answer 20

• combination of septum transversum (central tendon), pleuroperitoneal membranes, mesoderm from body wall and esophageal mesenchyme (crura)
• muscle migrates from cervical myotomes with phrenic nerve (C3, 4, 5) and neighboring body wall

Question 21

Congenital Diaphragmatic Hernia (foramen of Bochdalek)?

Answer 21

• insufficient growth of pleuroperitoneal folds or failure of folds to fuse with septum transversum and/or esophageal mesentery
• happens more on left side
• surgical repair at birth or prenatally as long as not severe pulmonary insufficiency (lungs not forming)

Question 22

Congenital Esophageal Hernia?

Answer 22

• delay in descent of stomach so that diaphragm forms around it leaving an expanded esophageal hiatus
• common, symptomatic in middle age
• congenital shortness of esophagus leaving stomach permanently trapped and potentially constricted by diaphragm
• uncommon, symptomatic in childhood

Question 23

Congenital Eventration of Diaphragm?

Answer 23

• failure of muscle to migrate from body wall to diaphragm (10th week)
• weak diaphragm can balloon into thoracic cavity leading to potential hypo plastic lungs
• rare, symptomatic any age

Question 24

Sternal cleft?

Answer 24

• failure of left and right somatic mesoderm to fuse
• commonly asymptomatic
• surgical repair at birth

Question 25

Ectopia Cordis?

Answer 25

-failure of lateral wall closure results in heart lying outside body cavity

Question 26

Cantrell Pentalogy?

Answer 26

spectrum that includes ectopia cordis, anterior diaphragm defects, absence of pericardium, sternal cleft, abdominal wall defects (omphaloceles and gastroschisis)

Question 27

What forms the lung buds?

Answer 27

respiratory diverticulum from ventral wall of foregut

Question 28

What genes are expressed in the formation of lung buds?

Answer 28

- Nkx2.1 expression in ventral endoderm of foregut tube | - induced by mesodermal expression of Fgf10 and Wnt2/2b

Question 29

What separates the trachea from the esophagus?

Answer 29

-mesodermal ridges expand under influence of Wnt signaling to separate them

Question 30

What gives rise to the lobes of the lung?

Answer 30

- secondary bronchial buds give rise to each lobe of lung - 3 buds in right lung and 2 buds in left lung - in 6th week tertiary buds form the bronchopulmonary segments of mature lung

Question 31

What separates pleural and pericardial cavities?

Answer 31

pleuroperitoneal folds

Question 32

What becomes visceral pleura?

Answer 32

- splanchnic mesoderm | - highly vascularized

Question 33

What becomes parietal pleura?

Answer 33

-somatic mesoderm

Question 34

16th week of lung development?

Answer 34

14 rounds of branching occurs to produce terminal bronchioles

Question 35

16-28 weeks of lung development?

Answer 35

further division into respiratory bronchioles

Question 36

36th week of lung development?

Answer 36

- formation of mature alveoli | - continues into childhood

Question 37

Molecular control of bronchial branching?

Answer 37

1. mesodermal expression of Fgf10 induces mitosis and outgrowth of respiratory duct 2. BMP4 in apical epithelial cells inhibits mitosis 3. Tgfb1 inhibits Fgf10 and promotes matrix synthesis and maturation 4. Fgf10 expression lateral to tip induces new outgrowth in either direction

Question 38

Stages of Lung development?

Answer 38

1. Embryonic (weeks 4-7) - respiratory diverticulum - initial branching 2. Pseudoglandular (weeks 8-16) - 14 generations of branching, terminal bronchioles 3. Canalicular (weeks 17-26) - respiratory bronchioles 4. Terminal sac (weeks 26-36) - specialized cells, surfactant 5. Alveolar (weeks 36 to birth) - maturation of alveoli 6. Postnatal - growth of existing alveolar sacs

Question 39

Tracheoesophageal Fistulas?

Answer 39

- abnormal separation of tracheal bud from esophagus - allow milk and stomach fluids to be aspirated into lungs - build up of amniotic fluid as it cannot be swallowed and returned to mother via fetal circulation - surgically repair

Question 40

Tracheal or pulmonary genesis?

Answer 40

- abnormal formation of lung buds or early branching - bilateral or unilateral - incompatible with life

Question 41

Gross malformation of lungs?

Answer 41

- irregular branching leading to abnormal lobation | - asymptomatic

Question 42

Respiratory distress syndrome?

Answer 42

- birth after 26 weeks (terminal sac stage) infant has good change at survival - lungs rapidly maturing and thinning alveolar walls dependent on proper production of pulmonary surfactant by type 2 alveolar cells - labored breathing and poor oxygenation - can lead to bronchopulmonary dysplasia