Organogenetic Period Flashcards
When is the organogenetic period
Weeks 4-8
What are the germ layers
Ectoderm, endoderm, mesoderm
Ectoderm derivatives
skin, central nervous system, primary nervous system, eyes, internal ears, neural crest cells
Mesoderm derivatives
bones, connective tissue, urogenital system, cardiovascular system
Endoderm derivatives
Gut & gut derivatives
Mesoderm vs. Mesenchyme
mesoderm - derives from the mesodermal germ layer
mesenchyme - any loose connective tissue, may be derived from mesoderm, neural crest, etc.
End of the embryonic period
- beginnings of all organ systems appear
- by the end of the embryo period, the embryo appears human
Folding of the embryo
Results from the rapid growth of the neural tube and amniotic cavity but not the yolk sac
- folding occurs in the longitudinal and transverse planes
- Allows the flat trilaminar disc to become cylindrical
Folding in the longitudinal plane
- Results in the head and tail ends of the embryo swinging ventrally
- Septum transversum, primitive heart, oropharyngeal membrane turn onto the ventral surface
- Somatopleure becomes face and chest wall
- Part of the yolk sac is incorporated as the foregut
Folding in the Transverse plane
- The sides of the embryonic disc roll ventrally forming a cylindrical embryo
- Part of the yolk sac is incorporated as the midgut
- The splanchnopleure forms the wall of the gut
- The somotopleure forms the body wall
Neural tube defects
occur when neural pores stay open
Ancephaly
Neural tube defect, occurs when the anterior neuropore doesn’t close
Spina Bifida
Neural tube defect, occurs when the anterior neuropore doesn’t close
What prevents neural tube defects
Folic acid
What aids in the control of development
Retinoic Acid
Control of development
- embryonic tissues act as inductors and influence the development of adjacent tissues by passing signals to induced tissue
Placenta
Fetomaternal organ
- fetal: villus chorion
- maternal: decidua basalis of the endometrium
Amniochorinic cavity
result of the fusion of the amniotic cavity and the chorionic cavity
Erythroblastosis Fetalis
- Hemolytic disease of the newborn
- Rh incompatibility when there is a Rh+ baby and a Rh- Mother
Digestive tract
Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus
Accessory digestive organs
liver, gall bladder, pancreas
Primitive gut
straight tube consisting of the fore, mid, and hindgut
Derivatives of the forgeut
Pharynx, esophagus
Esophagus
developes caudal to the pharynx, is seperated from the trachea by the tracheoesophageal septum
Esophageal atresia
results from improper division of the trachea and esophagus, usually occurs with a tracheaesophageal fistula or failure of the esophagus to recanalize
(1/3000)
Stomach
- develops from the distal portion of the foregut
- enlarges and lies ventrodorsally
- dorsal border grows faster than the ventral border (U-shape)
- Rotates 90 degrees clockwise around the longitudinal axis (Cranial left, caudal right)
Cogenital pyloric stenosis
- Abnormal thickening of the pyloric sphincter, restricts movement of materials from the stomach into the small intestine
- Stomach becomes distended and projectile vomiting occurs
Omental Bursa
Also known as the lesser peritoneal sac
- Cavity formed when isolated clefts developed n the mesenchyme coalesce, forming the thick dorsal mesogastrium
Stomach enlargement
- Omental bursa expands and acquires an inferior recess of the omental bursa between the layers of the elongated dorsal mesogastrium (greater omentum)
Duodenum
- Develops from caudal/distal foregut in week 4
- Grows rapidly into a C-shaped loops that projects caudally
- Lumen becomes smaller & is temporarily obliterated due to proliferation of epithelial cells
- Vacuolation occurs as the epithelial cells degenerate
Duodenal Stenosis
- Due to the partial occlusion of the duodenal lumen
- Results from incomplete recanalization of the duodenum due to defective vacuolization
- Bile duct is connected to the duodenum, therefore the stomach’s contents, usually containing bile are vomited
Duodenal Atresia
- Complete occlusion of the duodenum
- Blockage occurs at the junction of the bile and pancreatic
Hepatocytes
derived from the endoderm
Hepatic Diverticulum
Liver bud, forms as an endodermal outgrowth from the foregut
- projects into splanchnic mesoderm and divides into cranial (liver) and caudal (gall bladder & cystic duct) parts
Cells derived from mesoderm
Hemopoietic/ fibrous tissue, Kupffer cells
Hemopoiesis
Formation of blood cells, occurs in week 6
What induces the liver bud outgrowth
secreted factors from cardiac mesoderm and te septum transversum
Site of liver bud outgrowth
hepatic field
What inhibits liver growth
factors secreted by noncardial mesoderm, ectoderm, notochord
What inhibits liver growth inhibitors
FGFs
FGFs
Fibroblast growth factors, secreted by cardiac mesoderm, inhibit liver growth inhibitors and stimulate bud outgrowth
BMPs
Bone morphogenic proteins, stimulate the action of FGFs
Development of the pancreas
Endodermal cells form dorsal and ventral pancreatic buds at the caudal end of the foregut, as the duodenum rotates the ventral bud is carried dorsally to lay posterior to the dorsal bud
Where is retinoic acid low
Pharynx
Where is retinoic acid high
rectum
Esophagus transcription factor
SOX1
Duodenum transcription factor
PDX1
Small intestine transcription factor
CDXC
Large intestine transcription factor
CDXA
Derivative of the midgut
Small intestine, proximal portions of the large intestine
When does the midgut herniate
week 6
Why does the midgut herniate
There isn’t enough room in the abdominal cavity
What does the cranial limb give rise to
Loops of the small intestine
What does the caudal limb give rise to
Parts of the large intestine
Rotation of the midgut loop
While it’s in the umbilical cord, it rotates 90 degrees counterclockwise around the axis of the superior mesenteric artery
When do the intestines return to the abdomen
Week 10
What happens when the intestines return to the abdomen
Reduction of the midgut hernia
Cogenital Omphalocele
Midgut hernia isn’t reduces and intestines remain in proximal part of the umbilical cord
1/5000
Ileal Diverticulum
Remnant of connection between midgut and yolk sac
2-4%
Derivatives of Hindgut
Distal portion of tranverse colon, descending colon, sigmoid colon, rectum, superior anal canal
Cloaca
Expanded terminal part of the hindgut
- Endoderm-lined chamber that is in contact with the surface enctoderm at the cloacal membrane
Proctoduem
anal pit
What is the cloacal membrane composed of
endoderm of the cloaca and ectoderm of the proctodeum
When does the cloaca partition
Week 7
Partitioning of the cloaca
By week 7, urorectal septum divides cloaca into ventral urogenital sinus and dorsal gastrointestinal part
When does the anal membrane rupture
End of week 8
What happens when the anal membrane ruptures
Brings the digestive tract into communication with the amniotic cavity
