16. Embryology: Major Organ System Development Flashcards
What do the following layers become?
a) Endoderm
b) Mesoderm
c) Ectoderm
What has happened by the end of week 3 of intrauterine development (week 3 of 3’s)?
When does the development of the major organ systems occur?
a) Digestive system, liver, pancreas, lungs (inner layers)
b) circulatory system, kidney, lungs (epithelial layers), skeletal system, muscular layers
c) hair, nails, skin, nervous system
Well implanted into uterine wall via tertiary villi of placenta. Gastrulation has produced ectoderm, mesoderm and endoderm. All body axes are specified. Heart beating. 1mm length.
Week 4-8. After that enter foetal period = growth.
Describe how development of the nervous system begins.
What is the notochord and what does it do?
What are the 4 different types of mesoderm at this stage?
Where does the CNS form?
Ectoderm cells invaginate at midline, go into mesoderm and push cells out. [pic]
Notochord = rod of mesoderm. Signals to ectoderm above, mesoderm either side and endoderm below it via a concentration gradient of growth factors. Specifies structures down the midline, and what is dorsal and ventral.
Paraxial: paralell to notochord, forms vertebrae and ribs, back and body wall muscles. Intermediate: forms kidneys. Lateral: forms CT in bones and limbs, and anterior body wall muscles/CT. Extraembryonic.
Ectoderm above notochord (at head end forms brain and at tail end forms SC).
How does the peripheral NS form?
Describe neuralation (week 4).
Neural crest forms (later becomes PNS) forms between CNS running down midline and more lateral epidermal cells (that become epidermis). It’s a small group of cells at the intermediate junction.
[Caused by signals from notochord.] Cells in ectoderm running down midline start to change shape and become columnar (rest are cuboidal). Columnar cells start to change shape: actin fibres constrict and form neural groove which runs the whole length of the embryo. Groove gets bigger and deeper by day 20 and is almost completely closed. Neural crest cells undergo change from epthelial -> mesenchyme and become migratory, moving out of the ectoderm and migrating off to become PNS. The groove pinches off and cuboidal epithelium reforms leaving complete neural tube underneath. The central area will form the brain and SC.
Apart from the PNS, what else does the neural crest form?
How does the neural groove close?
Give 2 congenital defects that arise from incorrect neural groove closure.
Sensory neurons, PNS glia, enteric NS, sympathetic ganglia, adrenal medulla, melanocytes. Cartilage, teeth, CT and bone of skull.
Closure starts in midline and moves posteriorly and anteriorly.
Spina bifida: failure of closure of posterior neural pore. Anencephaly: failure of closure of anterior neural pore = skull doesn’t close fully.
Describe branchial/pharyngeal arches.
What cranial nerves are assocaited with pharyngeal arches 1-4?
What do the archs form?
What do the pouches form?
Rods of tissue, same epithelial coating: ectoderm on outside (forms skin) and endoderm on inside (forms gut and mouth). In middle = undifferentiated mass, mix of neural crest, mesoderm, nerve (cranial nerve), BV. Remnants of gill apperatus from ancestors.
1: trigeminal. 2: facial. 3: glossopharyngeal. 4: vagus.
1: external auditory meatus. The rest = neck.
1: middle ear auditory tube. The rest = glandular tissue.
What is a branchial cleft cyst?
Describe how the face develops during week 5-7.
What does the primary palate consist of?
Congenital epithelial cyst, arises on the lateral part of the neck (along anterior border of SCM) usually due to failure of obliteration of the second branchial cleft (or failure of fusion of the second and third branchial arches) in development. Can get blocked and need draining.
Eyes on side of head first, mandible forms lower jaw, lots of cell death down midline of face -> narrows and by week 10 - looks like face. Eyes dragged onto front so faceforward. Maxilla merges with nose. Groove = fusion point.
Philtrum and 4 central incisor teeth.
How does the secondary palate develop?
What causes a cleft lip?
What causes a cleft palate?
Maxillary palatal shelves grow initially inferiorly either side of tongue, then rotate horizontally when toungue moves into throat. Soft muscle = uvula.
Failure of maxilla to fuse with the medial nasal prominence. Cleft between philtrum and rest of upper lip and between central and lateral incisors. Or not enough tissue has grown to allow fusion, or timing mismatch. Easy to correct but leaves defect of obicularis oris. Can be unilateral/bilateral/with or without cleft palate
Failure of palatal shelves to fuse (from maxillary prominences). Tongue too large/ shelves rotate upwards too late/ shelves too small to touch/ failure of ectoderm to break down and allow fusion
What are the following congenital defects and what are they caused by?
L = spina bifida**: failure of closure of posterior neural pore. **R = anencephaly: failure of closure of anterior neural pore = skull doesn’t close fully.
What forces primitive heart tubes into thoracic cavity?
Describe heart development.
What do the foetal shunts become after closure after birth?
Cranial folding. Lateral folding means tubes lie closer to each other and begin to fuse. NB: primitive heart forms above brain!
1st organ to work (starts pumping day 22). Tubes fuse and form simple tubes. Connects with umbilical arteries and vein. Ends of tubes and cavity it’s in is fixed which forces tube to bend, twist and loop around as it grows = chambers in correct position. Atria seperate. Outflow track partitioned into pulmonary trunk and aorta.
Foramen ovale (between 2 atria) = fossa ovalis. Ductus arteriosus = ligamentum arteriosus.
What are the different types of acyanotic and cyanotic cogenital heart defects?
When do limbs develop?
What are some common limb defects?
[pic] Acyanotic: blood moves L -> R. Cyanotic: blood moves R -> L.
Week 5-8, lots of cell death occurs to shape hands and feet
Missing muscles, syndactyly (no cell death), polydactyly (more digits)
Determine the following 3 outflow defects?
L: transposition of great vessels - pulmonary trunk coming out of L vein. Hypertrophy of R ventricle.
Middle: persistant truncus arteriosus - mixing O2 and unO2 blood, acyanotic
R: tetralogy of fallot, aorta 3x size it should be and pulmonary trunk v small, R sided hypertrophy of walls, cyanosis becuase 2 parallel systems of O2 and unO2 blood
What happens to the 3 overlapping kidney systems in week 5?
Describe kidney development.
How does the gut form?
Pronephros: completely regresses. Mesonephros: upper thoracic to lumbar (L3). Functional from 6-8 weeks. In males the mesonephric duct remains (ductus deferens). Regresses in females. Metanephros: uteric bud (outgrowth of mesonephric duct) grows into metanephic tissue.
Functional from week 7 onwards. Sacral to lower lumbar move and migrate upwards to lower thoracic level, migrate until hit adrenal gland.
Lateral folding from week 3-4 pinches off endoderm so have endodermal tube running full lenght of embryo = GI system.
What are the following kidney defects?
L: horseshoe kidney
Middle: pelvic kidney
R: bifid ureter
What are the derivatives of the primitve gut tube, the blood supply and the borders?
How does the stomach form? What innervates the anterior and posterior walls?
How does the midgut form?
Foregut: aortic arch and coeliac artery. Pharynx -> superior half of duodenum.
Midgut: superior mesenteric. Inferior half of duodenum -> right 2/3rd of transverse colon.
Hindgut: inferior mesenteric. Left 1/3 of transverse colon -> rectum.
Rotates 90o around craniocaidal axis so greater curvature lies to left and lesser to right. Left vagus innervates anterior wall and right vagus innervates posterior wall.
Liver takes up too much space in abdomen = not enough space for gut developement so it goes into the umbilical cord = physiologically herniates through the umbillicus at week 6, rotates alot (about 270o), then herniates back in at week 8.
Gut malrotation is common. What is nonrotation?
Distinguish between intraperitoneal and secondary retroperitoneal.
Congenital anomaly of intestines = small bowel occupies right side of peritoneal cavity and colon predominantly on left. Can be problem if mesoderm tightens and blocks flow of food to lower intestines. Ascending colon shortens and forms Ladd’s bands. Loops of intestine can twist around and digest self.
Intraperitoneal: at first all parts of small and large intestines have a mesentery from which they are suspended. After completion of gut rotation the mesenteries shorten and fuse with posterior abdominal wall for the duodenum (pancreas), ascending colon and descending colon. These are 2o retroperitonal b/c they grew in intraperitoneal space but became extraperitoneal later in development.
What is this gut defect? Explain it.
Omphalocele/exomphalos: failure of umbilicus to close completely combined with failure of mid-gut to herniate back into abdominal cavity fully.
What are these gut defects? Explain them.
Top 2: vitelline duct abnormalities. 2-4% have small portion of vitelline duct forming outpocketing of ileum. Can become blocked and lead to trapped food and appendicitis but usually no symptoms.
Bottom 3: gastroschisis, usually to R of umbilical cord. Body wall muscle doesn’t form - lateral mesoderm doesn’t close properly. Gut not protected. More prone to infections and dehydrated. Covered with plastic silo.
