embryology 2 Flashcards
define gastrulation
the stage following the implantation of the embryo into the endometrium. During this phase the bilaminar disc is converted into a trilaminar disc.
stomach formation
dilatation, differential growth of the tube to form the curvatures. There is then rotation, 90’ around the longitudinal axis, and then an anterior-posterior rotation
omental bursa formation
omental burse is produced by the rotation of the ventral and dorsal wall attachment of the stomach known as the mesogastrium, the dorsal portion is rotated along the longitudinal axis to the left to generate the omental bursa.
liver formation
liver primordium appears by the third week, outgrowth endoderm in the distal foregut. It grows into the septum transversum, the connection forms the bile duct and ventral outgrowth of the duct forms the gall bladder and cystic duct.
spleen development
end of the 4rth week, mesenchymal condensation develops in the dorsal mesogastrium near the body wall. 5th week it differentiates into the spleen, until week 14 it is a haematopoietic organ. 15-17 weeks become lobular and colonised with T-lymphocytes. Week 23 the B cell precursors arrive and becomes lymphatic.
pancreas formation
pancreas forms from 2 buds from the endodermal lining of the duodenum. As duodenum rotates the buds move closer. They fuse together.
mid gut formation
rapid elongation of the gut tube. Cephalic part of the primary intestinal loop becomes the distal duodenum, jejunum and proximal ileum. The caudal part of the primary intestinal loop will become the distal ileum, caecum, appendix, ascending colon, and proximal 2/3rd’s of the transverse colon. Begins 6th week around the axis of the superior mesenteric artery, rotation of 90’ degrees anti-clockwise. As it rotates the gut tube herniates into the extraembryonic cavity. Week 10 the intestinal loops begin to move the cord back into the abdominal cavity, jejunum enters first. The caecum is last part to re-enter, then there is further 180 degrees rotation anti-clockwise.
hind gut formation
terminal portion of the hindgut with the posterior part of the cloaca. The allantois enters the anterior part of the cloaca. The cloaca is endoderm lined cavity with ectoderm at its ventral boundary. Separating the two Is the cloacal membrane. Septum merges to cover the yolk sac and allantois, the embryo grows the tip of the urorectal septum lies close to the cloacal membrane. By week 7 the cloacal membrane ruptures opening the hindgut. The ectoderm of the anal canal proliferates closing the caudal end, week 9 the canal re-opens.
foregut abnormalities
incomplete separation results in oesophageal atresia and trachea-oesophageal fistula.
ventral bud fails to migrate around the duodenum causing an annular pancreas resulting in stenosis. Pancreatic migration results in accessory pancreatic tissue.
mid gut abnormalities
omphalocele herniation of abdominal viscera through the enlarged umbilical ring, failure of retraction. Gastrochisis herniation directly through the body wall into the amniotic cavity. Remnants of vitelline ducts forms the Meckel’s diverticulum, may form a fistula or ligament.
hind gut abnormalities
incomplete separation of the hindgut from the urogenital sinus by the urorectal septum resulting in a anorectal fistula, or imperforate anus.
describe the pharyngeal branches
series of arches that develop around the mouth and pharynx. They support the primitive pharynx and develop into the face and neck. 6 arches develop, but we are eventually left with 5. On the exterior is the ectoderm, in the middle is mesoderm forming cartilage and muscles, and endoderm on the inside forming pouches between the arches.
arch 1 forms and nerve
mandible + V3
arch 2 forms + nerve
styloid process + facial
arch 3 forms + nerve
greater horn of hyoid bone + glossopharyngeal
arch 4 forms + nerve
thyroid cartilage + superior laryngeal nerve
arch 6 forms + nerve
cricoid cartilage + recurrent laryngeal nerve
face development
face develops from 5 processes; 1 frontonasal process, 2 maxillary and 2 mandibular. Two mandibular processes fuse together in the midline. The ectoderm thickens from the frontal nasal process and invaginates to form the nasal pit. Medial growth of the nasal process forms the philtrum. The palate forms from the medial nasal process growing downward to form the primary palate, the maxillary process two palatine shelves grow inwards, and form a secondary palate.
cranial vault formation
cranial vault consisting of flat bones forms from membranous bones by membranous ossification. The base of the skull consists of irregular bones produced by endochondral ossification, and the viscerocranium is produced by the branchial arches and sensory capsules. They consist of somites that develop into cartilage and then ossify into bones.
head and neck developmental abnormalities
1st pharyngeal arch abnormality treacher collin’s syndrome
craniosynostosis.
cleft lip and palate.
development of the neural tube
following on from gastrulation then the formation of the three germ layers from the epiblast. There is the formation of the ectoderm which is the top layer that differentiates into the nervous system and the epidermis. There is migration of the ectoderm and thickening anterior to the primitive node to form the neural plate, is edges thicken and move upwards to form folds. They fuse at the midline to form a tube.
tube forms brain vesicles.
mesencephalon forms
(superior and inferior colliculi),
prosencephalon forms the
telencephalon (cerebral hemisphere, hippocampus, basal ganglia) and the diencephalon (thalamus, hypothalamus, pituitary gland, pineal),
telencephalon is the
telencephalon (cerebral hemisphere, hippocampus, basal ganglia)
diencephalon forms the
diencephalon (thalamus, hypothalamus, pituitary gland, pineal),
rhombencephalon forms the
forms the metencephalon (cerebellum, pons) and the myelencephalon(medulla).
metencephalon forms the
cerebellum and pons
myelencephalon forms the
medulla
CNS Neuroepithelium forms
most of the cells, and motor component of the spinal cord bar microglia which is produced by mesenchymal cells migrating.
Neural crest cells form
PNS neurones and glia, as well as the sensory aspect of the spinal cord
anterior neuropore closes around
25th day
posterior neuropore closes around
27th day
anencephaly is
the failure of the anterior neuropore to close, the skull fails to form resulting in brain tissue degeneration which is incompatible with life
encephalocele is
the herniation of tissue through a defect in the skull, a failure in closure of the rostral neural tube, it’s most frequent in the occipital region with variable degrees of deficits.
spina bifida is the
defective closure of the caudal neural tube, it affects the tissue overlying the spinal cord resulting in the non-fusion of the vertebral arches.
prenatal diagnosis of spina bifida
maternal blood screening; high levels of alpha fetoprotein 16-20 weeks
amniocentesis; AFP in amniotic fluid
US; anencephaly from 12 weeks, spina bifida from 16-20 weeks
what embryological tissue gives rise to the kidney
intermediate mesoderm gives rise to the kidney and the ureter, in particular it is the metanephros which gives rise to the definitive adult kidney, the metanephric blastema
metanephric blastema forms
the excretory tubules; bowman’s capsule PCT, loop of Henle, DCT
ureteric bud forms
From the ureteric bud we get the collecting portions of the kidney; collecting ducts, calyces, ureters.
cloaca forms
urethra and bladder
what part of the urogenital sinus forms the bladder
cranial part
trigone is developed from
The trigone is derived from the absorption of the caudal ends of the mesonephric ducts
ascent of the kidneys is stopped by
adrenal glands
abnormalities of kidney development
polycystic kidney, aberrant renal arteries, lobulated kidney, transposition of the kidney, horseshoe kidney, pancake kidney. May have a hourglass bladder or ectopia vesicae in which trigone and ureteric openings can be seen on the surface
