Embryology Flashcards
1
Q
3 Stages of Embryonic Development
A
- pre-embryonic: conception-day 14
- embryonic: day 14-end of 8th week
- fetal: end of 8th week to birth
2
Q
Pre-embryonic
A
- fertilization
- ovum released from ovary
- fertilization of ovum divides as it moves down the uterine tube into uterus
- morula (solid ball of cells) forms and then forms a cavity inside
- cells are now called blastocyst (hollow ball)
- blastocyst cavity: will become yolk sac which nourishes embryo until placenta is fully formed
- outer layer: trophoblast will become placenta
- inner layer: inner cell mass will become embryo; develops into embryonic disc which has 2 cell layers (ectoderm, endoderm, and a third layer later forms between as the mesoderm)
- blastocyst implants into endometrium
- mother doesn’t know she’s pregnant
3
Q
Embryonic Stage
A
- organs formed
- ectoderm: sensory organs, epidermis, and nervous system
- mesoderm: dermis, muscles, skeleton, excretory and circulatory systems
- endoderm: gut, liver, pancreas, and respiratory system
- neurulation occurs: folding process where neural plate forms neutral tube
4
Q
Fetal Stage
A
-nervous system develops more and myelination begins
5
Q
Formation of Nervous System
A
- occurs during embryonic stage
- two phases: phase 1-neural tube forms (day 21), develops into brain and spinal cord; phase 2-brain formation, begins when neural tube closes
6
Q
Neurulation
A
- neural plate: thickening of ectoderm, forms on surface of embryo and extends from head to tail, floor of amniotic sac and therefore bathed in amniotic fluid
- neural folds: 3rd week after fertilization
- neural tube: commences in neck region
- neuropores: closed off by end of 4th week, superior closes at 27 days, inferior closes at 30 days, closure coincides with establishment of blood supply
- neural crest: cells from neural folds; becomes cranial and spinal nerves and schwann cells
7
Q
Mantle
A
- by day 26 neural tube differentiates into 2 layers
- mantle layer: inner wall, contains cell body and becomes gray matter
- marginal layer: outer wall, contains processes of cells whose bodies are in gray and develops into white matter: axons and glial cells
8
Q
Neural Tube Defects
A
- anterior neural tube defect: anterior neuropores fail to close results in anencephaly
- posterior neural tube defect: posterior neuropores fail to close results in spina bifida or myelomeningocele
9
Q
Neurulation Pt 2
A
- walls of neural tube thicken to become the brain and spinal cord
- lumen becomes ventricular system and central canal
10
Q
Spinal Cord
A
- dorsal tube=alar plate: sensory neurons, receive dorsal nerve roots growing in from spinal ganglia, becomes dorsal horn
- ventral tube=basal plate: motor neurons, ventral nerve roots, becomes ventral horn
11
Q
Brain Vesicles
A
- prosencephalon: forebrain-made up of telencephalon (cerebral cortex, corpus stratum) and diencephalon (thalamus, hypothalamus, optic outgrowth)
- mesencephalon: midbrain-4th week=primitive brain folds at mesencephalon
- rhombencephalon: hindbrain made up of metencephalon (pons, cerebellum) and myelencephalon (medulla)
12
Q
Ventricular System
A
- neural canal dilates and forms ventricular system (next 4 parts)
- hemispheres=lateral ventricles 1 and 2
- diencephalon=3rd ventricle
- midbrain=cerebral aqueduct, for CSF
- hindbrain=4th ventricle anterior to pons, posterior to cerebellum
- choroid plexus: secretes CSF
13
Q
Cerebral Hemispheres
A
- by 14th week the frontal, parietal, temporal, and occipital lobes are identifiable
- insula only grows so much
- superior operculum (upper hat) covers insula top and inferior operculum covers bottom
- by 28th week the lateral, central and calcarine sulci are noticeable
14
Q
Hydrocephalus
A
- water on the brian
- excessive CSF in ventricular system
- imbalance between production and absorption of CSF
- congenital aqueductal stenosis
- obstruction of foramina from 4th ventricle to subarachnoid space: arnold-chiari malformation=herniation of part of cerebellum and brainstem into foramen magnum
- meningitis: adhesions may compromise CSF flow
- increased fluid leads to increased pressure on neural structures
- thinning of the bones of calvaria, prominence of forehead, atrophy of cerebral cortex and white matter, and compression of basal ganglia and diencephalon
- tx: early identification, pressure sensitive catheter or shunt into internal jugular vein
- shunt: can go into jugular vein or into peritoneum; can get blocked can lead to H/A, vomiting, memory impairment
15
Q
Microcephaly
A
- normal or slightly small calvaria
- fontanelles close during early infancy and sutures close during first year, brain is underdeveloped
- gross mentally impairments
- suture lines between skull plates not closed until 12-14 months
16
Q
Anencephaly
A
-failure of rostral neuropore to close during 4th week
-forebrain abnormal and calvaria defective
-due to abnormal structure and vascularization the nervous tissue undergoes degeneration
-brain is spongy mass consisting mostly of hindbrain structures with no bone or skin covering
-lethal
-accounts for 1/2 of severe neural tube defects: most common severe anomaly seen in stillborn fetuses
-causes: genetic factors; high exposure to nickel, chromium, lead, mercury; higher in areas where depleted uranium and man-made isotopes; can be induced in rats by teratogenic agents
-prevention: folic acid .4 mg/day before pregnancy
-dx: ultrasound, alpha-fetoproteins in amniotic fluid
fetal counterpart to serum albumen, increased in neural tube defects, decrease in down syndrome
17
Q
Naturally Occurring Folate
A
- beans and legumes
- citrus fruits and juices
- wheat bran and other whole grains
- dark green leafy vegetables
- poultry, pork, shellfish
- liver
18
Q
Arnold-Chiari Malformation
A
- most common congenital anomaly involving the lower brainstem and cerebellum
- structural defect of the cerebellum with herniation of the medulla and part of cerebellum through foramen magnum
- may cause hydrocephalus
- occurs 1+/1000 births and is frequently associated with spina bifida and syringomyelia
- S&S: neck pain, balance problems, muscle weakness, numbness of other abnormal feelings in arms or legs, dizziness, vision problems, difficulty swallowing, ringing or buzzing ears, hearing loss, vomiting, insomnia, depression, or H/A made worse by coughing or straining
- hand coordination and fine motor skills may be affected
19
Q
Spina Bifida
A
- nonfusion of embryonic halves of vertebral arches during 4th week
- types: spina bifida occulta, spina bifida cystica (with meningocele, or with myelomeningocele), spina bifida with myelocele
20
Q
Spina Bifida Occulta
A
- usually clinically unimportant
- occurs in L5 or S1 in about 10% of otherwise normal people
- small dimple with tuft of hair
- small percentage may have functional deficits
- vertebra don’t close completely
21
Q
Spina Bifida Cystica
A
- cystlike sac: covered by skin or a thin, easily ruptured membrane; most common in lumbar region
- causes: combo of genetic and environmental factors-DM and anticonvulsant medication, fever or external temperature during neural tube development, obesity
- 75% have latex allergies
- 1/1000 births
- 10% cyst in meningocele
- 90% cyst is myelomenigocele
22
Q
Spina Bifida with Meningocele
A
- protrusion of meninges through a defect in the vertebral arch
- varying levels of functional deficits depending on lesion site and extent of herniation
- high alpha-fetoproteins
23
Q
Spina Bifida with Myelomeningocele
A
- protrusion of the meninges and spinal cord through a defect in vertebral arch
- marked neurologic deficit inferior to the level
- more serious than meningocele
- paralysis=lower limb, bladder and bowel
- learning disability common
- prevention: folic acid prior to conception
24
Q
Spina Bifida with Myelocele
A
- most severe form of spina bifida
- neural folds have remained open
- CSF leaks out
- clinical outlook poor
25
Q
Cranium Bifidum
A
-herniation of brain and/or meninges
26
Q
Factors Affecting Brain Development
A
- genetic: down syndrome; brachycephaly (flat head on back)
- maternal infection: congenital rubella-mental retardation; toxoplasmosis-microcephaly, hydrocephalus, cerebral calcification
- plagiocephaly: flat head on one side
- environmental factors: radiation (cell depletion), steroids, chemical substances-alcohol (microcephaly), smoking (smaller frontal lobes and cerebellar volumes), marijuana (impairs nerve development and guidance-permanent cognitive deficits, concentration disorders, hyperactivity)
