L35 Flashcards
what is the function of notochord in the third week ?
Defines the primordial longitudinal axis of the embryo and gives it some rigidity.
- Induces the overlying ectoderm to differentiate into neuroectoderm to form the neural tube.
- Induces the formation of the vertebral bodies.
- Forms the nucleus pulposus of each intervertebral disc.
Abnormal Remnant of notochordal tissue cause ?
in normal condition after the notochord does its function it should disappear
chordoma it a disease that cause rare slow growing bone tumor and it most common location are
the base of the skull and sacrum or coccyx
formation of the primitive streak [in epiblast] defines all major body axes
what are these body axes ?
• Cranial- caudal axis:[head -tail] The primitive streak forms in the caudal midline of the embryonic disc, thus defining the cranial-caudal axis.
• Medial-lateral axis:[ medial =near primitve streak]
lateral=away from it
• Dorsal- ventral axis: At the time of primitive streak formation, the future dorsal-ventral axis of the embryonic disc is roughly equivalent to its ectoderm-endoderm axis. Later, with body folding the dorsal-ventral axis becomes better defined.
• Left- Right axis: when the epiblast is viewed looking down at it from inside the amniotic cavity, what lies to the right of the primitive streak represents the right side of the embryo and what lies to the left represents its left
side. Thus, formation of the primitive streak also defines the left-right axis.
Abnormal sidedness: Due to failure of establishing normal Left-Right asymmetry:
these abnormalities include ??
- Situs inversus totalis (1 in 10,000). - Dextrocardia.
- Laterality sequences (situs ambiguous).
What is neurulation?
The process by which the neural plate, neural folds, and neural tube form.
Describe neurulation, and state which week it occurs?
The ectodermal cells overlying the notochordal process becomes thick to form the neural plate It develops in the midline The neural plate becomes depressed along the midline to form the neural groove The two edges of the neural plate come nearer to each other to fuse, thus converts the neural groove into neural
tube
NEURAL PLATE-NEURAL GROOVE -NEURAL TUBE
➢Fusion begins at X and proceeds cranially and caudally, forming the Y
X=cervical region
Y=neural
tube
➢Until fusion is complete, the cephalic and caudal ends of the neural tube communicate with the amniotic cavity with the anterior (cranial) and ??
posterior (caudal) neuropores,
respectively
TRUE OR FALSE
Broader cephalic portion of the neural tube forms the brain and the narrow caudal portion forms the spinal cord
true
When does the anterior and posterior neuropore close?
Anterior neuropore - 25 (4th week)
Posterior neuropore- 28 (end of 4th week)
Give some examples of neural tube defects NTDs [3-4 weeks] and their causes
Anencephaly- [neural tube fails to close in the cranial region ] open brain and lack of skull vault (anterior neuropore did not close on day 25) V Poor prognosis
Myelomeningocele - open spinal chord with meningeal cyst (posterior neuropore did not close on day 28)
Spina bifida occulta -asymptomatic condition in which vertebra are not completely closed
Meningocele- protrusion of the meninges without spinal cord
How can 70% of neural defects be prevented?
By taking folic .4mg of folic acid daily beginning 3 months before conception and taking it throughout pregnancy.
If the family has a history of NTD increase dose to 1mg
17
What are the 3 main subdivisions fo the mesodermal germ layer?
1-Paraxial mesoderm -➢On 17th day, cells close to the midline form a thickened plate known as paraxial
mesoderm (future somites)
2-Intermediate mesoderm-connects paraxial and lateral plate mesoderm
3-Lateral plate mesoderm -➢On 19th day, more laterally the mesoderm layer remains thin and is
known as lateral plate
true or false
i can know the embryo age be count his somites number ?
true bcz somites, first appear in the cephalic region on the 20th day and their formation
proceeds craniocaudally, 3 pairs /day
The number of somites that develop over a given period can be correlated to the approximate age of the
embryo.
Each somite has 3 parts??
Sclerotome: Cells of the sclerotome migrate medially to surround the neural tube to give rise to vertebrae and ribs Dermatome: Cells migrate to the under surface of the ectoderm to give rise to dermis of the skin and subcutaneous tissue
Myotome: They give rise to skeletal muscles of the body wall and limbs.