L35

Question 1

what is the function of notochord in the third week ?

Answer 1

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.

Question 2

Abnormal Remnant of notochordal tissue cause ?

in normal condition after the notochord does its function it should disappear

Answer 2

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

Question 3

formation of the primitive streak [in epiblast] defines all major body axes
what are these body axes ?

Answer 3

• 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.

Question 4

Abnormal sidedness: Due to failure of establishing normal Left-Right asymmetry:
these abnormalities include ??

Answer 4

• Situs inversus totalis (1 in 10,000). - Dextrocardia.

- Laterality sequences (situs ambiguous).

Question 5

What is neurulation?

Answer 5

The process by which the neural plate, neural folds, and neural tube form.

Question 6

Describe neurulation, and state which week it occurs?

Answer 6

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

Question 7

➢Fusion begins at X and proceeds cranially and caudally, forming the Y

Answer 7

X=cervical region
Y=neural
tube

Question 8

➢Until fusion is complete, the cephalic and caudal ends of the neural tube communicate with the amniotic cavity with the anterior (cranial) and ??

Answer 8

posterior (caudal) neuropores,

respectively

Question 9

TRUE OR FALSE

Broader cephalic portion of the neural tube forms the brain and the narrow caudal portion forms the spinal cord

Answer 9

true

Question 10

When does the anterior and posterior neuropore close?

Answer 10

Anterior neuropore - 25 (4th week)

Posterior neuropore- 28 (end of 4th week)

Question 11

Give some examples of neural tube defects NTDs [3-4 weeks] and their causes

Answer 11

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

Question 12

How can 70% of neural defects be prevented?

Answer 12

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

Question 13

What are the 3 main subdivisions fo the mesodermal germ layer?

Answer 13

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

Question 14

true or false

i can know the embryo age be count his somites number ?

Answer 14

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.

Question 15

Each somite has 3 parts??

Answer 15

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.

Question 16

➢Intermediate mesoderm contributes to the formation of the

X and genital (gonads and ducts) systems

Answer 16

X=urinary

Question 17

What is the function of the lateral plate mesodermal layer?

Answer 17

Small cavities appear in the lateral space mesoderm, which merge and form a large cavity called INTRAembryonic coelom.
The Intraembryonic coelom splits the lateral plate mesoderm into 2 parts;
Somatic mesoderm- which give rise to bones, ligaments, blood vessels, abs connective tissue of the lungs and the parietal layer of the serous membranes.
Splanchnic mesoderm- formed the SMOOTH muscles of Wall of the GIT and respiratory organs of the visceral layer of the serous membranes

Question 18

Blood cells and blood vessels arise from which of the 3germ layers?

Answer 18

MESODERM