Embryonic Period (Weeks 3-8) - HY Flashcards Preview

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Flashcards in Embryonic Period (Weeks 3-8) - HY Deck (34):

Which complex of genes controls the basic segmentation of the human embryo in a craniocaudal direction, during the embryonic period?

The Hox (homeobox) complex of genes.


Why does embryogenesis proceed at a slower pace in female embryos?

Due to the presence of the paternally imprinted X chromosome.


What is basically the gastrulation?

A process that establishes the 3 primary germ layers, thereby forming a trilaminar embryonic disk.


As early as the bilaminar and trilaminar stages of embryogenesis, how does L/R axis determination begin?

With the ASYMMETRIC activity of sonic hedgehog (shh) only on the future left side since shh activity is suppressed on the future right side by ACTIVIN.


Which neurotransmitter plays an important role in L/R determination?



To what does ectoderm give further rise?

To neuroectoderm and neural crest cells.


To what does the mesoderm give rise?

1. Paraxial mesoderm (somitomeres and 35 pairs of somites).
2. Intermediate mesoderm.
3. Lateral mesoderm.


To what does the endoderm give rise?

Remains intact.


To what do the somites segment?

1. Into sclerotome
2. Into myotome
3. Into dermatome


What does the sclerotome form?

Axial cartilage and bone.


What does the myotome form?

Axial muscle.


What does the dermatome form?

The dermis of the skin.


What does the intermediate mesoderm form?

The urogenital system.


To what is the lateral mesoderm split and how?

Split into 2 layers:
1. Somatic layer
2. Splanchnic layer
by the formation of the intraembryonic coelom.


What forms the embryonic body wall or somatopleure?

The somatic layer of lateral mesoderm + ectoderm.


What forms the embryonic gut tube or splanchnopleure?

The visceral layer of the lateral mesoderm + endoderm.


True or false? All adult cells and tissues can trace their embryological origin back to the 3 primary germ layers.



What are the derivatives of the ectoderm?

1. Epidermis, hair, nails, sweat + sebaceous glands.
2. Adenohypophysis
3. Epithelial lining of the lower anal canal
4. Epithelial lining of the distal part of male urethra
5. Epithelial lining of the external auditory meatus


What are the derivatives of the mesoderm?

1. Muscle (smooth, cardiac, skeletal)
2. Muscles of tongue (occipital somites)
3. Connective tissue
4. Dermis + subcutaneous layer of skin
5. Bone and cartilage
6. Dura mater
7. Endothelium of blood vessels
8. RBCs, WBCs, microglia + Kuppfer cells
9. Kidney + adrenal CORTEX


What are the derivatives of the endoderm?

1. Hepatocytes
2. Acinar + islet cells of pancreas
3. Epithelial lining of the GI
4. Of trachea, bronchi, lungs
5. Of biliary apparatus
6. Of urinary bladder
7. Female urethra
8. Most of male urethra
9. Inferior 2/3 of vagina
10. Auditory tube + middle ear cavity


What are the derivatives of the neuroectoderm?

1. All neurons within brain and spinal cord (CNS).
2. Retina
3. Optic nerve
4. Dilator and sphincter pupillae muscles
5. Astrocytes, oligodendrocytes, ependymocytes, tanycytes, choroid plexus cells
6. Neurohypophysis
7. Pineal gland


What are the derivatives of the neural crest?

1. Neurons within ganglia (dorsal root, cranial, autonomic)
2. Scwann cells
3. Pia and arachnoid
4. Adrenal medulla
5. Melanocytes
6. Aorticopulmonary septum
7. Bones of the neurocranium
8. Pharyngeal arch bones (maxilla, mandible, malleus, incus)


What is the chordoma?

Either a benign or malignant tumor that arises from remnants of the notochord.


What is the usual location of the chordoma?

Either intracranially or in the sacral region.


When does chordoma usually occur?

In men late in adult life.


What is the age of the embryo at the time of the first missed period?

Already undergone 2 weeks of development.


Why is it crucial that a woman become aware of a pregnancy as soon as possible?

Because the embryonic period is a period of high susceptibility to teratogens.


What incr. risk do children whose mothers have been treated for depression with SSRIs?

Incr. risk of heart malformation --> probably due to the role of serotonin in L/R axis determination.


What is the sacrococcygeal teratoma?

It is a tumor that arises from remnants of the primitive streak, which normally degenerates and disappears.


Where is sacrococcygeal teratoma more commonly found?

In female infants and usually becomes malignant during infancy (must be removed by age 6 months).


To what does sirenomyelia (caudal dysplasia) refer?

Constellation of syndromes ranging from minor lesions of lower vertebra to complete fusion of the lower limbs.


What is the cause of caudal dysplasia?

Caused by abnormal gastrulation, in which the migration of mesoderm is disturbed --> associated with various cranial anomalies.


What is the VATER syndrome of caudal dysplasia?

Vertebral defects
Anal atresia
TracheoEsophageal fistula
Renal defects


What is the VACTERL syndrome of caudal dysplasia?

Similar to VATER, but also includes:
Cardiovascular defects
upper Limb defects.