Embryology Week 7 - Key Concepts and Definitions

T or F: Somites are more strongly segmented than somitomeres

True

What is the name of the area where new somites form?

Presomitic zone

How many new pairs of somites form every day?

3

How many pairs of somites are present by the end of the 5th week?

43

What area of the axial skeleton contains somitomeres instead of somites?

Cranial region

How many pairs of somitomeres are in the cranial

7

How many pairs of somites are in the occipital region?

4

How many pairs of somites are in the cervical region?

8

How many pairs of somites are in the thoracic region?

12

How many pairs of somites are in the lumbar region?

5

How many pairs of somites are in the sacral region?

5

How many pairs of somites are in the coccygeal region

2

What do somites give rise to?

Axial skeleton (including spine and skull)

Muscles of the axial skeleton

Most of the body's dermis

Dura and its blood vessels

Auditory ossicles and hyoid

What genes inhibit somitogenesis?

FGF-8 and Wnt

What region is FGF-8 and Wnt turned off in?

Presomitic zone

What occurs if FGF-8 and Wnt are turned off in mesoderm aside from the presomitic zone?

Lack of growth/mitosis

Which gene product turns off FGF-8 and Wnt?

Retinoic acid

Where is retinoid acid first produced?

The first somite

What is the wavefront model?

the paraxial mesoderm of the embryonic disc has a gradient of FGF-8 and Wnt and retinoic acid going on within it

Which gene responsible for somatization is turned on in presomitic tissue?

Notch gene

What gene is activated alongside notch?

Mesp-2

Which transcription factors are produced by Notch gene?

Lunatic fringe

C-hairy

What is secreted by somites to prevent them from sticking together?

Ephrin B

What is the name of the fissure between somites created by Ephrin B?

Intersomitic fissure (space)

What is the last step of somite formation?

mesenchymal-to-epithelial conversion

What is expressed from ectodermal cells overlying the new somites to begin mesenchymal-to-epithelial conversion?

Wnt-6

What gene does Wnt-6 turn on in somites?

Paraxis gene

What gene is downregulated by paraxis gene?

Snail gene

What occurs in somites when Snail is turned off?

mesenchymal-to-epithelial conversion

What is the first step of interlomite differentiation?

Comitocoel formation

What is the process where epithelial cells in the middle of the somite are renamed to simtocoel cells?

Circling the wagons

What is the name of the lumen between the somitocoel cells?

Simitocoel

What do the somitocoel cells develop into?

Annulus fibrosus( Including lamellae)

The articular facets surfaces of the Z joints

What secretes sonic hedgehog gene and noggin?

Notochord and neural tube

What do sonic hedgehog gene and noggin bind to?

Ventromedial somite

What two genes are activated by the binding of hedgehog and noggin to ventromedial somite cells?

Pax-1

Pax-9

What is Pax-1 used to form?

Bone and cartilage of vertebra

What is the effect of pax-1 and pax-9 on the somites?

Causes them to morph back into mesenchymal cells

What is the name of somites that have morphed back into mesenchymal cells?

Secondary mesenchymal tissue

What is the name of cells are the secondary mesenchymal cells within the ventromedial somite?

Sclerotome cells

What does the sclerotome give rise to in general?

Vertebrae

Ribs

What specifically does the sclerotome give rise to?

Ventral region

Dorsal region

Central region

Lateral region (syndetome)

Medial region (meningotome)

What are the components of the ventral region?

Vertebral bodies

Cartilaginous endplates

Some parts of the annulus fibrosis

How many sclerotomes are required to make the ventral region?

2

What are the components of the dorsal region of the sclerotome?

Spinous process and laminae

What are the components of the central region of the sclerotome?

Superior and inferior articular processes (articular pillars)

Pedicles

transverse processes

proximal ribs

What are the components of the lateral region of the sclerotome?

Distal ribs and some tendons for intrinsic muscles of the back

What are the components of the medial region of the sclerotome?

meninges (dura, arachnoid, pia mater)

Blood vessels of the meninges

What is the AKA of the lateral region of the sclerotome?

Syndetome

What is the AKA of the medial region of the sclerotome?

Meningotome

What important molecules of the IVD are derived from the sclerotome?

Glycosaminoglycans

Core proteins

What are normal disc biomechanics dependent on?

Proteoglycans

What are proteoglycans made of?

Glycosaminoglycans (GAGs)

What % of the nucleus pulpsosus is water?

80%

T or F: GAGs are extremely hydrophobic

False (they are extremely hydrophilic)

What is the shape of the nucleus pulpous?

Ball-bearing

What is the pivot point of the motion segments of the spine, where all spinal range of motion occurs?

Nucleus pulposus

What changes occur due to an annular tear?

Center of gravity shifts to the posterior part of the disc

With time, this change overloads and wears out the Z joints

Premature disc degeneration

Which gene products are turned on by Wnt in the dermomyotome?

Pax-3

Pax-7

Paraxis genes

What type of tissue is on the edges of the dermomyotome?

Mesenchymal tissue

What type of tissue is in the center of the dermomyotome?

Epithelial tissue

What two layers are formed by the migration of the mesenchymal ends of the dermomytoome beneath the epithelial center?

Myotome

Dermatome

What does the dermatome give rise to?

Dorsal dermis of the trunk

What gives rise to the lateral trunk dermis and dermis of the limbs?

Lateral plate mesoderm

Which non-dermal tissues arise from the central region of the dermatome?

Certain skeletal muscles

brown fat

Where is most of the epidermis derived from?

Ectoderm

What parts of the skin is the stratum lucidum found in?

Glabrous skin (palms and soles)

What are somite cells called while segregating?

Somitocoel cells

What, generally, does the myotome become?

Abdominal wall muscles

Intrinsic back muscles (everything but the lats and traps)

Almost all muscles of upper and lower extremities

What does the medial myotome become?

intrinsic back muscles

extensor muscles of the limbs

Which muscles of the back are not considered intrinsic?

Trapezius

Latissimus dorsi

What does the lateral myotomebecome?

muscles of the ventrolateral body wall

Flat abdominal muscles

(External oblique, internal oblique, transversus abdominis muscle)

Rectus abdominis and pyramidalis

Flexor muscles of the limbs

T or F: The extensor muscles of the extremities come from the lateral myotome while the flexor muscles of the extremities come from the medial myotome

False (the flexors come from the lateral and the extensors come from the medial)

What do somitocoel cells give rise to?

Part of the annulus fibrosus

Facet joint articular surfaces and proximal ribs (and central region of sclerotome)

What other miscellaneous structures are somites capable of differentiating into?

Blood vessels

Adipocytes

Chondrocytes

Osteocytes

Endothelial cells of vessels

Pericytes

Fibroblasts

Myocytes (skeletal and smooth)

Nervous system cells