Embryology Flashcards

1
Q

What is Ovum Factor?

A

Signal from the zygote at 3-5 hours telling the mother’s immune system not to attack it

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2
Q

What is EPF?

A

Early Pregnancy Factor. Released by the zygote at 24 hours, this protein further suppresses the mother’s immune system.

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3
Q

What two signals are absolutely necessary for implantation to take place?

A

Ovum factor and EPF

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4
Q

When does implantation occur?

A

6 - 10 days

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5
Q

What is the bilaminar disc and when does it form?

A

Forms at 12 days. It is the source of all future tissues in the body, including MSK tissues.

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6
Q

What comprises the bilaminar disc (i.e., why is it called bilaminar)?

A

It is two layered. Has an epiblast cellular layer and a hypoblast cellular layer

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7
Q

What occurs at 15 days?

A
  1. Epiblast cells detach and migrate to the primitive streak 2. When they arrive, they submerge and fan out between the two layers to become the endoderm, mesoderm, and ectoderm. This migration and sorting is called gastrulation
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8
Q

Primitive streak?

A

Deep groove and portal for the rapidly moving cells to enter, submerge beneath the epiblast layer, and stream cranially. Displacing the hypoblast cells, these migrating cells become the mesoderm.

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9
Q

Primitive node?

A

Acts on the migrating cells via specific factors, and after the modified cells reach their destinations, they attach, grow, and become specific organs of the body.

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10
Q

Common condition caused by EtOH uptake during gastrulation

A

Holoprosencephaly - Forebrain fails to develop into two hemispheres, usually leading to death before birth. Those that live will range in symptoms, but most have defects in the face and brain along with brain function.

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11
Q

Common condition associated with taking seritonin reuptake inhibitors for depression and axiety

A

Caudal Dysgenesis - Malformation/lack of formation of tailbone or lower vertebrae

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12
Q

During development, what do we see at 21 days?

A

2 distinct layers: Ectoderm, mesoderm, and endoderm

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13
Q

Where does the MSK system develop from SPECIFICALLY?

A

Paraxial and lateral plate mesoderm (which later becomes mesenchyme) + neral crest cells

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14
Q

What are somitomeres?

A

Pairs of tissue blocks formed from the loose masses of paraxial mesoderm alongside the neural tube. Some are destined for the head region and some eventually become the somites of the body wall and limbs

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15
Q

What is longitudinal folding, when does it occur and what does it cause?

A

Longitudinal folding occurs at Days 17-28 and involves bringing the structures of the heart ventrally. Differential growth will further position these structures in the right places.

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16
Q

What is lateral folding, when does it occur?

A

Lateral folding occurs simultaneously to longitudinal folding at 15-21 days. It involves layers migrating ventrally to pinch off part of the yolk sac which forms the alimentary canal, and also forms the body wall.

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17
Q

What is the segmentation clock?

A

Cyclic waves of expression and suppression from extremely specialized genes

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18
Q

Stages of Somite progression:

A
  1. Start as initially solid clumps of mesodermal cells 2. Hollow out, migrate and differentiate into MSK precursors of bone, muscle, connective tissues and skin
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19
Q

Abaxial Myotome

A

Becomes the ventral muscles of the limb and body wall

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20
Q

Primaxial myotome

A

Becomes the dorsal muscles of the back

21
Q

Sclerotome

A

Becomes the skeleton

22
Q

Intermediate Strip

A

Becomes the dermis of the neck, back, and trunk

23
Q

Two meanings for Dermatome:

A
  1. Part of a somite 2. Strip of skin innervated by one spinal segment
24
Q

Developmental layers that make up the axial skeleton

A

Sclerotome, which si the paraxial and lateral plate mesoderm and the cephalad part of the neural crests which makes up the brain case

25
Q

Folic Acid supplements during development can help with what?

A

Preventing spina bifida occulta

26
Q

What is meningocele?

A

Interruption of the development process causing the midline to not fully close

27
Q

Pectus Excavatum

A

Thought to be related to an overgrowth of the rib cartilages

28
Q

When do limb buds appear?

A

4 weeks

29
Q

When does limb rotation occur?

A

7-8 weeks

30
Q

Upper limb rotations at 7 weeks?

A

Rotate laterally so that the thumbs are positioned on the radial side and the elbows point posteriorly (palms up)

31
Q

Lower limb rotations at 7 weeks?

A

Rotate medially so that the great toes are medial and the knees point anteriorly (soles down)

32
Q

What programs limb growth?

A

AER - Apical Ectodermal Ridge

33
Q

What does the AER do SPECIFICALLY?

A

Induces outward growth along the limb axis and is present by day 29.

34
Q

What is the “progress zone?”

A

Subjacent to the AER, this strip contains coordinating cells.

35
Q

Processes of Endochondral Ossification:

A
  1. Mesenchymal cells condense into chondrocytes which move into patterns to form the shape of the future bone. 2. Angiogenesis occurs 3. Epiphyseal plates are formed 4. Osteoblasts differentiate and bind in a pattern, leading to production of the osteoid which is then mineralized into bone.
36
Q

What causes syndactyly?

A

When apoptosis between the AER segments fails, leading to fusion of the fingers.

37
Q

What is intramembranous ossification?

A

Ossification process of the skull. Radiating bone spicules coalesce into flat bones

38
Q

What is the neurocranium?

A

Brain case

39
Q

What is the viscerocranium?

A

Facial Skeleton

40
Q

What forms the viscerocranium?

A

1st and 2nd pharyngeal arches - A core of neural crest cells and somatic and lateral plate mesoderm

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49
Q

Specifics on Limb rotation Progression

A

At 5 weeks, upper and lower limbs have formed as finlike appendages pointing laterally and caudally

At 6 weeks, limbs bend anteriorly, so elbows and knees point laterally, palms and soles face the trunk

At 7 weeks, upper limbs have undergone 90 degree torsion about their long axes, but in opposite directions [elbows point caudally, knees cranially]

At 8 weeks, torsion of lower limbs results in twisted or “barber pole” arrangement, resulting in birth positions