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Yr 1 - Embryology > Gastrulation > Flashcards

Gastrulation Flashcards

1
Q

When does gastrulation commence?

A

In week 3

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2
Q

How does gastrulation commence?

A

Formation of the primitive streak

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3
Q

What makes up primitive streak?

A
  1. Primitive pit: top, rounded end
  2. Primitive node: outer edges
  3. Primitive groove: middle
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4
Q

What does gastrulation involve?

A

Formation of 3 germ layers

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5
Q

Cranial/caudal and right/left axes of embryo are firmly established in this period.

What forms towards cranial end?

A

Oropharyngeal membrane (mouth and throat)

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6
Q

What is the cranial end?

A

Head end

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7
Q

What is the caudal end?

A

Tail end

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8
Q

What forms towards caudal end?

A

Cloacal membrane (GI and urinary systems)

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9
Q

What is primitive streak?

A

A groove formed on dorsal aspect of embryo in epiblast. Appears at caudal end at bilinear disc stage. Marks beginning of gastrulation. Epiblast cells migrate through primitive streak to form 3 germ layers.

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10
Q

What is situs inversus?

A

Complete reversal of left axis - left and right side of body are switched around (e.g. liver on left not right)

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11
Q

Is complete situs inversus dangerous?

A

Sometimes harmless (asymptomatic)

20% of patients suffer from Kartagener syndrome

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12
Q

What is Kartagener syndrome?

A

Problem with cilia cells - sweep in wrong direction cause cells to go to wrong side of body

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13
Q

What are dangers of partial situs inversus?

A

Associated with malformations

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14
Q

What is an example of a malformation due to partial situs inversus?

A

Dextrocardia

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15
Q

What is involved in dextrocardia?

A

Isolated right sided heart causes problems with circulatory systems

  • If correct blood vessels are attached to correct chambers it can cause no problems as oxygenated blood still goes to body and deoxygenated blood still goes to lungs
  • If this isn’t correct, oxygenated blood can go to lungs and deoxygenated blood can go to body
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16
Q

How are 3 germ layers formed?

A

Epiblast cells migrate through primitive streak

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17
Q

What are 3 germ layers?

A
  1. Endoderm
  2. Mesoderm
  3. Ectoderm
18
Q

How is endoderm formed?

A
  1. Epiblast cells move through primitive streak
  2. Push hypoblast cells out of way and replace them
  3. Once completely replaced, forms 1st germ layer (definitive endoderm)
19
Q

What are adult structures developed from?

A

Epiblast cells - hypoblast cells are only transient (replaced)

20
Q

How is mesoderm formed?

A
  1. Epiblast cells continue to migrate though streak (keep on replicating)
  2. Form middle layer between epiblast and endoderm - 2nd germ layer (mesoderm)
21
Q

How is ectoderm formed?

A
  1. Epiblast cells left behind make up 3rd and final layer (ectoderm)
  2. This completes gastrulation
22
Q

What do we end up with after gastrulation?

A

Trilaminar disc consisting of 3 germ layers all derived from epiblast cells

23
Q

What is purpose of these germ layers?

A

Form all our body systems

24
Q

What does endoderm go on to form?

A
  • Epithelial lining of respiratory tract, gut tube (GI tract), urinary bladder, urethra
  • Liver
  • Pancreas
  • Gallbladder
25
Q

What does mesoderm go on to form?

A
  • Dermis of skin
  • Epithelial lining of blood vessels, lymph vessels, body cavities, joint cavities
  • Muscle tissue
  • Heart
  • Connective tissue
  • Kidneys & ureters
  • Spleen
  • Internal reproductive organs
26
Q

What does ectoderm go on to form?

A
  • Epidermis of skin & epidermal derivatives (hair, nails)
  • Nervous tissue & sense organs
  • CNS & spinal cord & brain
  • Pituitary gland
  • Enamel of teeth
  • Lens of eye
27
Q

The mesoderm becomes highly organised into what structures?

A
  1. Paraxial mesoderm
  2. Intermediate mesoderm
  3. Lateral plate mesoderm
28
Q

What does paraxial mesoderm go on to form?

A

Majority of skeleton, skeletal muscles, dermis of skin

29
Q

What does intermediate mesoderm go on to form?

A

Gonads, internal reproductive tracts, kidney

30
Q

What does lateral plate mesoderm go on to form?

A

Lining of body cavities

31
Q

Paraxial mesoderm starts dividing into blocks. What are these blocks called?

A

Somites

32
Q

When does this dividing into somites happen?

A

Day 20 post fertilisation

33
Q

In what direction does this dividing into somites occur?

A

Begins in cranial region and progresses towards caudal region

34
Q

Why is this dividing into somites useful in estimating the age of the embryo?

A

Very predictable process

35
Q

When does this dividing into somites stop?

A

When 42-44 pairs have formed

36
Q

What is the feature of Sirenomelia?

A

‘Mermaid syndrome’ - legs appear stuck together

37
Q

What is Sirenomelia caused by?

A

Insufficient mesoderm formed in caudal region of embryo as primitive streak regresses too early - don’t have sufficient migration of epiblast cells

38
Q

Why is the cranial end normal during Sirenomelia?

A

Mesoderm forms cranial to caudal end

39
Q

What is the feature of Sacrococcygeal Teratoma?

A

Tumours

40
Q

What is cause of Sacrococcygeal Teratoma?

A

Remnants of primitive streak persist - too much mesoderm formed

41
Q

What happens to the primitive streak once sufficient migration occurs?

A

It regresses

Yr 1 - Embryology (11 decks)

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