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Medicine Year 1 Semester 1 - Part 2 > Gastrulation and Neurulation > Flashcards

Gastrulation and Neurulation Flashcards

1
Q

Describe the 1st week of embryological development

A
  • Ovulation
  • Fertilisation- conception in uterine tube
  • Migration - to uterus
  • Cleavage - cell division to morula then blastocyst
  • Implantation - in uterine mucosa, complete by day 9
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2
Q

Describe the state by the end of the 2nd week of embryological development

A

Bilaminar disc with connecting stalk
Within the chorionic sac

Amniotic sac on the dorsal side
Yolk sac on the ventral side

Epiblast and Hypoblast are in contact

Day 14 primitive streak appears and the cells begin to move.

Gastrulation has begun
In the next 3-4 days a lot happens

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3
Q

When does the primitive streak form ?

A

Around day 14-15

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4
Q

Gastrulation

A

Bilaminar disc becomes the trilaminar disc
2 layers ————-> 3 layers

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5
Q

Describe early week 3

A

Formation of the primitive groove.

A groove with raised edges and a pit, formed on the epiblast along ahead-tail axis.

Groove – Primitive Streak

Pit - Primitive pit, associated with the primitive node which is a key signalling region in gastrulation.

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6
Q

Where does the primitive streak develop ?

A

Develops at the caudal end of the embryo

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7
Q

Primitive node function

A

A key signalling region in gastrulation
Sends out signalling factors

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8
Q

Describe what happens in cell migration 1

A

The epiblast cells divide and migrate through the primitive streak.

The epiblast cells displace and replace the hypoblast cells.

The epiblast cells start becoming endoderm.

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9
Q

Describe what happens in cell migration 2

A

Second wave of epiblast migration “fills in” between 2 layers.

This establishes a trilaminar disc, except at 2 locations.

The epiblast is now ectoderm.

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10
Q

Describe the location of the notochord

A

From the primitive pit rostrally, into the mesoderm, grows a tube-shaped structure.

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11
Q

Describe development of the notochord

A

Changes form a tube to a disc to a solid rod (17-20 days)

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12
Q

Describe the dorsal/ventral axis

A

The primitive node/notochord organise dorsal-ventral axis.

Skin/ ventral (belly) development uses signals from bone morphogenic proteins (BMP)

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13
Q

BMP

A

Bone Morphogenic Protein

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14
Q

Function of the notochord

A

Notochord is essential for setting up dorsal and ventral axes and inducing neurulation.

Node and notochord release factors (chords, noggin, follistatin) that block BMP.

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15
Q

Function of BMP

A

BMP would drive formation of skin on the back, but notochord drives back/neural tissue development instead.

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16
Q

Neurulation

A

The neural plate converts to a groove then a tube.

Forming of neural tissue, induced by the bar shaped tissue-notochord (deep to the neural epithelium)

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17
Q

epithelial cells

Describe neurulation

A

Epithelial cells become columnar in an area called the neural plate.

The neural plate converts to a groove then a tube (neurulation)

Middle neural groove becomes apparent after day 19

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18
Q

Neurulation - fold and groove

A

Cells on the edge of the plate thicken, forming a grove and then a fold.

Occurs between day 20-21

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19
Q

Neurulation - tube

A

The edges of the fold roll over to make a tube.

Occurs from day 22 onwards

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20
Q

Neurulation - closure

A

The folds close like a zip in cephalic and caudal directions, the open ends being the anterior and posterior neuropores.

They close to form a complete tube.

Anterior neuropore - 25 days
Posterior neuropore - 28 days

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21
Q

What forms the brain ?

A

Three dilations within the rostral tube - primary brain vesicles - go onto form the brain.

22
Q

Describe secondary neurulation

A

The neural tube is lengthened caudally by a process of secondary neurulation

The medullary cord forms and develops a lumen before fusing with the caudal end of the neural tube.

23
Q

Explain the formation of neural tube during neurulation

A

Fold and groove
Tube
Closure

24
Q

Neural tube defects causes

A

Failure of the neuropores to close, leads to various levels of :

  • Brain/skull defects : anterior neuropore
  • Spina bifida : posterior neuropore
25
Q

Neural tube defects linkage

A

Closely linked to low levels of folate which is essential for cell division.

26
Q

Origin of neural crests

A

Neural crests derive from the edges of the neural tube.

They undergo an epithelial to mesenchymal transformation, become motile and migrate away from the neural tube to widespread destinations.

Neural crests migrate all over the body, but in particular contribute to the sensory and autonomic nervous systems.

27
Q

State some things that the neural crest forms

A

Peripheral nervous system

Melanocytes
Schwann cells

Head mesenchyme

28
Q

Describe some neural crest linked problems

A

Hearing problems
Abnormal pattern of melanocytes

29
Q

Neural crest cell link syndromes

A

Waardenburg’s syndrome (1/50,000)

Treacher Collins Syndrome (autosomal dominant 1/50,000)

30
Q

Treacher Collins Syndrome

A

Defective protein called treacle (TCOF1 gene)

Failure of formation/apoptosis of neural crest cells

31
Q

Parts of the mesoderm

A

Paraxial mesoderm
Intermediate mesoderm
Lateral plate mesoderm

32
Q

How is mesoderm formed ?

A

Cells from the epiblast flow into the primitive streak/groove (invagination)

These cells replace the hypoblast cells to form endoderm

Cells lie between the hypoblast and epiblast form mesoderm.

Cells that remain in the epiblast become ectoderm.

33
Q

How are different regions of mesoderm formed ?

A

Epiblast cells migrate through the streak to form different regions of mesoderm.

34
Q

What does the lateral plate mesoderm split into ?

A

Visceral and Parietal layers

35
Q

What does paraxial mesoderm form ?

A

Paraxial mesoderm becomes segmented to form somites

36
Q

Paraxial mesoderm

A

Paired condensations of paraxial mesoderm in the future trunk - NOT HEAD

Day 20-30, 3/4ths form a day from cranial to caudal.

42-44 pairs develop, but regression in the tail end leaves approx. 37 pairs.

37
Q

Name the 37 pairs of spinal cord segments and nerves

A

4 Occipital
8 Cervical
12 Thoracic
5 Lumbar
5 Sacral
3 (ish) Coccygeal

38
Q

Describe somite formation

A

Cells the paraxial mesoderm have an internal timer

They go through cycles every 90 minutes defined by a notch signalling clock.

A wave of FGF signal that passes along the embryo in a rostral caudal direction.

When the FGF wave passes cells, they are programmed to change into part of a somite according to where they are in the clock cycle.

39
Q

Crucial part of somite formation

A

If the wave passes cells early in the clock cycle, they become the front end of that segment

If the wave passes cells late in the cycle, they become the tail end of the segment

This process is repeated over and over forming a number of somites

40
Q

Notch clock

A

A genetic process that has a clock

41
Q

Homeobox genes (Hox genes)

A

Expressed by somites and tells structures what to become and when to become it.

The direct formation of body structures AT THE RIGHT PLACE along the body e.g., form CORRECT body segments.

42
Q

Derivatives of the paraxial mesoderm

A

Head and Somites.

Somites are differentiated into :

  • Sclerotome —> Axial skeleton
  • Myotome —> Skeletal muscle
  • Dermatome —> Dermis
43
Q

Derivatives of the intermediate mesoderm

A

Kidney
Gonads
Urogential structures

44
Q

Derivatives of the lateral plate mesoderm

A

Splanchnic and Somatic

Splanchnic :

  • Visceral coverings
  • Heart
  • Blood vessels
  • Blood
  • Spleen

Somatic :

  • Parietal coverings
  • Limb cartilage
  • Limb bone
  • Limb, lateral, ventral, trunk dermis
45
Q

Derivatives of the midline mesoderm

A

Prechordal plate :

  • future site of the mouth

Notochord :

  • nucleus pulposus
46
Q

Endoderm process

A

Craniocaudal folding and lateral folding pinches of the endoderm lined yolk sac.

This becomes the primitive gut lining.

Note the former epiblast – now amnion encapsulating the folded embryo.

Small connection to the yolk sac.
The vitelline duct, closed by 5/6 weeks

Note the arrangement of LPM lining the cavities and surrounding the gut tube

47
Q

Endoderm derivatives

A

Lining of gut tube
Distal urogenital system

48
Q

What is Meckel’s diverticulum ?

A

Remnant of the vitelline duct (yolk sac/ gut connection)

49
Q

Meckel’s diverticulum statistics

A

Meckel diverticulum occurs in 2% of the population,
2% are symptomatic,
mostly in children < 2 years
affects males twice as often as females,
is located 2 feet proximal to the ileocecal valve,
is ≤ 2 inches long, and can
has 2 types of mucosal liningE

50
Q

Ectoderm derivatives

A

Epidermis and associated glands

Nails and enamel of teeth

Lens and cornea in the eye

Olfactory epithelium

Oral Cavity and anal canal epithelium
Sensory organs of ear

Glands: Salivary glands and Mammary Gland
Adenohypophysis

Terminal male urethra, labia majora and outer surface of labia minora

Medicine Year 1 Semester 1 - Part 2 (37 decks)

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