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Microanatomy > Gastrulation > Flashcards

Gastrulation Flashcards

1
Q

What are monozygotic twins and their incidence?

A

develop from one zygote, which splits and forms two embryos 4/1000 births

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2
Q

What are dizygotic twins and their incidence?

A

dizygotic (‘fraternal’), meaning that each twin develops from a separate egg and each egg is fertilized by its own sperm cell. 2 separate oocytes 10/40 in blacks, 7-10/1000 in whites, 3/1000 in asians

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3
Q

Whats the incidence of triplets and quadruplets?

A

1/7000-10000 for triplets 1/600k for quadruplets

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4
Q

What is sesquizygosity?

A

twins genetically identical to each with respect to one parent but differ from each other by approx 50% with respect to DNA inherited from other parent - likely occurs after heterogoneic assortment of 2 paternal genomes and one maternal genome during first postzygotic cleavage division.

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5
Q

What is the primary yolk sac?

A

Primary yolk sac: the vesicle which develops in week 2. Floor = Heuser’s membrane Ceiling = hypoblast. It is also known as the exocoelomic cavity.

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6
Q

What is the secondary yolk sac?

A

Secondary yolk sac: formed when the extraembryonic mesoderm separates to form the extraembryonic coelom; cells from the mesoderm pinch off an area of the yolk sac, and what remains is the secondary yolk sac.

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7
Q

What is the final yolk sac?

A

The final yolk sac: in week 4, part of the yolk sac is surrounded by endoderm and incorporated into the embryo as the gut. The remaining part of the yolk sac is the final yolk sac.

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8
Q

What are the numbers labelled and what day does this occur on?

A
  1. Extra-embryonic mesoblast
  2. Extra-embryonic reticulum
  3. Primary umbilical vesicle
  4. Cytotrophoblast

DAY12

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9
Q

What are the numbers labelled and what day does this occur on?

A
  1. Extra-embryonic mesoblast
  2. Lacunae in the reticulum
  3. Hypoblast
  4. Heuser´s membrane between hypoblast and mesoblast cells

DAY12

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10
Q

What are extra-embryonic mesoblast cells?

A

Extra-embryonic mesoblast cells, derived from epiblast cells, grow into the extra-embryonic reticulum. Beginning of the reticular vacuole formation that will form the future chorionic cavity.

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11
Q

What are the numbers labelled and what day does this occur on?

A
  1. Extra-embryonic mesoblast (EEM)
  2. Chorionic cavity
  3. Secondary umbilical vesicle

DAY13

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12
Q

What are the numbers labelled and what has happened what day does this occur on?

A
  1. Extra-embryonic mesoblast (EEM)
  2. Chorionic cavity
  3. Remains of the primary umbilical

vesicle

  1. Secondary umbilical vesicle

DAY13

The chorionic cavity has been created. The primary umbilical vesicle has collapsed and is now replaced by a smaller secondary umbilical vesicle.

The remains of the primary umbilical vesicle form small vacuoles in the EEM. The embryonic disk with the definitive secondary umbilical vesicle is now surrounded by the chorionic cavity.

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13
Q

What is the bilaminar disc and when is it seen?

A

At week 2, the embryo consists of two flat layers of cells:

EPIBLAST + HYPOBLAST = BILAMINAR DISC

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14
Q

What is gastrulation and when does it occur?

A

As week 3 begins, the embryo enters GASTRULATION

The bilaminar disc is converted into a trilaminar disc and formation of three germ layers

◦Ectoderm

◦Mesoderm

◦Endoderm

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15
Q

What is meant by embryogensis?

A

The point in embryogenesis where basic organization of the organism is established.

Groups of cells that will give rise to specific organ systems and tissues are moved into the right position both externally and internally.

Groups of cells that will influence each other are positioned so they can have an effect on each other.

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16
Q

What is the first thing to form in gastrulation?

A

Gastrulation begins with the formation of the primitive streak

17
Q

What is the structure and orientation of the primative streak?

A

Primitive Streak – includes groove, node and pit

The Primitive Streak defines

Anterior – cranial

Posterior – caudal

Right and Left – lateral

The tip of the streak is the Primitive Pit and the Primitive Node (also called Hensen’s Node)

18
Q

What do the arrow represent?

A
19
Q

What do the labels represent?

A
  1. Primitive groove
  2. Epiblast
  3. Extraembryonic mesoderm
  4. Definitive endoderm
  5. Invading epiblastic cells forming

the intraembryonic mesoderm

  1. Hypoblast

Transverse section at the level of the primitive groove with the immigration of epiblast cells, which form the future mesoblast, as well as the endoblast, which replaces the hypoblast

20
Q

Describe the image

A

Epiblast cells roll over the primitive ridge and involute into the groove. The cells lose contact with one another and migrate inwards by ingression.

3 germ layers are established

First cells through the streak integrate and displace hypoblast cells

ENDODERM (yellow/green)

Some lie in the middle MESODERM (orange)

Cells remaining in the epiblast ECTODERM (blue)

21
Q

What are the changes which occur here?

A

Epithelial: Cell polarity, Cell adhesion, Stationary,High levels of E-cadherin, Low levels of N-cadherin

Mesenchymal: No cell polarity, Loss of cell adhesion, Ability to migrate and invade, Low levels of E-cadherin, High levels of N-cadherin

22
Q

What is epithelial-mesenchymal transition?

A

Process by which epithelial cells lose their cell polarity and cell-cell adhesion, and gain migratory and invasive properties to become mesenchymal stem cells; these are multipotent stromal cells that can differentiate into a variety of cell types

Tumors are often viewed as corrupt forms of normal developmental processes.

Genes that are important in embryonic development are frequently found to be culprits in cancer.

23
Q

What forms from endoderm, mesoderm and ectoderm?

A

Endoderm: epithelial lining of the GIT, respiratory tract bladder and urethra; thyroid and parathyroid glands, liver, pancreas.

Mesoderm: connective tissue (cartilage, bone, blood); striated and smooth muscles; heart; blood and lymphatic vessels; kidneys; ovaries and testes; spleen; serous membranes lining the body cavities (pericardial, pleural, peritoneal).

Ectoderm: CNS (brain and spinal cord); PNS; sensory epithelia of the eye, ear, nose; epidermis and its appendages (hair and nails); mammary glands; pituitary gland.

24
Q

What are the results of gastrulation?

A

(1) The primary germ layers are formed
(2) Creation of body axes: Anterior-posterior, Dorsal-ventral, Left-right

Microanatomy (3 decks)

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