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Block 1 Week 2 > Early Embryology and the Gut Tube > Flashcards

Early Embryology and the Gut Tube Flashcards

1
Q

By what week (post-fertilisation) of development have many of the major organ systems formed?

A

Week 8.

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2
Q

What is the approximate length of an 8 week old embryo?

A

30mm.

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3
Q

As the fertilised ovum moves down the uterine tube and undergoing mitotic division, what is surrounding the ovum?

A

Zona pellucida.

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4
Q

What is the Zona pellucida?

A

A thick transparent membrane surrounding the ovum.

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5
Q

List 2 functions of the Zona pellucida.

A
  1. To prevent polyspermy.

2. Protect the ovum.

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6
Q

What is a morula?

A

A solid ball of cells resulting from division of a fertilised ovum, and from which a blastula is formed.

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7
Q

How many cell types form a blastocyst? What are they and how are they arranged?

A

Trophoblast and embryoblast. The outer layer is the trophoblast and the inner layer is the embryoblast.

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8
Q

What does a morula develop into?

A

Blastocyst.

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9
Q

Around what day of fertilisation is the Blastocyst formed?

A

Day 5.

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10
Q

What is the fluid within a Blastocyst called?

A

Blastocoele

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11
Q

Around which day does the Zona pellucida begin to degrade and disappear?

A

Day 6

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12
Q

List 2 reasons why it’s vital that the Zona pellucida disappears.

A
  1. To enable to Blastocyst to grow rapidly.

2. To enable to Blastocyst to stick to the epithelial covering of the uterine lining.

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13
Q

What new cell layer is formed when the Blastocyst moves into the endometrium?

A

Syncytiotrophoblast.

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14
Q

On what day is the bilaminar embryonic disc created?

A

Day 8

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15
Q

What are the 2 layers of the bilaminar embryonic disc?

A

Epiblast and hypoblast.

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16
Q

On day 9 of fertilisation, what fluid filled sac begins to develop below the hypoblast?

A

Primary yolk sac.

17
Q

What is a syncytium?

A

A single cell or cytoplasmic mass containing several nuclei, formed by fusion of cells or by division of nuclei.

18
Q

On day 12 of fertilisation, what now surrounds the developing embryo?

A

Extra-embryonic mesoderm.

19
Q

What can be found within the extra-embryonic mesoderm surrounding the developing embryo? What will they eventually do?

A

Fluid filled cavities called extra-embryonic coelom, which will join together around the embryo to form a fluid filled sac.

20
Q

In what week does gastrulation occur?

A

Week 3

21
Q

What is gastrulation?

A

The rapid division and downwards migration of epiblast cells to create a three layered (trilaminar) embryonic disc.

22
Q

Which 2 key structures can be found towards the tail end of the developing embryo?

A

Primitive node and primitive streak.

23
Q

In the developing embryo, what is the primitive streak?

A

A raised area of epiblast extending from the cloaca to the primitive node.

24
Q

In the developing embryo, what is the primitive groove? What is happening to the cells there?

A

An indentation in the centre of the primitive streak - it marks the region where cells are rapidly migrating downwards to form the three layered disc.

25
Q

Cells from the primitive streak migrate downwards to create which new cell layer?

A

Intraembryonic mesoderm.

26
Q

Cells from the primitive node and pit form which structure in the embryo?

A

The notochord

27
Q

In which layer of the trilaminar disc does the notochord sit?

A

The mesoderm

28
Q

What should eventually happen to the primitive node and streak? What will form if this does not happen?

A

They should disappear - if not can lead to the formation of a teratoma at the distal end of the vertebral column.

29
Q

What does the ectoderm form?

A

Skin and neural tissue.

30
Q

What does the mesoderm form?

A

Serous membranes, somites, renal, and gonad

31
Q

What does the endoderm form?

A

Lining of the gut tube, respiratory system, and urinary system.

32
Q

How many degrees, in what direction, and around what axis does the gut tube rotate during development?

A

270 degrees anticlockwise around the SMA.

33
Q

What is the condition in which the gut tube does not fully return to the abdomen? Is the gut tube in direct contact with the outside world?

A

Omphalocele - not in direct contact, surrounded by amniotic membrane.

34
Q

What is the condition at birth in which the gut tube herniates through the abdominal wall?

A

Gastroschisis.

35
Q

Which structure separates the cloaca into the bladder and rectum?

A

Urorectal septum

Block 1 Week 2 (10 decks)

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