Embryonic Disc Formation Flashcards Preview

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Flashcards in Embryonic Disc Formation Deck (27)
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1

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

8 weeks

2

Describe the formation of a Morula

Day 1 - 4
Morula forms by repeated mitotic divisions

3

Describe the formation of a Blastocyst

Day 5
Blastocyst forms: Trophoblast and Embryoblast (Inner cell mass)

4

What happens on day 6?

Implantation

5

What needs to disintegrate before implantation?

Zona Pellucida

6

What happens on day 8?

Amniotic Cavity opens up
Bilaminar disc: Epiblast (Top)
Hypoblast (Bottom)

7

What happens on day 9?

Primary Yolk Sac forms below hypoblast

8

What is a syncytium?

A single cytoplasmic mass containing multiple nuclei

9

What cell layers will eventually form the placenta?

Extraembryonic mesoderm, Syncytium and Cytotrophoblasts

10

What happens on day 12?

Extraembryonic mesoderm develops and forms cavities within (Will eventually form Chorionic Cavity)

11

What happens on day 13?

Connecting stalk forms and chorionic cavity fills with fluid.

12

How is the trilaminar disc formed?

Week 3 - Gastrulation
Rapid epiblast cell division at the primitive groove and downwards migration forms 3 layers: Ectoderm, Mesoderm and Endoderm.

13

What is the Primitive node and pit?

Week 3 - Neural Tube Formation
Raised area of epiblast. Cells migrate from the node to form the Notochord.

Tip: Node = 'Nodochord'

14

What are the derivatives of the Endoderm?

Lining of gut tube, respiratory system and urinary system

15

What are the derivatives of the Ectoderm?

Skin & neural tissue

16

What are the derivatives of the Mesoderm?

Organs and muscles

17

Define Somites

Somites form parts of the axial skeleton (skull, vertebrae, ribs), associated musculature and the dermis of the skin

18

Describe the 2 directions of embryonic folding

Longitudinal - Moves heart, brain, mouth & anus into an adult position (process called Reversal)
Lateral - draws amniotic cavity around the embryonic disc

19

Briefly describe gut tube folding

The gut tube grows rapidly and herniates out of the umbilical region. The gut tube rotates 270º anticlockwise along the axis of the SMA

20

Name 2 pathologies of gut tube development

Omphalocele - The gut tube may not fully return to the abdomen
Gastroschisis - Gut tube may herniate through the abdominal wall

21

What is a volvulus

Twisting of a loop of intestine and supporting mesentery resulting in bowel obstruction.

22

Name the remnants of the vitellointestinal duct and their clinical significance.

Cyst, band, fistula, sinus or diverticulum
Clinical:
Cyst - protrusion from umbilicus
Fistula - faeces leaking from umbilicus
Meckel's Diverticulum - can inflame and cause tenderness

23

What is the cloaca?

The cloaca is separated by the urorectal septum into the urogenital sinus (developing bladder) and rectum

24

What problem(s) can occur if the urorectal septum does not form properly?

Imperforate Anus

25

What are pharyngeal arches and what to they form?

4 Interconnecting loops of ectoderm, mesoderm and endoderm (lower face and neck)

26

What layer does the notochord form within?

Mesoderm - creates a longitudinal axis in the embryo

27

What does the 1st pharyngeal arch form?

Nerve supply: CNV (Trigeminal nerve)
Muscles: e.g. Mastication and tensor tympani
Bones: e.g. malleus, incus, maxilla, zygoma & mandible