Embryology Flashcards

1
Q

During the first week after fertilisation, the zygote travels along…?

A

The uterine tubes

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2
Q

When travelling along the uterine tubes the zygote is surrounded by what? What is its function?

A

A layer of glycoproteins called a zona pellucida

The zona pellucida stops the zygote from increasing in size, despite the increasing cell number due to cleavage, as it travels through the uterine tubes, so it doesn’t get stuck there, thus embedding in the tube, resulting in an ectopic pregnancy

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3
Q

What is the zygote nourished by as it travels down the Fallopian tubes?

A

Glycogen from the goblet cells of the uterine tubes, and later the secretory cells of the uterus

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4
Q

What is cleavage?

A

The mitotic cellular replication the zygote undergoes as it travels to the uterus into smaller cells called blastomeres

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5
Q

By three days after fertilisation how big should the zygote be, and what will it now be called?

A

16 cells,

Morula

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6
Q

What day does the blastocyst enter the uterus?

A

Day 4

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7
Q

When in the uterine cavity, the blastocyst digests its way out of:

A

The zona pellucida

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8
Q

What two masses is the blastocyst made of?

A

Trophoblast (outer cell mass) which becomes the chorion and placenta

Embryoblast (inner cell mass) which become the embryo, amnion and umbilical cord

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9
Q

What layers do the trophoblast differentiate into in week 2?

A

Synctio-trophoblast & inner cytotrophoblast

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10
Q

What is the role of the syncytiotrophoblast layer in implantation?

A

The syncytiotrophoblast layer forms finger like villi projections deep into the decidua (uterine endometrium) and spaces called lacunae, which fill with the mothers blood. The villi branch and contain blood vessels, thus allowing gaseous exchange between mother and foetus

The syncytiotrophoblast cells also produce hCG which prevents menustation & sustains the pregnancy by maintaining the corpus luteum

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11
Q

The embryoblast differentiates into two cell types, what are they and what shape do they form?

A

Epiblast (closest to the trophoblasts) & hypoblast (closest to the blastocyst cavity

They form a flat disc called the bilaminar embryonic disc

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12
Q

What is gastrulation?

A

The rearrangement and migration of of cells due to pre determined genetic coding to turn the bilaminar embryonic disc into a TRIlaminar embryonic disc of three primary germ layers

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13
Q

What is the first appearance of the three primary germ layers known as and when does it occur by?

A

The primitive streak

Day 15

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14
Q

What are the three layers of the trilaminar embryonic disc

A

Ectoderm: forms the epidermis layer of the skin, the hair and the nails, also forms the nervous system

Mesoderm: forms the muscle, skeleton, dermis of the skin, connective tissue, urogenital glands, blood vessels, blood and lymph cells

Endoderm: forms the epithelial lining of the respiratory, digestive and urinary systems and glandular cells of organs such as the liver and the pancreas

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15
Q

Describe neurulation and how it can go wrong?

A

The formation of the notochord, from mesodermal cells, and neural plate and therefore neural tube, occurring the in middle of the embryo and developing towards each end.

Tetratogens, diabetes or folic acid deficiency can cause neural tube defects

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16
Q

Describe the embryo at 4 weeks post fertilisation

A

There is a distinct head-rump polarity
The embryo is c shaped due to construction between the embryo and the yolk sac, which provides nutrition until the placenta takes over
Primitive beating heart present
Large liver - blood detoxification important from early on

17
Q

Describe the storage functions of the placenta

A

The placenta stores glycogen, ready to metabolise into glucose as and the fetus requires it
Stores iron and fat soluble vitamins

18
Q

Describe the endocrine functions of placenta?

A

Produces steroid and placental protein hormones

Steroid: oestrogen and progesterone

Placental protein hormones: hGC, hPL, PAPP-A