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Mariam Respiratory System > Embryology > Flashcards

Embryology Flashcards

1
Q

When is the Pre-embryonic Phase?

A

0-3 Weeks

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2
Q

When is the embryonic phase?

A

4-8 weeks

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3
Q

When is the foetal phase?

A

9-40 weeks

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4
Q

What do we call the parent cells of meiosis?

A
  • Spermatogonium

- Oogonium

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5
Q

What happens to the cells produced as a result of oogenesis?

A

3 of them degenerate to polar bodies and only one forms an active gamete

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6
Q

What section of the sperm enters the ovum?

A

Only the DNA (pronucleus), it leaves the rest of its cell behind.

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7
Q

What 2 processes occur during week 1?

A

1 - The zygote is formed and eventually divides to form a blastocyst
2 - The pre-embryo moves through the fallopian tube to the uterine cavity

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8
Q

What does a zygote become after dividing?

A

A solid ball of cells called a Morula

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9
Q

What happens to the morula as the number/size of cells increases?

A

It has trouble getting nutrition to the central cells.

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10
Q

How does the morula respond to difficulty getting nutrition to its internal cells?

A

It forms a blastocyst:
1 - Some cells form an outer lining called a trophoblast
2 - others form an Inner Cell Mass in one corner of the blastocyte
3 - This produced a blastocystic cavity inside.

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11
Q

Whats different about each consecutive cell division?

A

Theyre faster, almost as if the cell is learning how to do them

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12
Q

Where does fertilisation occur?

A

In the Fallopian Tube

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13
Q

How does the pre-embryo move through the fallopian tube?

A

Using ciliated epithelium much like the muco-ciliary escalator of the airway

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14
Q

What hapens when the ciliated epithelium of the fallopian tube fails?

A

Etopic Pregnancy occurs, i.e. the pregnancy occurs somewhere other than the uterus, most often the fallopian tube

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15
Q

What 3 things occur during week 2?

A

1 - Implantation & placenta develops
2 - Bilaminar disc forms
3 - Sacs, membranes and cord to nourish the conceptus form

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16
Q

What happens to the trophoblast prior to implantation?

A

The trophoblast divides into 2 layers collectively called the Chorion

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17
Q

What are the 3 functions of the chorian?

A
  • Uses its villi in the implantation process
  • Eventually forms part of the placenta
  • Secretes HCG
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18
Q

What is the function of Human Chorionic Gonadotropin?

A

HCG is secreted by the chorian.
It stimulates the ovary to continue producing the hormones that maintain the endometrium (effectively preventing the monthly ritual of vaginal blood letting)

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19
Q

What do clinicians use HCG for?

A

Detecting pregnancy

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20
Q

When/how does implantation begin?

A

~7 days the blastocyte begins burrowing into the uterine wall (endometrium) using the Chorion

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21
Q

What do we call the part of the endometrium deep to the implanted conceptus?

A

The decidua Basalis

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22
Q

How do HCG levels change over time?

A

Maternal HCG levels increase till ~12 weeks.

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23
Q

What is the muscular wall surroundin the endometrium called?

A

The Myometrium

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24
Q

What happens to the Inner Cell Mass once implanted?

A

The inner cell mass forms a bilaminar disc within the conceptus

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25
What are the layers of cavity & cells formed by the inner cell mass?
Inner cell mass forms a bilaminar disc. Uterus -> endometrium direction: Yolk Sac -> Hypoblast -> Epiblast -> Amniotic Cavity
26
What is the function of the allantoic cavity?
It holds the embryos waste. So it grows as the yolk empties.
27
What are the functions of the placenta?
- Foetal Nutrition - Waste/gas Transport - Immunity
28
Describe the 2 surfaces of the placenta
The inner foetal surface is smooth with foetal blood vessels | The outer maternal surface is the decidua basalis of the endometrium. Its rough with maternal blood vessels.
29
How do fraternal (Dizygotic) twins develop?
2 Ova are released and 2 sperm get to them resulting in 2 seperate zygotes. Therefore they have different genetic makeups & form 2 placentae.
30
How do identical/monozygotic twins develop?
1 ovum -> 1 zygote It divides in 2 & then each cell develops into seperate embryos. Share genetic makeup & 1 placenta.
31
What things happen during week 3?
- Gastrulation - Neurulation - Somite development - Early cardiovascular development
32
What are gastrulation & neurulation?
``` Gastrulation = Germ layer formation Neurulation = Neural tube formation ```
33
What is the primitive streak & how does it form?
The primitive streak is a dip in the midline of the epiblast that forms by invagination of the cells.
34
What do we learn once the primitive streak has formed?
The axis of the embryo. Helps us identify the 'head' & 'tail' ends.
35
How do the 3 germ layers form?
Cells from the primitive streak migrate into the space between the layers and then displace the hypoblast.
36
How do the 3 germ layers relate to the original bilaminar disc?
The ectoderm replaces the epiblast The mesoderm sits between the 2 The endoderm replaces the hypoblast
37
What do we call the 3 germ layers together?
A trilaminar disc
38
In what way are the germ layer cells specilaised?
They are now destined to form certian structures
39
Where is the notochord located?
Between the mesoderm & endoderm
40
How does the notochord form?
Cells from the primitive streak sink down and form a solid tube along the layer
41
What does the notochord do?
Induces ectoderm cells in the midline to form a neural plate
42
What happens to the neural plate?
It sinks to between the ectoderm & mesoderm and forms a neural tube
43
What does the neural tube do to the mesoderm?
It induces the mesoderm to thicken and split into 3 sections on either side of the tube
44
What are the 3 sections of mesoderm?
Paraxial Mesoderm Intermediate Plate Mesoderm Lateral Plate Mesoderm
45
What happens to the lateral plate mesoderm after separating from the rest of the mesoderm?
It splits into 2, remaining connected at the medial end. | It forms the somatic mesoderm & splanchnic mesoderm
46
What do we call the space between the somatic & splanchnic mesoderm?
The intraembryonic coelom
47
What is the intermediate plate mesoderm destined to become?
The urogenital system. i.e. the kidneys & reproductive systems
48
What happens to the paraxial mesoderm after separating from the rest of the mesoderm?
It separates further into somites.
49
What comes of a somite?
Each somite divides into 3 parts which will become: 1 - A dermatome of skin (dermis) 2 - A myotome of muscle 3 - A sclerotome of bones
50
Why does each somite develop to form a specific dermatome?
Because they are ordered and so each relates to a specific vertebra & spinal nerve.
51
What happens to the lateral mesoderm in the 4th-8th weeks?
The lateral mesoderm becomes heavy and begins to fold inwards, eventually forming a ring with the opposite lateral mesoderm.
52
What is the result of lateral folding of the embryo
The embryo now forms a ring, this produces the foetal position we all know and love so much
53
What happens to the endoderm due to lateral folding?
It forms a tube at the centre of the embryo which will eventually form the respiratory system & Gut.
54
which section of the lateral mesoderm will be "inside" and which "outside" after lateral folding?
The splanchnic mesoderm will be 'inside' bordering the endoderm. The somatic mesoderm will be 'outside' bordering the ectoderm.
55
What section of skin does the ectoderm form?
The epidermis of the skin | The neural Tube
56
What body parts are evenutally formed by the lateral plate mesoderm?
The peritoneum Pleura Body Cavities.
57
Define Teratology?
The study of congenital abnormalities & abnormal formations
58
What is a teratogen?
An environmental factor that causes abnormal development (teratogenesis)
59
Give some examples of teratogens:
German measles contracted while pregnant -> Congenital Rubella Syndrome Use of thalidomide while pregnant -> Malformed Limbs
60
What causes most abnormal development:
In most cases we don't know but many are: - Environmental - Genetic - Multifactorial
61
What are some types of teratogen?
Drugs (Inc. Alcohol/Tobacco) Infectious agents (ToRCH) Radiation
62
What does ToRCH stand for?
``` Toxoplasma Rubella Cytomegalovirus Herpes All infectious agents that can transfer through placenta and affect the embryo ```
63
What genetic factors can cause teratogenesis?
Abnormal chromosome no. | Structural changes to chromosomes
64
What can cause genetic problems leading to abnormal development?
- Increased maternal Age | - DNA damage due to enviromental factors (e.g. radiation)
65
How does the risk of teratogenesis vary over the pregnancy?
Weeks 1-3: A high risk of death if exposed to teratogens Weeks 4-8: Highest sensitivity to teratogens Weeks 9-38: Decreasing sensitivity
66
What factors influence the risk posed by a teratogen?
The Dosage The genetics of the embryo, some are more/less susceptible The period of development
67
What kind of prenatal tests can be done to diagnose an abnormality?
Blood Tests Ultrasound scans Chorionic Villus Sampling Amniocentesis
68
Why dont we do chorionic villus sampling & amniocentesis often?
Very invasive & therefore dangerous
69
What do we look for on a prenatal blood test?
The mothers alpha-foetal protein level
70
What is tested postnatally to check for abnormal growth?
The babies hip stability The descent of the testes Fingers/Toes Hearing

Mariam Respiratory System (31 decks)

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