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Embryo > Fertilization and Gastrulation > Flashcards

Fertilization and Gastrulation Flashcards

1
Q

Human pregnancy is divided into ____ trimesters. The first trimester is known as the ________ period (weeks _-__.)

A

Human pregnancy is divided into three trimesters. The first trimester (week 0-8) are known as the embryonic period.

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2
Q

The embryonic period are weeks ___-___.

A

0-8.

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3
Q

When is the critical period? And why?

A

Critical period are the first 8 weeks of pregnancy (1st trimester). This is when a majority of problems in pregnancy occur.

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4
Q

What are the two types of calanders?

A
  1. Obstetrical/gestational calendar–> begins with the first day of your last period. At day 14, ovulation (fertilization) will occur. Thus, there are 2 weeks (2 weeks after LMP where nothing is happening).
  2. Ovulatory calendar–> the ovulatory calendar begins at day 14 of the obstetrical/gestational calendar. Thus, day 1 for the ovulatory calendar is when ovulation/fertilization occurs.
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5
Q

What is the anatomy of the ovum?

A

Going out–>in

  1. Follicular cells of the corona radiata
  2. Zona pellucida
  3. Perrivitelline space
  4. Plasma membrane
  5. Nucleus
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6
Q

What is the zona pellucida?

A

A glycoprotein meshwork

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7
Q

Anatomy of the sperm

A

A sperm has a head, neck and tail.

  • Head is made up of the acrosome and nucleus (nucleus is either 23X or 23Y).
  • Neck

Tail- flagella like structure.
Middle piece of the tail has mT, which are important for ATP.

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8
Q

What is the acrosome?

A

The acrosome is a part of the head of the tail. It contains the enzymes that are important for the sperm to penetrate the egg.

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9
Q

What happens in week 1 of fertilization?

A
  1. Fertilization (occurs in the ampulla- distal portion of the uterine tube).
  2. Cleavage
  3. Formation of the blastocyst.
  4. . Formation of the embryoblast (inner cell mass)
  5. Implantation begins
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10
Q

What is the embryoblast also called?

A

Inner cell mass

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11
Q

Where does fertilization occur?

A

In the ampulla of the uterine tube- the distal portion of the uterine tube.

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12
Q

What is step 1 of fertilization?

A

CAPACITATION.

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13
Q

What is capacitation?

A

The process in which the sperm sheds glycoproteins and seminal plasma proteins, allowing the acrosome reaction occurs.

  • Occurs in the uterus and uterine tubes.
  • takes about 7 hours.

In order for the sperm to penetrate the egg, capacitation must occur.
Sperm sheds glycoproteins and seminal plasma proteins from its plasma membrane, causing perforations in the acrosome wall.

The acrosome reason will now occur: Acrosome then releases enzymes (hylauronidase) from the acrosome of the sperm. Hylauronidase will then allow the sperm to penetrate the corona radiata of the egg.

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14
Q

What enzyme release from the acrosome allows for the sperm to pass through the corona radiata of the egg?

A

Hylauronidase

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15
Q

What is step 2 of fertilization?

A

Penetration of the zona peullucida

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16
Q

How does step 2 of fertilization occur?

A

The sperm penetrates the zona pellucida of the egg via esterases, acrosin and neuraminidase released from the acrosome.
After penetration, a ZONA REACTION occurs. Zona reaction is a change in the glycoprotein network of the zona pellucida to prevent polyspermy. Perivitilline space releases granules that help with this process.

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17
Q

Zona reaction

A

After the sperm penetrates the zona pellucida using [neuraminidases, acrosin and esterases], a ZONA REACTION occur. It is a change in the glycoprotein network of the zona pellucida, preventing polyspermy. Perivitilline space releases granules that help.

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18
Q

Enzymes to get through the corona radiata and the zona pellucida

A

Corona radiata–> hylauronidase

Zona pellucida–> Esterases, acrosin and neuramindases

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19
Q

Step three of fertilization

A

Sperm can fuse into the cytoplasm of the egg. The head, neck and tail of the sperm will enter the egg, HOWEVER THE MT will not.

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20
Q

Why are most mT disorders maternal in nature?

A

Because when the sperm fuses with the egg, the mT of the sperm do not enter

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21
Q

Step 4 of fertilization

A

2nd meiotic division is completed: A male pronucleus is made and it fuses with the female pronucleus, creating a zygote.

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22
Q

What are the results of fertilization?

A
  1. Completion of the 2nd meiotic division
  2. Diploid chromosomes are made
  3. Determination sex of the embryo
  4. Metabolic activation of the oocyte.
  5. Cleavage can now be initiated
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23
Q

What are the 4 steps of fertilization

A
  1. Penetration of the corona radiata
    - Capacitation
    - Acrosome reaction
  2. Penetration of the zone pellucida
    - Zona reaction
  3. Sperm fuses into the cytoplasm of the egg
  4. 2nd meiotic division is complete: male pronucleus is made and can combine with the females to make a zYgOtE!
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24
Q

What happens after fertlization and the formation of a zygote?

A

Cleavage

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25
Q

How long after does the formation of a zygote (completion of fertilization) does cleavage occur?

A

30 hours.

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26
Q

What occurs in cleavage?

A

30 hours after the completion of fertilization, cleavage occurs.

In cleavage, cells begin to divide and create blastomeres. As cell number increases, their size decreases.
Day 3- morula (12-32 cells)
Day 3 and 4- morula enters the uterus and fill up with fluid, forming a blastocytic cavity
Day 5- blastocyst is created.

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27
Q

In cleavage, what are cells called as they begin to divide?

A

blastomeres

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28
Q

When is the morula made?

A

Day 3

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29
Q

How many cells make up a morula

A

12-32

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30
Q

How is a blastomere made and when?

A

On days three and four, the morula will enter the uterus and fill up with fluid, forming a blastocystic cavity.
On day 5, a early blastocyst made and matures into a late blastocyst on day 7.

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31
Q

Cleavage is complete when? What comes after cleavage?

A

Cleavage is complete on day 5 and on day 6, implantation can begin.

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32
Q

Day 5, will have our early blastocyst. What are features of our early blastocyst?

A

Early blastocyst will have:
1. Inner cell mass, which gives rise to the embryo

  1. Degenerating zona pellucida. By day 7 (formation of our late blastocyst, it is gone). This is called hatching of the embryo
  2. Trophoblast–> gives rise to the placenta
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33
Q

When does the early blastocyst become a late blastocyst?

A

Day 7

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34
Q

Day 7- late blastocyst

A

More pronounced inner cell mass.

More pronounced trophoblast.

No longer has a zona pellucida. This is called hatching of the embro.

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35
Q

What is the inner cell mass?

A

Gives rise to the embro

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36
Q

What is it called when the zona pellucida begins to degenerate?

A

hatching of the embryo

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37
Q

What is the trophoblast?

A

The trophoblast gives rise PlAcEnTa.

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38
Q

Implantation begins when?

A

Day 6

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39
Q

Assisted reproductive technologies affect everything that happens in

A

week 1

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40
Q

In-vitro fertilization

A
  1. Stimulate the ovaries and collect eggs
  2. Get sperm and capacitate it.
  3. Combine the sperm and eggs
  4. Transfer the embryos (1-3) to mom
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41
Q

Cryopreservation of embryos

A

Freeze embryos and save for mom

42
Q

Intracytoplasmic sperm injection

A

If something is wrong with the egg, you can automatically inject the sperm into the cytoplasm of the egg.

43
Q

Embryonic stem cells are derived from _________

A

the inner cell mass.

44
Q

Embryonic stem cells are pluripotent/totipotent, meaning what?

A

PLURIPOTENT.

Meaning that they can give rise to any type of cell tissue.

45
Q

How do we receive embroyonic stem cells?

A

from cyropreserved embryos

46
Q

What is somatic cell nuclear transfer?

A

Somatic cell nuclear transfer is used to make MORE embryonic stem cells.

The nucleus is taken out of a donor egg and injected with the nucleus from a stem cell (nucleus).

47
Q

In the late blastomere, what does the trophoblast release?

A

Once we have the late blastomere, the trophoblast will release early pregnancy factor- a immunosuppresent protein that protects the egg as it implants.

48
Q

When is early pregnancy factor made?

A

Early pregnancy factor is made by the trophoblast. It protects the cell as it begins implantation. It is made in the first 10 days.

49
Q

What do trophoblast cells differentiate into?

A

Cytotrophoblasts.

50
Q

What is a cytotrophoblast?

A

A stem cell layer that is mitotically active. It will divide and give rise to the syncytiotrophoblast.

51
Q

What is a syncytiotrophoblast?

A

Derived from the cytotrophoblast.

It is a multi-nucleated cell with no plasma membrane that does two things:

  1. Releases proteolytic enzymes that help with implantation.
  2. Releases chorionic gonadotropin, which is responsible for the initial signal of pregnancy.
52
Q

What part of the embryo attaches to the endometrium?

A

Syncytiotrophoblast.

It is a multi-nucleated cell that has no plasma membrane. It has proteolytic enzymes that are responsible for implantation and it releases HCG.

53
Q

When is a hydratidiform mole formed?

A

When a fetus aborts or when we have improper implamentation.

54
Q

What are hydratidiform moles?

A

Hydratidiform moles are trophoblastic proliferations that release an excessive amount of HCG, causing pregnancies to come out positive.

55
Q

What kind of hydratidiform moles are there and how are they made?

A

Hydratidiform moles can be a partial mole or a complete mole.

A partial hydratidiform mole has 69 chromosomes. It occurs when a normal oocyte (egg) is fertilized by 2 sperms. Thus, the zona reaction and polyspermy was not blocked

A complete hydratidiform mole has 46 chromosomes

56
Q

How is a complete hydratidiform mole made?

A

A complete hydratidiform mole is formed when a empty egg is fertilized by 2 sperm.

Or when a empty egg is fertilized by 1 sperm, which duplicates in the egg.

57
Q

Are hydratidiform moles paternal or maternal in nature?

A

Paternal.

58
Q

What are the sx of a hydratidiform mole?

A
  1. Vaginal bleeding
  2. Pelvic pain
  3. Enlarged uterus
  4. Hyperemesis gravidurum (morning sickness).
59
Q

If we do not take care of hydratidiform moles, what can happen?

A

We can develop choriocarninomas (cancer developed by a hydratidiform mole).

This can then spread to the 
lungs
liver
vagina
itestines
bones 
brain
60
Q

What happens in week 2?

A

We have the formation of the bilaminar disk and implantation continues.

61
Q

Now that the syncytiotrophoblast is on the endrometrium, what happens?

A

Inner cell mass will give rise to our bilaminar disk. Our bilaminar disk is made up of our

  1. Epiblast.
  2. Hypoblast.
62
Q

Once our epiblast forms, what happens?

A

It gives rise to the:

  1. embryo proper
  2. amnion
  3. amniotic cavity
63
Q

What is the amnion?

A

Our amnion forms a roof over our epiblast. Once this happens, it creates our amniotic cavity.

64
Q

Once our hypoblast forms, what happens?

A

Our hypoblast is ONLY present during week 2.

Our hypoblast will give rise to our endoderm.

65
Q

______ gives rise to our biilaminar disk, which is made up of what?

A

Inner cell mass gives rise to our bilaminar disk, which is made up of the epiblast and hypoblast.

66
Q

Epiblast gives rise to what?

A
  1. embryo proper
  2. amnion
  3. amniotic cavity
67
Q

Hypoblast gives rise to what?

A

Extra-embryonic endoderm.

Our hypoblast is ONLY present for week 2.

68
Q

Endoderm gives rise to what?

A
  1. Prechordal plate
  2. Primary yolk sac
  3. secondary yolk sac
  4. Extraembryonic mesoderm
69
Q

What is the pre-chordal plate?

A

Pre-chordal plate fuses with the epiblast to form the future location of our mouth and where the head is organized.

70
Q

Primary and secondary yolk sac is also called what?

A

the primary and secondary umbilical vesicle.

71
Q

What is the endoderm

A

The endoderm is extra-embryonic. It is not incoperated in the embryo and acts as a placeholder for our bilaminar disk (since the hypoblast is only present during week 2).

72
Q

How are the products of the hypoblast created?

A

Our bilaminar disk is going to be made up of our epiblast and hypoblast.

Cells from the hypoblast will migrate down to form our primary yolk sac. Overtime, this will re-distribute and create our secondary yolk sac. Our primary yolk sac will degenerate. As our primary yolk sac is being formed, this creates our extraembryonic mesoderm, which coats the trophoblast cells.

73
Q

Where does the embryo form?

A

The embryo forms at the bilaminar disk, where the epiblast and hypoblast meet.

74
Q

What is the extraembryonic coelum (extraembryonic cavity)?

A

The hollow cavity outside of the embryo.

75
Q

What types of extra-embryonic mesoderm do we have?

A
  1. Extraembryonic somatic mesoderm

2. Extraembryonic splanchnic mesoderm

76
Q

What is the extraembryonic somatic mesoderm and where is it located near?

A

Lines the trophoblast and surrounds the amnion

Located near the ectoderm

77
Q

Extraembryonic splanchnic mesoderm

A

lines the yolk sac.

Located near the endoderm.

78
Q

Derivates of our extraembryonic mesoderm

A
  1. Connecting stalk
  2. Primitive blood
  3. Chorion
79
Q

What is the connective stalk

A

The connective stalk is a derivative of our extraembryoic somatic mesoderm. It creates our umbillical cord

80
Q

What is primitive blood

A

The primitive blood is a derivate of our extraembroyonic splanchnic mesoderm.

It forms in the wall of our yolk sac

81
Q

What is the chorion

A

Chorion is a derivate of our [extraembryonic somatic mesoderm, cytotrophoblast and syncytiotrophoblast].

It gives rise to the wall of our placenta.

82
Q

Syncytiotrophoblast releases proteolytic enzymes that do what?

A

They are responsible for implantation, eroding the wall of the uterus.

83
Q

Where do most implantations occur?

A

On the posterior wall of the uterus.

84
Q

Implantation begins on day 6. What abnormal implantations can occur

A

Ectopic pregnancies can occur.

This is occurs when implantation occurs on the uterine tube (tubal pregnancy) or an organ of the abdomen.

85
Q

If a ectopic pregnancy occurs on an organ in the abdomen, it is still viable?

A

Yes. However, their is a 90% that the mom will die.

86
Q

What is placenta previa?

A

Placenta previa is when the placenta implants over the internal cervical os.

87
Q

If a female comes in with vaginal bleeding over 20 weeks and has not had a ultrasound, what do doctors do?

A

Doctors will assess for placenta previa via an ultrasound. If a digital exam is done, this can rupture the placenta and cause hemmorhaging.

88
Q

In week 1, we mentioned that an embryoblast forms. What is it?

A

Embryoblast is formed in week 1 when the inner cell mass gives rise to embryo tissue called embryoblast.

89
Q

What happens during week 3 of pregnancy?

A
  1. Gastrulation (formation of the germ cell layers that give rise to all tissues)
  2. Neurulation (formation of the spine and brain)
  3. Formation of the heart and circulatory system.

Mom can also determine if she is pregnant because she does not have her period.

90
Q

What is gastrulation?

A

Gastrulation is going to be the formation of our 3 germ layers from our epiblasts.

  1. Ectoderm
  2. Mesoderm
  3. Endoderm
91
Q

What does our ectoderm give rise to?

A

THINGS THAT MAKE US PRETTY AND SMART + SPINE

skin
hair
nails
CNS

92
Q

What does our mesoderm give rise to?

A

connective tissue

muscles
bone
blood
spleen
heart
93
Q

What happens if an area does not have mesoderm?

A

There will be no blood supply so that area becomes not viable

94
Q

Endoderm

A

gives rise organs

lungs, bladder, glands, GI,

95
Q

What is the process in which gastrulation occurs?

A

Cells on the caudal end of the epiblast will proliferate and invaginate, forming a primitive streak.

These cells will encounter signals that allow them to become

  1. true endoderm (replaces endoderm formed by hypoblast)

—-cells continue to invaginate—-

  1. form true mesoderm
  2. cells that were the epiblast are now the ectoderm, (outer layer that forms the things that make us look pretty and smart)
96
Q

What is the septum transversum?

A

Future diaphragm

97
Q

What is the cardiogenic area?

A

Future heart

98
Q

What are the two most rostral parts of the embryo?

A
  1. Septum transversum (future diaphragm)

2. Cardiogenic area

99
Q

What two germ layers fuse to create the pre-chordial plate?

A

fusion of the [ectoderm and endoderm]

**This makes sense, because we want it to form out mouth, so no mesoderm

100
Q

What two germ layers fuse to create the chloachal membrane?

A

also our [ectoderm and endoderm]. No mesoderm=no blood supply. Forms our digetive and urinary system.

Embryo (5 decks)

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