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BIOL155 > Fertilization and Pregnancy > Flashcards

Fertilization and Pregnancy Flashcards

1
Q

How many eggs are released in a typical menstrual cycle

A

Only 1!

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2
Q

How many eggs do you have at birth? At puberty? In a typical menstrual cycle?

A

Birth = 2 million
Puberty = 400,000
Typical menstrual cycle = 1

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3
Q

What are the products of gametogenesis and where does it occur

A

Occurs in the gonads
- sperm and eggs are released by the gonads
- sperm and secondary oocytes
- leads to the release of many sperm and one secondary oocyte

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4
Q

How many sperm are released in gametogenesis

A

MANY

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5
Q

How many eggs are released in gametogenesis

A

Just one!

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6
Q

Compare the size of sperm to eggs

A

Eggs are REALLY BIG in comparison to the miniature sperm cells

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7
Q

What is fertilization

A

Fusions of two haploid gametes, which produce a zygote
- successful fertilization involves the combined actions of many many sperm in order for one sperm to fuse with the oocyte

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8
Q

When does successful fertilization occur

A

Within a day of ovulation
- not long after the occyte enters the uterine tube

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9
Q

How long is ejaculated sperm viable in the uterine tube? How long is a secondary oocyte viable after ovulation?

A

At least some of the ejaculated sperm can reach the uterine tube within a few hours of ejaculation
- can remain viable for 5-7 days in the female reproductive tract

A secondary oocyte remains viable for 24 hours after ovulation

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10
Q

How many sperm actually reach the egg after penetrating the oocyte’s membrane

A

Many sperm are required to break through the oocyte’s membrane, but only ONE sperm can penetrate the oocyte

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11
Q

Which part of the sperm is used to break down the layers of follicular cells surrounding the occyte

A

The enzymes in the ACROSOME (tip) of the sperm are used to break down the layers of follicular cells that make up the corona radiata

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12
Q

What is the corona radiata

A

The outer layer of follicular cells surrounding the oocyte

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13
Q

How does an oocyte get activated during fertilization

A

When one sperm breaks the oocyte membrane, the oocyte is activated
- must break down the outer layer to penetrate the ovum and fertilize it

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14
Q

What is the zona pellucida

A

A thick membrane inside of the corona radiata that protects the ovum from having more than one sperm penetrate it
- biochemical reactions in the zona pellucida prevent more than one sperm from entering the ovum by releasing enzymes

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15
Q

Determine if fertilization will or will not occur in the following scenario:

Sperm reach the uterine tube days before ovulation.

A

FERTILIZATION MIGHT OCCUR

Sperm can remain viable for days, as long as they are in the area where the ovum will end up after ovulation (Fallopian tubes) fertilization might occur
- especially if the sperm is still viable in that window

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16
Q

Determine if fertilization will or will not occur in the following scenario:

Ovulation occurs more than a day before sperm enter the female reproductive tract.

A

FERTILIZATION MIGHT NOT OCCUR

The ovum is only viable within 24 hours of ovulation, so if sperm enters the female reproductive tract more than a day after ovulation, fertilization will be difficult because the egg is not viable anymore

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17
Q

Determine if fertilization will or will not occur in the following scenario:

The ejaculate contains low numbers of sperm, so too few reach the oocyte.

A

FERTILIZATION MIGHT NOT OCCUR

Penetration requires many sperm together to break through the ovum, so too few sperm would not be enough to reach the ovum for fertilization
- there is a threshold number of sperm

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18
Q

What happens after a sperm enters the ovum and how does a zygote form

A

After a sperm has entered the ovum, two haploid pronuclei develop and mingle their chromosomes
- this is what develops a zygote
- as soon as the chromosomes mingle, the first mitotic cell division begins -> around 24 hours after the point of fertilization

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19
Q

Where does fertilization occur

A

In the Fallopian/uterine tubes of the female reproductive system

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20
Q

Describe step 1 of fertilization:

Oocyte at ovulation

A

Secondary oocyte is released at ovulation (occurs on day 14 of the uterine cycle)

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21
Q

Describe step 2 of fertilization:

Fertilization and oocyte activation

A

Sperm penetrates the corona radiata and fertilizes ovum
- oocyte is activated
- zona pellucida releases enzymes to prevent more than one sperm from entering the ovum

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22
Q

Describe step 3 of fertilization:

Pronuclei develop and DNA

A

Once the sperm has entered the ovum, the nuclei from the sperm and egg develop into two haploid pronuclei and mingle their chromosomes
- a zygote is formed

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23
Q

Describe step 4 of fertilization:

Spindle formation begins

A
  • male and female pronuclei are developing
  • spindle formation also begins
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24
Q

Describe step 5 of fertilization:

Amphimixis occurs and cleavage begins

A
  • mitosis begins and metaphase of the first cleavage division occurs
  • starts with 46 chromosomes and undergoes mitotic division
  • size of the zygote itself does not change, the cells within the zygote just get smaller
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25
Q

Describe step 6 of fertilization:

First cleavage forms two blastomeres

A
  • first cleavage division begins and eventually forms two blastomeres
  • the zygote itself is the same size, but the blastomeres are smaller
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26
Q

When does cleavage begin

A

Begins immediately after the zygote is formed

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27
Q

What is a pre-embryo

A

During the period of cleavage, the zygote starts a series of repeated mitotic cell divisions, increasing its cell numbers without growing in size
- it is now considered a pre-embryo

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28
Q

What is a(n advanced) morula and how does it differ from blastomeres

A

A solid ball of cells surrounded by zona pellucida

  • blastommeres are just two cells inside the zona pellucida
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29
Q

What is a plastomere

A

Daughter cells produced during cleavage

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30
Q

What happens on day 1-10 after the zygote is formed

A

First cleavage division
- cells get smaller but the size of the zygote remains the same

  1. Two-cell stage
    - AKA blastomeres
  2. Four-cell stage
    - AKA more blastomeres
  3. Early morula
    - solid ball of cells surrounded by zona pellucida
  4. Advanced morula
    - solid ball of cells surrounded by zona pellucida
  5. Shedding of zona pellucida and loss of zona pellucida allows for transport of zygote to uterus

6-9. Implantation of zygote into uterine wall

  1. Yolk sac formation
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31
Q

Where is the morula typically found

A

Found in the uterine tube

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32
Q

What is a blastocyst

A
  • develops from the morula
  • hatches from zona pellucida
  • around the time the morula enters the uterus, it sheds the zona pellucida and undergoes cell rearrangements, creating a blastocyst
  • hollow ball of cells with a fluid-filled inner cavity and an inner mass of cells that will become the embryo
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33
Q

What is the blastocoele

A
  • blastocyst cavity
  • hollow cavity
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34
Q

What is the embryoblast

A
  • inner cell mass of a blastocyst
  • will become the embryo
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35
Q

What is implantation

A
  • the process by which the blastocyst fuses with the functional layer of the endometrium
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36
Q

What is the endometrium

A
  • layer lining the lumen of the uterus
  • has a functional layer
  • functional layer gets shedded during menstrual cycle
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37
Q

What are trophoblasts

A

Outer cell layer of the blastocyst which later becomes part of the placenta
- drive erosion of the endometrial epithelium, lodging the blastocyst within the endometrium
- becomes implanted

38
Q

List the parts of a blastocyst

A

BLASTOCYST
- blastocoele (cavity)
- trophoblast
- inner cell mass (embryoblast)
- shedded zona pellucida
- trophoblast

39
Q

How does implantation work

A
  • multi-day process
  • involves changes to both the trophoblast and inner cell mass
  • trophoblast cells divide rapidly and separate into two layers which surround the inner cell mass
40
Q

The trophoblast cells divide rapidly and separate into two layers which surround the inner cell mass,

What are the two layers

A

Cytrotrophoblast
Syncytiotrophoblast

41
Q

What are cytotrophoblasts

A

Layer that has individual cells with plasma membranes

42
Q

What are syncytiotrophoblasts

A

Many nuclei sharing one cytoplasm

43
Q

The inner cell mass forms two layers of cells sandwiched between two new cavities,

What are the two new cavities

A

Amnion
Yolk sac
- these two layers of cells are surrounded by the cytotrophoblast and syncytiotrophoblast

44
Q

What is the amnion

A
  • a membrane forming a fluid-filled cavity (the amniotic sac) that encloses the embryo
45
Q

What is the yolk sac

A
  • supplies nutrients to developing embryo
46
Q

What happens if implantation occurs in an area other than the uterus = ECTOPIC PREGNANCY

AKA Why must implantation occur in the uterus

A
  • pregnancy cannot be carried out full term
  • myometrium / smooth muscles / uterus is designed to support a growing fetus
  • can expand, vascularized, has nutrients, blood supply, oxygen, ability to remove waste
  • same structural support is not available in the
47
Q

Where does fertilization occur
Where does implantation occur

A

Fertilization = fallopian tubes
Implantation = uterus

48
Q

What is gastrulation

A

Creation of three distinct germ layers for the developing embryo following implantation
- during gastrulation, cells from one layer of the inner cell mass migrate into the space between the two cell layers

49
Q

Order the following events correctly:

  • Gastrulation
  • Fertilization
  • Implantation
A
  1. Fertilization
  2. Implantation
  3. Gastrulation
50
Q

Describe where each of the following are in relation to the inner cell mass:

  • cytotrophoblast
  • syncytiotrophoblast
  • amnion
  • yolk sac
A
  • syncytiotrophoblast
  • cytrotrophoblast
  • yolk sac (or amnion)
    inner cell mass
  • amnion (or yolk sac)
  • cytrotrophoblast
  • syncytiotrophoblast
51
Q

What are the three germ layers that form during gastrulation

A
  1. Ectoderm
  2. Mesoderm
  3. Endoderm
52
Q

What is the ectoderm

A

layer of cells in contact with the amniotic cavity

53
Q

What is the mesoderm

A

middle layer between the endoderm and ectoderm

54
Q

What is the endoderm

A

layer of cells in contact with the yolk sac

55
Q

The three germ layers of the gastrula have distinct properties, and each will eventually be responsible for forming different _________

A

ORGANS

  • the three germ layers of the gastrula will eventually give rise to different organs
56
Q

Briefly describe what the ectoderm contributes to the body

A
  • epidermis
  • nervous tissue
  • pituitary gland and adrenal medullae
57
Q

Briefly describe what the mesoderm contributes to the body

A
  • dermis
  • subcutaneous layer (hypodermis)
  • all structures of the muscular system
  • all structures of the cardiovascular system
  • all structures of the lymphatic system
  • gonads
58
Q

Briefly describe what the endoderm contributes to the body

A
  • thymus
  • thyroid gland
  • pancreas
  • urinary bladder
59
Q

What are the four extra-embryonic membranes that form around the developing embryo

A
  1. Amnion
  2. Yolk sac
  3. Chorion
  4. Allantois
60
Q

What is the amnion

A

layer surrounding amniotic cavity where the embryo develops within

61
Q

What is the yolk sac

A

creates a pouch involved in storing, collecting and distributing nutrients to growing embryo

62
Q

What is the chorion

A

separates space in blastocoele from trophoblast (layer of cells as embryo is developing)

63
Q

What is the allantois

A

eventually becomes the umbilical stock/cord
- will form part of the umbilical cord

64
Q

How long is the first trimester

A

weeks 1-12

65
Q

How long is the second trimester

A

weeks 13-26

66
Q

How long is the third trimester

A

weeks 27 to end of pregnancy

67
Q

What is chorionic villous sampling (CVC)

A
  • testing on the chorion
  • retrieving cell samples
  • occurs in the first trimester
68
Q

What is amniocentesis

A
  • testing on the amnion
  • retrieving amniotic fluid samples
  • usually performed after 15 weeks
69
Q

What are the risks of CVC and amniocentesis

A

potential risk of termination of pregnancy
- you are inserting a syringe into the area where the embryo is developing
- can be dangerous for the baby

70
Q

What is the placenta and what are its three functions

A
  • fetal organ that acts as an interface between the fetus and the pregnant mother
  • way of passing materials to/from baby

FUNCTIONS:
1. Nutrient and oxygen exchange between fetal and maternal blood stream
2. Removal of CO2 and other wastes from fetal blood
3. Secretes hormones into both bloodstreams

71
Q

What connects the fetus to the placenta

A

Umbilical cord

72
Q

What is the umbilical cord

A

Connection from the placenta to the fetus and vice versa

73
Q

Describe the relationship between the placenta and embryonic/maternal issues

A

CHORION = major component of the placenta, forms chorionic villi

CHORIONIC VILLI = invade the endometrium and break down its blood vessels
- forms area of pooled blood which exchanges with fetal blood

TROPHOBLAST = layers surround each villus and are responsible for hormone secretion by the placenta

74
Q

Which hormones maintains the production of ovarian progesterone after formation of embryo

A

hCG = gonadotropin (peptide hormone that causes the release of FSH and LH)

75
Q

What is the role of hCG in the ovaries

A
  • closely related to LH
  • acts on the same tissues within the ovary
  • signals the corpus luteum to survive and keep secreting progesterone
76
Q

What happens during pregnancy tests, what is it looking for

A

Looking for hCG in the maternal blood/urine
= detectable sign of pregnancy

77
Q

Not long after the embryo forms, which layer of the embryo begins to secrete the human chorionic gonadotropin hormone

A

SYNCTIOTROPHOBLAST

78
Q

Before the end of the first trimester, ___________ cells take over the secretion of progesterone and estrogen

A

PLACENTA takes over the secretion of progesterone and estrogen

79
Q

Trace what part of the female body is in charge of synthesizing progesterone

A
  1. Uterine cycle = corpus luteum
  2. First trimester of pregnancy = corpus luteum
  3. Corpus luteum degenerates after first two months of pregnancy
  4. Placental trophoblast tissues begin to synthesize larger amounts of progesterone
80
Q

Why is the maintenance of high levels of progesterone necessary for pregnancy

A

Maintenance of endometrium

81
Q

What is the role of trophoblast after the first trimester of pregnancy

A
  • produce larger amounts of progesterone to maintain the integrity of the endometrium
  • begins to synthesize estrogens (especially estriol) as pregnancy progresses
82
Q

What is an abortion

A

A procedure to terminate a pregnancy

83
Q

What are the two types of abortions

A

Refers to the method of termination used

  1. Medical
  2. Surgical
84
Q

What is a medical abortion

A

Involves taking a combination of medicines to end the pregnancy by causing the uterine lining to be shed
- administration or intake of meds that cause endometrium to shed
- no structures to support developing embryo
- administration of progesterone antagonist

85
Q

What is a surgical abortion

A

Involves physical disruption to the lining of the uterus to end the pregnancy
- typically by suction

86
Q

True or False:

The endometrium becomes part of the placenta

A

TRUE!

87
Q

What is mifepristone

A
  • progesterone antagonist
  • antagonist = prevents binding of a certain hormone from its receptor to prevent further signalling
  • synthetic steroid derivative that is able to prevent progesterone from activating the progesterone receptors
88
Q

How do progesterone antagonists terminate a pregnancy

A

Blocking progesterone leads to the softening of the cervix
- smooth muscle relaxing
- disintegration of the endometrium
- detaches the placenta and embryo

89
Q

What is misoprostol

A

Medication that is combined with mifepristone

  • prostaglandin which induces the uterus to contract, aiding expulsion of the embryo
90
Q

Breakdown the roles of mifepristone and misoprostol in abortions

A

Mifepristone = causes progesterone blockade
= decidual necrosis (death of endometrial tissue)
= cervical ripening (disintegration of endometrium)

Misoprostol = causes uterine cramping and expulsion

91
Q
A

BIOL155 (34 decks)

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