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Embryology > Gametogenesis And Fertilization (wk 2) > Flashcards

Gametogenesis And Fertilization (wk 2) Flashcards

1
Q

Sex cells are called

A

Gametes

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2
Q

Spermatogenesis creates what

A

Sperm

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3
Q

Oogenesis creates

A

Oocyte in females

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4
Q

Haploid is

A

The number of chromosomes (23)

22+either x or y

Usual number is 46

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5
Q

Meiosis is

A

Process of cell division that occurs in the production of gametes

2 cell divisions (meiosis 1 & 2)

Results in 4 gametes - each contain 1/2 chromosomes

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6
Q

Meiosis step 1

A

Reduction division

  • reduced from 46 to 23 chromosomes
  • 22 homologues and one sex (x or y) chromosome

Secondary gamatocytes are produced

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7
Q

Meiosis step 2

A

Each secondary gamatocyte divides

Skips nml interphase (no DNA replication)

Forms 2 haploid cells

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8
Q

Spermatogonium

A

Primordial sperm cells (stem cells)

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9
Q

How long are spermatogonium sperm cells dormant

A

Until puberty

Inb the seminiferous tubles

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10
Q

During spermatogenesis, what occurs

A

1 spermatogonium becomes 1 primary spermatocyte (46 diploid)

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11
Q

What occurs to the primary spermatocyte during the first meiotic division

A

It becomes 2 secondary spermatocytes

The cytoplasm division is equal ***

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12
Q

What occurs to the 2 secondary spermatocytes during the second meiotic division?

A

They form 4 spermatids (23 haploid)

No DNA replication in the second meiotic division

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13
Q

Spermiogenesis is the process that

A

Transforms spermatids into mature sperm

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14
Q

Where are the spermitids stored

A

In the epididymis until they become functionally mature

2 months

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15
Q

What are the charateristics of mature sperm

A

Head
Tail
Majority of the sperm is the head - contains the nucleus w/ the 23 chromosomes
Free swimming and motile

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16
Q

Head of the sperm characteristics

A

Anerior 2/3 covered by the acrosome

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17
Q

What is an acrosome

A

A sac like organelle containing several enzymes that allow the sperm to penetrate the oocyte during fertilization

  • corona radiata and ZONA PELLUCIDA
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18
Q

Tail of the sperm characteristics

A

3 segments

Middle piece
Principal piece
End piece

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19
Q

What does the middle piece of the sperm contain

A

Mitochondria - provides ATP required for motility

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20
Q

Oogenesis is the process where

A

Oogonia (primordial oocytes) become mature oocytes

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21
Q

When does oogenesis occur/stop

A

Begins prior to birth early in the fetal period

Stops at birth

Resumes at puberty

Complete cessation at menopause

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22
Q

During prenatal maturation of oocytes the oogonia become what

During what period

A

Primary oocytes

Prenatal period

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23
Q

Are oogonia present in the post natal period

A

No

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24
Q

What forms as the primary oocyte forms

A

A connective tissue surrounds the oocyte producing a single layer of follicular cells

This is called the primordial follicle

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25
Q

During puberty what occurs to the primordial follicle

A

It enlarges to become a primary ovarian follicle

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26
Q

What is the primary oocyte surrounded by

A

A glycoprotein material called the zona pellucida

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27
Q

When does the first meiotic division begin

A

When the primary oocyte is surrounded by a glycoprotein material called the zona pellucida

But it is not completed

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28
Q

When is prophase completed

A

Not until puberty

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29
Q

What occurs between the time of the first meiotic division and puberty

A

No further development

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30
Q

When does a primary oocyte complete the first meiotic division?

(Postnatal maturation of oocytes)

A

Shortly before ovulation

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31
Q

First meiotic division what occurs

Postnatal maturation of oocytes

A

Cytoplasm division is unequal

Secondary oocyte is formed w/ most of the cytoplasm

First polar body is formed with little cytoplasm-degenerates

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32
Q

What happens to the secondary oocyte at ovulation

Postnatal maturation of oocytes

A

The nucleus of the secondary oocyte begins the second meiotic division

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33
Q

When does the second meiotic division stop

A

At metaphase

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34
Q

If fertilization occurs at ovulation, what happens

A

The second meiotic division is completed

Second polar body is also formed

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35
Q

What happens if no fertilization occurs at ovulation?

A

No fertilization - the oocyte is discarded in menses

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36
Q

Polar bodies

A

The left over chromosomes from meiosis

23 total

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37
Q

Ovarian vs menstrual cycle

A

Both approx 28 days

Ovarian - development of the primary oocyte and supporting tissues in the ovary

Menstrual - preparation of the uterus for implantation of the fertilized oocyte

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38
Q

Hypothalamus produces what

A

Gonadotropin-releasing hormone

Transported to the anterior lobe of the pituitary gland of the pituitary gland

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39
Q

What does the anterior lobe of the pituitary gland release

A

Follicle stimulating hormone (FSH)

Luteinizing hormone (LH)

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40
Q

FSH

A

Follicle stimulating hormone

Stimulates the development of ovarian follicles and the production of estrogen by the follicular cells

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41
Q

LH

A

Luteinizing hormone

Serves as the “trigger” for ovulation (release of the secondary oocyte) and stimulates the follicular cells and corpus luteum to produce progesterone

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42
Q

What does LH and FSH do during the ovarian cycle

A

They cause changes in the ovaries resulting in:

  • development of follicles (FSH) that produce estrogen
  • ovulation (LH)
  • corpus luteum formation (LH) produces progesterone
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43
Q

FSH stimulates primary follicular growth causing what

A

Connective tissue surrounding the follicle forms a capsule called the theca folliculi *

44
Q

Theca folliculi forms 2 layers

A
  • theca externa-outer capsule

- theca interna-vascular layer

45
Q

Follicle cells form a layer around the primary oocyte and what happens

A

It is pushed aside

The adjacent cavity is filled with a follicular fluid and is called there antrum*

Once the antrum is formed the ovarian follicle is called the secondary follicle*

46
Q

Characteristics of the secondary follicle

A

Becomes oval shaped

The primary oocyte is at the concentric end

The follicular cells surrounding the primary oocytes are called the cumulus oophorus

Follicular cells produce estrogen

47
Q

What occurs to the follicle mid ovarian cycle

A

It has a growth spurt

48
Q

What occurs during the follicles growth spurt

A

It produces a bulge on the surface of the ovary called a stigma*

Caused by both FSH and LH

49
Q

Prior to ovulation the primary oocyte completes what

A

Its first meiotic division

Primary oocyte and first polar body

50
Q

A surge of LH production is triggered by what and causes what?

A

Triggered by high levels of estrogen in the blood

Forms the growth of follicular cells

51
Q

High levels of LH cause the stigma to bulge out forming a vesicle and eventually ruptures, what is this called

A

Ovulation

12-24 hours after the LH surge

52
Q

When does the second meiotic division start and stop

A

Starts just after ovulation

Stops at metaphase

53
Q

Some follicular cells surround the primary oocyte and for what

A

The corona radiate

Covers the zona pelluicida - covers the oocyte

54
Q

After ovulation, the ovarian follicle and the theca folliculi collapse and form grandular tissue called

A

Corpus luteum

Secretes progesterone and small amounts of estrogen

55
Q

If fertilization occurs, the corpus luteum becomes

A

The corpus luteum of pregnancy and produces progesterone and estrogen until 20 weeks when it is replaced by the placenta

56
Q

If fertilization does not occur, the corpus luteum becomes

A

The corpus luteum of menstruation and degenerates

57
Q

Corpus albicans

A

White scar tissue on the ovary from the corpus luteum

58
Q

What does the menstrual cycle mirror

A

The ovarian cycle

59
Q

What are the 4 phases of the menstrual cycle

A

Menstrual : 1-5
Proliferative : 5-14
Luteal : 14-27 (secretory)
Ischemia : 27-28

60
Q

What occurs during the menstrual phase

A

The functional layer of the uterine wall is sloughed off and discarded with menstrual flow or menses 4-5 days

Compact and spongy layers

61
Q

What occurs during the proliferative phase

A

Lasts 9 days

Coincides with the growth of ovarian follicles and is controlled by estrogen secreted by the follicles

There is two- to three-fold increase in the thickness of the endometrium and in its water content during this phase of repair and proliferation

62
Q

What occurs during the luteal phase

A

Aka secretory phase

Ovulation is at the beginning of this phase

Lasts 13 days

Growth of the corpus luteum (from follicular cells)

Spiral arteries grow into the compact layer

The venous network grows and large lacunae (venous spaces) form

63
Q

Whats lacunae

A

Venous spaces

64
Q

If fertilization does not occur what happens and what phase comes up

A

The corpora lutea degenerate, menstration occurs

Estrogen and progesterone levels fall and the secretory endometrium enters the ischemic phase

65
Q

What occurs during the ischemic phase

A

Spiral arteries constrict

Corpora lutea degenerates dec progesterone levels

Uterine gland secretions stop

Endometrium shrinks

Necrosis occurs in functional tissues

Blood vessels rupture resulting in bleeding into the uterus

20-80 ml of blood is lost

Compact and most spongy layers are shed in menses

66
Q

If fertilization does occur what happens?

A

Cleavage of the zygote and formation of a blastocyst begin
- beginning of the embryo

The blastocyst begins to implant in the endometrium on 6th day of luteal phase

HCG keeps the corpora lutea secreating estrogens and progesterone - produced in the outer layer of the blastocyst (synchytiotrophoblast)

The luteal phase continues and menstration does not occur

67
Q

Zygote

A

Fertilized ovum

68
Q

Blastocyst

A

Pre-implantation embryo consisting of a thin-walled hollow sphere of 16-40 cells

69
Q

Trophoblast

A

The outer wall cells of the blastocyst which attach the zygote to the uterus

Becomes the placenta

70
Q

Syncytiotrophoblast

A

Outter layer of the trophoblast

Produces HCG

71
Q

Second Oocyte is expelled when and from where

A

At ovulation from the ovarian follicle

Fimbriae move back and forth over the overy

They sweep the secondary oocyte into the infundibulum of the uterine tube

Oocyte passes into ampulla of the uterine tube and on into the uterine body of the peristaltic action of the uterine tube

Fertilization occurs ampulla

72
Q

Ejaculation of semen - 2 phases

A

Emission - semen passes to the prostatic part of the urethra through the ejaculatory ducts by the peristaltic movements of the ductus deferens

Ejaculation - semen is expelled from the urethra through the external urethral orifice
- the prostates change shape, closing off the bladder and opening the ejaculatory duct into the urethra

73
Q

Semen is composed of how many sperm

A

400-600 million

2-6 ml

About 200 sperm reach the fertilization site in the ampulla

74
Q

Before fertilization can occur, sperm must undergo a maturation process called

A

Capacitation

Takes 7ish hours

Exposing the acrosome

75
Q

Once the sperm has matured, what happens

A

They pass through the corona radiata
They penetrate the zona pellucida

Membranes fuse, the sperm enters

76
Q

Once the sperm enters the zona pellucida what happens

A

It transforms into a zona reaction and becomes impermeable to other sperms

77
Q

What happens when the second meiotic division completes

A

Forms a second polar body and a zygote is formed

78
Q

Enzymes in the acrosome are called ____ and ___and do what?

A

Hyaluronidase to help the sperm transverse the coronat radiata

Acrosin to Help the sperm transverse the zona pellucida

79
Q

Results of fertilization

A

Stimulates the secondary oocyte to complete the second meiotic division

Restores the nml diploid number of chromosomes (46) in the zygote

Results in variation!

Determines sex of embryo
X = female
Y = Male

Causes metabolic activation of the oocyte which initiates cleavage of the zygote

80
Q

Cleavage of the zygote consists of

Begins when

Undergoes what

A

Consists of repeated mitotic divisions of the zygote resulting in a rapid increase in the number of cells - blastomeres

Begins 30 hrs after fertilization

Zygote still surrounded by the zona reaction

Undergoes compaction after the 8 cell stage - allowing greater cell to cell interaction

81
Q

Morula

A

12-32 blastomeres

2 layers

  • inner cells : embryoblast or inner cell mass
  • outer layer : layer of flattened blastomeres that form the trophoblast
82
Q

Trophoblast secrete what

A

An immunosuppressant protein called early pregnancy factor

  • appers in the maternal serum w/in 24-48 hrs after implantation
83
Q

Formation of the blastocyst

A

The morula enters the uterus
- 4 days after fertilization

Uterine fluid passes through the zona rxn to form a fluid filled space
- the blastocystic cavity aka blastocoele

As fluid increases in the cavity, the blastomeres are seperated into two parts

  • trophoblast - thin outer cells that give rise to the embryonic part of the placenta
  • embryoblast - primordium of the embryo
84
Q

Implantation occurs when

A

Approx 6 days after fertilization of the blastocyst attaches to the epithelium of endometrium

Embryonic pole - area where the embryoblast attaches to the trophoblast and then to the endometrial epithelium

85
Q

The trophoblast of the blastocyst being differentiating into 2 layers

A

Cytotrophoblast - inner layer of cells
Synchtiotrophoblast - outer layer

Begins at end of week 1

86
Q

Ctyotrophoblast

A

A layer of mononucleated cells

It forms new trophoblastic cells that migrateinto the increasing mass of the synchytiotrophoblast

87
Q

Synchtiotrophoblast

A

A rapidly expanding multinucleated mass in which no cell boundaries are discernible

88
Q

Fingerlike processes of synchytiotrophoblast extend through what to do what

A

Through the endometrial epithelium

To invade the endmetrial connective tissue

By the end of the first week the blastocyst is superficially implanted in the compact layer of the endometrium

89
Q

Synchtiotrophoblasts produce what

A

Proteolytic enzymes that cause adjacent endometrial cells to ungergo apoptosis (programmed cell death) to allow for implantation

90
Q

The degenerated cells (decidual cells) contain lipids and glycoproteins that do what

A

Provide an immunology privileged site for the conceptus

Provide nutrition for the embryo

Produce hCG

91
Q

When the syncytiotrophoblast produces proteolytic enzymes that erode the endometrium the blastocyst does what

A

Burrows into the endometrium

92
Q

What occurs during the hypoblast formation

A

A cuboidal layer of cells on the surface of the embryoblast, facing the blastocystic cavity

Appears at end of first week

This begins the formation of the embryonic disc

93
Q

What does hCG do

A

Maintains the development of the spiral arteries

Continues the development of the synchtiotrophoblast
- self maintaining

94
Q

How does the embryonic disc form

A

Embryoblast (inner cell mass) seperates into two layers forming the bilaminar embryonic disc

Epiblast - thicker layer, high columnar cells adjacent to the amniotic cabity

Hypoblast - thinner layer, small cuboidal cells adjacent to the exocoelomic cavity

Happens spontaneously w/ implantation

95
Q

How does the formation of the amniotic cavity occur

A

Simultaneously with implantation

A small space developos in the embryoblast - amniotic cavity
- lined with aminoblasts which form a thin membrane called the amnion - lines the amniotic cavity

Epiblast is the floor

96
Q

Exocoelomic cavity

A

When the amniotic cavity and embryonic disc from the exocoelomic membrane forms lining the blastocystic cavity
- lines the cytotrophoblast

Forms the exocoelomic cavity

Roof is the hypoblast

The exocoelomic membrane and cavity from the primary umbilical vesicle
- aka primary yolk sac

97
Q

Primary umbilical vesicle is

A

Aka yolk sac

Seperated from the amnion and embryonic disc

The outer layer of cells from extraembryonic mesoderm

  • connective tissue
  • premordium of multiple structures
98
Q

Lacunae formation

A

Takes place as the amnion, embryonic disc, and primary umbilical vesicle form

Isolated cavities filled with a mixture of maternal blood and cellular debris provide embryonic nutrition

Fluid in the lacunae called embryotroph

99
Q

Lacunae formation is the beginning of

A

Uteroplacental circulation

100
Q

What happens at the 10 day mark

A

Implantation is complete

The implantation site does not completely close until the 12th day

Covered by a closing plug - fibrous coagulum of blood

Day 12 the lacunae have fused to form large lacunar networks - spongelike

101
Q

Extraembryonic mesoderm enlarges after implantation is complete to form what

A

Extraembryonic coelomic spaces

Spaces rapidly fuse to form a lg cavity called the extraembryonic coelom

Extraembryonic coelom surrounds the amnion and the umbilical vesicle, except for where they are attached to the chorion by the connecting stalk

102
Q

As the extraembryonic coelom forms, the primary umbilical vesicle (yolk sac) does what

A

Decreases in size

Forms a larger secondary umbilical vesicle

Day 14

Part of the primary vesicle gets pinched off

103
Q

The extraembryonic coelom splits the extraembryonic mesoderm into two layers

A

1) extraembryonic somatic mesoderm - lines the trophoblast and covers the amnion
2) extraembryonic splanchnic mesoderm - surrounds the umbilical vesicle

104
Q

A new membrane surrounds the embryo called ____ that has what three layers

A

Called the Chorion

1) extraembryonic somatic mesoderm
2) cytotrophoblast
3) synchtiotrophoblast

The internal wall of the chorionic sac surrounds the chorionic cavity
- extraembryonic somatic mesoderm

105
Q

What is the role of the connecting stalk

A

Suspends the embryo in the chorionic cavity

This is the future site of the placenta

106
Q

When do primary chorionic villi appear

A

At the end of the second week

These are cellular extentions formed from cytotrophoblastic cells that grow into the overlying syncytiotrophoblast forming the primary chorionic villi

This is all caused by extraembryonic somatic mesoderm

107
Q

Prechordial plate forms when

A

Day 14

Endodermal cells in a localized are from a thickened circular area

This is the site of the mouth and is an important organizer of the head rgn

Embryology (4 decks)

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