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Human Embryology > Beginning of Human Development Weeks 1-3 > Flashcards

Beginning of Human Development Weeks 1-3 Flashcards

1
Q

Beginning of human development overview

A

Human development is a continuous process that begins when an oocyte (ovum) from a female is fertilized by a sperm (spermatozoon) from a male. Cell division, cell migration, apoptosis, differentiation, growth and cell rearrangement transform the fertilized oocyte into a highly specialized, Totipotent cell called a zygote into a multicellular human

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2
Q

Human embryology

A

The study of prenatal development

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3
Q

Gestation period in humans is

A

280 days from onset of LMP (overestimated by 2 weeks) or

266 days from fertilization

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4
Q

Pre-natal development is divided into three periods:

A
  1. Pre-embryonic period- fertilization to 2 weeks
  2. Embryonic period- 3-8 weeks
  3. Fetal period-9th week to birth
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5
Q

Fertilization results in these 5 processes

A

1.oocyte completing meiosis 2
2. Restoration of diploid chromosome number in zygote
3. Species variation
4. Determination of genetic sex
5 initiation of cleavage (mitosis) of zygote

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6
Q

Ootid

A

Secondary oocyte with 2 pronuclei- one from each parent

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7
Q

Gametogenesis

A

The process of forming and developing specialized generative cells called gametes

Gamete maturation in males is called spermiogenesis and in females is called oogenesis

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8
Q

Cell cycle

A 
G0- cell cycle arrest 
G1- cellular contents duplicate 
S-Each of the 46 chromosomes duplicate
G2- Cell double checks for duplication errors, and makes any repairs 
Mitosis 
Cytokinesis 
G0/ G1

Outside of mitosis and cytokinesis is interphase

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9
Q

Mitosis vs meiosis

A

Mitosis takes one diploid parent cell and creates two diploid identical daughter cells

Meiosis takes one diploid parent cell and creates 4 haploid daughter cells

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10
Q

Ad spermatogonia divide in which way

A

Asymmetrically

Can produce an identical Ad spermatogonia or a Ap spermatogonia (less potency)

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11
Q

Differences of spermatogeneis and oogeneis

A
  1. One diploid primary spermatocyte produces 4 haploid sperm. Whereas, only one mature oocyte results from maturation of a primary oocyte
  2. There is a follicle around oocyte
  3. Second meiosis completed after fertilization in females and before spermiogenesis in males.
  4. Sperm can be X or Y, oocyte is only X
  5. Polar bodies develop and degrade in females
  6. Tests vs ovaries
  7. Spermatogonium in soermatogeneis but no Oogonium in oogenesis
  8. Sperm are much smaller than eggs
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12
Q

Why no oogonium in oogenesis?

A

Oogonium develop into primary oocytes before birth (prenatal maturation). No more oocytes develop after birth. At birth you have 2M, which depletes to 40,000 by puberty, and only 400 become secondary oocytes for ovulation.

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13
Q

Gonium

A

Germ cell

High potency

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14
Q

Spermiogenesis phases

A

Rounded spermatid becomes an elongated sperm

  • formation of the acrosome derived from the golgi region, contains enzymes that are released at the beginning of fertilization to assist in breaking down corona radiata and ZP.
  • nucleus capped with lyric enzymes
  • Mitochondria concentrate and arrange themselves end to end in form of a tight helix, forming a collar-like mitochondrial sheath.
  • tail elongates
  • centrioles on opposite side of golgi
  • microtubules form to create cytoskeleton structure
  • residual cytoplasm is shed
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15
Q

Parts of sperm

A

Principal piece of tail
End piece of tail
Middle piece of tail (mitochondrial sheath)

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16
Q

Stages of oogenesis

A
  • Primary oocyte suspended in prophase and remain dormant until puberty (vulnerable to environmental agents)
  • Follicle matures and shortly before ovulation the primary oocyte completes meiosis 1, to become secondary oocyte and first polar body. (Division of cytoplasm is uneven and secondary oocyte receives almost all and polar body none)
  • at ovulation the secondary oocyte begins second meiosis but is arrested in metaphase 2
  • if sperm penetrate it completes meiosis 2 and the cytoplasm is uneven and second polar body is made.
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17
Q

FSH and LH produce_____

A

Cyclic changes in the ovaries-the ovarian cycle that includes growth of follicles, ovulation and the corpus luteum formation

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18
Q

Development of follicles is characterized by

A
  • growth and differentiation of primary oocyte
  • proliferation of follicular cells
  • formation of Zona Pellucida
  • Development of the Theca Folliculi
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19
Q

Ovulation characterization

A
  • Triggered by the surge of LH production
  • LH surge is elicited by increased levels of Estrogen
  • Formation of the stigma
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20
Q

HPO AXIS

A

Hypothalamus releases Gonadotropin-releasing hormone which causes the pituitary gland to release FSH and LH which causes the ovaries to mature follicles and develop corpus luteum

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21
Q

How do you know if an oocyte is a secondary oocyte?

A

Antrum is present

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22
Q

Theca folliculi

Produces??

A

Connective tissue surrounding a follicle that produces estrogen

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23
Q

Corpus luteum forms from…

A

During LH surge there is so much pressure build up the follicle ruptures and releases the secondary oocyte. The left over tissue folds and creates the corpus luteum which produces progesterone and estrogen

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24
Q

The inner layer of the uterus_____ goes through _____

A

Endometrium

Monthly changes (based off hormone levels)

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25
Q

What directs the secondary oocyte to enter the Fallopian tube?

A

Fimbriae- finger like projections on the infundibulum of the Fallopian tube

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26
Q

Cellular signalling in endometrial cells

A

Estrogen moves through the cell membrane into the cell to bind with an estrogen receptor. It phosphorylizes and dimerizes to another estrogen receptor and translocates to nucleus. The estrogen complex acts as a transcription factor to cause mitotic genes to grow rapidly to prepare for egg attachment

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27
Q

End of luteal phase sees crazy…

A

Proliferation with progesterone and progesterone receptors causing mitotic gene expression

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28
Q

When the corpus luteum degenerates (follicle is not fertilized) and stops releasing Progesterone and Estrogen it causes

A

Endometrium to shed= menstrual cycle

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29
Q

Iechemic phase

A

Cells can’t live with lack of progesterone and estrogen so they are sloughed and shed

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30
Q

As soon as a sperm contacts plasma membrane of a secondary oocyte it causes….

A

Zona Reaction

Protective layer forms so secondary oocytes are impermeable to any other sperm.

-maintains chromosome number

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31
Q

Phases of fertilization

A
  • passage of sperm through corona radiata (hyalurinidase)
  • penetration of ZP (acrosin)
  • fusion of plasma membrane of the oocyte and sperm
  • completion of second meiotic division of oocyte and formation of male pro nucleus
  • oocyte containing two haploid pronuclei is called ootid
  • fusion of pronuclei leads to the formation of zygote from ootid
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32
Q

Cleavage of Zygote

-time and phases

A
  • cleavage begins about 30 hours after fertilization
  • zygote becomes 2 identical blastomeres
  • cleavage consists of repeated mitotic divisions of the zygote, resulting in a rapid increase in the number of cells. These embryonic cells(blastomeres) become smaller with each successive cleavage division and forms the morula (solid hall of 12-32 blastomeres) by day 3.
  • by day 4, morula crimes a hollow ball called the blastocyst (now in uterus)
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33
Q

Formation of the blastocyst

A
  • shortly after morula enters uterus (4days), a fluid filled space called the blastocystic cavity appears inside the morula. The fluid passes through the uterine cavity into the zona pellucida to form a space. As fluid increases in the bladtocystic cavity, it separates the blastomeres into two parts:
  • trophoblast
  • inner cell mass (embryo blast)
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34
Q

Trophoblast

Gives rise to?

A

A thin, outer layer which gives rise to the embryonic part of the placenta

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35
Q

Inner cell mass or embryo blast

A

A group of centrally located blastomeres, the inner call mass, which gives rise to the embryo; because it is the primordium of the embryo.

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36
Q

Hatching

A

When the ZP of the blastocyst begins degenerating.

-disappears by day 5

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37
Q

Is there increase in size of a developing embryo prior to ZP degrading?

A

No, blastomeres become smaller and compacted

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38
Q

Blastogenesis

A
  • The conceptus of a blastocyst (day 4, morula becomes hollow ball)
  • embryoblast now projects into the blastocystic cavity and the trophoblast forms the wall of the blastocyst.
  • ZP degrades in uterine fluid after 2 days
  • At day 6 since fertilization (day 20-28 of cycle), the blastocyst attached to the endometrial epithelium, usually adjacent to the embryonic pole.
  • as soon as it attaches, the trophoblast starts to proliferate and differentiate into two layers.
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39
Q

What two layers does the trophoblast differentiate into?

A

Inner layer- cytotrophoblast

Outer layer- syncytiotrophoblast

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40
Q

First week development short overview of processes

A
  • cleave begins about 30 hours after fertilization
  • zygote becomes 2 identical blastomeres
  • morula is a solid ball of 12-32 blastomeres (3 days)
  • day 4, morula becomes a hollow ball called the blastocyst (now in uterus)
  • blastomeres separate into trophoblast and embryoblast
  • blastocyst has a fluid filled cavity called blastocyst cavity
  • blastocyst begins to implant in the wall of the uterus by end of first week.
  • trophoblast proliferated and differentiated into cytotrophoblast and syncyntiotrophoblast
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41
Q

What is the nuclear makeup of the two trophoblastic layers?

A

Cytotrophoblast is mono nuclear

Syncytiotrophoblast is multinucleated

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42
Q

ESC

A

Embryonic stem cells or Embryoblast cells

-can make all organs and tissues but are pluripotent because they can’t make extra embryonic structures like the placenta.

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43
Q

Syncytiotrophoblast _______ into epithelium of uterus

A

Invaginate

Highly regulated process unless cancer and parasites and stops at a point

44
Q

Second week of development events

A
  • implantation complete
  • bilaminar embryonic disc forms
  • 2 layers of trophoblast continue to develop
  • extra embryonic structures from (amniotic cavity, amnion, umbilical vesicle, connecting stalk and chorionic sac)
45
Q

Development of the bilaminar embryonic disc

A
  • As implantation progresses, a small space appears in the embryoblast. This space is the primordium of the amniotic cavity. Morphological changes occur in the embryoblast the result in the formation of a flat, almost circular bilaminar plate of cells called the embryonic disc. The disk has two layers:
  • Epiblast
  • Hypoblast
46
Q

Epiblast

A

The thicker layer, consisting of high columnar cells related to the amniotic cavity.

-amnion cells derived from it

47
Q

Hypoblast

A

In the embryonic disc, the smaller cuboidal cells adjacent to the exocoelomic cavity (Primary Yolk Sac)

Extracellular mesoderm is derived from it

48
Q

Why are cavities formed?

A

So cells have room to differentiate and migrate

49
Q

Is the extra embryonic mesoderm part of the germ layers?

A

NO

extraembryonic means outside of the embryo

50
Q

Amniotic cavity

A

Cavity between the inner cell mass and the cytotrophoblast

51
Q

The blastocyst cavity becomes the

A

Umbilical vesicle (or yolk sac) or (primary then Smaller secondary)

52
Q

The extraembryonic mesoderm splits into what?

A
  • Extraembryonic somatic mesoderm:
  • Extraembryonic splanchnic mesoderm

Spaces fuse and then Split creating chronionic sac cavity

53
Q

Extraembryonic somatic mesoderm

A

Lines the trophoblast and covering the amnion

54
Q

Extraembryonic splanchnic mesoderm

A

Surrounds the umbilical vesicle

55
Q

The end of the second week is characterized by the appearance of _______

A

Primary chronionic villi

Proliferation of cytotrophoblastic cells produce cellular extensions that grow into the syncytiotrophoblast

56
Q

What forms the chorion

A

The extra embryonic somatic mesoderm and the two layers of trophoblast

57
Q

Chorion

A

Forms the wall of the chorionic sac, within which the embryo and it’s amniotic sac and umbilical vesicle are suspended by the connecting stalk

58
Q

The extraembryonic coelom is now called the…… in the second week

A

Chorionic cavity

59
Q

Where does Extraembryonic mesoderm develop

A

Between the trophoblast and the amnion and umbilical vesicle

60
Q

Spaces appear within the extraembryonic mesoderm and form a cavity called the extraembryonic coelom which will become the

A

Chorionic cavity

61
Q

The extraembryonic mesoderm is split into 2 layers:

A
  1. Extraembryonic somatic mesoderm
    - which along with the 2 layers of trophoblast will become the chorion
  2. Extraembryonic splanchnic mesoderm
    - which covers the umbilical vesicle (yolk sac)
62
Q

Connecting stalk is made up of

A

Extraembryonic mesoderm

63
Q

The second week of development is called the week of 2’s why?

A

Trophoblast: syncytiotrophoblast and cytotrophoblast

Extraembryonic mesoderm: splanchnic and somatic

Embryonic disc: Epiblast and Hypoblast

64
Q

Primary chorionic villi develop with a core of _____ and covering of ______

A

Cytotrophoblast

Syncytiotrophoblast

65
Q

Primary chorionic villi are the primordia of:

Lacunar networks are the primordia of

A

Chorionic villi

Intervillous spaces

66
Q

Prechordal plate

A

Flat, bilaminar embryonic disc develops a thickening at one end of Hypoblast that indicates future site of mouth

67
Q

What prevents the decline of the endometrium

A

Blastocyst secreted human chorionic gonadotropin (hCG) to stimulate the corpus luteum to continue to produce estradiol and progesterone

-about 20 weeks in the placenta takes over hormone production

68
Q

Clinical significance chorionic (gestational) sac diameter

A

Using trans vaginal ultrasonography, the measurement of the chorionic sac diameter can help determine the age of the embryo, as well as early development and pregnancy outcomes

69
Q

How can implantation of a blastocyst be detected?

A
  • ultrasonography

- highly sensitive radioimmunoassays of hCG as early as the second week (pregnancy blood test)

70
Q

2 ways implantation goes wrong

A
  • implantation if the lower segment of the uterus - placenta previa
  • implantation sites other than the uterus (especially in the uterine tube)- ectopic pregnancy
71
Q

When do blood filled lucanae appear in the syncytiotrophoblast

A

Day 9

72
Q

At day 10, the blastocyst sinks be earth the endometrial epithelium and the _____ is filled by ____

Repaired?

A

Defect

A Closing plug

Defect Repaired day 13-14
Can be confused for menses

73
Q

Lacunar networks form by ____ of adjacent lacunae (day )

A

Fusion

10-11

74
Q

Uteroplacental circulation

A

The syncytiotrophoblast erodes endometrial blood vessels, allowing maternal blood to seep in and out of lacunar networks

Day 11-12

More nutrients by blood network than simple diffusion

75
Q

Prechordal plate develops as a ______

A

Localized thickening of the Hypoblast, which indicates the future cranial region of the embryo and the future site of the mouth

76
Q

Primary chorionic villi stages

A

Primary- contain syncytiotrophoblast and cytiotrophoblast

Secondary- contain above and extraembryonic somatic mesoderm

Tertiary-lined with blood vessels

77
Q

Third week of development is most noted for

A

Formation of germ layers and early tissue and organ differentiation

  • beginning of the embryonic period of development
  • coincides with the first missed menstrual period (5th week)
  • formation of primary streak which gives rise to 3 germ layers
  • notochord, neural tube and somites
78
Q

Gastrulation

A

The process by which the bilaminar embryonic disc is conveyed to a trilaminar embryonic disc

  • occurs via the formation of the primitive streak
  • develops on dorsal aspect, caudally along midline
  • includes primitive streak, groove, bode and pit

-embryo is called the Gastrula

79
Q

What creates the primitive groove

-what signalling pathway allows this movement

A

Differentiation and proliferation of cells on caudal end move to midline and create a groove by pushing against each other.

-E-Cadherin is a cell adhesion molecule that is down regulated by Fibroblast Growth Factor (FGF-8) produced by Eli last cells. This allows cells to be less attached and move

80
Q

Cells of epiblast origin migrate down the primitive groove and displace Hypoblast cells to establish the _________ and _________ then the Epiblast is renamed the

A

Intraembryonic mesoderm

Endoderm

Ectoderm

81
Q

Ectoderm is the germ layer that creates

A

Skin, CNS, PNS, eyes, internal ears, neural crest cells (bones and connective tissue if the face and part of skull)

82
Q

Mesoderm is the germ layer that creates

A

Bones, connective tissue, Urogenital system and cardiovascular system

83
Q

Endoderm is the germ layer that creates

A

Gut and gut derivatives (liver, pancreas, lungs), epithelial linings, respiratory and digestive tracts

84
Q

When does the primitive steaks regress

A

End of the 4th week (Sacroccygeal teratoma)

85
Q

Notochordal process grows cranially from the ______ to the ____

A

Primitive pit

Prechordal plate

86
Q

Notochord serves as

A
  • an axis for the development of the axial skeleton
  • induced the formation of the bodies of the vertebrae
  • part persists as the nucleus purposes of the intervertebral discs
  • induced the overlying ectoderm to form the neural plate
87
Q

Neurulation

A
  • neural tube formation begins in the 3rd week and is complete by end of 4th week
  • ectoderm thickens to form the neural plate
  • day 18, neural tube invaginated to form the neural groove with neural folds on either side
  • by end of third week, neural folds fuse converting the neural groove into the neural tube
  • begins in the Center and progressed cranially to caudally
  • neural crest cells form from margins of folds
88
Q

Neuropore closure dates

A

Anterior neuropore closes day 25

Posterior neuropore closes day 27

89
Q

The cardiogenic field is established cranial to the ____

A

Neural plate (brain)

90
Q

Cariogenic field is within the

A

Mesoderm

Blood islands

91
Q

What happens if neuropore as soon not close?

A

Neural tube defects (NTD)

92
Q

Development of the somites

A

Paraxial mesoderm forms paired, cubed shaped blocked called somites (day 20-30)
-somites give rise to vertebrae (sclerotomes, muscles of neck, body wall and limbs (myotomes), and dermis of scalp, neck and trunk (dermatomes)

93
Q

Neural plate secreted _____ to regulate nodal (GF) in left side of the embryo

A

5-HT (serotonin)

94
Q

Primitive node released _____ to cause epiblast to release E-Cadherin

A

FGF-8 and ZIC3

95
Q

What ventralizes mesoderm

A

BMP4

96
Q

What inhibits the left side genes of the developing embryo from activating right side? What happens if this doesn’t occur

A

Shh

Situs Inversus

97
Q

Notochord causes ectoderm cells to create

A

Notochord plate

98
Q

What signalling pathways cause the formation of a cranial and caudal end

A

Up regulation of FGF and down regulation of BMP’s in cranial end

Upregulation of both FGF’s and WNT3a in caudal end

99
Q

Delveopment of the intrembryonic coelom

A

Spaces appear in the lateral mesoderm and coalesce to form the intraembryonic coelom
-this divides the intraembryonic meoderm into a somatic layer and a splanchnic layer

100
Q

Intraembryonic somatic mesoderm plus the ectoderm form the ____

Intraembryonic splanchnic mesoderm plus the endoderm form the ____

A

Somatopleure (body wall)

Splanchnipleure (gut wall)

101
Q

Intrembryonic coelom will give rise to

A

The pericardial (heart) , pleural (lungs) and peritoneal (abdominal) cavities

102
Q

The cardiogenic field is established _____ to the neural plate (brain)

A

Cranial

103
Q

Vasculogenesus

Angiogenesis

A

The formation of new vascular channels by assembly of individual cell precursors called angioblasts

The formation of new vessles by budding and branching from preexisting vessels (secondary structures)

104
Q

Decelopment of chorionic villi

A
  • Primary villi appeared in week 2
  • in 3rd week, mesoderm grows into the prinary villi converting them to secondary villi
  • mesoderm differentiates to form blood vessels converting villi to tertiary
  • by end of 3rd week, there is circulation between the chorionic villi and the embryo

-primordual cardiovascualr system forms in a similar manner

105
Q

The cardiovascular system is the____functional system in the embryo

A

First

106
Q

Somite parts what they become

A

somites give rise to vertebrae (sclerotomes, muscles of neck, body wall and limbs (myotomes), and dermis of scalp, neck and trunk (dermatomes)

107
Q

What cell type creates endoderm, mesoderm and ectoderm?

A

Epiblast

Human Embryology (6 decks)

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