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embryology (E1 Woods) > The first week of Human development > Flashcards

The first week of Human development Flashcards

1
Q

what is gametogenesis

A

formation of gametes

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2
Q

what are homologous chromosomes

A

a pair of similar autosomes

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3
Q

define ploidy

A

number of chromosomes

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4
Q

how does gametogenesis begin

A

meiosis

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5
Q

what does meiosis result in

A

formation of gametes (sex cells)

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6
Q

what occurs during meiosis I

A

homologous chromosomes are separated after synapsis and crossing over occurs

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7
Q

what occurs in Meiosis II

A

sister chromatids are separated in a sequence of phases that resembles mitosis

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8
Q

define chromatid

A

one of the 2 strands of a chromosome joined together by a centromere

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9
Q

define chromosomal crossover

A

important step in genetic recombination in which 2 chromosomes, normally homologous, pair up and exchange DNA. Shuffling of genes (called independent assortment), is heritable and increases the variation

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10
Q

what occurs during prophase I

A

Homologous double-stranded chromosomes pair up (synapsis), and the pair forms a tetrad. Crossing over occurs between maternal chromosomes and paternal chromosomes ensuring genetic diversity

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11
Q

what occurs during metaphase I

A

homologous double-stranded chromosomes line up above and below the equator of the cell, forming a double line of chromosomes. Spindle fibers attach to the chromosomes.

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12
Q

What occurs during anaphase I

A

maternal and paternal pairs of chromosomes are separated and pulled the the opposite ends of the cell (reduction division). The sister chromatids remain attached in each -double stranded chromosome

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13
Q

what occurs during Telophase I and cytokinesis

A

Nuclear division finishes and the nuclear envelopes re-form. The cytoplasm divides and 2 new cells are produced, each containing 23 chromosomes only. The chromosomes are still double-stranded

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14
Q

what occurs during Prophase II

A

nuclear envelope breaks down, and the chromosomes gather together

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15
Q

what occurs during metaphase II

A

double-stranded chromosomes line up along the equator of the cell, spindle fivers extend from the centrioles to the chromosomes

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16
Q

what occurs during anaphase II

A

Sister chromatids of each double-stranded chromosome are pulled apart at the centromere. Sister chromatids migrate to opposite ends of the cell

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17
Q

what occurs during Telophase II and cytokinesis

A

Nuclear division finishes, and the nuclear envelopes re-form. The four new daughter cells that are produced each contain 23 single-stranded chromosomes only

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18
Q

what are spermatogonia

A

parent or stem cells that produce sperm

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19
Q

define spermatids

A

haploid cells produced from primary spermatocytes that have undergone meiosis

20
Q

what starts the process of meiosis

A

oogonia

21
Q

what occurs after the primary occyte completes the first meiotic division

A

2 cells are produced

22
Q

define polar body

A

nonfunctional cell that eventual degenerates that is the second cell (besides the 2nd oocyte) that results from Meiosis

23
Q

define nondisjunction

A

process of separation of homologous chromosome pairs fails

24
Q

Define Teratogens

A

external agents that produce developmental malformations

25
Q

where does fertilization occur

A

widest part of the uterine tube

26
Q

define cleavage

A

division of zygote and formation of blastocyst

27
Q

define organogenesis

A

germ layers differentiate so as to give rise to all organs in the human body

28
Q

define gamete

A

germ cell that originate in the wall of the yolk sac of the embryo and migrate into the gonad region

29
Q

when does ovulation occur

A

When the secondary oocyte enters meiosis and the chromosomes align at metaphase

30
Q

what secretes gonadotropin-releasing factor (GnRF)

A

hypothalamus

31
Q

what hormone stimulates ovulation

A

LH

32
Q

what hormone stimulates the endometrium of the uterus to enter the secretory phase

A

progesterone

33
Q

Define endometriosis

A

Appearance of foci of endometrial tissue in abnormal locations outside of the uterus

34
Q

what must degenerate in order for implantation to occur

A

zona pellucida

35
Q

what does the syncytiotrophoblast produce?

A

human chorionic gonadotropin (hCG)

36
Q

what does hCG do

A

it is a glycoprotein produced by syncytiotrophoblast that stimulates the production of progesterone by the corpus luteum of the ovary

37
Q

what are the stages of embryogenesis and define them

A
  1. cleavage: series of mitotic divisions of the zygote
  2. gastrulation: process that establishes 3 germ layers
  3. organogenesis: germ layers differentiate so as to give rise to all organs in the human body
38
Q

what does Sonic Hedgehog Protein (Shh) do?

A

It helps to determine the L/R determination (activity is only on the left because Shh activity is suppressed on the future right side by activin)

39
Q

what is the result when nondisjunction occurs during meiosis I

A

gametes divide into 2 that have n+1 and 2 that have n-1

40
Q

what is the result when nondisjunction occurs during meiosis II

A

2 normal offspring, one with n+1 and one with n-1

41
Q

list the major events in fertilization

A
  1. Penetration of corona radiate
  2. attachment to zone pellucida
  3. acrosomal reaction and penetration of ZP
  4. binding and fusion of sperm and eggs
  5. prevention of polysperm
  6. metabolic activation of the egg
  7. decondensation of the sperm nucleus
  8. completion of egg meiosis
  9. development and fusion of male and female pronuclei (now have embryo)
42
Q

What are the events of implantation

A
  • zone pellucid must degenerate for implantation to occur
  • blastocyst implants within the posterior superior wall of the uterus (and trophoblast differentiation)
  • blastocyst implants within the functional layer of the endometrium during secretory phase of the menstrual cycle
  • trophoblast differentiates into cytotrophoblast and syncytiotrophoblast
43
Q

Explain ectopic pregnancy

A

Occurs when the blastocyst implants within the uterine tube due to delayed transport (ampulla of uterine tube is most common)
clinical signs: abnormal uterine bleeding, unilateral pelvic pain, increased levels of hCG and massive first trimester bleed

44
Q

what is the main difference between dizygotic twins and monozygotic?

A

dizygotic results from fertilization of 2 different secondary oocytes by 2 different sperm. monozygotic results from fertilization of one secondary oocyte by one sperm

45
Q

what are the steps of oogenesis

A
  1. primordial germ cells arrive in the ovary at week 6 & differentiate into oogonia
  2. oogonia enter meiosis I and undergo DNA replication to form primary oocytes
  3. ovarian cycle: primary oocyte completes meiosis I and secondary oocyte and first polar body form
  4. secondary oocyte enters meiosis II
  5. at fertilization= secondary oocyte completes meiosis Ii to form a mature oocyte and 2nd polar body
46
Q

Explain the proliferation and differentiation of the trophoblast

A

trophoblast becomes the outer cell mass

  1. trophoblast separates into a cellular cytotrophoblast (closer to inner cell mass) and a multinucleate syncytiotrophoblast (closest to endometrium)
  2. syncytiotrophoblast projections penetrate the endometrial basal lamina and then begin to invade the endometrial sertoma
  3. trophoblastic lacunae appear
  4. trophoblast is less invasive at this point
47
Q

what is the mother’s contribution to the baby

A

endometrium

embryology (E1 Woods) (3 decks)

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