Embryology Lecture 1 Flashcards
(143 cards)
1
Q
What does āNā stand for?
A
The amount of DNA
2
Q
what does 2N mean?
A
The cell is diploid. Human cell that is 2N has 46 DNA strands (chromatids)
3
Q
What is Gametogenesis?
A
The production of gametes
4
Q
What occurs in Meiosis I that allows for more genetic diversity?
A
Synapsis and crossing over
5
Q
What is a chromatid?
A
One of the two strands of a chromosome, which are bound together by a centromere
6
Q
What is crossing over
A
An important step in Meiosis I that allows for the independent assortment of genes.
7
Q
what is a spermatogonia
A
The parent cell that is divided at the beginning of spermatogenesis.
Diploid
Reside in the testes
First divides by mitosis into primary spermatocyte
8
Q
What is ploidy?
A
The number of chromosomes
9
Q
New sperm cells possess what?
A
Head, mid-piece, and tail
22 autosomes and either a single X or Y
10
Q
what are the major stages of embryogenesis
A
Cleavage, gastrulation, and organogenesis
11
Q
what is cleavage
A
division of zygote & formation of blastocyst
12
Q
What is gastrulation
A
Formation of germ layers
13
Q
What is organogenesis
A
Germ layers differentiate so as to give rise to all organs in the human body
14
Q
When are spermatogonia present
A
At birth but not active till puberty
15
Q
Why are men able to produce more sperm throughout aging
A
the spermatogonia undergo mitosis before meiosis
16
Q
When is K selection favorable
A
For longer living, larger animals, long time till gestation and invest more with offspring
17
Q
What is polar body twinning
A
If secondary oocyte divides more evenly than normal then both can be fertilized by separate sperm
18
Q
In cleavage what increases
A
The cell number increases but cells decrease in size so that the zygote remains the same size
19
Q
What is a Morula
A
Cluster of blastomeres (16-32), tightly bound ball of cells, after the 8-stage cell cycle
20
Q
What are blastomeres
A
Totipotent up to eight-cell stage
21
Q
What is asynchronous
A
One cell will divide at a time
22
Q
What is a blastocyst
A
Occurs when fluid secreted within the morula forms a blastocyst cavity
23
Q
what are the three germ layers
A
Ectoderm, mesoderm, and endoderm
24
Q
what forms the embryonic disk
A
Ectoderm, mesoderm, and endoderm
25
what is the difference between embryology and teratology
Embryology- branch of biology that deals with the development of an embryo from the fertilization of the ovum to the fetus stage
Teratology- is the study of congenital abnormalities and abnormal functions
- can account for non-birth developmental stages (ex. Puberty)
26
what is nondisjunction
when the separation of homologous chromosome pairs fails to happen
leads to monosomy and trisomy
27
Is it worse for nondisjunction to be in the first meiotic division or the second
The first
because if nondisjunction happens in Meiosis I then all four gametes will have a trisomy and monosomy
if it happens in Meiosis II then only half of the gametes will have a monosomy or trisomy (1 each)
28
Examples of monosomy
Turner's syndrom (XO)
| - phenotypic female
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Example of trisomy
```
Trisomy 21 (Down's syndrom) most common
Klinefelter syndrom (XXY)- phenotypic male
```
30
Where does fertilization occur
in the ampulla
- Lateral 1/3 of the uterine tube
- widest part of the uterine tube
31
What stage of meiosis is the secondary oocyte arrest in till fertilization
Metaphase II
32
What is the acrosome reaction
When the sperm binds to the zone pellucida of the secondary oocyte
- trigger the release of acrosomal enzymes (acrosin) which allow the sperm to penetrate the zone pellucida
33
What is the cortical reaction
After a sperm penetrates the zone pellucida then lysosomal enzymes form cortical granules near the oocyte of the cell membrane
- these lead to a change in the oocyte cell membrane potential and inactivate sperm receptors on the zone pellucida
- changes are called the polyspermy block
34
What is the polyspermy block
Changes in the cell membrane potential that inactivates sperm receptors on the zona pellucida
35
What is a male pronucleus
- when the nuclear contents and central pair of the sperm enter the cytoplasm of the oocyte
- tail and mitochondria of the sperm degenerate
36
The establishment of a functional zygote depends on whose centriole pair
The sperms because the oocyte loses its centriole pair during meiosis
37
when is the mature ovum present
after the secondary oocyte completes meiosis II
38
What is the female pronucleus
The nucleus of the ovum
39
what is syngamy
term to describe a successful completion of fertilization and formation of a zygote, when the male and female pornuclei fuse and the cytoplasmic machinery for the proper cell division exists
40
what must degenerate for implantation to occur
The zona pellucida must degenerate
41
Where does the blastocyst implant
within the posterior superior wall of the uterus, within the functional layer of the endometrium during the secretory phase of the menstrual cycle
42
What implants in the posterior superior wall of the uterus
The blastocyst
43
During what phase of the menstrual cycle does the blastocyst implant within the functional layer of the endometrium in the posterior superior wall of the uterus
The secretory phase
44
when does the blastocyst enter the lumen of the uterus
By the end of the first week after fertilization
45
what does a trophoblast differentiate into
The cytotrophoblast and the syncytiotrophoblast
46
what is gametogenesis
Formation of gametes
47
how much DNA content do oocytes and sperm have
half of the regular DNA content, haploid, 23 chromosomes , N
48
how many autosome pairs do humans have
22 pairs
49
How many pairs of sex chromosomes do humans have
1
50
What do autosomes contain
The genetic information for most human characteristics
51
what is a pair of similar autosomes called
Homologous chromosomes
52
What does Ploidy mean
Number of chromosomes
53
What does (N) mean
The amount of DNA
54
how many secondary oocytes are formed by female gametogenesis
1
55
how many sperm are produced by gametogenesis by males
4
56
When are homologous chromosomes separated
Anaphase I, after synapsis and crossing over events
57
When are sister chromatids separated
Anaphase II
58
what is a chromatid
One of the two strands of a chromosome joined together by a centromere
59
What is independent assortment
When two chromosomes, normally homologous (functionally the same) pair up and exchange DNA
is heritable and increases variation
60
Prophase I
homologous double-stranded chromosomes pair up (synapsis), and he pair forms a tetrad. crossing over occurs between maternal and paternal chromosomes
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Metaphase I
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
62
Anaphase I
Maternal and paternal pairs of chromosomes are separated and pulled to the opposite ends of the cell, a process called reduction division. Note that at the sister chromatids remain attached in each double-stranded chromosome
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Telophase I and Cytokinesis
nuclear division finishes and the nuclear envelope re-form. the cytoplasm divides and two new cells are produced, each containing 23 chromosomes only. The chromosomes are still double-stranded
64
prophase II
Nuclear envelope breaks down
| chromosomes gather together (no crossing over)
65
Metaphase II
Double-stranded chromosomes line up along the equator of the cell. spindle fibers extend from the centrioles to the chromosomes
66
Anaphase II
Sister chromatids of each double stranded chromosome are pulled apart at the centromere. Sister chromatids (now called single-stranded chromosomes) migrate to opposite ends of the cell
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Telophase II and cytokinesis
Nuclear division finishes and the nuclear envelopes re-from. The four new daughter cells that are produced each contain 23 SINGLE-stranded chromosomes
68
what are spermatogonia
parent or stem cells that produce sperm, They are diploid
69
Where do spermatogonia reside
in the testes
70
Spermatogenesis
Process of meiosis that primary spermatocyte undergoes to form spermatids
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what are three distinct structural characteristics sperm
distinctive head, mid piece, and a tail
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For spermatids to become sperm they must undergo what changes
Lose much of their cytoplasm and grow a long tail called a flagellum
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where do oogonia reside
in the ovaries
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what are oogonia
Diploid cells that divide to form primary oocytes
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what stage are Primary oocytes arrested in till puberty
from about the 5th month in utero they are arrest in Prophase I
76
How many secondary oocytes are ovulated each month
normally one
77
Do the ovaries alternate which one ovulates each month
Maybe
| 50-50 chance of releasing egg from the opposite side as the month before
78
The secondary is arrested in what phase until fertilization
Metaphase II
79
what is a polar body
A second cell that receives only a tiny bit of the cytoplasm
80
what eventually happens to the polar
Eventually degenerates
81
What happens if a secondary oocyte is not fertilized
It degenerates in about 24 hours after ovulation, still arrested in metaphase II
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what are mosaics
individuals who possess cells with a different number of chromosomes in them.
83
What is a chimera
cells that have a different number of chromosomes in them but the they are from different individuals
-example mother has kids with different genes than hers because her oogonium was part of her sister
84
What are some of the issues with offspring in older women
higher incidence of chromosomal abnormalities
prolonged dormancy of oocytes
incidence of trisomy 21 increases with maternal age
primary cause is maternal meiotic nondisjunction
- clinical findings include: severe mental retardation, , epicanthal folds, brush field spots, simian creases, and association with a decrease in alpha-fetoprotein
85
what are some of the issues with offspring in older men
accumulated chromosomal aberrations and mutations occurring during the maturation of the male germ cells
some evidence shows that offspring of older fathers have reduced fertility and an increased risk of birth defects, some cancers, and schizophrenia
- achondroplasia (autosomal dominant congenital skeletal anomaly characterized by retarded bone growth in the limbs with normal-sized head and trunk)
- Marfan syndrome
86
what are some genetic factors to chromosome structure
Breakage (radiation or chemical teratogens)
Reciprocal and unbalanced translocations
deletions
duplications
87
what are teratogens
anything that can cause a congenital birth defect
| external ages that produce developmental malformations
88
give some examples of teratogens
Radiation, prenatal infections, temperature extremes, prescription drus/dietary supplements, recreational drugs (especially alcohol), environmental toxins, maternal malnutrition or disease, mechanical forces (crowding examples to many buns in the oven)
89
what are the four reasons for different responses to teratogens
- Concentration and method of teratogen delivery
- timing of exposure during development
- variation in susceptibility due to genetic variation
- Synergistic interactions between the teratogen and other compounds
90
does only the secondary oocyte have the potential to be fertilized
Yes
91
what are the protective layers around a secondary oocyte
The corona radiata and the zona pellucida
92
how many sperm cells are deposited in the female reproductive tract during intercourse and how many have a chance at fertilization
a few hundred
93
only the first sperm to ender the secondary oocyte is able to fertilize it
True
94
what is phase 3 of fertilization
Sperm head and tail enter the oocyte
| second mitons division with production of second polar body
95
In mammals the process of nuclear fusion, whereby 2 haploid cells fuse into a single diploid cell or zygote, takes how long
12 hours
96
What marks the beginning of embryogenesis
The fusion of the pronuclei
return to diploid chromosome number
mitotic divine of the zygote begins
97
how long is the embryonic period
3rd through the 8th week of development during which all major organ system appear (Critical period)
98
how long is the pre-embryonic period
The first 2 weeks of development when the zygote becomes a spherical, multicellular structure
99
how long is human pregnancy/development
about 38 weeks
100
what is the fetal period
includes the remaining weeks of development prior to birth (9-38wks)
fetus continues to grow
its organs increase in complexity
101
When does cleavage occur
shortly after fertilization, zygote undergoes a series of divisions
102
What happens to individual cell size in succeeding divisions of cleavage
they get smaller and smaller
103
What is the Morula
after the third cleavage division, 8-cell stage, cells are tightly compacted into a ball
104
cleave of the zygote first forms
2-celled blastula, then 4-stage blastula and then 8-cell blastula, morula
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what are blastomeres
individual cells in a blastomere
106
What is a blastocyst
Morula forms a fluid filled blastocyst cavity
has an inner cell mass (embryoblast)
and outer cell mass (trophoblast)
107
When does the zona pellucida begin to dissipate
When the blastocyst prepares to invade the endometrium
108
What causes conjoined twins
Secondary fusion of ICM or development of 2 primitive streaks
109
when does the blastocyst enter the lumen of the uterus
by the end of the first week after fertilization
110
What is the cell stage that enters the lumen of the uterus
The blastocyst
111
what is implantation
The process by which the blastocyst burrows into and embeds within the endometrium
112
what is an ectopic pregnancy
Implantation of the blastocyst outside the uterine cavity
can be predisposed by condition that have caused inflammation & scarring of the uterine tubes (endometriosis, PID)
most common site is in the ampulla
clinical signs of an ETP: abnormal uterine bleeding, unilateral pelvic pain, increased levels of human chorionic gonadotropin (hCG) (but lower than expected for uterine implantation pregnancy), and a massive first-trimester bleed
113
what is twin to twin transfusion syndrome
Twin is stealing all of the resources while the other one is starved
114
what marks the second opportunity for cellular differentiation
Implantation
115
The trophoblast differentiate on what day
around day 7
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the trophoblast differentiates into what two layers
Syncytiotrophoblast and cytotrophoblast
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What are the two layers that the embryoblast differentiates into
The Epiblast and the hypoblast
118
what cavity is formed by the hypoblasts below the bilaminar disc
The yolk sac cavity
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What cavity is formed by the epiblasts above the bilaminar disc
The amniotic sac cavity
120
what is the bilaminar disc
disk that marks the line between epiblasts and hypoblasts and the separation of the yolk sac cavity from the amniotic sac cavity
121
Human chorionic gonadotrophin (HCG) is made by what cells
The syncytiotrophoblast
122
what is the function of HCG
signals the ovary to continue to secrete hormones to maintain the pregnancy
123
what day is ovulation
day 14
124
what day is fertilization
Day 15
125
What day is implantation
Day 22-24
126
What day is expected menses
Day 28
127
Most critical period overall is termed what
Period of organogenesis
128
Where do primordial germ cells (from which gametes are descendants) originate
in the wall of the yolk sac of the embryo and then migrate into the gonad region
129
At what week of embryonic development do primordial germ cells arrive in the ovary and differentiate into oogonia
at week 6
130
at what month of fetal life are all primary oocytes present
the fifth month of fetal life
131
What is the ploidy of a primary oocyte
46 duplicate chromosomes, 4N
132
what is the ploidy of a primary spermatocyte
46 duplicated chromosomes, 4N
133
what is capacitation
Unmasking of spermglycosyltransferases and removal of proteins coating the surface of the sperm
done in the female reproductive tract
134
Diandric triploidy
an embryo with three sets of chromosomes, two of which come form the father
- quite common
- caused when polyspermy block fails
135
When is the mature ovum formed
When the secondary oocyte completes meiosis II
136
How long is the life span of a zygote
only a few hours because its existence terminates when the first cleavage division occurs
137
The blastomeres are totipotent until when
the eight-cell stage
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what is totipotency
refers to a stem cell that can differentiate into every cell within the organism, including extraembryoinic tissues
139
Embryoblast cells are what degree of potency
Pluripotent
140
what is pluripotency
refers to a stem cell that can differentiate into ectoderm, mesoderm, and endoderm
141
What is rectouterine punch (pouch of Douglas)
A common site for an ectopic abdominal pregnancy
142
Steps in monozygotic (identical) twinning
cleavage divisions produce a cluster of blastomeres called a morula surrounded by a zona pellucida. the molecular mechanisms of "twinning" cause a splitting in the inner cell mass.
the twinning morula can now become monochorionic or dichorionic
- if splitting occurs after the differentiation of the trophoblast, then monochorionic twins will form
- if the splitting occurs before the differentiation of the trophoblast, then dichorionic twins will form
143
Steps in dizygotic (fraternal) Twinning
secondary oocyte is fertilized by TWO sperm. nuclear contents and centriole pair of both sperm enter the oocyte cytoplasm. Secondary oocyte completes meiosis II, but does not form a secondary polar body. Instead, the DNA that would have been sequestered in the second polar body forms another female pronucleus. They each form their own separate cellular entities within the zona pellucida. The morula is a chimera, consisting of an assortment of cells with two different genotypes. Twinning causes splitting. can be monochorionic or dichorionic
