Week 2 Embryology 1 Flashcards
1
Q
Gametogenesis
A
Formation of gametes (oocyte, sperm)
2
Q
Gametes
A
Oocyte (female)
Sperm (male)
Half regular DNA content
Formed by either spermatogenesis or oogenesis through meiosis
3
Q
What we use to make human beings
A
Gametes
4
Q
Spermatogenesis
A
Formation of Sperm
5
Q
Oogenesis
A
Formation of oocyte (egg)
6
Q
Chromosomes
A
Human somatic cells contain 23 pairs of chromosomes - 46 total
22 pairs autosomes
One pair sex chromosomes
7
Q
Autosomes
A
Contain genetic information for most human characteristics. A pair of similar autosomes are called homologous chromosomes.
22 pairs
8
Q
Homologous chromosomes
A
A pair of similar autosomes (functionally the same)
9
Q
Ploidy
A
Number of chromosomes
Human cell has 46 chromosomes
10
Q
N
A
amount of DNA
11
Q
2N
A
Dipoid
12
Q
1N
A
Haploid (gamete)
1/2 number of paired chromosomes
13
Q
How many chromosomes humans have
A
46, 23 pair
14
Q
In normal cell, gamete has how much DNA?
A
1N
15
Q
Gametogenesis
A
Begins with meiosis
Produces secondary oocytes in female
Produces sperm in male
Gametes contain 1/2 number of paired chromosomes and are called haploid (1N)
16
Q
How to decrease to 1/2 the chromosomes
A
Meiosis
17
Q
Meiosis I
A
Meiosis results in the formation of gametes (sex cells)
Homologous chromosomes are separated after synapsis and crossing over occurs
18
Q
Meiosis II
A
Sister chromatids are seperated in a sequence of phases that resembles mitosis
19
Q
Sister chromatids aka
A
Duplicated chromosome
20
Q
Meiosis starts with this
A
Duplicated chromosome (aka sister chromatids)
21
Q
Chromatid
A
One of the two strands of a chromosome joined together by a centromere
In Meisosis II, this seperates
22
Q
Chromosomal Crossover
A
An important step in genetic recombination in which two chromosomes, normally homologous pair up and exchange DNA
23
Q
Independent Assortment
A
Shuffling of genes
Increases variation and is heritable
24
Q
_N at start of Meiosis 1, Prophase 1
A
4N
25
Spermatogenesis
Diploid cells that reside in the testes
Each one first divides by mitosis to make an exact copy of itself called a primary spermatocyte first
Then undergo meiosis and ultimately produce haploid cells called spermatids
26
Spermatogonia
Parent or stem cells that produce sperm
27
Primary spermatocyte
Sperm first divides by mitosis to make an exact copy of itself
28
Spermatids
When spermatocytes undergo meiosis they produce these haploid cells (23 chromosomes)
Lose much of their cytoplasm and grow long tail called flagellum
29
Sperm
22 autosomes
X or Y chromosomes
From a single spermatocyte, 4 new sperm are formed.
30
Acrosomes
Hydrolytic enzymes in sperm that punch hole in egg
31
Oocyte
*Secondary
The gamete produced
22 autosomes and one X chromosome
Parent cells called oogonia and reside in ovaries
32
Oogonia
Parent cells that produce oocytes and reside in the ovaries
| Oogonia start process of meiosis and form primary oocytes prior to birth. Arrested in Prophase 1 until puberty
33
Meiosis 1 Oogenesis
End of meiotic division, two cells are produced
Division of cytoplasm is unequal
Secondary oocyte receives bulk of cytoplasm and is arrested in Metaphase II
The second cell is called a polar body
34
Polar body
The second cell, only receives a tiny bit of the cytoplasm
| Nonfunctional cell and eventually degenerates
35
If secondary oocyte is not fertilized
(24-36 hours after ovulation)
| it degenerates while arrested in metaphase II
36
If secondary oocyte is fertilized
Finishes the process of meiosis. Two cells are produced and cytoplasm is unequal. The cell with very little cytoplasm becomes another polar body
37
Ovum
The cell that receives the majority of the cytoplasm and can be fertilized
38
Aneuploidy
Total chromosome number not equal to 46
39
Congenital defect
Things that can go wrong
* Mutations of genes
* Abnormalities of chromosome division
- numerical errors (too many or too few chromosomes) Results in aneuploidy
- Structural errors
40
Nondisjunction
Process of separation of homologous chromosome pairs fails
* *sorting problem, in Meiosis 1 or 2
- leads to abnormal chromosome number
- too many (trisomy) or too few (monosomy)
41
Trisomy
Too many copies of a chromosome
This type of disorder is named for chromosome involved
Process of separation of homologous chromosome pairs fails
42
If nondisjunction occurs in Meiosis I
2/4 have trisomy
| 2/4 have monosomy
43
If nondisjunction occurs in Meiosis II
2/4 are normal
1/4 trisomy (n+1)
1/4 monosomy (n-1)
44
Down syndrome
Trisomy 21
45
3 most common Autosomy
21, 18 and 13
46
Klinefelter syndrome
47 XXY
| Males. Tall, masculine features not as developed
47
Turner's syndrome
45 XO
Female. Monosomy
Treatable with estrogen
48
47, XYY karyotype
? 'syndrome' because phenotype is normal
| Male with 2 Y chromosomes, appear to be normal, fertility might be an issue, gametes without right number
49
Offspring of Older Women
Higher incidence of chromosomal abnormalities
Prolonged dormancy of oocytes. Dormant since 5th month in utero
Incidence of trisomy 21 increases
Primary cause is maternal meiotic nondisjunction
50
Primary cause of increased trisomy 21 with advanced maternal age
Maternal meiotic nondisjunction
| Prolonged dormancy of oocytes
51
Offspring of Older Men
Less of an issue with men, but some evidence of reduced fertility and possible increase in cancer and schizophrenia
52
Problems with Chromosome Structure
Breakage (radiation or chemical teratogens)
Reciprocal and unbalanced translocations
Deletions
Duplications
53
Teratogens
External agents - extrinsic to the fetus - that produce developmental malformations
Critical period is 3-8 weeks
54
Potential Teratogens
```
Radiation
Prenatal infections
Temperature extremes
Prescription drugs/dietary supplements
Recreational drugs - esp alcohol
Enviro toxins (lead, mercury)
Maternal malnutrition or disease
Mechanical forces (ex. IVF)
```
55
4 reasons for teratogen variation
1. Concentration and method of teratogen delivery
2. Timing of exposure
3. Variation in susceptibility due to genetic variation
4. Synergistic interactions between the teratogen and other compounds (ex. what else you are taking)
56
Secondary Oocyte
Only this one has potential to be fertilized (about 14 days)
This is ovulated
Corona radiata and the zona pellucida form protective layers around secondary oocyte
57
Zona pellucida
Glycoprotein coat, receptors to help sperm identify and for protection
58
Fertilization
Two gametes fuse to form a new cell containing genetic material derived from both parents
Restores the diploid number of chromosomes
Determines the sex of the organism
Initiates cleavage
Occurs in the widest part of uterine tube
59
The Ampulla
Widest part of the uterine tube
| Where fertilization occurs
60
During Fertilization
Millions of sperm cells are deposited in female reproductive tract during intercourse
Only few hundred have chance at fertilization, only first to enter gets to fertilize
61
Sperm at Fertilization
Hundreds try to get in, one wins. When one gets in, electric shock sent out to others and then receptors are taken away.
62
Phase 3
Sperm head and tail enter oocyte
| Second meiotic division with production of second polar body
63
of weeks in pregnancy
Dated at 38 weeks, occurs between fertilization and birth
| Dated at 40 weeks because include since last period
64
Pre-embryonic Period
The first 2 weeks of development when the zygote vecomes a spherical, multicellular structure
65
Embryonic Period
3-8 weeks of development during which all major organ systems appear
**CRITICAL time period
Major events of embryogenesis occur now
66
3 major events of embryogenesis
1. Cleavage
2. Gastrulation
3. Organogenesis
67
Cleavage
Major event of embryogenesis
| Division of zygote (fertilized egg) & formation of blastocyst
68
Gastrulation
Major event of embryogenesis
| Formation of 3 germ layers
69
Organogenesis
Germ layers differentiate so as to give rise to all organs in the human body
70
Embryo leaves zona pellucida
when it is a blastocyst at the end of Cleavage
71
Fetal Period
Weeks 9-38
Fetus continues to grow
Organs increase in complexity
*can have abnormalities but less severe than weeks 3-8
72
Cleavage
Shortly after fertilization, zygote begins to undergo a series of divisions
Divisions increase number of cells, but remains the same size
During each succeeding division, the cells are smaller and smaller
Cells at this stage are exactly alike
73
Blasto
build
74
Osteoblast
Build bone
75
Morula
After the third cleavage, cells are tightly compacted into a ball
Means blackberry
If you took it out, it could grow the exact same thing
76
Embryoblast
Inner cell mass
| *builds the embryo
77
Blastocyst cavity
Cavity gives space to grow and change
78
Trophoblast cells
Outer cell mass
*will form part of the placenta
Part comes from moms uterus
79
Blastocyst 3 parts
1. Inner cell mass
2. Blastocyst cavity
3. Trophoblast cells
80
Twinning
A. Cleavage of early embryo
-two blastocysts = monozygotic twins. Split early so have two placentas
B. Splitting of ICM
-one trophoblast so they share same placenta, causes more problems
C. Incomplete division of ICM
-Monozygotic where inner cell doesn't split
81
Conjoined twins
Occurs when inner cell doesn't split in cleavage
Incomplete division of monozygotic twins
Extent of bridging is variable
Due to secondary fusion of ICM or development of 2 primitive streaks
82
Implantation
First week after fertilization, blastocyst enters the lumen of the uterus
Zona pellucida around blastycyst begins to break down as blastocyst prepares to invade the endometrium
Implantation is the process by which the blastocyst burrows into and embeds within the endometrium
83
Embryoblast
Embrionic stem cells
| Must have trophoblast to use
84
What attaches to wall in uterus
Trophoblast
85
Ectopic Pregnancy
Implantation of blastocyst outside the uterine cavity
Can be predisposed by conditions that have caused inflammation and scarring of the uterine tubes (endometriosis, PID)
Can survive, just need C-section to get out
86
What day does implantation occur?
Day 7
87
Second opportunity for cellular differentiation
Implantation
88
3 parts of Implantation
1. Trophoblast cells differentiate
2. Embryoblast cells differentiate
3. Two cavities form
89
2 layers in second week
1. Epiblast
| 2. Hypoblast
90
Cytotrophoblast and Syncytiotrophoblast
Tasked with invading. Find glands (energy) and find blood supply.
Will set up placenta
91
hCG
Human chorionic gonadotrophin
| Signals to the ovary to continue to secrete hormones to maintain the pregnancy
92
Extraembryonic (XE) Mesoderm
Gives mechanical and trophic support
| More spaces begin to form --> a larger cavity (coelom)
