Embryo Flashcards
Functions of the plasmalemma (plasma membrane)
3
- Separation of the cytoplasm from the extracellular fluid
- Regulation of exchange of materials with the extracellular environmental.
- Sensitivity to chemical changes in the extracellular fluid
Of all newborns w/ anatomical alterations…
50% have known cause while 50% have unknown origin.
_% of anatomical alteration have an environmental etiology
7%
Examples of environmental Etiology
Diabetes Infections (Rubella) Mechanical (radiation) Drugs Chemicals Alcohol
Teratology
The science of birth defects
“Terato”= monster
Teratogen
Anything that can cause a birth defect
can be a good substance just the wrong dose & time
Embryonic Period
From conception to 8 weeks
What happens the last week of the embryonic period?
Organogenesis
When do teratogens cause the most birth defects?
The embryonic period (organogenesis)
Teratogens can cause malformation of some or all of the organ system
_% of woman who drink while pregnant ?
Their children’s IQ?
30%
60
Fetal Alcohol Syndrome symptoms
Growth Retardation
Heart Defects
Microcephaly
Mental Retardation
Thalidomide
- Anti-nausea pill
- Inhibits vessel development
- Amelia (lack of limbs)
Amelia
Complete Lack of Limbs
What is Thalidomide currently being used to treat?
AIDS, Leprosy, Leukemia
considered a teratogen
Human Development-Outline
- Pregenesis (Progenesis/Pro-ontogenesis)
- Blastogenesis
- Organogenesis
- Metamorphosis
- Phenogenesis
Pregenesis (In General)
Developmental pre-conditions in parents allowing for successful reproduction
Pregenesis Step 1
Formation and migration of parental primordial germ cells.
First cells that form (become our gametes)
Pregenesis Step 2
Cortico-medullary differentiation of gonads in mother (ovaries) and in father (testes)
Pregenesis Step 3
Increase the number of cortico and medullary cells by mitosis
Pregenesis Step 4
Gametogenesis (Meiosis) maturation of gametes, fertilization
Cortico and medullary each correlate with which sex?
Cortico- Female
Medullary- Males
Migration of Parental Primordial Germ Cells
Leave and go ….
Leave Ectoderm and go into the yolk sac wall
? weeks
Migration of Parental Primordial Germ Cells
When and where do they return …
When they come back they cross the dorsal mesentery, where gonads are found
(4-6 weeks)
Teratoma
When Germ Cells go to extragonadal sites
What can cause teratoma?
- Chemicals are used to coordinate the migration of the germ cells, the cells are mutant
- When primordial germ cells migrate to the wrong place
- Defects in gastrulation (totipotent cells)
Meiosis
Formation of 4 daughter cells after doubling of DNA and two meiotic divisions
In males when does meiosis occur?
Puberty
In females when does Meiosis occur ?
germ cells become primary oocytes
Eggs stuck in Meiosis 1 until puberty, Meiosis 2 is completed only when fertilization occurs
Spermatogonia
Primordial germ cells in males diploid (46 chromosomes)
SPERMATOGENESIS
Where do spermatogonia orginate from ?
Seminiferous Tubule
Oogensis
Primordial Germ Cells in female Oogonia
All organelles come from …
your mother
Follicular Cells
Give nutrients to the oocyte
Meiotic Nondisjunction
Irregular distribution of homologous chromosomes t
When does Meiotic Nondisjunction occur?
- Cell Poles
- Failure of paired chromosomes to separate during Anaphase I
- Unpaired homologues to the same cell pole (aneupliod)
Aneuploid
product of meiosis that result in an abnormal number of chromosomes
Most Common Monosomy
(Meiotic Nondisjunciton)
Monosomy X
99% lethal before birth
Most Common Trisomy before birth
(Meiotic Nondisjunciton)
Trisomy 16
Most Common Trisomy after birth
(Meiotic Nondisjunciton)
Trisomy 21 “Down Syndrome”
The later the Trisomy
The greater the chance of survival
19>3
When does nondisjunction usually occur?
1st or 2nd meiotic division
(50%)
leading cause of death in early embryogenesis
Ovulation
Follicle Rupture
Sticky Cumulus Corona Radiata -second human egg shell, outer protective layer of the ovum
Embryo Phase
0-8 weeks
Fetal Phase
8-end
Where do eggs get fertilized ?
ampulla of the oviduct
Human fertilization requires?
~200 sperm and an egg
Normal ejaculation contains?
Infertile?
noromal- 250,000,000 sperm
infertile
Capacitation
Sperm in female reproductive tract :
- Gains motility
- Increases Metabolism
- Hyaluronidase Enzymatic activity
Barriers Sperm must Penetrate
Corona Radiata ->
Zona Pellucida ->
Egg Plasma Membrane
Acrosome Reaction
male/sperm reaction
Helps sperm navigate past Corona Radiata, Zona Pellucida, Egg Plasma Membrane
Cortical Reaction
Female/Oocyte Reaction.
After fertilization–> increase in Calcium –> prevents polyspermy
Cortical granules
located under the egg plasma membrane.
respond by releasing lysomesal enzymes into the space outside of the egg
After fertilization enzymes……
change egg membrane and zona pellucida to prevent polyspermy
Pronuclei
The fusion of two haploid cells (oocyte and sperm nucleus)
Cleavage
After Zygote forms, embryo starts mitosis cell division
Cleavage cell division produces
Daughter cells that are 1/2 the size as the parent
2 cells= ½
4 cells= ¼
8 cells=1/8
In cleavage individual cells are called
Blastomeres
Fraternal Twins
Dizygotic
Two cell embryos cleave so early before the formation of placenta
Identical Twins
Monozygotic
Share placenta
What are the three types of twins?
Fraternal (dizygotic)
Identical (Monozygotic)
Conjoined
Compaction
- Outer cells flatten
- First Overt Signs of differentiation
- Morula is formed
How long does it stay a Zygote
until it becomes a two cells (now it is an embryo)
Compaction
outer cells flatten by…
Tight junctions btwn. outer cells
Gap junctions link inner cells
Compaction
First overt sign of differentiation
Outer cells = placenta
Inner cells= fetus
What is a Morula ?
a solid ball of cells resulting from division of a fertilized ovum, blastula is then formed.
due to compaction
When does a Morula form?
3-4 days post fertilization