Fertilization and fetal development Flashcards
what is external fertilization?
fertilization occurring outside the body– usually in water
what is internal fertilization?
sperm cells transferred into the body during copulation( sex)
animal examples of internal and external fertilization
1) aquatic animals(fish) 2) reptiles and birds and humans
advantages of internal fertilization
1) increases the chance that the gametes will meet = species have to produce fewer gametes
2) fertilized ovum can be enclosed in a protective covering = shell/ remain in the body during development.
when does human fertilization occur?
when one sperm cells fuse with the secondary oocyte
what does the fusion of a sperm and secondary oocyte create?
a zygote
where does the formation of a zygote take place in?
the oviduct
what is the purpose of the human fertilization system?
to prevent polyspermy– entry of more than one sperm cell nucleus
what is the first step in fertilization?
large amounts of sperm ejaculated into vagina during sexual intercourse
how many sperm survive getting to through the vagina?
only a few make it to through the cervix and uterus
second step to fertilization-name?
aerosome reaction
what happens during aerosome reaction?
sperm binds to the zona pellucida the contents of the aerosome are released
what helps the sperm get through the zona pellucida?
the head of the sperm contains sacs of enzymes that help it digest through the zona pellucida to get to the egg.
what enzyme is contained in the sperm head?
aerosome enzyme
what happens in the third step of fertilization?
penetration of the egg membrane
how is step 3 of fertilization done?
aerosome reaction exposes an area of the membrane to the sperm where its protein can bind to the egg membranes receptors.
result of step 3 of fertilization?
the binding of sperms protein to egg membranes proteins, allows its membrane to fuse with the eggs membrane
step 4 of fertilization
cortical reaction– entry of sperm nucleus activates egg(complete meiosis 2) cortical granules released from egg that causes binding proteins on egg membrane to degenerate so no more sperm can bind.
what causes the hardening if the zona pellucida?
the breaking down of the proteins on the egg membrane
what does the hardening of the zona pedullcida achieve?
further protect the egg as well as keeping other sperm out
what are cortical granules?
secretory vesicles located in the cortex of unfertilized oocytes
what do cortical granules cause?
the binding of proteins from sperm to egg
end result of fertilization step 4?
an embryo development
what stage comes right after successful fertilization?
blastocyst stage
what happens in the blastocyst stage?
after division of mitosis, the cells made are similar– after 2 weeks they specialize
what happens after fertilization?
the zygote travels down the oviduct towards the uterus, while it divides through mitosis a series of times
what happens when zygote reaches the uterus?
it has divided into an almost hollow ball of cells (blastocyst)
whats a blastocyst?
hollow ball of cells created by continues division of mitosis after fertilization of eggs
what do the outer walls of the blastocyst become?
placenta
what do the inner walls of the blastocyst become?
embryo
what is implantation?
6-10 days after fertilization– the blastocyst attach itself to the endometrium lining
what happens after blastocyst implants itself in uterine wall?
sends a signal (hormone)=HCG
what does HCG mean?
travels blood steam and affects the ovary, as well as signals to ovary to maintain the corpus luteum.
what does the corpus luteum do in first trimester?
produces progesterone and estrogen
at what stage is the zygote called an embryo?
first trimester
what’s the process of specialization of cells called?
gasturiation
what does gastrulation produce?
a gasturla
what does a gastrula contain?
3 germ layers
what does gasturiation do?
causes cells to get specialized by placing cells in the 3 germ layers
what does the cells in the ectoderm form?
skin, nervous system,
what does the cells in the mesoderm form?
kidney, skeleton, muscles, blood vessels and gonads
what does the cells in the endoderm form?
lungs and lining of the digestive tract
when does the embryo form important parts?
10-14th day
what part of the embryo form important structures?
outer portions of embryo
what does the yolk sac do?
supplies nutrients for the first 2 months of development
what is the amnion ?
fluid filled sac that protects the body of embryo
what is does the allantois do?
removes waste
what does the chorion do?
surrounds everything
what are 4 important structures of the embryo?
yolk sac, amnion, allantois, chorion
when does the placenta fully form?
3 months in
what does is the placenta responsible for?
secreting estrogen and progesterone to maintain pregnancy
and
developing nutrients and removing waste for the developing fetus
what is the placenta made up of ?
endometrium material and small projections from the chorin surrounding the embryo called chorionic villi
what is the chronic villi?
grow out of the chorin into the endometrium and are rich in capillaries
what do the chronic villi do?
provide a large surface area for the exchange if nutrients and waste between the mothers blood and that of the fetus
the relationship between fetus blood and mothers blood?
never mix,– fetal blood remain in the chronic villi
surrounded by maternal (mothers) blood flowing into the endometrial spaces.
what are endometrial spaces?
the inner most lining of the uterus
the purpose of having the maternal blood flowing into the endometrial spaces?
allows the mothers blood to come in as close contact as possible without the 2 mixing.
what attaches the embryo to the placenta?
the umbilical cord
what is the job of the umbilical cord?
to carry fetal blood to the placenta
how does the umbilical cord carry blood to the fetus?
umbilical arteries to the placenta and umbilical veins (singular) to the fetus
how does the mother provide oxygen and nutrients to child?
through her blood– umbilical arteries divide into capillaries in the chronic villi, where the blood can diffuse from mom to baby.
what happens to the cellular respiration byproduct?
co2 gets diffuses from the fetus back to the mother
what is gestation?
period of time between conception and birth
how long is human gestation?
40 weeks
what id gestation divided into?
trimesters– 3
how long do each trimester last?
3 months~
what happens in trimesters?
major development changes occurring in every trimester
what happens in trimester 2 week 24?
fetus– 300 mm long becomes more active and all organs are formed but done function
at happens in trimester 1 week 9?
first bone cells are formed, embryo id called fetus
what happens during the 3rd trimester?
rapid increase in size and vital brain tissue is build and nervous system is develop.
what happens in 2nd trimester week 16
skeleton begins to form, brain grows rapidly and the nervous system begins to form
+ mother can feel movement.
what happens in 1st trimester week 12
all major organs begin to form (liver ,brain, stomach, heart)
the fetus is 100 mm long
noticeable head and limbs
sex can be identifies by ultra sounds
what happens in trimester 1 week 6
eyes begin to form as well as spin formation
what trimester plus week does the nervous system begin developing and when it finish’s?
2nd trimester– week 16
3rd trimester–week 26-27
why is it important for mother to eat healthy when pregnant?
because the fetus receives all of its nutrients and oxygen from mother blood. – anything she eats drinks inhales from environment gets in her blood
what’s the most crucial period of development for the baby?
1ist trimester– because the limbs eyes and major organs are formed in this stage, complications here can result in unhealthy baby/unfinished
what effect does ciggrete smoke have on baby?
constricts blood vessels= prevents it from getting enough oxygen
alcohol affects on baby?
the function of the fetus’s brain and central nervous system as well as physical development (FAS)
FAS is caused by what substance abuse during pregnancy?
alcohol
why is the age of the mother a problem in pregnancy?
too old(45)– body is weak unable to carry baby + body gets tired of meiosis so its not done as well=chromosomes mutation(1/20)
too young+ lots of strain on the body, needs energy to grow mom and baby + higher risk of premature birth
other risk factors of pregnancy?
radiation, pollutants-PBC’s and mercury
what can cause genetic mutation?
radiation, pollutants-PBC’s and mercury and if woman over 45 gets pregnant.
