Human Development and Aging Flashcards
What is embryogenesis?
Events in development leading up to the embryo
The preembryonic stage is___
the first 16 days after fertilization
What is the fertilization window?
egg must be fertilized within 12-24 hours of ovulation
What is sperm capacitation?
the process that migrating sperm must undergo to make egg penetration possible
What are the two important events that occur during capacitation?
- Female fluids leech cholesterol from sperm
- sperm becomes permiable to to Ca2+ increasing powerful flagella movements
How long is sperm viable for after ejaculation?
6 days
What reaction does sperm undergo when it encounters the egg?
An acrosomal reaction
What is a acrosomal reaction?
The exocytosis of the acrosome causing the release of enzymes needed to penetrate the egg
Once acrsomoal enzymes clear a path through the granulosa cells the next step is?
-sperm binds to the zona pellucida releasing more enzymes to help it to contact the egg
Once the sperm contacts the egg?
The egg destroys the sperms mitochondria so only the head enters
Fertilization is a combination of ___
The haploid set from the egg and spem combind
When the two haploid sets combine what is the produce?
a diploid. Fertilization is complete
What is polyspermy?
Fertilization of an egg by two or more sperm
What two mechanisms prevent polyspermy?
- Fast block-when sperm binds it opens Na+ channels causing depolarization preventing additional binding
- slow block-Penetration by sperm causes inflow of Ca2+ causing a swell of fluid beneth the zona pellucida pushing the rest of the sperm away
What step occurs after fertilization?
-The secondary oocyte completes meiosis II
What becomes of the egg and sperms nuclei after fertilization?
- The egg discards one chromatid from each chromosome
- the sperm and egg swell to become pronuclei
- pronucli rupture and mix into a single diploid set
Once a diploid set is formed the egg is now called a ___ and is ready for___
Zygote ready for mitotic division
____ of all embros die in the first trimester. Why?
- more than 50%
- Conceptus is most vulnerable at this stage and precautions may not be taken because pregnancy may not have been noticed yet
What developments occur in the second trimester?
- Most organs complete development
- Distinct human form
- Possible to survive if born
What occurs during the thrid trimester
- Fetus growth is rapid
- organs can support life
- birth occurs at end of third trimester
When is a fetus considered mature?
35 weeks and 5.5 pounds
What are the three major processes during the preembryonic stage?
- Cleavage
- Implantation
- Embryogenesis
What is cleavage?
mitotic divisions in the first 3 days after fertilization
What is implantation?
The zygote implants itself into the endometrium
What is embryogenesis?
the arrangement of the three primary germ layers
How many cells are produced during cleavage?
how long is the process of cleavage?
about 100 cells in about 72 hours
The end result of cleavage is called the___. How long does it rest in the uterus until implantation?
Morula?
4-5 days
The morula becomes a blastocyst after___
The zona pellucida disintegrates and releases the conceptus
What is the internal cavity of the blastocyst?
The blastocel
What is the inner mass within the blastocel?
The embryoblast
Which portion of the blastocyst becomes the placenta?
the outer layer of cells called thee trophoblast
Which portion of the blastocyst secretes HCG?
The trophoblast
The three portions of the blastocyst are_
BTE
- Blastocoel: internal cavity
- Trophoblast: future placenta
- Embryoblast: future embryo
Implantation occurs when the ____attaches to the _____. This occurs ___ days after ovulation
Blastocyst
Placenta
6
How does the blastocyst attach to the endometrium?
The trophoblast cells that come into contact with the endometrium form two layers and invade the endometrium causing the endometrium to grow over the blastocyst
What are the two layers of cells formed by the trophoblast during implantation?
- Syncytiotrophoblast
- Cytotrophoblast
What is the function of the syncytiotrophoblast?
it is the layer of the trophoblast that invades the endometrium
How long does the process of implantation take?
about one week
What is the first step of embryogenesis?
The embryoblast forms an embryonic disc separates into two layers
- Epiblast
- Hypoblast
After the first seperation what is the next step in embryogenesis?
The emergence of three primary germ layers from the embryonic disc.
What are the three primary germ layers?
- Ectoderm
- Endoderm
- Mesoderm
What are the two paces that flank the embryonic disc?
The Amniotic cavity and the Yolk sac
What is the primitive groove?
A split in the epiblast (soon to be sctoderm)
What is gastrulation?
The process of epiblast cells migrating into the groove and forming replacing the hypoblast with endoderm
Inbetween the endoder and the ectoderm forms the____
Mesoderm
Mesoderm eventually becomes ___
Mesenchyme
When is Embryogenesis complete
Once all three primary germ layers are fully formed
Once embryogenesis is complete the zygote is officially a ____
Embryo
When does the placenta form?
6 weeks from the begining of the embryonic stage begins
When are nearly all organs present?
at 8 weeks
Explain the process of embryonic folding
- The flat embryonic disc converts into a cylindrical form
- The embryo folds around the yolk
- the ectoderm doubles over and eventually covers the entire embryo
- The mesoderm splits and forms two layers.
What form does the embryo have after the process of embryonic folding
A ball with a tube down the middle
The ectoderm eventually becomes the ____
epidermis
the mesoderm eventually becomes the ___
connective tissue
The endoderm eventually becomes the ___
Inner epithelial layers of the digestive tract
What are somites?
Segmentations of the mesoderm that eventually become the vertebral column, trunk muscles, and the dermis
What is the Amnion?
- Amniotic sac
- a transparent sac that develops from the epiblast
- completely encloses the embryo
- penetrated by the umbilical cord
What is the yolk sac?
- A sac a fluid that forms from the hypoblast
- contributes to formations of GI tract, blood cells, and future egg and sperm
What is the Allantois?
- A pocket that forms from the yolk sack.
- forms the base of the umbillical and part of the bladder
What is the chorion?
the outtermost embryonic membrane that encloses all of the rest
What are the chorionic villi?
Pertrusions of embryonic blood vessels that pull nutrients from the mothers blood. Eventually form the placenta
What are the three sources of prenatal nutrition?
- Uterine milk
- Trophoblastic nutrition
- placental nutrition
What is uterine milk?
glycogen-rich secretion of the uterine tubes and endometrial glands
-Used for nutrition before implantation
What is trophoblastic nutrition.
-Nutrition derived from the consumption of endometrium cells.
How long does is trophoblastic nutrition used for?
Up to 12 weeks but declines as the placenta grows
What is the placenta?
a disc-shaped organ attached to the uterine wall and to the fetus on the other
What is placental nutrition?
Nutrients diffused from the mothers blood through the placenta
What is the placental stage?
The period beginning around 9 weeks until birth where nutrition is supplied by the placenta.
What is placentation?
The development of the placenta
What is contained within the umbilical cord?
two umbilical arteries and one umbilical vein
What pumps blood from the placenta?
The fetal heart
Blood returns to the fetus via the
umbilical vein
An embryo is considered a fetus after ___ weeks
8
How any circulatory shortcuts are present in the fetus?
3
The two umbilical arteries form from the ____
Internal iliac arteries
O2 rich blood flows from the placenta to the _____ via the _____
Inferior vena cava
umbilical vein
How does the flow of blood differ in the fetus compaired to an infant?
- Blood mostly bipasses the pulmonary circuit
- Passes from atrium to atrium via fossa
