objective 10 pt 1 Flashcards
begins with fertilization
ends with birth
38 weeks after conception
prenatal development
what are the divisions of prenatal development?
preembryonic
embryonic
fetal periods
the state of carrying a developing conceptus
pregnancy
developing offspring
conceptus
from fertilization through week 8
embryo
from week 9 through birth
fetus
union pf sperm and egg to create a fertilized egg or zygote
sperm reach secondary oocyte
fertilization
what happens to the sperm that does not make the 12cm trip to join with egg?
- Some leak out of vagina immediately after
intercourse - Some are destroyed by acidic vaginal environment
- Some fail to make it through cervix
- Some are dispersed in uterine cavity or destroyed
by phagocytes - Only a few thousand out of millions of sperm reach
uterine tubes
lasts about 2 weeks following fertilization
pre-embryonic period
early cell divisions
cleavage
first cleavage division completed within 36 hrs result in 2 cells
blastomeres
by end of 3rd day, 16 cells in a ball
morula
By 5th day, hollow sphere of about 100 cells,
consisting of flattened cells called trophoblast cells and a small
cluster of 20-30 rounded cells called embryoblast inside
blastocyst
- By the 21th day of the cycle (7th day after
ovulation) endometrium is ready to receive the
blastocyst - Blastocyst attaches to it & “burrows” into
endometrium - Endometrial cells grow over the blastocyst until it
is completely implanted (by 12th day after
ovulation) - Blastocyst secretes human chorionic gonadotropin
(hCG) - hCG travels by blood to the ovary - causes corpus
luteum to continue to secrete progesterone to
maintain the endometrium - Secretion of hCG declines as placenta develops &
secretes its own progesterone to maintain the
pregnancy (~3 mths)
implantation
what are the 3 primary germ layers that are developing while the blastocyst is implanting?
ectoderm
mesoderm
endoderm
- Beginning of 3rd week to end of 8th week (embryo)
- Lasts 6 wks
- Placenta & extraembryonic membranes formed
- The skin forms during 3rd week
- End of 4th week, heart is pumping blood
The most critical time of development
Tissues differentiate & all the organ systems are
formed by the end of this period (end of 8th week)
1 inch (2.5 cm) long, weighs 1 gram
Appears human
embryonic period
what are the 3 extraembryonic membranes formed during 1st 2-3 weeks?
amnion, yolk sac, allantois, and chorion
filled with amniotic fluid
* Completely surrounds the embryo
* Cushions & protects
* Allows symmetrical development, movement;
prevents parts from fusing together
* Initially, amniotic fluid comes from maternal blood;
later, fetal urine contributes to the volume
* Ruptures naturally or surgically (break)
amniotic sac
sac that hangs from ventral surface of embryo
forms part of digestive tube
source of earilest blood cells and blood vessels
yolk sac
small outpouching at caudal end of yolk sac
structural basis for umbilical cord
becomes part of the urinary bladder
allantois
develops villi that penetrate the endometrium
helps form placenta
eventually fuses with amnion
encloses embryonic body and all other membranes
chorion
- Develops from endometrium & the chorion
- Fully functioning by end of embryonic period
- Has nutritive, respiratory, & excretory role for embryo/fetus
- Functions as temporary endocrine gland - secretes hCG,
estrogen, progesterone
placentation
- The chorionic villi become very vascular & extend to the
umbilical vessels - Umbilical cord connects to fetus (2 arteries, 1 vein)
- Expelled as afterbirth
- The membranes of the fetal capillaries & chorionic villi
normally prevent actual mixing of maternal/fetal blood - These membranes serve as a barrier that protect
the baby from harmful substances that may enter
mother’s blood - However, alcohol, drugs, & some infectious agents
can cross this barrier & cause injury - If placental hormones are inadequate, the
pregnancy is aborted
placenta
what does the maternal portion of the placenta include?
decidua basalis
decidua capsularis
