Packet 28 Flashcards
From fertilization to birth
fertilization implantation placental development fetal development gestation labor parturition (birth)
Haploid sperm nucleus & haploid secondary oocyte nucleus merge to form
single diploid nucleus
Occurs in uterine tube within 24 hours after ovulation (oocyte dies in 24 hours)
fertilization
events occurring before fertilization
- peristalsis of uterine tube and cilia transport oocyte to uterus
- sperm swims to oocyte by flagella
- capacitation (final maturation) of sperm occurs within female
sperm swim towards oocyte by means of flagella
—–stimulate uterine contractions that help move sperm towards the oocyte
prostaglandins
sperm penetrates the ___ cells around the oocyte
granulosa
Sperm digests its way throughthe
zona pellucida
First sperm to fuse with oocyte membrane triggers the slow & the fast block to
polyspermy
1-3 seconds after contact, oocyte membrane depolarizes & other cells can not fuse with it =
fast block to polyspermy
depolarization triggers the intracellular release of Ca+2 causing the exocytosis of molecules hardening the entire zona pellucida
slow block to polyspermy
Events within the egg
–sperm entry triggers___
oocyte to complete meiosis II and dump second polar body
Events within the egg
—Once inside the oocyte
the sperm loses its tail & becomes a male pronucleus
Events within the egg
—the true moment of fertilization is when
Fusion of male & female haploid pronuclei
fertilized ovum (2n) is called
zygote
Rapid mitotic cell division of embryo is called
cleavage
Formation of the morula
Day 1-4
Day 1. 1st cleavage in 30 hours produces 2 blastomeres
Day 2. 2nd cleavage on 2nd day
Day 3. By 3rd day has 16 cells
Day 4. By day 4 has formed a solidball of cells
By day 4 has formed a solidball of cells called
morula
is a hollow ball of cells that enters the uterine cavity by day 5
blastocyst
outer covering of cellscalled
trophoblast
fluid-filled cavity called
blastocele
Trophoblast & part of innercell mass will develop into
fetal portion of placenta
most of the inner cell mass will become
the embryo
Implantation consists of
- Attachment of blastocyst to endometrium
- Trophoblast develops 2 distinct layers
- Trophoblast secretes human chorionic gonadotropin
occurs 6 days after fertilization
implants with inner cell mass in contact with the endometrium
attachment of blastocyst to endometrium
Trophoblast develops 2 distinct layers
- syncytiotrophoblast
2. cytotrophoblast
secretes enzymes that digest the endometrial cells
syncytiotrophoblast
distinct layer of cells that defines the original shape of the embryo
cytotrophoblast
secretes human chorionic gonadotropin (hCG) that helps the corpus luteum maintain the uterine lining
Trophoblast
Development of an embryo outside the uterus
Most often in uterine tube
–common causes are blockages of uterine tube such as tumors or scars from pelvic inflammatory disease
–symptoms are missed menstrual cycles, bleeding & acute pain
ectopic pregnancy
ectopic pregnancy are twice as common in smokers because
nicotine paralyzes the cilia
Day 8
- cytotrophoblast forms
- ectoderm & endoderm together form
amnion and amnionic cavity
embryonic disk
cells of inner cell mass on amnionic cavity form
ectoderm
cells bordering on blastocele form
endoderm
endodermal cells divide to form a hollow sphere (yolk sac)
cytotrophoblast cells divide to fill the spaces surrounding the yolk sac with extraembryonic mesoderm
Day 12
Day 14
cells of embryonic disc produce 3 distinct layers
endoderm
mesoderm
ectoderm
forms epithelial lining of GI & respiratory
endoderm
forms muscle, bone & other connective tissues
mesoderm
develops into epidermis of skin & nervous system
ectoderm
Formation of Embryonic Membranes
Yolk sac
amnion
chorion
allantois
site of early blood formation
gives rise to gonadal stem cells (spermatogonia & oogonia)
Yolk sac
surrounds embryo with fluid: shock absorber, regulates body temperature & prevents adhesions
fluid is filtrate of mother’s blood + fetal urine
examine a sample of it for embryonic cells (amniocentesis)
Amnion
becomes the embryonic contribution to the placenta
derived from trophoblast & mesoderm lining it
gives rise to human chorionic gonadotropin (hCG)
Chorion
outpocketing off yolk sac that becomes umbilical cord
allantois
all of endometrium lost as placenta
–equals all of the endometrium, except stratum basalis
Decidua
portion of endometrium deep to chorion
Decidua basalis
part of endometrial wall that covers implanted embryo
Decidua capsularis-
part ofendometrial wall not modifiedby embryo until embryo bumps into it as it enlarges
Decidua parietalis-
Decidua capsularis fuses with
decidua parietalis
forms during 3rd month
chorion of embryo & stratum functionalis layer of uterus
Placenta
extend into maternal blood filled intervillous spaces --- maternal & fetal blood vessels do not join & blood does not mix
--diffusion of O2,
nutrients, wastes
--stores nutrients &
produces hormones
--barrier to
microorganisms, except
some viruses
-----AIDS, measles,
chickenpox,
poliomyelitis,
encephalitis
--not a barrier to drugs such as alcoholChorionic villi
contents of umbilical cord
- 2 arteries that carry blood to the placenta
- 1 umbilical vein that carries oxygenated blood to the fetus
- primitive connective tissue
Stub drops off in 2 weeks leaving a scar called
umbilicus
