Development Flashcards
Gestation Period
The time span from fertilization to birth ( 38 weeks )
Prenatal period ( before birth )
Embryological development: developing human for the first 2 months after fertilization ( the embryo )
Fetal development: from 9 weeks until birth ( is not the fetus and not the embryo )
By the end of the 3rd month, the placenta is now functioning
Events before fertilization
This all occurs in the uterine tubes within 24 hours after ovulation
Fertilization likely 2 days before to 1 day after ovulation
Oocyte travels towards the uterus through the uterine tubes and the movement of cilia
The sperm swim towards the oocyte by flagella
-uterine contractions help the sperm move towards the oocyte
Final maturation of the sperm occurs inside the female
-acrosomal membrane becomes fragile
Sperm spends 7 hours in the female reproductive tract before capable of fertilization
*sperm only survives 48 hours in female
*Oocyte viable 24 hours after ovulation
Embryonic period
Extends from fertilization through the eighth week of development
Fertilization
The merging of genetic information between a
Haploid sperm cell and a haploid secondary oocyte merging into a single diploid nucleus
Fertilization of an egg
Sperm penetrates the corona radiata and the zona pellucida around the oocyte
Acrosome enzymes
allows the sperm to penetrate the corona radiata
Fertilization cycle
Day1-12
- Zygote
Day 1: Begins mitotic division, known as cleavage. First division takes about 6 hours
Day 2: two days after fertilization, a second cleavage is completed, now 4 cells (blastomeres)
Day 3: there are 16 cells. all small cells are blastomeres
Day 4: the clusters are now a morula, still surrounded by the zona pellucida
On day 4 or 5: Morula enters uterine cavity, nourished by the uterine milk.
At the 32 cell stage , the fluid inside morula rearrange the blastomeres into blastocyst.
Day 6 or 7: blastocyst implants to endometrium wall of uterus
Day 8: trophoblast develops into syncytiotrophoblast and cytotrohoblast, becoming part of the chorion.
The embryo blast develops two layers, cells of those structures form bilaminar embryonic disc.
The amniotic cavity forms from the epiblast & fills with amniotic fluid
Yolk sac is formed
Day 9: lacunae form
Day 12: yolk sac and lacunae form lacunar networks
Blastocyst
Two cells populations:
Embryoblast and trophoblast
Placenta
provides nutrients to embryo
The chorion
Blocks antibody production by the mother
Promotes the production of T lymphocyte
Produces human chorionic gonadotropin
Secretes estrogens after the first 3-4 weeks of pregnancy and progesterone by the 6th week
Gastrulation
first major event of the 3rd week
- Bilaminar disc transforms into a two dimensional trilaminar disc, made up of ectoderm, mesoderm and endoderm
- Involves rearrangement and migration of epiblast cells
Placentation
Process of forming the placenta
Produced hormones used to sustain the pregnancy
Site of exchange for nutrients and wastes between the mother and fetus
Placenta
Two parts
Fetal portion
maternal portion
True labor
Stage of dilation
Stage of expulsion
Placental stage
Development anatomy
The study of the sequence of events from the fertilization of a secondary oocyte to the formation of an adult organism
Syngamy
The fusion of a sperm with a secondary oocyte
Dizygotic twins
Fraternal twins
Produced from the independent release of two ova and the subsequent fertilization of each by different sperms
Monozygotic twins
Derived from a single fertilized ovum that splits at an early stage in development
Contain exact same genetic material and always the same sex
Yolk Sac
Transfers nutrients to the embryo, is an early source of blood cells and produced primitive germ cells
Capacitation (ZP3)
The series of functional changes that prepare its plasma membrane to fuse with oocyte’s
Polyspermy
The fusion of sperm cells and oocytesets in motion events to block another sperm from fertalizing the egg
Embryoblast
Inner cell mass- develops into embro
Trophoblast
Outer layer that forms wall and will ultimately develop into outer chronic sac surrounding fetus and fetal portion of placenta
Implantation
7 days after fertilization, it attaches more firmly and burrows in
Endometrium becomes more vascularized and glands enlarge
now called a dicidua (endometrium that is modified after implantation )
Development of trophoblast
Day 8.
Digests its way into endometrium(dicidula), to become part of the chorion (where vasculature develops)
Now secretes hCG, signals corpus luteumn to stay in place and not shed ( aka period)
Which leads to estrogen and progesterone continue to secrete
THIS STOPS MENSTRATION FROM OCCURING NOW GOES A DIFFERENT PATH
Development of bilaminar disc
8 days after fertilixzation
Cells of embryoblast, into 2 layers : hypoblast & epiblast
Development of amnionic fluid
Amnion forms roof of amniotic cavity and epiblast forms floor
Amnion eventually surrounds the entire embryo, cavity is now filled with amniotic fluid
Development of yolk sac
from exocoelomic membrane
Relativley small and empty since nutrition derived from endometrium
Will give a rise to easy nutrients, source of blood cells, germ cells that will migrate to form gametes, form part of the gut, shock absorber and prevent desiccation
Development of sinusoids
creating endometrium capillaries dilate to form maternal sinusoids,
more material will diffuse into and will allow chorion to develop
Cloacal membrane
Once it appears in gastrulation, wall of yolk sac forms allantois
Development of somites
3 regions
myotome: skeletal muscles of neck, trunk and limbs
dermatome: connective tissue
sclerotome: vertebrae and ribs
Angiogenisis
Formation of blood vessels
By end of 3rd week, heart forms and begins to beat
Process of forming placenta
2 umbilical arteries carry deoxygenated fetal blood to placenta
1 umbilical vein carries oxygenated blood away from placenta
Afterbirth it detaches from uterus
Hormones of pregnancy
3-4 months: corpus lute secretes estrogen and progesterone
3rd month on the Placenta produces high levels of estrogen and progesterone and produces CRH
Chorion secretes hCG and produces hCS
Relaxin is produced by corpus lute and placenta
LAbor
expelled from uterus through vagina
estrogen rises to overcome effect if progesterone on contractions
estrogen increases number of receptors for oxycontin, which stimulates contractions
Relaxin increases flexibility of pubic synthesis and dilates the cervix
Control of labor through positive feedback
Contractions force fetal head to the cervix which stretches
stretching causes release of more oxycontin
more oxycotin=more stretching
Adjustnentf of infants after birth
Foramen vale closes
-diverts blood to lungs for the first time
now called fossa ovalis
Ductus arterioles constricts and becomes the ligaments arteriosum
Umbilical arteries become medial umbilical ligaments and umbilical been becomes round ligaments of the liver
Lactation after birth
Prolactin promotes milk secretion
secreted by anterior pit.
After delivery, inhabitation removed as estrogen and progesterone levels fall and prolactin can begin
-Sucking maintains prolactin secretion
