Human Embryology 2 Flashcards
why do eggs need to accumulate resources before fertilization?
- initial cell divisions immediately after fertilizations are done entirely by egg
- doesn’t bring in outside material, so accumulates proteins, energy resources in cytoplasm to prepare
Where does egg arrest in women?
- in prophase 1 as a baby
- in metaphase 2 until reach puberty
Polar body 1 and 2 expulsion occur? Is chromosme count equivalent in 1 vs 2 polar body?
1) after meisosis 1
2) after meisos 2, when egg is fertilized
-no, first polar body will be diploid, second will be haploid
polar bodies contribution to embryonic process?
- different by species, some polar bodies don’t contribute to baby others contribute to the protection of developing fetus
oogenesis general steps:
1) oogonium (2n) becomes primary oocyte
2) primary oocyte (2n) grows & matures undergoes meisosis 1
3) secondary oocyte (1n) + first polar body, they undergo meisos 2
4) fertilization, meiosis 2 complete, get ootid & second polar body
5) differentiation occurs & get ovum
How often is an oocyte released from ovary?
-once a month in post-puberty women
sperm vs egg differences
1) stay in syncytium until maturation complete
2) complete meiosis
sperm vs egg differences
1) sperm stay in syncytium until maturation complete
2) sperm complete meiosis & continually make more cells
3) eggs don’t finish meiosis 2 until fertilization; have a set number of oocytes are born with
oocyte movement overview
1) each month (at ovulation), oocyte released from ovary
2) fimbriae of uterine tube sweep over the ovary (usually the two are separate)
3) oocyte is brought into the ampulla of the uterine tube
4) ovary travels through uterine tube towards the Uterine Cavity
How specifically does oocyte get into the fallopian tube?
1) secondary oocyte has a vesicle sticking out called stigma which pops the wall of the ovary when timbre of tube is close
2) follicular fluid from the 2 oocyte flows into the tube, cilli push secondary oocyte with it, then the fluid pulls oocyte rest of way through tubes to the uterus
how sperm fertilize egg?
-sperm enters at end of vagina, has to go through cervix then all theway to meet egg in middle of fallopian tube (pretty far)
Fertilization and the cervix?
-usually cervix blocked by thick layer of mucus, during ovulation becomes thin layer of mucus so the sperm can break through and enter uterus
Uterus structure and embryonic development?
- uterus structure is important for new embryo
- has uterian glands, dense vascularization, veins, arteries, and spaces inbetween with lacunae
- makes good place to receive embryo
lacunae?
spaces that fill with blood in the uterus to help keep embryo nourished
What are they Female Reproductive organs?
Uterus, Uterine Tubes and Ovaries
What 2 hormones control gametogenesis?
1) Steroid hormones
2) Peptide hormones
- both have similar regulatory loops sperm & oocyte formation
steroid hormones?
- cholesterol derivatives
- include testosterone, estrogen, & progesterone
- act via series of nuclear receptors (receptors that lie within the cell, not membrane-bound)
nuclear receptors?
receptors that lie within the cell, not membrane-bound
Peptide hormones
including:
1) follicle-stimulating hormone (FSH)
2) luteinizing hormone (LH)
3) gonadotropin-releasing hormone (GNRH).
Why/how release same hormones w/ same feedback loops but get 2 different gametes? What happens if sperm gametes don’t reach testes?
- cell components in ovary & testes are diff
- interpret hormonal signals in diff ways
- all gametes are identical before reach testes/ovaries
- once reach…differentiation occurs
- if male gamete does NOT reach, testes, then will mature into an oocyte, require testes signals to become sperm
The three major naturally occurring forms of estrogen in women are:
1) Estradiol
2) Estriol
3) Estrone
Me stroll cycle and hormone levels?
1) beginning, uterine wall very thin
2) LH surge is signal for uterine wall to become thick & ovulation to occur
3) if embryo received wall will continue to grow, if not receieved go through menstrual cycle returns to thin uterian wall
When does LH surge occur?
- production of secondary oocyte (end of meiosis 1), right before ovulation occurs
- signals for ovulation to happen
sexual intercourse-mediated fertilization?
1) how oocyte & sperm normally meet
2) erect penis inserted into vagina
3) ejaculation of sperm at cervix lets sperm enter uterus & uterine tubes
4) 100 million sperm per ml of ejaculate ( 2 -6 ml; ~400 x10^6)
How much sperm per ejaculation
- 100 million sperm per ml of ejaculate -usually 2 -6 ml so:
- ~400 x10^6 sperms
How long does it take for sperm to meet egg? Sperm lifespan in normal humans?
1) 30min- 2hr to reach egg
2) life span is short, sometimes can maintain viability for couple days is rare
Sperm lifespan in other species?
- if sperm has longer life span, can be released into uterus, then days fertilize egg,
- some species store sperm in inert stage; save for later better procreation states then activate & fertilize
Steps for spermatozoa maturation, activation and fertilization?
1) mature sperm form, stored in epididymis in immobile state
2) activation when ejaculate get mobile sperm
3) Capacitation in proximity to the oocyte
4) Acrosome reaction when meet egg
Capacitation
- destabilisation of acrosomal sperm head membrane allows greater binding between sperm & oocyte
- membrane changes in sperm occur, hyperactivity facilitates passage through corona radiata to access the Zona Pelucida
Acrosome reaction
1) sperm binds zona pelucida (at ZP3) & release hydrolytic enzymes stored in acrosome vesicle
2) these enzymes degrade Zona Pelucida
3) allows sperm movement into perivitelline space, fusion with Oocyte’s plasma
zona pelucida
the thick transparent membrane surrounding a mammalian ovum before implantation
-contains glycoprotein ZP3 on extracellular matrix
perivitelline space
-space between the zona pellucida and cell membrane of an oocyte or fertilized ovum
complications sperm can experience when released into uterus?
1) immune cells can attack sperm (see as foreign)
2) sperm has to move against the flow of liquid trying to push egg from Fallopian tube into the uterus
Oocyte response after fusion with sperm?
1) Oocyte Activation
2) Fast Blockade
3) Slow Blockade
- Oocyte starts fast, needs to block further entry of other sperm or get polyspermy and get fucked up chrom. #
Oocyte Activation
1) once sperm enters oocyte
2) creates blockade against polyspermia
3) completion of Meiosis 1
oocyte fast blockade?
-membrane depolarizes; prevents fusion of new sperm membranes even if already in the space
oocyte slow blockade?
1) Ca2+ influx leading to Oocye vesicle secretions that inactivate ZP3 (glycoprotein on ECM of zone pellucida)
2) prevents acrosome rxt
ZP3
- a glycoprotein on the zona pellucida’s extracellular matrix
- receptors on sperm plasma membrane attach to ZP3
- contents it’s acrosome, (hydrolytic enzymes) spill out & degrade zona pellucida near sperm head
what happens when have fussion of one Sperm and the Oocyte (5 general steps?
1) sperm uses ZP3 mediated binding to bind ZP
2) Release acrosome vesicle enzymes, to digerst ZP.
3) move into perivitelline space,
4) fusion w/ Oocyte’s plasma membrane
5) sperm head, neck and tail enter oocyte
Mitochondria of the sperm
- entire sperm enters the oocyte including mitochondria
- BUT mitochondrial proteins enter ubiquinated…so are automatically sent to proteomes for degradation therefore only express mothers mitochondrial DNA
fertilization steps (x5)
1) fertilization occurs in the ampulla of fallopian tube
2) sperm passed through corona radiata
3) acrosome of sperm breaks down zona pellucida. Zona rxt prevents other sperm from entering oocyte
4) head & tail of sperm enter the oocyte
5) pronuclei combine to form zygote w/ 46 chromosomes. cleavage begins
how estrogen + progesterone, and progesterone only contraceptives work?
1) block ovulation
2) block uterus endometrium maturation (change lining of uterus, so can’t implant egg into uterus)
3) reduce sperm passage through cervix (increase mucus at cervix)
* ONLY WOMEN USE*
what is ovulation exactly?
release of an egg from the ovaries into the fallopian tube and eventually uterus
concerns about implant birth control?
-can potentially cause inflammation & rejection
male contraceptives?
- hormone processes are same for sperm & egg production yet only women take BC
1) vasectomies
2) Vasalgel
3) male BCP
vasectomies
- block epidermis and prevent relase of new sperm
- sperm is made but then degraded
- not popular cuz is permanent
Vasalgel
- daily gel that stops sperm production
- polymer injected into sperm-carrying tubes; through the scrotum
- blocks sperm & is reversible through a second injection that dissolves it
male birth control pills?
-entering phase two clinical studies
issue: the sperm-suppressing hormone changes that the drug induces clear the body too quickly, would require more
than a once daily dose
-once daily dose only last 18hr
assisted reproductive technologies?
1) cryopreservation: freeze sperm & egg
2) surrogate Mothers
3) artificial insemination
4) in Vitro Fertilization and Embryo Transfer (IVF)
5) intracytoplasmic Sperm Injection (inject sperm directly into eggs)
Who did first IVF fertilization?
Sir Robert G. Edwards, Louise Brown was first test tube baby in 1978
IVF process?
1) Super ovulate get lots of eggs, put in petri dish, add sperm
2) Sperms active & mobile, fertilize egg
3) blastocyst screen and check for genetic defects,
4) choose 1 early embryo & deposit in back of uterus (normal implantation area)
assisted reproductive technologies?
1) cryopreservation: freeze sperm & egg
2) surrogate Mothers
3) artificial insemination
4) in Vitro Fertilization and Embryo Transfer (IVF)
5) intracytoplasmic Sperm Injection (inject sperm directly into eggs)
Who did first IVF fertilization?
Sir Robert G. Edwards, Louise Brown was first test tube baby in 1978
IVF process?
1) Super ovulate get lots of eggs, put in petri dish, add sperm
2) Sperms active & mobile, fertilize egg
3) blastocyst screen and check for genetic defects,
4) choose 1 early embryo & deposit in back of uterus (normal implantation area)
Prenatal vs Postnatal
Prenatal Embryonic: First 8 weeks, day 1-56 Fetal: After 8th week until birth Postnatal: Infancy, childhood, puberty, adulthood
First week of pregnancy?
1) fertilization
2) cleavage
3) blastocyst
Cleavage of the zygote definition?
-the rapid, multiple rounds of cell division that turn zygote into blastula
Cleavage of the zygote mechanism?
1) two cell stage
2) 4 cell stage
3) 8 cell stage
4) Morula blastomers
5) (first differentiation event) tropoblasts or early blastocyst
6) late blastocyst develop embryo blast (or ICM)
blastomere
a cell formed by cleavage of a fertilized egg
Morula?
- contain identical cells, each has potential to give rise to full new embryo
- still contains zone pellucida around it, haven’t excepts help from sperm yet, done this on own
first differentiation event?
- from identical Morula blastomers to Trophoblasts
- loose the zone pellucida
Trophoblasts
are cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta
late blastocysts?
-embryoblast or inner cell mass (ICM ) forms in blastocysts
Animal vs Vegetal Pole
animal pole: used for implantation, directly contacts uterus, acts as anchor for attachment
-was where inner cell mass was
vegetal pole=the opposite side
embryoblast or inner cell mass (ICM )
generate all tissue of futrure embryo, characterized by many TF like OCT4 (key stem cell gene)
First step of Implantation?
- blastocyst attachment to endometrium*
1) trophoblast attaches the blastocyst (through animal pole) to the endometrium
2) trophoblast divides into a syncytiotrophoblast (syncytium) and cytotrophoblast
3) Syncytiotrophoblast layer invades endometrium pulling embryo with it
What day of pregnancy does attachment happen?
day 6
Types of trophoblasts?
1) syncytiotrophoblast invade endometrium
2) cytotrophoblast are all the rest
What happens in stage 1, 2, 3 and 4 of pregnancy?
Stage 1: Zygote formation
Stage 2: days 2-3, 2 to 16 cells
Stage 3: morula–> trophoblasts–> ICM–> mature blastocyst (days 4-5)
Stage 4: Attach to posterior wall of the uterus (days 5-6)
first step in Implantation (post attachment)?
Embryoblast (ICM) forms a bilaminar, embryonic disc:
1) Epiblast (on top)
2) Hypoblast (on bottom)
embryo proper?
- the amniotic membrane, yolk sac & allantois
- compared to the fetal part of the placenta
Epiblast & Hypoblast contribute to?
Epiblast: embryo proper,
Hypoblast: fetal part of the placenta, make endoderm, but not actual fetus
Embryoblast/ ICM cell types?
- initially though all cells were homogenous pluripotent cell population (similar to morulas)
- actually contains cells with different expressions, which segregate to generate epiblast and hypoblast
How distinguish between cell types in embryo blasts/ICM?
- diff trxn factors cause diff proteins to be expressed in the two cell types:
1) oct6 expression= hypoblasts, 2) hyp4 expression= epiblasts
Implantation days 8-9 (steps x4)
- Invading Syncytiotrophoblasts break down glands & vessels.
- Amniotic cavity formed between the cytotrophoblast and the epiblast.
- Embryonic disc lies between amniotic cavity and exocoelomic cavity/primary umbilical vesicle
- Hypoblast derived endoderm lines the umbilical vesicle, and this extraembryonic endoderm generates extraembryonic mesoderm
Epiblasts make?
- ectoderm
- mesoderm
- endoderm
hypoblasts make?
- extra embryonic tissue
- lines umbilical vesicle
- creates protective sack
Implantation days 10-12 (steps x4)
- Conceptus completely embedded in uterine wall. Endometrial scar corrected by a closing plug
- Hypoblast derived endoderm lines the umbilical vesicle
- Primordial uteroplacental circulation: communication of the eroded endometrial capillaries with the lacunae provides resources to nourish the early embryo
- Endometrial capillaries around embryo become congested & dilated to form maternal sinusoids
maternal sinusoids
thin-walled terminal vessels that are larger than ordinary capillaries
Embryotroph
Maternal blood, and uterine gland debris accumulated in lacunae, provide food/ resoruces to nourish early embryo
day 13/14 of pregnancy (implantation( x4?
1) Endometrial epithelium plug has been repaired;
2) Formation of small secondary umbilical vesicle;
3) Large extraembryonic coelom, surrounds the umbilical vesicle and amnion;
4) Primary Chorionic Villus. The first stage towards chorionic villi of the placenta
Chorionic Sac Formation?
The extraembryonic coelom splits the extraembryonic mesoderm into two layers:
1) Extraembryonic somatic mesoderm, lining the trophoblast and covering the amnion
2) Extraembryonic splanchnic mesoderm, surrounding the umbilical vesicle
Placenta
feto-maternal metabolic interchange organ
The connecting stalk appears at where?
at the chorionic vesicle stage
-it is extraembryonic somatic mesoderm that connects the caudal end of the embryo to the Chorion
what 2 layers forms Chorion? What is the chorion?
fetal part of the placenta; noutermost fetal membrane, forms wall of chorionic sac
1) extraembryonic somatic mesoderm
2) trophoblast
chorionic sac
The embryo, amniotic sac, and umbilical vesicle are suspended in this sac
Ectopic pregnancies examples? How occur?
-abdominal
- many ways
1) ovary fall out in transfer
2) not enough cilia to push through to uterus
Abdominal pregnancies?
Higher maternal mortality, baby mortality and morbidity compared to other ectopic pregnancies
-Occasionally
lead to a healthy delivery
Most common place for fertilization of the egg?
ambula of tube (near fibers of tube)
