Fertilization - Lecture Flashcards
What is capacitation? What are the steps involved and where does it occur?
Capacitation - sperm membrane becomes fragile and permeable to Ca
process begins during contact with seminal gland’s secretions, complete after entering the female reproductive tract
- triggered b HCO3- ions in the vagina - activate adenylate cyclase pathway
changes include:
1. destabilization of the acrosomal head plasma membrane began in the epididymus which resulted in greater membrane permeability
2. increase in intracellular Ca ion, which increases cAMP and motility of sperm flagellum and head
3. cholesterol withdrawal and surface protein redistribution
What is the acrosomal reaction?
breakdown of the acrosomal membrane due to entrance of Ca and release of acrosomal enzymes across and hyaluronidase
acrosomal reaction initiated by binding of sperm PLASMA MEMBRANE to ZP3 receptor on zone pellucida
acrosomal enzymes break down the hyaluronic acid material that binds the follicular cells that surround the zone pellucida
part of the INNER ACROSOMAL MEMBRANE fuses with the membrane of the secondary oocyte
- binding allows the inner acrosomal membrane to digest through
When sperm enters the vagina, where does it go? How does it get moved into the uterus?
typically stay in the posterior fornix until closer to ovulation - seminal fluid thickens and allows the sperm to orient and swim towards the external os
sperm swim and accumulate in the opening of the isthmus
- primary moved by peristaltic contraction of the smooth muscle of the oviduct
What is the classical model for receptor recognition between spermatozoan and oocyte?
fertilin - sperm surface protein
- necessary for sperm movement thought the oviduct
- necessary for sperm to bind to oocyte
fertilin binds to oocyte with integrin alpha 6 beta 1
What is the modern model of receptor recognition between the spermatozoan and oocyte? What does it trigger?
IZUMO (sperm membrane protein) interacts with Jumo (oocyte protein)
- equatorial segment of spermatozoa binds with microvilli membrane segmane to oocyte
Docking restyle in:
- blocks to polyspermy
- completion of 2nd meiosis and formation of second polar body
What are the components of the sperm that enter the egg?
- sperm nucleus - DNA
- 2 centrioles - absent in the secondary oocyte
- mitochondria and microtubules - both degenerate f
What is the fast block to polyspermy?
contact of the sperm plasma membrane with the proteins on the oocyte plasma membrane result in the opening of Na channels
- Na depolarizes oocyte membrane
occurs in sea urchins, some amphibians but not humans
What is the slow block to polyspermy?
after sperm binds to the egg membrane, Ca wave across oocyte plasma membrane occurs
- triggers secondary oocyte to complete meiosis II (extrusion of 2nd polar body)
- triggers cortical reaction
cortical reaction: oocyte releases contents of cortical granules that cause:
1. ZP3 receptors to be destroyed by by cortical enzymes
2. zona pellucida glycoproteins harden
Describe the pronuclei movement and zygote formation
after oocyte goes through meiosis II, it becomes an ootid/ovum (n)
Pronuclei - ovum and spermatozoan
- both replicate their chromosomes within their own membrane
- as they approach each other, membranes disintegrate - chromosomes intermingle and new nuclear membrane forms around newly formed zygote (2n)
zygote - formed as soon as replicated chromosomes of each pronucleus are aligned
- never a time where chromosomes of zygote are surrounded by common nuclear membrane
What is a morula? How is it formed?
morula - solid ball of 16 cells seen about 72 hours after fertilization
- cleavage: produces series of smaller and smaller cells during rapid mitotic division
- cells are smaller due to constriction of zone pelludica
- found within the isthmus
Once the morula is in the uterine cavity, what is it considered? What day does implantation occur?
blastocysts - hollow ball of trophoblast cells surrounding the inner cell mass
- forms around day 4
- trophoblasts - part of the placenta
- inner cell mass becomes the amnion, embryo and yolk sac
binds to uterus on side with inner cell mass
implantation on uterine wall on day 7-10
After the blastocyst begins implantation, what happens next? How does the endometrial tissue respond?
adhering trophoblasts proliferate, secrete digestive enzymes and growth factors
endometrium responds with inflammatory response
- increased permeability of blood vessels
- increased number of WBC
What are syncytiotrophoblasts? What are they derives from, and what do they do in implantation?
syncytiotrophoblasts - outer trophoblasts that have fused their plasma membranes
- burry their tissue into the maternal tissue and surround maternal blood vessels
- form pools of maternal blood (lacunae) so that maternal blood gets passed to the fetal tissue
What are cytotrophoblasts? What are they derives from and what do they form?
cytotrophoblasts - inner trophoblasts that rapidly divide at day 11-13 to form the extraembryonic mesoderm layer called the chorion
chorion - forms fetal loose connective tissue and form CHORIONIC VILLI
- villi grow out laterally through the synctiotrophoblast forming a TROPHOBLASTIC SHELL
What is the name for endometrial tissue during pregnancy? What are the different types?
decidua - endometrial tissue during pregnancy
- true placenta is forming at the stratum functionalis
decidua basalts - region of endometrium underlying site of implantation
decidua capsularis - region of endometrium overlying the implantation side and deem to the surface of uterine lumen
decidua parietalis - remaining endometrial tissue not associated with implantation
During week 8 of placentation, some chorionic villi begin to degenerate. Where do they degenerate and what are they called?
villi in the decidua capsularis degenerate
- chorion levae - smooth avascular surface of placenta
villi in the decidua basalts remain and rapidly develop
- chorionic villi
both types of chorion are considered fetal tissue and have the same chromosomes as the zygote
The placenta functions as an endocrine organ. What are the hormones it produces?
progesterone
estrogens
human chorionic gonadotropin
human placental lactogen
insulin growth factors
endothelial growth factors
What is the inner cell mass? What composes the bilaminar disc? What do they turn into?
inner cell mass - round cluster of cells that develop to form the amnion and embryo
bilaminar disc:
- hypoblast - forms the yolk sac
- epiblast - forms the amniotic cavity and developing mesoderm
trilaminar disc - epiblast cells separate to form a secondary, amniotic cavity whose roof goes into the trophoblast cells
What is the primitive streak? How is it formed, and what is it made of?
primitive streak arises as epiblast cells proliferate
contains:
- primitive groove
- primitive pit
- primitive node
epiblast goes down through the primitive streak to add another layer between epiblast and hypoblast
- epiblast becomes the ectoderm
- Endoderm - first layer that goes down through primitive streak and replaces the hypoblast
- mesoderm - second layer that goes down and separates the endoderm and ectoderm
What is the trilaminar disc? What does each layer become?
ectoderm - skin, nervous system
mesoderm - connective tissue, muscle, bone, cartilage and membranes
endoderm - epithelial lining for respiratory, GI, etc
What is the notochord? What does it develop from and what does it develop into?
develops from axial intraembryonic mesoderm
- causes the ectoderm to form the neural plate that eventually develops into the neural tube and the rest of the nervous system
- persists as the jelly center of intervertebral discs
What does the lateral plate of the mesoderm turn into? What is a coelom?
somatic mesoderm (top/lateral)
- associated with ectoderm to form body wall lining and drunk dermis
- skeletal muscle
splanchnic mesoderm (bottom/medial)
- associated with endoderm to form viscera of digestive system and heart
- visceral peritoneum
coelom - space between the splanchnic and somatic mesoderm formed during lateral folding
What does the paraxial mesoderm turn into?
somites - cells that are precursors for the skeletal muscle tissue of the head and torso
- trunk muscles, skeleton, dermis of the skin, blood vessels and connective tissue
What does the intermediate mesoderm turn into?
contains cells that are precursors to the urinary and reproductive organs
What kind of folding does the embryo go through?
transverse and longitudinal
What are the tissues that are derived from the ectoderm?
epidermis
lens
anterior pituitary
brain and spinal cord
teeth
facial bones
What are the tissues that derives from the mesoderm?
dermis
circulatory system
muscles
bones and cartilage
connective tissue
What are the tissues that are derives from the endoderm?
lining of the GI tract
lining of the lungs
glandular tissue
thymus and tonsils
How does a vasectomy prevent pregnancy?
vas deferens cut so that sperm cannot enter urethra
- no change in sperm or testosterone synthesis
- can still ejaculate
How does a salpingectomy prevent pregnancy?
egg is still allowed to ovulate and enter oviduct, but passage into the uterus is not allowed
- sperm cannot meet it
How does hormonal birth control prevent pregnancy? How does plan b work?
prevents egg release
- estrogen/progesterone cause negative feedback on GNRH
- prevents release of LH and FSH
- follicle cannot grow - egg not ovulated
similar to birth control but at higher doses
- prevents egg from being released or implanted
How does a non-hormonal IUD prevent pregnancy?
copper coat changes nature in the uterus
- egg is still allowed to be released and fertilized
- prevents implantation only
