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
