Fertilization and Early Embryo Development Flashcards
site of sperm deposition
- fornix or cervix
sperm transport: effects of vaginal secretions (2)
- immobilize sperm within 1-2 hours
- rapid transport is essential to evade female innate immune system
sperm transport: advantage of artificial insemination
- semen can trespass barriers by being inserted into the uterus
semen transport: seminal plasma (5)
- vehicle for transport
- energy
- motility
- pH
- block capacitation until timing is right
how do sperm achieve rapid transport (2)
- major: contractile activity of uterus myometrium and oviduct
- minor: sperm motility
how quickly do sperm reach site of fertilization
- around 15 min
colonization of sperm reservoirs (3)
- anatomic/physiological barriers prevent excessive sperm amount in site of fertilization
- phagocytosis and sperm loss over time
- avoids polyspermy
- where are the sperm reservoirs (2)
- between cervix and uterus in cervical crypts
- between uterus and oviduct in utero-tubal junction
gamete transport in oviduct (3)
- sperm and oocyte travel in opposite directions
- peristalsis and anti-peristalsis driven by estradiol
- complex nervous control
sperm survival in female (2)
- normally max of 24 hours survival
- loss by phagocytosis and physical barriers
sperm transport summary (4)
- fast transport of sperm
- loss of a lot of sperm cells
- has to reach oviduct in certain time
- timing must be synchronized by male/female gametes
spermatozoa changes (4)
- maturation in the epididymis
- mixing with accessory glands fluid
- capacitation
- acrosome reaction
maturation in the epididymis (2)
- motility development
- loss of cytoplasmic droplet
what is capacitation necessary for
- sperm/ovum fusion
where does capacitation occur (2)
- through the female tract
- in the uterus then the isthmus
what occurs during capacitation (3)
- spermatozoa surface components are modified or removed
- secretions and accessory gland fluids
- mitochondria modification
capacitation: spermatozoa surface (2)
- cholesterol efflux
- PKA-dependent phosphorylation
capacitation: mitochondria modification
- become loosely wrapped around the axoneme or distended
what is the result of capacitation (4)
- phospholipid layer destabilized
- spermatozoa prepped for acrosome reaction and hypermotility
- hyperactivated sperm with expression of receptors for zona glycoprotein
- Ca2+ influx
major factors affecting capacitation: vaginal environment (2)
- cholesterol efflux in normal sperm
- Ca2+ influx
major factors affecting capacitation: cervical mucus (2)
- cervical mucus scrubbing supports capacitation
- leukocytes release ROS which affect capacitation speed
major factors affecting capacitation: uterine environment
- sialic acid binding protein binds to receptor on sperm
major factors affecting capacitation: oviductal environment
- progesterone from granulose/cumulus cells
what affects Ca2+ influx (5)
- physical environment
- ROS
- SABP
- progesterone
- HCO-3
acrosome reaction (3)
- sperm plasma membrane fuses with outer acrosomal membrane
- vesiculation of acrosome
- release of hydrolytic enzymes
what hydrolytic enzymes are released in the acrosome reaction (2)
- hyaluronidase
- acrosin
fertilization requirement (2)
- zona pellucida has 3-4 glycoproteins
- fertilization requires a strong and physical binding between glycoproteins and receptors on acrosome
what do ovulated egg pickup by oviducts depend on (4)
- characteristics of fimbriae of the infundibulum; ciliated cells create negative pressure toward oviduct lumen
- pattern of cumulus cells and egg release
- biophysical properties of follicular fluid released
- coordinated contraction of the fimbriae, utero-ovarian ligaments, and the oviduct muscle layer
transport time of ova to ampulla
- will reach ampulla within first few hours
transport time of ova to uterus if fertilization occurs (2)
- usually a few days (72 - 96 hours)
- first few days of embryo development occur in oviduct and not the uterus
transport of ova if no fertilization occurs (2)
- egg gets transported to the uterus where it is digested/reabsorbed
- mare exception: unfertilized ova is retained in oviduct for months
fertile life of the egg (2)
- 12-24 hours after ovulation
- delayed egg increases chances for polyspermy
ovum maturation (3)
- prophase I during follicle development
- metaphase II during ovulation
- maturation of ovum completed after fertilization and zygote formation
fertilization
- fusion of male and female pronuclei
fertilization events (4)
- nuclear envelope disperses
- intermixing of chromosomes
- 1st cleavage division
- creation of the zygote
zygote
- one cell diploid embryo (2N)
how is polyspermy blocked (2)
- changes in ova surface immediately after fertilization from the 1st sperm
- block is performed at zona pellucida
polyspermy
- fertilization of an egg by more than one sperm
what occurs if polyspermy blocking fails (4)
- failed pregnancy
- polyspermic fertilization
- polyploid embryos
- embryonic death/abnormal development
how is polyspermy blocked at the zona pellucida after sperm penetration (3)
- cortical granules release into the peri-vitelline space (Ca++)
- hardened zona pellucida
- increased peri-vitelline space
