Sperm Transport & Fertilization

summary:

active transport

-sustained phase: Motile sperm trickle through the uterotubal junction (UTJ) hours after mating

summary:

passive transport

-rapid phase: Uterine smooth muscle contractions move sperm within minutes after mating, but these sperm quickly die

summary:

sperm loss mechanisms

-retrograde flow: Depends on deposition site; ejaculate qualities like viscosity or copulatory plugs can minimize loss. ​

-phagocytosis by neutrophils: Estrus primes the cervix and uterus for immune responses.

What is sperm reservoir formation, and why is it important for fertilization?

• Formation:

  • Sperm bind to ciliated oviductal epithelial cells in the isthmus, forming a reservoir. ​

• Importance:

  • Prolongs sperm viability and motility for several days in domestic species. ​

  • Ensures capacitated sperm are available when the oocyte enters the ampulla for fertilization.

summary:

sperm capacitation product

-hyperactivated motility

-release from the oviductal reservoir

-ability to fertilize.

summary:

acrosome reaction (AR)

-triggered by binding to zona protein 3 (ZP3) on the oocyte. ​

-leads to enzyme release for zona pellucida penetration, fusion of acrosomal membranes, and exposure of fusion proteins

Where does fertilization occur?

-ampulla of the oviduct

what are the key events of fertilization?

• Hyperactivated motility. ​

• Zona pellucida binding and acrosome reaction. ​

• Zona pellucida penetration. ​

• Sperm-oocyte membrane fusion. ​

• Decondensation of the sperm nucleus. ​

• Formation of male and female pronuclei, followed by syngamy to create a zygote

Why is the timing of insemination relative to ovulation important?

• Oocytes must be fertilized within 10-12 hours post-ovulation due to rapid quality decline. ​

• Sperm require several hours for capacitation. ​

• Ideal timing ensures capacitated sperm are in the reservoir before ovulation, ready to fertilize the oocyte upon entry into the ampulla. ​

• Exception: In dogs (the Bitch), sperm are needed 3-4 days post-ovulation due to delayed oocyte maturation.

definition: 

uterotubal junction (UTJ)

(uterus meets the oviduct)

-connection between the uterine horn and the oviduct (uterine tube/fallopian tube)

fertilization steps:

immediate transport

step 1

-retrograde loss

-phagocytosis

-entrance into cervix/uterus

fertilization steps:

cervix

step 2

-privilege pathways

-removal of non motile sperm

-removal of some abnormalities

fertilization steps:

uterus

step 3

-capacitation initiation

-phagocytosis

fertilization steps:

oviduct

step 4

-complete capacitation

-hyperactive motility

fertilization steps:

fertilization

step 5

-acrosome rxn

-spermatazoon penetrates oocyte

-male, female pronuclei form

sperm loss and selection:

SP role

-immunomodulatory

Why else would post-mating inflammation be important?

-clear out excess and dead sperm

-remove bacteria introduced during mating

-sperm transport

-filter for quality control

summary:

privileged pathways

-bottom of cervical crypts where low viscous mucus favors transports

(most relevant for spp with complex cervix and semen deposition)

purpose:

reservoir for sperm

-Prolongs sperm viability and motility – up to several days in domestic species

summary:

IVM

-oocyte maturation outside of body

-maturation steps before ovulation can be replicated

summary:

cumulus expansion

-Cumulus cells separate from each other

-COC increases in size and becomes “fluffy” or expanded

-extracellular space fills with a hyaluronic acid–rich matrix

-imp in meiosis restart

AR results

•Release of enzymes to help ZP penetration

•Fusion of outer and inner acrosomal membranes

•Exposure of fusion proteins on the sperm head

Why is there a biological mechanism regulating the number of sperm that enter the ampulla around the time of ovulation?

-polyspermy

-abnormal number of chromosomes (lethal) or mitotic spindles (chaotic creation)

-

which spp is most prone to polyspermy in IVF

pigs

AI:

cows

-requires 2x/daily heat detection

-cows will all be inseminated at different times

A sperm is undergoing the acrosome reaction.

Which process has NOT yet occurred?

A.Release from the oviductal reservoir

B.Syngamy

C.Capacitation

D.Hyperactivated motility

E.Secretion of hyaluronidase

B

-fusion of male and female pronuclei