Lect. 5 - Gamete transport and fertilization Flashcards
What are the major mechanisms that propel the egg down the uterine tube?
contractions of tubal smooth muscle
What hormone is necessary for egg rapid transport through the isthmus?
progesterone
What is the time line for the itinerary for the transport of the egg down the uterine tube?
Departure time = day 0
- slow transport in ampulla - 72 hours
- rapid transpsort through isthmus - 8 hrs
- Uterine arrival time 3-4 days.
What are the mechanisms that propel the immobile sperm through the male tract?
Passive transport via testicular fluid, smooth muscle contractions, and cilia from seminiferous tubules
What is the sequence of structures sperm must traverse to reach the epidiymis?
through rete testis
through efferent ductules
to head of epididymis
Where does sperm maturation occur, and how long does it require?
In the head of the epididymis - 12 days
Changes in glycoproteins in plasma membrane of sperm head.
What contributions are made to semen by the seminal vesicles and the prostate gland?
From seminal vesicles: fructose and prostaglandins
From prostate: citric acid, Zn, Mg, phosphatase
What is the optimum pH for sperm motility?
6.0-6.5
What is the pH of the upper vagina?
4.3 —> 7.2 - b/c seminal fluid buffers acidity of vaginal fluids
What is the pH of the cervix?
6.0-6.5 (optimal)
Initial rapid transport
Some spermatozoa reach uterine tubes w/ 15-20 min. following ejaculation; relies mostly on muscular movements of female tract; these sperm are not as capable of fertilizing egg
Slow transport
involves swimming through cervical mucous; 2-3mm per hours; storage in cervical crypts; may not reach oviducts for 2-4 days
What mechanisms move sperm up the oviduct?
swimming movements and peristaltic contractions
Where does fertilization in the oviduct typically occur?
In the ampulla
What is the purpose of capacitation?
it is required for sperm to undergo acrosomal reaction to fertilize the egg
Where does capacitation occur in the female tract?
inside the uterine tube in isthmus
What mechanisms are involved in capacitation?
*binding sperm to tubal epithelium which involves removal of cholesterol form sperm surface (inhibits premature capacitation) and removal of glycoproteins
followed by a period of hyperactivity and release of sperm in small numbers
How does the sperm penetrate the corona radiata?
- fusion of the outer acrosomal membrane w/ the sperm plasma membrane creates portals through which the contents of the acrosome can be released.
- Fragmentation of fused acrosomal membrane and plasmalemma of the perm results in the release of acrosomal enzymes
- swimming movements of spermatozoa also help in the penetration
What enzyme is involved in the penetration of the corona radiata by sperm and what is its source?
Hyaluronidase - in the acrosome
What is the function of ZP3 in the acrosomal reaction?
it simulates acrosomal reaction in mammals - acts through G proteins in the sperm plasma membrane - it mediates the attachemnt of sperm to the ZP
Where is the acrosin (zona lysin) initially found?
attached to the portion of the acrosomal membrane that fuses to the remaining sperm plasmalemma and overlies the nucleus.
What is the function of acrosin (zona lysin) in fertilization?
most important enzyme involved in the penetration of the zona pellucida; it digests a small hole through the ZP and assists in the penetration of swimming spermatozoa through ZP
Fast block to polyspermy in sea urchins.
Consists of rapid depolarization of egg plasmalemma; -70 - +10 mV w/i 2-3 seconds; may last a little longer in mammals; temporarily blocks polyspermy and allows time for the egg to establish slow block.
slow block to polyspermy in sea urchins
release of polysaccharides from the cortical granules located just under the plasmalemma of the egg; polysaccharides enter perivitelline space, hydration produces a swelling that increases the width of the perivitelline space
