Gamete Transport And Fertilization Flashcards
How is the ovulated egg transported?
-contractions of the tubal smooth muscle
Outline of the transport time of the egg through the uterine tube.
- departure time: day 0
- slow transport in ampulla: 72hrs
- rapid transport through isthmus: 8hrs (requires progesterone)
- uterine arrival time: 3-4 days
How is sperm transported after spermiogenesis?
-passive transport via testicular fluid, smooth muscle contractions, and cilia from seminiferous tubules
+through rate testis
+through efferent ductules
+to head of epididymis
When and where do sperm fully mature in the male?
-maturation in the head of the epididymis (12 days)
+changes in glycoproteins in plasma membrane of sperm head
-sperm are capable of fertilization by the time they reach the tail of the epididymis
What is the path of ejaculation?
-ductus deferens
-addition of fluid secretions
+seminal vesicles
+prostate
What do the seminal vesicles add to the sperm?
-fructose and prostaglandins
What does the prostate add to the sperm?
-citric acid, Zn, Mg, phosphatase
What are some obstacles the sperm will encounter in the female reproductive tract?
-upper vagina
+seminal fluid buffers acidity of vaginal fluids (pH: 4.2-7.2)
-cervix
+pH: 6-6.5 -> optimal for sperm motility
-cervical canal
+mucus block -> composition and viscosity of mucus changes during mid-cycle from thick to thin and watery
Outline the path sperm takes in the female reproductive tract.
-initial rapid transport
+some spermatozoa reach uterine tubes within 5-20mins after ejaculation
+relies mostly on muscular movements of female tract
+these sperm are NOT capable of fertilizing an egg
-slow transport
+swims through cervical mucus (2-3mm/HR)
+storage in cervical crypts
+may not reach oviducts for 2-4 days
-isthmus
+capacitation
+after release following capacitation, sperm move up oviduct (swimming and peristaltic contractions)
Where does fertilization typically occur?
-ampulla of uterine tubes
What is capacitation? And what does it involve?
-required for sperm to undergo acrosomal reaction
-occurs inside the uterine tube in isthmus
-requires binding of sperm to tubal epithelium
-followed by a period of hyperactivity and release of sperm in small numbers
-involves:
+removal of cholesterol from sperm surface (inhibits premature capacitation)
+removal of glycoproteins (from epididymis)
What are the steps in fertilization?
- Penetration of corona radiata
- Attachment to zona pellucida
- Acrosomal reaction and penetration of ZP
- Binding and fusion of sperm and egg
- Prevention of polyspermy
- Metabolic activation of the egg
- Decondensation of the sperm nucleus
- Completion of egg meiosis
- Development and fusion of male and female pronuclei
What is involved in the penetration of the corona radiata?
- fusion of the outer acrosomal membrane with the sperm plasma membrane creating portals through which the contents of the acrosome can be released
- fragmentation of sperm membrane to release acrosomal enzymes
- swimming movements also help in the penetration through the corona radiata
What is one of the major enzymes in the acromegaly and what does it do?
-hyaluronidase
+helps to breakdown the hyaluronic acid component of the intracellular matrix between the corona radiata cells
What are the steps in the acrosomal reaction?
- ZP3 is one of four glycoproteins in ZP
- attachment of sperm to ZP is mediated by ZP3 -> stimulates acrosomal reaction in mammals (acts thought G proteins in the sperm plasma membrane)
- massive influx of Ca+2 through sperm plasma membrane
- exchange of Na (influx) and H (effluent) increase pH
- followed by penetration of sperm through ZP
What is acrosin? Where is it found in the sperm? What does it do?
- a serine proteinase involved in the penetration of the ZP
- originally referred to as zona lysin
- NOT released from the acrosome, but attached to the main portion of the acrosomal membrane that fuses to the remaining sperm plasmalemma adn overlies the nucleus
- acrosin digests a small hole through the ZP and assists in the the penetration of swimming sperm through the ZP
How many blocks are there?
2 types
What is the fast polyspermy block?
- consists of rapid depolarization of egg plasmalemma
- goes from -70 to 10mV in 2-3 secs
- temporarily prevents polyspermy and allows time for the egg to establish the slow block
What is the slow block to polyspermy?
-characterized by release of polysaccharides from the cortical granules located under the plasmalemma of the egg
+polysaccharides enter perivitelline space and become hydrated, producing a swelling that increases width of perivitelline space
What are the three final steps in fertilization?
- metabolic activation of egg
- decondensation of sperm nucleus
- completion of meiosis in oocyte
What happens during metabolic activation of the egg?
-initiated by release of Ca+2 within egg cytoplasm in response to introduction of phospholipase C zeta by sperm-released calcium
+initiates blocks to polyspermy
+stimulates increase in egg respiration and metabolism via the Na-H exchange mechanism
+results in an increase in pH and an increase in oxidative metabolism
What occurs during the decondensation of the sperm?
- sperm nuclear membrane becomes more permeable and allows entry of egg cytoplasmic factors which reduce disulfide cross-linkage to sulfhydyl groups
- tightly packed sperm chromatin becomes more loosely packed and male pro nucleus is established
What are pronuclei?
-nuclear material of the head of the sperm and egg after the egg has been penetrated by the sperm
What is a zygote?
-single called stage at which the male and female pronuclei have fused together and share a common membrane, establishing a diploid chromosome number
What does the sweeping of the fimbriae on the uterine tube do?
- increase in ciliate on of tube epithelial cells
- increase in activity of tubal smooth muscle cells
