Lect. 5 - Gamete transport and fertilization

Question 1

What are the major mechanisms that propel the egg down the uterine tube?

Answer 1

contractions of tubal smooth muscle

Question 2

What hormone is necessary for egg rapid transport through the isthmus?

Answer 2

progesterone

Question 3

What is the time line for the itinerary for the transport of the egg down the uterine tube?

Answer 3

Departure time = day 0

• slow transport in ampulla - 72 hours
• rapid transpsort through isthmus - 8 hrs
• Uterine arrival time 3-4 days.

Question 4

What are the mechanisms that propel the immobile sperm through the male tract?

Answer 4

Passive transport via testicular fluid, smooth muscle contractions, and cilia from seminiferous tubules

Question 5

What is the sequence of structures sperm must traverse to reach the epidiymis?

Answer 5

through rete testis
through efferent ductules
to head of epididymis

Question 6

Where does sperm maturation occur, and how long does it require?

Answer 6

In the head of the epididymis - 12 days

Changes in glycoproteins in plasma membrane of sperm head.

Question 7

What contributions are made to semen by the seminal vesicles and the prostate gland?

Answer 7

From seminal vesicles: fructose and prostaglandins

From prostate: citric acid, Zn, Mg, phosphatase

Question 8

What is the optimum pH for sperm motility?

Answer 8

6.0-6.5

Question 9

What is the pH of the upper vagina?

Answer 9

4.3 —> 7.2 - b/c seminal fluid buffers acidity of vaginal fluids

Question 10

What is the pH of the cervix?

Answer 10

6.0-6.5 (optimal)

Question 11

Initial rapid transport

Answer 11

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

Question 12

Slow transport

Answer 12

involves swimming through cervical mucous; 2-3mm per hours; storage in cervical crypts; may not reach oviducts for 2-4 days

Question 13

What mechanisms move sperm up the oviduct?

Answer 13

swimming movements and peristaltic contractions

Question 14

Where does fertilization in the oviduct typically occur?

Answer 14

In the ampulla

Question 15

What is the purpose of capacitation?

Answer 15

it is required for sperm to undergo acrosomal reaction to fertilize the egg

Question 16

Where does capacitation occur in the female tract?

Answer 16

inside the uterine tube in isthmus

Question 17

What mechanisms are involved in capacitation?

Answer 17

*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

Question 18

How does the sperm penetrate the corona radiata?

Answer 18

• 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

Question 19

What enzyme is involved in the penetration of the corona radiata by sperm and what is its source?

Answer 19

Hyaluronidase - in the acrosome

Question 20

What is the function of ZP3 in the acrosomal reaction?

Answer 20

it simulates acrosomal reaction in mammals - acts through G proteins in the sperm plasma membrane - it mediates the attachemnt of sperm to the ZP

Question 21

Where is the acrosin (zona lysin) initially found?

Answer 21

attached to the portion of the acrosomal membrane that fuses to the remaining sperm plasmalemma and overlies the nucleus.

Question 22

What is the function of acrosin (zona lysin) in fertilization?

Answer 22

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

Question 23

Fast block to polyspermy in sea urchins.

Answer 23

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.

Question 24

slow block to polyspermy in sea urchins

Answer 24

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

Question 25

What role does phospholipase C zeta play in the metabolic activation of the egg following fertilization?

Answer 25

metabolic activation of the egg is initiated by the release of Ca ion w/i egg cytoplasm in response to indroduction of phospholipase C zeta by sperm

Question 26

What are the results of the release of Ca ion w/i the egg cytoplasm following fertilization?

Answer 26

• initiates blocks to polyspermy
• stimulates increase in egg respiration and metabolism via the Na-H ion exchange mechanism
• results in an increase in pH and an increase in oxidative metabolism

Question 27

pronucleus

Answer 27

the nuclear material of the head of the spermatozoan (male pronucleus) or of the oocyte (female) after the oocyte has been penetrated by the spermatozoan

Question 28

zygote

Answer 28

term used to denote the single-celled stage at which the male and female pronuclei have fused together and share a common membrane, establishing the diploid chromosome number.