URGENT: reproduction question

[eavivona]

The Kaplan book says that the acrosomal reaction triggers a cortical reaction which is a release of calcium ions which eventually leads to the formation of the fertilization membrane.

Another text book that I have says that the acrosomal reaction causes 2 subsequent reactions: 1. membrane depolarization = Sodium ions flow into the ovum (not calcium), which changes the membrane potential and leads to a "fast block to polyspermy" and 2. the cortical reaction.

This is confusing because it seems to me that reaction #1 from the text book describes a process which results in the same thing as the cortical reaction: a way to prevent multiple fertilization.

If any of you can explain exactly what happens after the acrosomal reaction, please let me know.

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[wendywellesley]

The Kaplan book says that the acrosomal reaction triggers a cortical reaction which is a release of calcium ions which eventually leads to the formation of the fertilization membrane.

Another text book that I have says that the acrosomal reaction causes 2 subsequent reactions: 1. membrane depolarization = Sodium ions flow into the ovum (not calcium), which changes the membrane potential and leads to a "fast block to polyspermy" and 2. the cortical reaction.

This is confusing because it seems to me that reaction #1 from the text book describes a process which results in the same thing as the cortical reaction: a way to prevent multiple fertilization.

If any of you can explain exactly what happens after the acrosomal reaction, please let me know.

wow. you do not need to know that much detail for the MCAT. is this for homework or for the MCAT? this isn't covered in basic biology, i learned about it in my undergrad embryology class. answer the question- there are two types, fast block and slow block to polysermy. fast block is like you said, depolarization of the membrane. slow block involves expanding the membrane so that it becomes thicker as to block more sperm. this thickening of the membrane (or is it the zona pellucida?) is indirectly caused by the release of Ca ions.
in the end they are two steps, the first one has two double effect (i believe) of inhibiting another sperm from coming into the egg and inducing the second step, the expansion of the membrane to further block more sperm.
i hope this helps.

 

[SanDiegoSOD]

I have nothing productive to say. I just thought that It was funny that this question was deemed urgent.

 

[UCLAstudent]

The fast block occurs through influx of Na+ ions, within ~ 1-2 seconds of fertilization. The slow block takes ~ 1 minute (due to Ca++ influx), but it is permanent (sugars are produced to attract water so that the barrier between the egg and other sperm thickens). The reason why this takes 1 minute is that the Ca++ influx initiates from the sperm entry point, moves in a wavelike fashion, and takes about a minute to pass through the entire cell.

 

[mercaptovizadeh]

In TPR prep book, they called the thickened membrane zona pellucida or vitelline membrane.

 

[Fermata]

In TPR prep book, they called the thickened membrane zona pellucida or vitelline membrane.

I most often hear it referred to as the zona pellucida.

 

[Stitch626]

I most often hear it referred to as the zona pellucida.

I could be wrong, but I believe the zona pellucida refers to the reproductive barrier present in mammals while the vitelline membrane is the layer in all other "evolutionarily developed" organisms (the typical example is the sea urchin).

 

[Medikit]

It takes two baby

 

[DieselPetrolGrl]

I have nothing productive to say. I just thought that It was funny that this question was deemed urgent.

thats ok it's 12 30 on the east coast my reaction to the thread was:
"wow come on now you can open up novak's like the rest of us romantic premeds....i dont know if sdn is good for nuch personal questions!..not to mention its sunday and dont u have 8am classes!"

 

[Ypo.]

!"

DPG, I just saw your quote.

 

[tsazmand]

actually u should know for the MCAT (its on the MCAT syllabus); anyway the second one, the cortical reaction is the "slow block" b/c it can i think up to 30sec for the Ca ions to spread throughout the ovum; the depolariztion is the fast block, which obviously happens first (i think within a sec)