There are several things that can come into play here.
First extroverts tend to interrupt as part of their ordinary way of doing business. This tends to make introverts more uncomfortable as they tend to prefer not to interrupt. You are not going to change people's basic personalities. You can learn to live with the interuptions understanding that to them there is nothing rude about it, they get excited about an idea and just start talking. There will alwys be at least some level of this in a group with extroverts. I bring this up becasue not all interupting is meant to be rude, just a differnt way differnt personality types communicate. Doesn't mean they can't learn to hold back some if they are out of hand, but there will always be some level of this type of interuption and if the end result is a good brainstorming session, then I wouldn't worry about it.
However, there is interupting that is rude and meant to shut down the other person. If you think the interuption is trying to do that, then you can speak up even if it is not you being interrupted. If it is someone else being interrupted and you want to go give them support to say what they want to say, then you interrupt the interrupters with, "I want to hear the rest of what Kathy was saying." If you are interrupted and don't want to be, then say, "Excuse me, I wasn't finished yet" and start talking again. Try to do this realtively infrequently and only when it seems to be important. Otherwise you can come across as looking like the rude person.
There is also interupting to get a person back on track or to get someone to stop talking about something that shouldn't be brought up. This kind of interuption is valid and entirely correct. This interuption is about managing the flow of the meeting to make sure the right information is being covered. Usually it happens when someone has gone on and on and on and is thoroughly off the topic or when someone looks to be saying something that might be confidential.
So basically use your judgement about interruptions. Sometimes they are productive and sometimes they are not. You need to learn to recognize the times when interruptions are just part of the process of throwing out ideas and when they are being used legitimately to get the discussion back on track and when they are being used to prevent certain people from contributing. Watch people's expressions/body language to see if they feel annoyed or put down. Watch for patterns. Does a specific person always get interrupted and shut down. (This tends to happen to women in mixed groups.) Does the interupter then proceed to suggest the same thing the interrupted was saying in order to grab the credit?