How does knowledge about a subject aid in its recall? I've experienced it many times with my students and also with myself. Let me illustrate with example:

When I'm teaching, I say something like this:


  Gastrointenstinal Track has following sections
  
  
  Buccal Cavity
  Pharynx
  Esophagus
  Stomach
  Duodenum
  Jejunum
  Ileum
  Caecum
  


To help them remember I repeat above thing multiple times. But still they don't remember much of the list.

Alternatively instead of just saying those things (even though that's all I need my students to remember), I spoke about each of the above item for few minutes. i.e. I gave more details of about each of those things. Result is that, now my students do not remember most of the details about each of those items, but they could remember the list. Which is exactly I want.

Whats happening here? Whats the science behind it? Is there more to what I'm describing?
The first method (repeat the terms over and over) is called rote rehearsal. It's not actually a very good way to learn, though it has the benefit that it always "works" because you can always repeat a list. You may be unable to perform certain other encoding tricks such as elaborative rehearsal due to the context of the items, like a list of random words. Consider it more of a fallback than a learning strategy.

The second method (talking about the item at length) is elaborative rehearsal, which, as Cheatboy2 points out, benefits from the levels of processing effect. The deeper you know something the more "connections" you can make, which has the advantage of making things easier to remember in general and easier to remember in the context of specific, related items. 

Elaborative rehearsal has the benefit of creating understanding rather than simple knowledge of a term. Buccal Cavity is just a word until you realize what it means. Once you know what it means you can additionally draw connections between related words, which, in this case, is very helpful as all the words on the list to remember are in fact connected in various ways. If you don't elaborate on the connections between them in your own memory, you won't benefit from that effect.

I suggest giving both articles (in bold) a read to understand the deeper intricacies of both, but those are the general ideas behind why elaborative rehearsal is preferred. Note that a Mnemonic device may be a more effective method of teaching lists where the list is what's important, not a deeper understanding, or where there is little to elaborate on, such as ROYGBIV to remember the colors of the rainbow.