Otok je zbog upale.

Upale is in the genitive singular.

The dictionary form is upala (inflammation). After the preposition zbog (because of / due to), Serbian normally uses the genitive case, so:

• upala → nominative singular
• upale → genitive singular

So zbog upale means because of inflammation or due to the inflammation, depending on context.

Je is the 3rd person singular present form of biti (to be).

Here it works like is in English:

• Otok = swelling
• je = is
• zbog upale = because of inflammation

So structurally, the sentence is basically:

• Otok
  • je
    • zbog upale
• The swelling
  • is
    • due to inflammation

Otok is in the nominative singular because it is the subject of the sentence.

It is the thing being talked about: the swelling.

Also, otok is a masculine noun, so its nominative singular form is simply otok.

Because Serbian does not have articles like English the and a/an.

So otok can mean:

• a swelling
• the swelling

And upala can mean:

• an inflammation
• the inflammation

The exact meaning depends on the situation and context, not on a separate article.

Yes, it is understandable, especially in a short explanation, but it can sound a little elliptical or compressed.

A native speaker might also say:

• Otok je posledica upale. = The swelling is a result of the inflammation.
• Otok je nastao zbog upale. = The swelling occurred because of the inflammation.
• Došlo je do otoka zbog upale. = Swelling occurred because of the inflammation.

So your sentence is fine, but there are slightly fuller or more natural-sounding alternatives.

Sometimes, yes.

Common options include:

• zbog upale = because of / due to inflammation
  This is the most neutral and common choice.

• usled upale = as a result of inflammation
  This sounds more formal or medical/administrative.

• od upale
  This can sometimes be heard in everyday speech, but it is often less precise here. For a learner, zbog is the safest choice in this sentence.

This is a good question because it can be confusing.

In this sentence, otok clearly means swelling.

The word otok can also mean island in some varieties of the language, especially more typically in Croatian usage. In standard Serbian, ostrvo is the more usual word for island.

So for Serbian learners, it is helpful to remember:

• otok = swelling
• ostrvo = island (usual in Serbian)

They are related medical ideas, but they are not the same thing.

• otok = swelling
• upala = inflammation

Inflammation can cause swelling, which is exactly what this sentence is saying.

So the sentence does not mean that the two words are interchangeable. It means one thing is the cause of the other.

Yes, Serbian word order is fairly flexible, but not every version sounds equally natural.

The neutral order here is:

• Otok je zbog upale.

You may also hear other structures, but they often sound more marked or are used for emphasis. For example:

• Otok je zbog upale, a ne zbog povrede.
  = The swelling is because of inflammation, not because of an injury.

If you change the order too freely, the sentence may become less natural. So as a learner, it is best to keep the neutral order unless you have a reason to emphasize something.