Лікар оглянув ясна.

Ukrainian has no articles, so it does not use words like the or a/an.

So:

• Лікар can mean the doctor or a doctor
• ясна can mean the gums or just gums

Which one is intended depends on context. In a simple sentence like this, English usually translates it as The doctor examined the gums.

Лікар is in the nominative case because it is the subject of the sentence — the person doing the action.

So in:

• Лікар оглянув ясна

the doctor is the one who examined, so лікар stays in the nominative.

Ясна is the direct object, so it is in the accusative case.

However, for many inanimate plural nouns in Ukrainian, the accusative plural looks exactly the same as the nominative plural. That is what happens here.

So:

• nominative plural: ясна
• accusative plural: ясна

Even though the form does not change, its role in the sentence is still object, not subject.

It is plural.

Ясна means gums, not gum. In Ukrainian, this word is normally used in the plural, just like in English we usually say gums rather than gum when talking about the tissue in the mouth generally.

So the sentence is talking about the gums as a whole, not one single spot.

Оглянув is the past tense masculine singular form of the verb.

It agrees with the subject лікар, which here is understood as male.

So:

• оглянув = he examined / looked over
• if the doctor were female, you would normally expect оглянула

For example:

• Лікар оглянув ясна. = a male doctor examined the gums
• Лікарка оглянула ясна. = a female doctor examined the gums

The dictionary form is оглянути.

That is the infinitive, meaning to examine, to inspect, or to look over, depending on context.

So the forms are:

• оглянути = to examine
• оглянув = examined, for a masculine subject in the past

It is perfective.

That means it presents the action as completed: the doctor examined the gums and finished doing so.

So оглянув is closer to:

• examined
• looked over
• inspected

If you wanted an imperfective idea such as was examining or examined habitually, you would use a different verb form, such as оглядав.

Very roughly:

• оглянув = examined, completed
• оглядав = was examining / used to examine

Grammatically, лікар is a masculine noun, but as a profession word it can sometimes refer more generally to a doctor.

In this particular sentence, though, the verb оглянув is masculine, so the sentence is clearly presenting the doctor as male.

If you wanted to make the doctor clearly female, a very common choice would be:

• Лікарка оглянула ясна.

Yes. Ukrainian word order is fairly flexible because case endings help show what each word is doing.

The most neutral order here is:

• Лікар оглянув ясна.

But other orders are possible for emphasis, such as putting focus on ясна or on the action itself.

Still, for learners, subject + verb + object is the safest and most natural starting point.

Because ясна is a direct object of the verb оглянути.

In Ukrainian, direct objects usually do not need a preposition. The verb simply takes the object directly:

• оглянути ясна = to examine the gums

So this structure is completely normal:

• subject: лікар
• verb: оглянув
• direct object: ясна