Лікар оглянув ребро.

• Лікар = the subject, doctor
• оглянув = the verb, examined / looked over
• ребро = the object, rib

So the sentence structure is basically Doctor examined rib.

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

So лікар can mean:

• a doctor
• the doctor

And ребро can mean:

• a rib
• the rib

Context tells you which one is meant.

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

In Ukrainian, the subject of a normal finite sentence is usually in the nominative case.

Ребро is in the accusative singular because it is the direct object of оглянув.

It looks the same as the dictionary form because for many inanimate neuter nouns, the accusative singular is identical to the nominative singular.

So:

• nominative: ребро
• accusative: ребро

That is completely normal.

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

Ukrainian past tense agrees with the subject in gender and number.

Because лікар here is grammatically masculine singular, the verb is also masculine singular:

• masculine singular: оглянув
• feminine singular: оглянула
• neuter singular: оглянуло
• plural: оглянули

In this sentence, the grammar is masculine, so the sentence presents the doctor as masculine singular.

A very common way to say female doctor would be:

• Лікарка оглянула ребро.

Learners should notice that Ukrainian often shows gender more clearly than English, especially in the past tense.

This is a question of aspect.

• оглянув = perfective
  It presents the action as completed, as a whole: the doctor examined the rib.

• оглядав = imperfective
  It presents the action as ongoing, repeated, or descriptive: the doctor was examining the rib / used to examine it / examined it in a process-focused way.

So in a simple completed event, оглянув is very natural.

Yes. Ukrainian word order is more flexible than English because case endings help show who is doing what.

The neutral order here is:

• Лікар оглянув ребро.

But other orders are possible for emphasis, for example:

• Ребро оглянув лікар. = It was the rib that the doctor examined.
• Оглянув лікар ребро. = more marked or stylistic

Even when the order changes, the basic roles are still clear from grammar and context.

It can overlap with all of those depending on context.

Оглянути often means:

• to examine
• to inspect
• to look over

In a medical context, examined is usually the best English translation.

So Лікар оглянув ребро is naturally understood as The doctor examined the rib.

Yes. Ребро can mean:

• rib in the body
• a rib, edge, or ridge of an object in some contexts

But with лікар and оглянув, the anatomical meaning is the obvious one.

The dictionary form is оглянути.

That is the infinitive, meaning to examine / to inspect / to look over.

From that infinitive, you get the past masculine singular form оглянув.

Because оглянути is perfective, it does not normally form a true present tense meaning.

You would usually get:

• Лікар оглядає ребро. = The doctor is examining / examines the rib.
  This uses the imperfective verb оглядати.

• Лікар огляне ребро. = The doctor will examine the rib.
  This is the future of the perfective verb.

So:

• оглядати = imperfective
• оглянути = perfective

The usual stress is:

• лі́кар
• огля́нув
• ребро́

Stress is important in Ukrainian because it is not always predictable, so it is worth learning words together with their stress.