Der Arzt untersucht die Brust.

These are the definite articles in German, and they depend on the noun’s gender and case.

• Arzt is a masculine noun, so in the nominative (subject) it takes der.
• Brust is a feminine noun, so it takes die.

In this sentence:

• Der Arzt = the doctor → the subject
• die Brust = the breast/chest → the direct object

So the sentence structure is:

• Der Arzt = nominative subject
• untersucht = verb
• die Brust = accusative object

They do, but feminine articles are the same in the nominative and accusative singular.

For die Brust:

• nominative: die Brust
• accusative: die Brust

So even though Brust is the object here, the article stays die.

Compare that with a masculine noun:

• nominative: der Arzt
• accusative: den Arzt

That is why article changes are often easiest to notice with masculine nouns.

untersucht is the 3rd person singular present tense form of untersuchen.

The infinitive is:

• untersuchen = to examine

Present tense forms:

• ich untersuche
• du untersuchst
• er/sie/es untersucht
• wir untersuchen
• ihr untersucht
• sie/Sie untersuchen

Since der Arzt is he / a singular subject, German uses untersucht.

Because German main clauses usually follow the verb-second rule.

That means the finite verb goes in the second position in the sentence.

Here:

1. Der Arzt
2. untersucht
3. die Brust

This is the most neutral word order: subject + verb + object.

German can move other elements to the front, but the verb still stays second:

• Heute untersucht der Arzt die Brust.
• Die Brust untersucht der Arzt.
  This is possible, but much less neutral and puts special emphasis on die Brust.

It can mean breast, and in some contexts it can also refer more generally to the chest area.

The exact meaning depends on context:

• In anatomy or medicine, Brust may refer to the breast or chest region.
• In everyday language, it often means breast.
• For chest in a broader sense, German also uses Brustkorb in more anatomical contexts.

So a learner should know that Brust can sometimes cover a slightly wider meaning than English breast.

Yes, Arzt is grammatically masculine and usually refers to a male doctor.

The feminine form is:

• die Ärztin = female doctor

So:

• Der Arzt untersucht die Brust. = The male doctor examines the breast/chest.
• Die Ärztin untersucht die Brust. = The female doctor examines the breast/chest.

In some older or general usage, masculine forms were sometimes used more generically, but modern German often prefers more explicit gendered forms where relevant.

Because German usually uses the simple present tense where English might use either:

• examines
• is examining

So Der Arzt untersucht die Brust can mean either:

• The doctor examines the breast/chest.
• The doctor is examining the breast/chest.

German does have ways to emphasize an ongoing action, but they are much less common than in English. In normal German, the plain present tense usually does the job.

There are two main clues:

1. Meaning: the doctor is doing the action, so der Arzt is the subject.
2. Verb type: untersuchen usually takes a direct object—you examine something.

So:

• Der Arzt = who does the action
• die Brust = what is being examined

If the object were masculine, the article change would make this even clearer:

• Der Arzt untersucht den Patienten.

Here den Patienten clearly shows accusative.

Yes. Since Brust is feminine, the accusative pronoun is sie.

So:

• Der Arzt untersucht sie. = The doctor examines it/her.

Here sie can mean it because it refers to the feminine noun die Brust.

Be careful: sie can also mean she or they, depending on context. German pronouns often depend heavily on context.

Arzt can be tricky for English speakers because of the rz/tz combination.

A rough guide:

• Arzt sounds approximately like ahrtst
• Brust sounds roughly like broost but with a shorter vowel than English oo

A few tips:

• The A in Arzt is a long vowel.
• The r is usually not pronounced like a strong English r in many accents of German.
• The zt ending is pronounced clearly.

If pronunciation is your goal, it helps to listen for the whole word as one sound chunk rather than trying to say each letter separately.

Yes, that is grammatically possible, because German allows more flexible word order than English.

But it changes the focus:

• Der Arzt untersucht die Brust. = neutral statement
• Die Brust untersucht der Arzt. = emphasis on the breast/chest

This kind of fronting is more marked and would usually be used only in a specific context, for example to contrast it with something else:

• Den Rücken untersucht er nicht. Die Brust untersucht der Arzt.

So for a beginner, the normal version to learn first is definitely:

• Der Arzt untersucht die Brust.