Il medico controlla il sangue.

Because Italian usually uses the definite article much more often than English does.

• il medico = the doctor
• il sangue = the blood

In English, you might sometimes say The doctor checks blood, but in Italian that would sound incomplete in most normal contexts. Italian prefers controlla il sangue when referring to the blood as the thing being examined.

Controllare is the infinitive, meaning to check.

In the sentence, the verb has to match the subject:

• controllare = to check
• controlla = he/she checks or is checking

Since the subject is il medico (the doctor), Italian uses the third person singular form:

• Il medico controlla = The doctor checks / is checking

It can mean either, depending on context.

Italian present tense often covers both:

• The doctor checks the blood
• The doctor is checking the blood

If you want to be more explicitly progressive in Italian, you can say:

• Il medico sta controllando il sangue = The doctor is checking the blood

But controlla is perfectly normal on its own.

Yes, this is an important point. Controllare often means to check, to examine, or to inspect, not just to control in the English sense.

So in this sentence:

• Il medico controlla il sangue = The doctor checks/examines the blood

If you translated it as The doctor controls the blood, that would usually sound wrong in English.

Normally, no. In standard Italian, singular countable nouns usually need an article.

So:

• il medico = the doctor
• un medico = a doctor

Saying just medico by itself in this sentence would sound unnatural.

Yes, Italian often allows the subject to be omitted because the verb ending already gives information about the subject.

• Controlla il sangue = He/She checks the blood or is checking the blood

However, if you specifically want to say the doctor, then you include it:

• Il medico controlla il sangue

Italian does this a lot because it is a pro-drop language.

This is the most neutral and common word order in Italian:

• Il medico = subject
• controlla = verb
• il sangue = object

So yes, this is a standard subject-verb-object sentence.

Italian can change word order for emphasis, but the basic pattern is very similar to English:

• Il medico controlla il sangue.

Because sangue is normally an uncountable noun, like blood in English.

You usually talk about it in the singular:

• il sangue = the blood

If you wanted to talk about different blood samples or different kinds of blood in a very specialized context, you might use other wording, but in normal usage sangue is singular.

A simple pronunciation guide:

• medico → MEH-dee-ko
• controlla → kon-TROL-la
• sangue → roughly SAHN-gweh

A few useful notes:

• In controlla, the double ll should be held a little longer than a single l
• In sangue, the gu is pronounced, so it is not just san-ge

Because medico begins with a normal consonant sound, so it takes il.

Italian definite articles depend on the sound that follows:

• il
  • most masculine singular nouns
    
    • il medico
• lo
  • nouns beginning with s + consonant, z, ps, gn, etc.
    
    • lo studente
    • lo zio

Since medico starts with m, the correct article is il.

Yes, often you can.

• il medico = the doctor / physician
• il dottore = the doctor

In everyday Italian, dottore is very common when addressing or referring to a doctor.
Medico can sound a bit more formal or specifically medical/professional.

So both can work, depending on tone and context:

• Il medico controlla il sangue
• Il dottore controlla il sangue