La kuracisto kontrolas la sangon.

A word-for-word breakdown is:

• la = the
• kuracisto = doctor
• kontrolas = checks / is checking / checks over
• la = the
• sangon = blood (marked as the direct object)

So the whole sentence means The doctor checks the blood.

In Esperanto, nouns normally end in -o.

So:

• kuracisto = doctor
• sango = blood

This -o ending is one of the most basic and regular parts of Esperanto grammar. If you see a word ending in -o, it is usually a noun.

The -n marks the direct object. This is called the accusative ending in Esperanto.

In this sentence:

• La kuracisto = the doctor → the one doing the action
• kontrolas = checks
• la sangon = the blood → the thing being checked

Without the -n, sango just means blood as a noun.
With -n, sangon means it is the object of the verb.

So:

• sango = blood
• sangon = blood, as the thing receiving the action

Because kuracisto is the subject, not the direct object.

In Esperanto, the -n usually goes on the noun that receives the action.

Here:

• La kuracisto = the doctor performs the action
• la sangon = the blood receives the action

So only sangon gets -n.

The ending -as marks the present tense in Esperanto.

So kontrolas means:

• checks
• is checking
• sometimes simply does check, depending on context

Esperanto does not change the verb ending for different subjects the way English does.

For example:

• mi kontrolas = I check
• vi kontrolas = you check
• li kontrolas = he checks
• la kuracisto kontrolas = the doctor checks

The verb stays kontrolas every time.

Yes, it is related in form, but you should be a little careful with meaning.

kontroli usually means:

• to check
• to inspect
• to verify
• to examine

So in this sentence, kontrolas is best understood as checks or examines, not controls in the English sense of ruling or operating something.

La is the definite article, meaning the.

So:

• la kuracisto = the doctor
• la sangon = the blood

Esperanto has only one definite article: la. It does not change for gender, number, or case.

Also, Esperanto has no indefinite article. So:

• kuracisto can mean a doctor or just doctor, depending on context
• la kuracisto specifically means the doctor

Yes. Because Esperanto marks the direct object with -n, word order is more flexible than in English.

For example, these can mean the same basic thing:

• La kuracisto kontrolas la sangon.
• La sangon kontrolas la kuracisto.
• Kontrolas la kuracisto la sangon.

However, the most neutral and common order is still subject–verb–object, which is exactly what you see here:

• La kuracisto → subject
• kontrolas → verb
• la sangon → object

So the given sentence is the most straightforward way to say it.

The dictionary form is kontroli, which means to check.

Esperanto verbs have regular endings:

• -i = infinitive → kontroli = to check
• -as = present → kontrolas = checks / is checking
• -is = past → kontrolis = checked
• -os = future → kontrolos = will check

So kontrolas is built from the root kontrol- plus the present-tense ending -as.

Kuracisto can be broken down into meaningful parts:

• kurac- = heal / treat medically
• -ist- = a person professionally involved in something
• -o = noun ending

So kuracisto literally means something like a medical-treating professional, which we translate as doctor.

This is very typical of Esperanto: many words are built from smaller meaningful pieces.

Usually sango is used like blood in English: as a mass noun.

So:

• sango = blood
• la sango = the blood
• la sangon = the blood, as direct object

You would not normally say a blood in the ordinary sense. If you needed a special context, Esperanto would usually express that idea in some other way.

A rough pronunciation guide is:

• la = lah
• kuracisto = koo-rah-CHEE-stoh
• kontrolas = kon-TROH-lahs
• la = lah
• sangon = SAHN-gon

A few helpful points:

• c in Esperanto is always like ts
• ci sounds like tsi
• g is always a hard g, as in go
• stress is usually on the second-to-last syllable

So:

• ku-ra-CIS-to
• kon-TRO-las
• SAN-gon

Yes, it could.

Compare:

• La kuracisto kontrolas la sangon. = The doctor checks the blood.
• Kuracisto kontrolas sangon. = A doctor checks blood or Doctor checks blood, depending on context

Without la, the nouns become less specific. Esperanto often leaves indefiniteness unmarked, whereas English usually uses a/an.

So la is important when you want to say the specifically.