La paciento sentas doloron en la makzelo.

Because doloron is the direct object of sentas.

In Esperanto, the direct object usually takes the accusative ending -n. Here:

• La paciento = the subject
• sentas = feels
• doloron = pain, the thing being felt

So doloro becomes doloron because it is what the patient feels.

Because en can be used in two different ways:

• en + nominative = in, inside, at a location
• en + accusative (-n) = into, indicating movement toward a place

Here there is no movement. The pain is located in the jaw, so Esperanto uses:

• en la makzelo = in the jaw

If there were movement, then -n could appear, as in something like meti ion en la skatolon = put something into the box.

La is the definite article, meaning the.

In la paciento, it means we are talking about a specific patient, not just any patient.

In la makzelo, Esperanto often uses la with body parts when the owner is obvious from context. So en la makzelo naturally means in the jaw or in his/her jaw, depending on context.

This is similar to how some languages use the with body parts where English prefers a possessive.

Because Esperanto often leaves the possessor unstated when it is obvious.

In this sentence, the natural assumption is that the patient feels pain in their own jaw, so en la makzelo is enough.

If you really wanted to make it explicit, you could say:

• en sia makzelo = in his/her own jaw

But in many normal contexts, that would be unnecessary.

Sentas is the present-tense form of senti, which means to feel.

Esperanto verb endings are regular:

• senti = to feel
• sentas = feels / is feeling
• sentis = felt
• sentos = will feel

So La paciento sentas doloron literally means The patient feels pain.

Yes. That is also possible and natural.

• sentas doloron = feels pain
• havas doloron = has pain

Both work, but the nuance is slightly different:

• sentas doloron focuses on the sensation
• havas doloron focuses on the condition or state

In many practical situations, either would be understood perfectly well.

Usually, that would not be the best choice.

In Esperanto, dolori means to hurt / to be painful, but the thing that hurts is normally the body part or injured area, not the person as a whole.

So these are more natural:

• La makzelo doloras. = The jaw hurts.
• La paciento sentas doloron en la makzelo. = The patient feels pain in the jaw.

Saying la paciento doloras sounds less natural for the intended meaning.

Paciento means a medical patient.

A patient person in the sense of calm or not easily annoyed is:

• pacienca

So:

• La paciento = the patient
• Li estas pacienca. = He is patient

This is an important distinction for English speakers because English uses the same word for both meanings.

Esperanto often expresses this idea with a noun:

• senti doloron = to feel pain

That is a very normal structure. English can also do this: feel pain.

If you wanted an adjective, Esperanto has dolora = painful, but that would be used differently, for example:

• La makzelo estas dolora. = The jaw is painful.

So the sentence uses the noun because the structure is feel + pain.

Makzelo means jaw.

It can refer to the jaw area generally. If needed, Esperanto can be more specific:

• supra makzelo = upper jaw
• malsupra makzelo = lower jaw

But in this sentence, makzelo simply means jaw, which is enough.

Because this is the most neutral and natural word order in Esperanto:

• subject + verb + object + other information

So:

• La paciento = subject
• sentas = verb
• doloron = object
• en la makzelo = location of the pain

Esperanto word order is fairly flexible, but this order is the clearest and most standard for a basic statement.