Врач заметил кровотечение.

Врач is in the nominative singular, because it is the subject of the sentence.

Russian does not have articles, so there is no separate word for the doctor or a doctor. Whether it means the doctor or a doctor depends on context.

So structurally this is:

• врач = subject
• заметил = verb
• кровотечение = object

Заметил is the past tense masculine singular form of the verb заметить.

A few important pieces are packed into this form:

• заметить = the dictionary form, meaning to notice
• past tense in Russian is often built with -л
• заметил shows that the subject is masculine singular

So if the subject were feminine, you would usually get:

• врач заметила кровотечение

And if it were plural:

• врачи заметили кровотечение

Not always.

The noun врач is grammatically masculine, but it can refer to either a male or a female doctor. In real usage:

• врач заметил strongly suggests a male doctor
• врач заметила is very commonly used for a female doctor

So the noun itself does not force a male meaning, but the verb form here points to a masculine subject.

This is a question of aspect, which is very important in Russian verbs.

• заметить → perfective
• замечать / замечал → imperfective

Here, заметил presents the action as a single completed event: the doctor noticed the bleeding.

If you used замечал, it would suggest something more like:

• repeated noticing
• habitual noticing
• ongoing/background observation

So in a simple one-time event, заметил is the natural choice.

It is in the accusative singular, because it is the direct object of the verb заметил.

The doctor noticed what?
→ кровотечение

That makes it the direct object, so accusative is expected.

Because for many inanimate neuter nouns, the accusative singular is identical to the nominative singular.

So:

• nominative: кровотечение
• accusative: кровотечение

They look the same, even though the grammatical role is different.

This is very common in Russian. The case is understood from the sentence structure and the role the word plays.

Кровотечение is neuter.

A good clue is its ending:

• nouns ending in -о
• nouns ending in -е
• many nouns ending in -ие

are often neuter.

Here the ending -ие is a strong hint that the noun is neuter.

That matters because neuter nouns follow their own declension patterns, and it also explains why nominative and accusative singular are the same here.

The most neutral word order here is:

• Врач заметил кровотечение.

That is a normal subject–verb–object order.

But Russian word order is more flexible than English, so other orders are possible, for example:

• Кровотечение заметил врач.
• Заметил врач кровотечение.

These alternatives change the focus or emphasis, not the basic meaning. The original sentence is the most straightforward, neutral version.

The main stress pattern is:

• врач — one syllable, so the stress is just on that syllable
• замЕтил — stress on ме
• кровотечЕние — stress on че

A rough pronunciation guide:

• врач ≈ vrach
• заметил ≈ za-MYE-til
• кровотечение ≈ kra-va-ta-CHYE-ni-ye

The exact sounds are not identical to English, but the stress placement is very important in Russian and worth learning early.

This sentence follows a very common Russian pattern:

• subject in nominative
• verb
• direct object in accusative

So the grammar skeleton is:

• Врач → nominative subject
• заметил → past tense verb
• кровотечение → accusative object

This is one of the most useful basic patterns in Russian, and you will see it constantly with other nouns and verbs too.