Me alegra que la herida no haya vuelto a sangrar desde ayer.

Because alegrar is being used as a verb meaning to make someone happy / to please someone.

• Me alegra que... = I’m glad that...
• Literally, it is closer to It makes me happy that...

So in this sentence:

• Me = to me
• alegra = it makes happy / pleases

The thing that causes the happiness is the whole clause que la herida no haya vuelto a sangrar desde ayer.

Estoy alegre means I am happy / cheerful, but it does not introduce the same kind of that-clause in the same natural way here.

The subject is the whole clause after que:

que la herida no haya vuelto a sangrar desde ayer

In other words, the thing that makes me glad is the wound not having bled again since yesterday.

So the structure is:

• Me alegra = It makes me glad
• que... = introduces the thing that causes that feeling

This is very common in Spanish with verbs of emotion:

• Me molesta que... = It bothers me that...
• Me sorprende que... = It surprises me that...
• Me encanta que... = I love that...

Because que introduces a subordinate clause: the event or situation that causes the emotion.

So:

• Me alegra que vengas. = I’m glad that you’re coming.
• Me alegra que la herida no haya vuelto a sangrar... = I’m glad that the wound hasn’t bled again...

Without que, the sentence would need a different structure, for example with a noun:

• Me alegra tu visita. = Your visit makes me happy.

But here the speaker is talking about a whole action or situation, so que is needed.

Because after expressions of emotion like me alegra que, Spanish normally uses the subjunctive.

This is one of the most important patterns to learn:

• Me alegra que...
• Me preocupa que...
• Es bueno que...
• Siento que...

All of these often trigger the subjunctive because they express feelings, reactions, value judgments, or attitudes rather than just stating facts neutrally.

So:

• ha vuelto = present perfect indicative
• haya vuelto = present perfect subjunctive

Here, me alegra que requires the subjunctive, so haya vuelto is the correct form.

Because the sentence refers to something connected to the period since yesterday up to now, so Spanish uses a perfect form.

Compare:

• Me alegra que no vuelva a sangrar.
  = I’m glad it doesn’t bleed again / won’t bleed again / isn’t bleeding again
  This is less tied to a completed time period up to now.

• Me alegra que no haya vuelto a sangrar desde ayer.
  = I’m glad it hasn’t bled again since yesterday.
  This clearly refers to the time from yesterday until now.

So haya vuelto is the present perfect subjunctive, which fits the idea of up to the present moment.

Volver a + infinitive means to do something again.

So:

• volver a sangrar = to bleed again
• volver a llamar = to call again
• volver a intentarlo = to try again

In your sentence:

• no haya vuelto a sangrar = has not bled again

This is a very common Spanish structure, and it is often more natural than using a separate word for again.

Because after volver a, Spanish uses an infinitive.

The pattern is:

• volver a + infinitive

So:

• volver a comer = to eat again
• volver a salir = to go out again
• volver a sangrar = to bleed again

That is why the sentence has vuelto a sangrar, not something like vuelto a sangra or a conjugated form after a.

Desde ayer means since yesterday.

It marks the starting point of a time period that continues up to now.

So the sentence means that from yesterday until the present moment, the wound has not bled again.

This works very naturally with a perfect tense:

• No ha sangrado desde ayer. = It hasn’t bled since yesterday.
• No haya vuelto a sangrar desde ayer = it has not bled again since yesterday

Because the speaker is happy about the absence of a repeated problem.

• sangrar = to bleed
• volver a sangrar = to bleed again
• no haber vuelto a sangrar = not to have bled again

So the idea is that the wound did bleed before, but since yesterday it has not started bleeding again. That is good news, which is why the speaker says Me alegra...

Yes. Me alegra que... and me alegro de que... can both mean I’m glad that...

For example:

• Me alegra que la herida no haya vuelto a sangrar desde ayer.
• Me alegro de que la herida no haya vuelto a sangrar desde ayer.

Both are natural.

A small difference in feel:

• Me alegra que... often sounds a bit like It makes me glad that...
• Me alegro de que... feels more directly like I’m glad that...

In everyday use, both are common and correct.

Spanish often uses the definite article where English might not.

Here, la herida means the wound. It refers to a specific wound already known from context.

Using the article is normal and expected here:

• la herida
• el brazo
• la fiebre
• el dolor

If you said just herida here, the sentence would be incomplete or ungrammatical.

Because the noun herida is feminine:

• la herida
• una herida

That is why any related words must agree with it when needed.

For example:

• la herida profunda = the deep wound
• la herida infectada = the infected wound

Its gender is grammatical, so it takes the feminine article la.

Because the clause introduced by que is treated as a singular idea.

Spanish commonly uses a third-person singular verb in these structures:

• Me alegra que...
• Me sorprende que...
• Me molesta que...

You can think of it as an implied it in English:

• It makes me glad that...
• It surprises me that...

So alegra is singular because the whole following idea functions like one single subject.

Yes. It comes from volver, whose past participle is irregular:

• infinitive: volver
• past participle: vuelto

So:

• ha vuelto = has returned / has done again
• haya vuelto = may have returned / has done again, in subjunctive contexts

The auxiliary verb is haber in the present subjunctive:

• yo haya
• tú hayas
• él/ella haya
• nosotros hayamos
• vosotros hayáis
• ellos hayan

Then you add the participle vuelto.

It could be, but it would not mean exactly the same thing.

Compare:

• no haya sangrado desde ayer = has not bled since yesterday
• no haya vuelto a sangrar desde ayer = has not bled again since yesterday

The version with volver a emphasizes repetition. It suggests that bleeding had happened before and the speaker is relieved that it has not happened again.

So volver a adds the idea of again, which is important here.

In Spain, the present perfect is very commonly used for actions connected to the present time period, especially with expressions like:

• hoy = today
• esta semana = this week
• últimamente = lately
• desde ayer = since yesterday

So in Spain, no haya vuelto a sangrar desde ayer sounds very natural.

In some varieties of Latin American Spanish, speakers might more often prefer a past tense in similar situations, depending on context. But for Spain Spanish, the perfect here is exactly what many learners should expect.

Yes, a little, but the original order is the most neutral and natural.

For example, these are possible:

• Me alegra que la herida no haya vuelto a sangrar desde ayer.
• Desde ayer, me alegra que la herida no haya vuelto a sangrar.

But the original sentence is clearer and more standard.

Inside the clause, moving desde ayer is also possible in some contexts, but the usual placement is at the end:

• ...no haya vuelto a sangrar desde ayer

That placement makes the timeline easy to understand.

It is neutral and natural. It works in both everyday conversation and more careful speech.

Nothing in it is especially formal or especially casual. It would sound normal in situations like:

• talking to a doctor
• talking to a friend about recovery
• giving someone an update about an injury

So it is a very useful real-life sentence pattern to learn.