What's the meaning of “take” here (He takes it all in …)?

Question

The word take has multiple meanings, and I don't understand what does "take" mean in sentence below:

He takes it all in with a practiced eye, and feels unaccountably weary.

So,

• Could you tell me please what the meaning of take is here?

• And Could you please tell me what the relationship between this sentence and following phrase "and feels unaccountably weary" is?

  Note: David is a defense attorney.

The full text is:

David squats down and studies the body without touching it, a grimness taking hold of him. Finally he says, “She’s been dead for a while. She must have fallen in the middle of the night.” He wonders aloud, “Why would she have been out of her room?” He’s noted the terrible gash on the side of her head, the blood on the edge of the bottom step. He takes it all in with a practiced eye, and feels unaccountably weary.

An Unwanted Guest By Shari Lapena

Answer 1

The phrasal verb being used here is take in, which has several meanings, including:

take in (verb) see or watch

I suppose an apt synonym for this particular usage would be observes or studies:

He observes it all with a practiced eye...

He studies the scene with a practiced eye...

Answer 2

To take in means to bring {something|someone} in and process it|them appropriately, and in a figurative sense it means to bring {something} into the mind and process it appropriately, that is, not only to perceive it but to "register" it properly. Registering it could entail recognizing or assimilating it, that is, seeing it for what it is, or processing it mentally with the psyche remaining whole and sound, without becoming "disturbed" in some way or overwhelmed.

The shelter was taking in refugees. ^literal

The shelter was admitting refugees and giving them a temporary place to live.

Her fever is very high, and she has bouts of nausea. Has she been taking in fluids? ^literal

Has she been able to drink fluids and keep them down?

Her eyes took in the room. ^figurative

She observed the room and noted its salient features.

All this bad news coming at once was more than he could take in. ^figurative

The news was more than he could assimilate mentally and emotionally at one time.

When encountering phrasal verbs, many of them at least, not all, you need to think analogically, so that you can arrive at a potential figurative meaning from the raw physical action of the verb.