The dietitian says, "This is the school cafeteria."

Question

What does the school cafeterian mean?
1. This is the (only) school cafeterian of our school.
2. This is the specific school cafeterian of our school.
[What does "This is the school cafeteria." mean?]

I'm the school nurse. I take care of sick students.
Why is 'the ' used before 'school nurse'? Can't we use 'a' instead of 'the'?
3. I'm the (only) school nurse of our school.
4. I'm the specific school nurse of our school.
5. I'm a school nurse.
6. I'm the school nurse.
[What does 'I'm the school nurse' mean? What is the difference between #5 and #6?]

Answer 1

Here are many examples of what "school cafeteria" means:
https://www.google.com/search?q=define+%22school+cafeteria%22&oq=define+%22school+cafeteria%22&aqs=chrome..69i57.9235j0j7&sourceid=chrome&ie=UTF-8

#1 means this is the only place where students and teachers can buy their lunches at school. I'd rephrase that sentence a bit, though. ~~> This is the cafeteria in our school. (no repetition!)
#2 is wordy and awkward. The best sentence of all these is this. ~~> "This is the school cafeteria."

Rephrased --
3. I'm the school nurse at our school.
4. I'm the nurse at our school.
5. (fine as it is; could work at any school, but hasn't indicated which one)
6. (fine as it is; works at THIS school -- whichever school is being referred to)

The school nurse is the qualified nurse who works at a school. In the schools around here, each school has a qualified nurse on campus, plus other people who assist her or him. The assistants usually don't have specific degrees or titles. The larger schools have more than one or two assistants.