ngFor not updating DOM when array is updated Angular2

I tried this answer and also this one, but I couldn't make it work.

I have this:

HTML:

<span *ngFor="let block of blocks; let i = index; trackBy: trackByFn">
   {{block.description}}:
</span>

Component:

@Component({
moduleId: module.id,
styleUrls: [ 'component.css' ],
templateUrl: 'component.html'})

export class UserComponent implements OnInit {
blocks: any = [];

constructor(private userService: UserService) {}

  ngOnInit(): void {
    this.loadCourse();
    }

    private loadCourse(){ 
  this.http.get(url + parseInt(localStorage.getItem('id'))).map((response: Response) => response.json())
      .subscribe(resp => {
        this.blocks = resp.blocks;
      });

    }

    trackByFn(index, item) {
      return index;
    }

An then, after some user interaction, I trigger this two lines:

 localStorage.setItem('id','4');
 this.loadCourse();

And the blocks array is updated, but the DOM is not updated, so I don't see the new descriptions in the HTML.

What's missing?

Thanks!!