GR translation: headborn anorexias and constipations

[Mike Jing]

P172.36-P173.2   They are blacks, Indians, Ashkenazic Jews speaking
dialects you never heard in Harley Street: they have been bombed out,
frozen, starved, meanly sheltered, and their faces, even the
children’s, all possess some ancient intimacy with pain and reverse
that amazes Pointsman, who is more polarized upon West End catalogues
of genteel signs and symptoms, headborn anorexias and constipations
the Welshman could have little patience with.

What does "headborn" mean?