The doctor SPECIALIZE in blood disease.
Urologist
Gynecologists specialize in the female reproductive system.
cardiologist
A doctor can specialize in a certain field by completing residency requirements in that field. In addition, they can also complete a fellowship in another sub speciality.
Radiologist.
Depends upon, if you specialize and in what area.
Rheumatologists specialize in joint health.
There are usually not doctors that exclusively work with just knee's but their are doctors that work in this area. The difference is that they specialize in muscle/bone procedures, making them a bit different from a doctor that may specialize in another area.
A neurologist is a surgeon/doctor that specializes in the nervous system...
About 8 to 10 years after qualifying as a Doctor
A Trichologist, they specialize in hair and scalp health:Trichology.