A nephrologist is a physician who is specially trained to diagnose and treat conditions affecting the kidneys or renal system.
A nephrologist will determine through urine analysis, blood test, X-ray, sonogram, or kidney biopsy how well the kidneys are functioning and will then prescribe a special diet and exercise program, medication or dialysis - a process by which a machine filters the blood when the kidney is no longer capable of doing so.

An internist is a physician who focuses on the diagnosis and treatment of conditions that affect the adult population—both acute and chronic.
These doctors are often who adults see as their primary physicians because they treat a broad range of illnesses that do not require surgical or specialist interventions. They also work to help a patient maintain optimal health in order to prevent the onset of disease.
In addition to treating the common cold and flu, internists also treat chronic diseases like diabetes and heart disease.

Anesthesiologists are physicians who are trained to administer anesthetics, which are medicines used to block nerve sensation. Anesthesia can be either local to one specific part of a body, like a tooth, or regional to block feeling to a larger portion of the body, such as during an epidural for child birth. It can also be more general to block sensation to the entire body, resulting in unconsciousness.
Anesthesiologists assist in surgery by determining how much anesthesia is necessary and by monitoring the patient's level of responsiveness and vital signs throughout the procedure. The anesthesia specialist will also bring the patient out of anesthesia and then continue to monitor his or her vital signs post-operation.
Besides assisting in surgeries, anesthesiologists may also treat patients suffering from chronic pain.