People who are in jail have a constitutional right to receive reasonable medical care. These rights apply to both pre-trial detainees (people awaiting trial) and convicted inmates (people who have already been convicted).
The amount of medical care a prisoner is entitled to depends on the severity of their medical need, and the medical conditions and situations that may arise from a lack of medical care is varied.
Ultimately, when a person is incarcerated against his or her will, the state has the constitutional responsibility to act humanely and to protect the prisoner's health and safety.