Final answer:
Most cases of hypertension have an unknown cause, classified as primary hypertension. Secondary hypertension has identifiable causes such as chronic kidney disease or hormonal imbalances. However, the exact mechanisms of primary hypertension are not fully understood.
Step-by-step explanation:
In the context of hypertension, which is a chronic medical condition with persistently elevated blood pressure, most cases are classified as either primary (essential) hypertension or secondary hypertension. When it comes to the cause of hypertension in most cases, the correct answer is d. unknown. Primary, or essential, hypertension accounts for about 90% of all cases and does not have a clear cause; however, it is influenced by a combination of genetic factors and lifestyle choices such as poor nutrition, lack of exercise, excessive intake of dietary salt, and excessive alcohol use. Secondary hypertension, which accounts for the remaining 10%, can be attributed to identifiable causes such as chronic kidney disease or hormonal imbalances, like Cushing's disease. Despite some risk factors being identified, the exact mechanism that causes primary hypertension remains largely unknown to researchers and medical professionals.