Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Prostate Enlargement: Benign Prostatic Hyperplasia ?
    ### Response:
    The prostate is a walnut-shaped gland that is part of the male reproductive system. The main function of the prostate is to make a fluid that goes into semen. Prostate fluid is essential for a mans fertility. The gland surrounds the urethra at the neck of the bladder.
    