The seminal vesicles are two small glands located behind the bladder in males. They produce a fluid that makes up a significant portion of semen, which is the fluid that carries sperm during ejaculation. This fluid contains nutrients, such as fructose, that provide energy for sperm cells. During ejaculation, the seminal vesicles release their fluid into the vas deferens, where it mixes with sperm from the testes and fluid from the prostate gland. This combination helps to nourish and transport sperm, playing a crucial role in male fertility.