The seminal vesicles secrete a viscous, whitish-yellow fluid containing the sugar to nourish the sperm.

The seminal vesicles are a pair of glands that are positioned below the bladder and in front of the rectum in males. They produce about 70% of the fluid that ultimately becomes semen.

Here are the steps of how seminal vesicles secrete a viscous, whitish-yellow fluid to nourish the sperm:

1. The seminal vesicles are stimulated to produce their secretion during sexual arousal. This stimulation is mediated by the autonomic nervous system, specifically the sympathetic division.

2. The fluid produced by the seminal vesicles is rich in fructose, a type of sugar. This fructose serves as an energy source for the sperm, allowing them to move and survive in the female reproductive tract after ejaculation.

3. In addition to fructose, the seminal vesicle fluid also contains other substances such as prostaglandins (which stimulate contractions in the female reproductive tract to help move the sperm) and proteins (which help to coagulate the semen after ejaculation, presumably to help keep it in the female reproductive tract).

4. The fluid from the seminal vesicles mixes with sperm from the testes and fluids from other accessory glands (like the prostate) to form semen. This mixing occurs in the ejaculatory ducts, which then transport the semen out of the body through the penis during ejaculation.

5. The whitish-yellow color of the fluid is due to the presence of various substances, including fructose and proteins. The viscosity (thickness) of the fluid helps to protect the sperm and assist in their transport.