Final answer:
Cholesterol exists in animal tissues as part of cell membranes and is necessary for bodily functions. It is excreted as bile acids, formed in the liver and stored in the gallbladder, with about 50% being reabsorbed and the remainder excreted in feces.
Step-by-step explanation:
Cholesterol exists in animal tissues as an integral component of the plasma membrane, giving it structure and fluidity, and serves as the precursor for various important biological molecules. In the liver, it is synthesized and then converted into bile acids which are stored in the gallbladder. When excess cholesterol is present, it is transported via the blood to the gallbladder where it may sometimes form gallstones.
Bile acids, which are derived from cholesterol, play a crucial role in digestion by emulsifying fats, allowing them to be absorbable by the cells. Once bile acids have facilitated digestion, they are excreted through the feces, carrying with them cholesterol, thus aiding in its removal from the body. Approximately 50% of this cholesterol is reabsorbed back into the bloodstream from the small intestine, while the rest is excreted as waste.
Overall, cholesterol is essential for the production of bile salts, steroid hormones such as testosterone and estradiol, and vitamins like vitamin D. Despite its negative reputation, cholesterol is necessary for various bodily functions, including cellular communication and the production of substances crucial to our health.