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Digestive Anatomy
Leeches have jaws that are modified into suckers for attaching to hosts and eating blood. The blood passes through the throat, travels down the esophagus and lands in the leech's crop, which is analogous to the human stomach.
Blood Storage
Leeches secrete an anticoagulant, which prevents blood from clotting. This allows blood to remain in the leech's crop and be used for nutrients for an extended period of time. Bacteria inside the leech's crop prevents the blood from decaying. Some leeches can retain blood in their crop for several months. This dramatically cuts down on the need to eliminate wastes. A leech who eats more than it needs in a single meal will simply store the food until it needs to extract its nutrients.
End Digestive Tract
The end of a leech's digestive tract is an important part of its waste elimination process. Nephridia are tiny organs analogous to kidneys that aid in digestion and excretion. Excess water in blood is excreted directly by the nephridia, which can release small quantities of water through the leech's skin. After blood processes through the nephridia and exits the crop, it enters the gizzard. This digestive organ mechanically digests the food and then passes waste products into the leech's intestine.
Excretion
After blood has been processed through leech intestines, it exits via the leech's anus. The anus is on the top portion of the leech's rear end, located next to the posterior sucker, which the leech uses during locomotion.