Final answer:
A decrease in the number of thrombocytes is called thrombocytopenia, leading to improper blood clotting and risk of excessive bleeding. It is the opposite of thrombocytosis, which involves too many platelets and can result in thrombosis.
Step-by-step explanation:
A decrease in the number of thrombocytes, which are cell fragments also known as platelets, is called thrombocytopenia. These platelets are crucial for blood clotting, as they gather at the site of vessel injury to form a plug that helps to stop bleeding. When a person has thrombocytopenia, their blood does not clot properly due to the low number of platelets, which may lead to excessive bleeding. This condition contrasts with thrombocytosis, where there is an excessive number of platelets, increasing the risk of excessive clot formation known as thrombosis. Both conditions can have serious health implications, including fatal risks.