Final answer:
Ostia are openings in blood vessels, the pericardium protects the heart, and peripheral resistance is the force against blood flow in vessels. Red blood cells transport oxygen, while platelets aid in blood clotting, and the pulmonary circulation oxygenates blood.
Step-by-step explanation:
The term 'ostia' refers to holes between blood vessels that allow movement of hemolymph in organisms with open circulatory systems, such as insects, arthropods, and mollusks. The 'pericardium' is a membrane layer that protects the heart and is also a part of the epicardium. 'Peripheral resistance' is the resistance offered by the walls of arteries and blood vessels to the force exerted by the heart when it pumps blood. Red blood cells are small, biconcave cells that transport oxygen throughout the body, and platelets or thrombocytes are cellular fragments that form a plug to prevent blood loss at wound sites. Systems like the 'pulmonary circulation' involve the flow of blood through the lungs for oxygenation and back to the heart.