Evolution of the Circulatory System

Open vs Closed System Open Circulatory System Exists in invertebrates Insects, mollusks some crustaceans Blood vessel pumps blood through peristalsis to large sinuses where organs are bathed in blood. Only works in small organisms where cells are close to environment.

Open vs Closed Circulatory System Closed System Found in some invertebrates and higher order organisms Blood pumped through closed system of arteries, veins and capillaries Blood pumped directly to organs Allows for regulation of blood flow Increased pressure and speed of blood flow Allows for larger organisms with cells farther from the environment

Evolution of the heart Hearts can be found in animals with 2, 3 and 4 chambers.

2 Chambered Heart Found in fish One atria and one ventricle Blood pumped to gills to pick up O 2 and then travels to organs and then back to heart. Low blood pressure Single Circulation

3 Chambered Heart Found in reptiles and amphibians 2 atria and 1 ventricle 1 atria deoxygenated blood from body 1 atria oxygenated blood from lungs. Single ventricle pumps blood out to both lungs and body. Oxygenated and deoxygenated blood mixed In ventricle causing dilute O 2 blood.

4 Chamber Heart Birds and mammals 2 atria and 2 ventricles Oxygenated and deoxygenated blood kept separate. Allows for increased blood pressure, thermal regulation and sustained muscle movement.