Rucete ✏ Campbell Biology In a Nutshell
Unit 7 ANIMAL FORM AND FUNCTION — Concept 42.1 Circulatory Systems Link Exchange Surfaces With Cells Throughout the Body
1. Gastrovascular Cavities
- Cnidarians and flatworms use a central cavity for digestion and transport
- Fluid is circulated by ciliated cells; diffusion suffices due to thin body walls
- These animals don’t need separate circulatory systems
2. Need for a Circulatory System
- Diffusion alone is insufficient in large or complex animals
- Circulatory systems efficiently transport materials across longer distances
3. Open and Closed Circulatory Systems
- Open system (e.g., arthropods): hemolymph directly bathes organs
- Hemolymph returns to the heart through pores with the help of body movement
- Closed system (e.g., vertebrates): blood confined to vessels for targeted, faster delivery
4. Basic Components of Circulatory Systems
- All systems have: a fluid (blood or hemolymph), vessels, and a heart
- Heart-generated pressure moves fluid
- Capillary beds are the main sites of exchange
5. Types of Circulatory Pathways
- Single circulation (e.g., fish): one loop; heart → gills → body
- Double circulation (e.g., mammals): heart → lungs → heart → body
- Double circulation allows higher pressure and efficiency
6. Variations in Vertebrate Circulation
- Amphibians: 3-chambered heart, can bypass lungs underwater
- Reptiles: partial septa control lung vs. body circulation
- Mammals and birds: 4-chambered heart fully separates oxygenated and deoxygenated blood
7. Mammalian Circulation Overview
- Right ventricle → lungs via pulmonary arteries
- Oxygen-rich blood returns to left atrium → left ventricle → body via aorta
- Capillaries deliver nutrients and collect waste
- Veins return deoxygenated blood to right atrium via vena cava
In a Nutshell
Circulatory systems solve the limits of diffusion by transporting materials quickly and efficiently. Open systems are simpler and more energy-saving, while closed systems offer precision. Double circulation supports the high metabolic demands of vertebrates like mammals, with their 4-chambered hearts and extensive vascular networks.