CH 45 CIRCULATORY SYSTEMS
1. Gastrovascular cavities
2. Open Circulatory systems
3. Closed Circulatory systems
- The primary function of circulatory systems is to transport necessary materials to all the cells of an animal’s body and
waste products away from the cells where they can be released into the environment.
o Organic and inorganic nutrients and gases are necessary materials
o Waste products must be eliminated are CO and2breakdown products of metabolism – urea.
1. Gastrovascular Cavities
- In cnidarians (jellyfish and hydras), the surrounding water not only contains the nutrients and O2to sustain life, it also
serves the functions of the animals’ circulatory system.
- Water enters the gastrovascular cavity, a body cavity with a single opening to the outside.
- Food is digested in the cavity and absorbed by body cells and wastes excreted into cavity.
- In some cnidarians, cilia line opening of gastrovascular cavity propel water through and muscular stretching and
relaxing of the body wall move water throughout cavity.
- These body muscles act like a heart because the pulsing of these muscles are regulated by nerves.
2. Open Circulatory Systems
- Arthropods and molluscs have true circulatory systems with 3 components:
1. Blood/hemolymph: an internal body fluid with dissolved solutes
o Hemolymph is blood and interstitial fluids all in one fluid.
2. Blood vessels: hollow tubes for blood to travel
3. Heart(s): muscular structure to pump blood.
- These 3 components form a cardiovascular system.
- In an open circulatory system, vessels open into animal’s body cavity so fluid in vessels and interstitial fluid mingle in
one large mixed compartment.
o Hemolymph is pumped by several muscular hearts
o Nutrients and wastes are exchanged by diffusion
- In molluscs, hemolymph is recirculated back into heart through vessels and it brings O t2 cells
- In arthropods, it returns to heart through openings in heart called ostia.
- In insects, hemolymph primarily transports nutrients and wastes, not oxygen.
- Hemocytes in blood offer immunity against foreign invaders through phagocytosis and encapsulation.
- Open circulatory systems don’t need a lot of energy to circulate hemolymph and can adapt to change in metabolic
o Ex. Animal takes flight flight muscles contract more forcefully and rapidly compress and expand