Cardiovascular systems in animals come in various forms, from open to closed systems. The 's structure ranges from two to four chambers, each adapted to the animal's specific needs and environment. These differences impact how blood flows and oxygen is delivered throughout the body.
Circulation pathways vary among species, with in aquatic animals and in air-breathers. Some animals have developed specialized adaptations, like marine mammals' ability to dive deep for extended periods, showcasing the incredible diversity of cardiovascular systems in the animal kingdom.
Circulatory System Types
Open vs Closed Circulatory Systems
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pumps blood into body cavities (hemocoel) allowing direct contact with tissues and organs
Found in arthropods (insects, spiders) and most mollusks (snails, clams)
pumps blood through a network of vessels that transport blood to tissues without direct contact
Blood remains separate from interstitial fluid surrounding cells
Found in annelids (earthworms), cephalopod mollusks (octopus, squid), and all vertebrates
Variations in Heart Structure
has one atrium and one ventricle
Found in fish
Blood flows in single loop, first to gills for oxygenation then to rest of body
has two atria and one ventricle
Found in amphibians and most reptiles
Oxygenated and deoxygenated blood mix in the single ventricle
has two atria and two ventricles
Found in birds, mammals, and crocodilians
Oxygenated and deoxygenated blood remain completely separated
Allows for higher blood pressure and more efficient to tissues
Circulation Pathways
Gill and Pulmonary Circulation
Gill circulation in fish and some amphibian larvae
Heart pumps deoxygenated blood to gills where occurs
Oxygenated blood then flows to rest of body
Pulmonary circulation in air-breathing animals
Heart pumps deoxygenated blood to lungs
Gas exchange occurs in lungs, oxygenating the blood
Oxygenated blood returns to heart to be pumped to body
Systemic Circulation
delivers oxygenated blood from heart to body tissues
In fish, blood flows from gills directly to systemic circulation
In animals with pulmonary circulation, oxygenated blood returns to heart first
Deoxygenated blood from tissues returns to heart to be re-oxygenated
Countercurrent Exchange
is a mechanism for efficient transfer of heat or gases between fluids flowing in opposite directions
Examples include heat exchange in limbs of marine mammals and oxygen uptake in fish gills
In fish gills, water and blood flow in opposite directions over gill filaments
Maintains a constant diffusion gradient for efficient oxygen uptake from water into blood
Specialized Adaptations
Diving Adaptations in Marine Mammals
Marine mammals like whales and seals have adaptations for prolonged deep dives
Increased in blood and muscle
High levels of in blood and in muscles
Reduced heart rate () and restricted blood flow to non-essential organs during dives
Maintains blood flow to heart, lungs and brain
Collapse of lungs at depth to avoid nitrogen absorption and decompression sickness
Efficient oxygen extraction allows some whales to dive for over 2 hours on a single breath