Chapter 49

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University of Toronto Scarborough
Biological Sciences
Kamini Persaud

Chapter 49 Circulatory Systems 49.1 Why Do Animals Need a Circulatory System? - Circulatorycardiovascular system = a muscular pump (heart), a fluid (blood), a series of conduits (blood vessels). - Function of the system = transport heat, hormones, respiratory gases, blood cells, platelets, nutrients, & waste products. - Not all animals have circulatory systems because their cells are close enough to the external environment for such transport to occur wo one; SA = , diffusion path length = . - Sometimes acquatic invertebrates have highly branched central cavities called gastrovascular systems that bring the external environment into the animals. Problem: inactive, slow, sedentary animals. Ex: Sponges. - All cell nutrients come from extracellular fluid and all waste is disposed of there. - Open system = vessels of these animals empty their fluid directly into the tissues and later the extracellular fluid flows back into the circulatory system to be pumped back out again. - Insects have open system but can achieve high levels of metabolic output because they do not depend on their circulatory systems for respiratory gas exchange. - Closed system = completely contain the circulating fluid, blood, in a continuous system of vessels BUT liquid and solutes are still exchanged bw the blood and the extracellular fluids surrounding the cells of the body. - The term extracellular fluid refers to both the fluid in the circulatory system and the fluid bw the cells of the body. to distinguish, the fluid in the circulatory system = blood plasma, and the fluid around the cells = interstitial fluid. Open circulatory systems move extracellular fluid - In open circulatory systems, excracellular fluid squeezes through intercellular spaces as the animal moves and the muscular pump assists with the distribution of the fluid. The contraction of the pump propels the extracellular fluid through vessels leading to different regions of the body, but the fluid leaves the vessels and trickles through the tissues and eventually returns back to the heart. - Such systems found in arthropods (fluid returns to the heart through valved openings called ostia), mollusks. Closed circulatory systems circulate blood through a system of blood vessels. Ex: worms. - Advantages: 1) Fluid flows more rapidly and therefore so does nutrients and wastes 2) By changing resistance in the vessels, can be more selective in directing blood to specific tissues. 3) Specialized cells and large molecules stay in the vessels, but can drop their cargo in the tissue where it is needed. 49.2 How Have Vertebrate Circulatory Systems Evolved? - Vertebrates have circulatory systems with heat of 2 or more chambers. - Arterioles = smaller vessels than arteries which feed blood into capillary beds. - Capillaries = thin-walled vessels where materials are exchanged bw the blood and the tissue fluid. - Venules = small vessels that drain capillary beds. - Veins = venules join together to form larger vessels called veins, which deliver blood back to heart. - Pulmonary circuit blood is pumped from the heart to the lungs and back to the heart. - Systemic circuit From the heart, blood is pumped to the rest of the body and back to the heart. Fish have two-chambered hearts - Fish heart has two chambers: an atrium (receives blood from the body and pumps it into a more muscular chamber), the ventricle. - The ventricle pumps deoxygenated blood to the gills, where gases are exchanged.
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