Animal Circulatory Systems

1. Animal Circulatory Systems Types of circulatory systems: gastrovascular, open, closed. Vascular system: arteries, veins, capillaries. Capillary - tissue fluid exchange.

2. Absence of a Circulatory System Very small animals may not need a circulatory system. Small size may permit nutrients and other substances to reach all the body parts by simple diffusion

5. Circulatory Systems Two types of circulatory system are found: Open Circulatory Systems Closed Circulatory Systems

6. Open Circulatory System Hemolymph leaves the heart in short, branched arteries that open up into large spaces called sinuses. Hemolymph percolates around organs, directly bathing the cells. Hemolymph then returns to the heart directly or through short veins.

7. Open Circulatory System Advantage - Exchange of materials is direct between the hemolymph and tissues. There is no diffusion barrier. Disadvantage - Little fine control over distribution of the hemolymph to body regions. No mechanism for reducing flow to a specific part of an organ.

8. Open Circulatory System Open circulatory systems tend to be found in more inactive animals. Most molluscs have an open system, but the highly active cephalopods (squid and octopus) have evolved a closed system. Insects have circumvented limitation of their open system by their tracheal system for oxygen supply.

9. Closed Circulatory System The blood is contained within a completely closed system of vessels. Vessels form a closed loop, usually with some sort of pumping organ like a heart or contractile vessels. Vessels branch into smaller and smaller tubes that penetrate among the cells of tissues.

10. Closed Circulatory System Fine-scale control over the distribution of blood to different body regions is possible. Muscular walls of vessels can constrict and dilate to vary the amount of flow through specific vessels. Blood pressures are fairly high and the circulation can be vigorous.

11. Earthworm Circulation

12. Coelomic Cavities - Circulatory Function Coelomic cavities are filled with fluid that can transport materials around the body. Nematode worms have an extensive body cavity, the pseudocoel, but lack a separate circulatory system.

13. Ascaris Cross-Section

14. The Vertebrate Vascular System: Arteries, Veins, and Capillaries

17. Capillaries Capillaries are very small, about the diameter of a red blood cell (8�m or less). Capillary walls are a single layer of very thin endothelial cells, attached at their edges and surrounded by a basement membrane (extracellular matrix).

22. The Lymphatic System

23. Capillary - Tissue Fluid Exchange The bulk flow of fluid out of the capillary exchanges material much faster than would be possible by simple diffusion alone. Nutrients and O2 are released to the tissues rapidly. Wastes from cell metabolism are more rapidly cleared away by the circulatory system.

24. Control of Capillary Circulation Arteries and arterioles that feed blood to the capillaries contain a circular layer of smooth muscle in their walls. Contraction of these smooth muscles (vasoconstriction) is important in controlling the blood flow through capillary beds. Relaxation of smooth muscles results in vasodilation, an expansion of the vessel diameter that increases blood flow.

26. Circulatory Patterns in Vertebrates

30. Cardiac cycle

32. Human blood components