1. Animal Circulatory Systems
Chapter 44: pp
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

3. Larger Animals Without a Separate Circulatory System
figure jpg
Larger Animals Without a Separate Circulatory System
Cnidarian Gastrovascular Systems
Some larger animals such as sea anemones, jellyfish, and flatworms lack a true circulatory system.
The gastrovascular cavity extends to most areas of the body in these animals and serves as a circulatory system as well as a digestive cavity.

4. Flatworm Gastrovascular System

5. Circulatory Systems
For larger or more active animals, some form of more efficient circulatory system is necessary for internal transport.
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
Advantages:
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
Extensive capillary beds:
Body wall
Gut wall
Excretory tubules

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
Pseudocoel
(fluid-filled space)

14. The Vertebrate Vascular System: Arteries, Veins, and Capillaries
Arteries and arterioles have a layer of smooth muscle tissue which allows them to contract (vasoconstrict) and expand (vasodilate), altering their diameter and thus blood flow.
Walls of arteries and arterioles have many elastic fibers enabling them to withstand high pressures.

15. Artery and Vein
Artery
Vein
Note the much thinner walls in veins.

16. Blood Pressure and
Flow Velocity

17. Capillaries
Capillaries are very small, about the diameter of a red blood cell (8µm 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).
Endothelial cells

18. Vesicles; large, lipid-insoluble (proteins)
Filtration; fluid and small, lipid-insoluble molecules (water, amino acids,
NaCl, glucose,
urea)
Blood cells, most proteins.
Diffusion;
lipid-soluble molecules
(O2, CO2, lipids)

19. Capillary - Tissue Fluid Exchange
Blood hydrostatic pressure exceeds the opposing negative colloidal osmotic potential of the blood plasma.
Water, containing small dissolved molecules, is forced out of the capillary through small pores in the capillary wall by the excess hydrostatic pressure.

20. Capillary Fluid Exchanges
Blood pressure (hydrostatic)
32 mm Hg
Plasma colloidal osmotic potential
-22 mm Hg
Net pressure
10 mm Hg

21. Capillary Fluid Exchanges
Frictional
Blood pressure (hydrostatic)
32 mm Hg
resistance
Blood pressure (hydrostatic)
15 mm Hg
Plasma colloidal osmotic potential
-22 mm Hg
Plasma colloidal osmotic potential
-22 mm Hg
Net pressure
10 mm Hg
Net pressure
-7 mm Hg
Less water re-enters the capillary than originally left at the arterial end.

22. The Lymphatic System
The lymphatic system, returns excess tissue fluid to the blood.

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.

25. figure jpg

26. Circulatory Patterns in Vertebrates
The circulatory pattern has been modified during evolution of the major groups of vertebrates.

27. (and capillaries)

30. Cardiac cycle

31. Blood flow in veins
One-way flow of blood (toward heart) is determined by valves.

32. Human blood components