1. Circulatory systems – general questions What is a circulatory system? Do all animals have circulatory systems? Why do animals have circulatory systems? What kinds of animals lack circulatory systems?

2. Rate of diffusion Diffusion is slow over long distances Einstein’s diffusion equation t α x 2 DistanceTime required 100  m 5 seconds 200  m 20 seconds 500  m 2 minutes 1 mm8 minutes 1 m16 years

3. Limits of Diffusion Unicellular organisms and some small metazoans lack circulatory systems and rely on diffusion to transport molecules Diffusion can be rapid over small distances, but is very slow over large distances Rather than rely on diffusion, large animals move fluid through their bodies by bulk flow, or convective transport Convection mechanisms are needed to move molecules rapidly over large distances Movement of fluid molecules as a group Requires input of energy Physiologists use the symbol Q to represent flow in circulatory systems You may also see the symbol Q, the dot indicates that this is a rate process

4. Convection systems: speed has a cost Diffusion is ‘free’, convection is not Vertebrate hearts cost ~ 1-4% of resting metabolism lung and gill ventilation cost ~ 1-10% of resting metabolism What are the roles for convection systems? 1.To carry gases (O 2, CO 2 and others) to and from tissues 2.To carry nutrients, wastes & hormones between organs 3.To provide structural support & locomotion 4.To provide filtration Fundamental Components Fluid: water; cytoplasm; lymph; hemolymph; blood Energy: ATP  kinetic energy via potential energy Conduits: cellular spaces; sinuses; vessels; circuits

5. Components of Circulatory Systems Circulatory systems move fluids by increasing the pressure of the fluid in one part of the body The fluid flows through the body down the resulting pressure gradient Three main components are needed Pump or propulsive structures A system of tubes, channels, or spaces A fluid that circulates through the system

6. Different needs for bulk flow

7. Different types of pumps Skeletal muscle Pulsating blood vessels  peristalsis Chambered hearts One way valves help to ensure unidirectional flow Figure 9.2

8. Different types of circulations Open - circulatory fluid comes in direct contact with the tissues in spaces called sinuses Closed – circulatory fluid remains within the blood vessels and does not come in direct contact with the tissues

9. Types of Fluid Interstitial fluid – extracellular fluid that directly bathes the tissues Blood – fluid that circulates within a closed circulatory system Lymph – fluid that circulates in the secondary system of vertebrates called the lymphatic system Hemolymph – fluid that circulates within an open circulatory system

10. Evolution of Circulatory Systems First evolved to transport nutrients Very early on they began to serve a respiratory function Closed systems evolved independently in jawed vertebrates, cephalopods, and annelids Closed systems evolved in combination with specialized oxygen carrier molecules

11. Evolution of Circulatory Systems, Cont.

12. Intracellular convection systems All cells & unicellular animals Microfilaments & microtubules move organelles & DNA

13. Animals That Lack Circulatory Systems Sponges, cnidarians, and flatworms Lack true circulatory systems, but have mechanisms for propelling fluids around their bodies Cilia: sponges and flatworms Muscular contractions: cnidarians

14. Bulk flow using cilia A choanocyte cell water + suspended nutrients

15. Law of Bulk Flow Q=  P/R Fundamental physical law exploited by circulatory systems, respiratory systems, excretory systems, digestive systems etc.

16. Bulk Flow

18. Hemolymph = plasma (water, ions, proteins, nutrients, hormones, etc.) + respiratory pigment + white blood cells Blood = plasma + red/pink blood cells + white blood cells Invertebrate respiratory pigments: intracellular & extracellular 1.Red blood cell hemoglobins (Fe): Some molluscs, annelids, echinoderms 2.Pink blood cell hemerythrins (amino acids): Some marine worms: annelids, sipunculids 3.Extracellular hemoglobins & chlorocruorin (Fe): Some annelids; bivalve molluscs, arthropods 4.Molluscan extracellular hemocyanin (Cu): Cephalopods, gastropods & some bivalves 5.Arthropod extracellular hemocyanin (Cu): Decapod crustaceans Invertebrate circulatory fluids

19. All arthropods have an open circulatory system Insects: Highly successful terrestrial animals & capable of high metabolic rates Role of circulatory system: To deliver nutrients, immune cells & hormones Tracheal system moves respiratory gases directly to tissues) Multiple, segmental hearts Large dorsal vessel Sluggish flow rates Accessory pumps: wings, limbs

20. All arthropods have an open circulatory system Crustaceans: Highly successful aquatic animals & decapods are capable of high metabolic rates Decapod circulatory system: Respiratory function, respiratory pigments, gills Large ostial heart Many branching outflow vessels Small tissue sinuses

21. The decapod crustacean heart The ostial heart sits in a pericardial sac that contains hemolymph Cardiac cycle Cardiac muscles contract in unison, ejecting hemolymph into arteries & stretching suspensory ligaments Cardiac muscles relax, recoil of suspensory ligaments expands the heart chamber, drawing hemolymph from the sinus via the ostia into the heart Cardiac control Neurogenic: CNS controls heart rate & force of contraction (stroke volume) Neural control of arterial sphincters

22. Crayfish cardiac cycle - systole Heartbeat is initiated in neurons of cardiac ganglion (neurogenic heart) Neural signal closes ostia Causes cardiomycocytes to contract Volume of heart chamber decreases, pressure increases Blood exits via arteries Suspensory ligaments are stretched

23. Crayfish cardiac cycle - diastole When neural signal is absent, cardiomyocytes relax Releases tension on suspensory ligaments Ligaments spring back Pulls on the walls of the heart, increasing volume of heart chamber Reduces pressure inside heart Ostia open, blood is sucked into the heart

24. Annelids have open & closed circulatory systems Three Main Classes Polychaeta – tube worms Oligochaeta – earth worms Hirudinea – leeches Most also have vessels that circulate fluid with oxygen carriers Can be an open (polychaetes) or closed (oligochaetes) systems Aquatic and terrestrial animals that have low metabolic rates & can live in hypoxic environments Pumping systems Chambered heart Body wall movements ie muscular contractions Cilia Earthworms Five, segmental contractile tubes Segmental connecting vessels

25. Molluscs have open & closed circulatory systems Bivalves: Sedentary & low metabolic rates Cephalopods: High locomotory abilities (except Nautilus) Cephalopod circulatory system Myogenic, chambered heart Systemic heart pumps oxygenated blood to tissues Paired branchial hearts pump deoxygenated blood to gills Coronary arteries Distributional arteries

26. Common features Muscular ‘hearts’ Unidirectional flow, one-way ‘valves’ Large distribution vessels away from (artery) & to (veins) the heart Hemolymph in which respiratory pigments may be dissolved Benefits No building and maintenance costs Low resistance to flow b/c there are no small distribution vessels Lower pump pressures needed for flow  saves energy Hemolymph readily bathes most cells Large hemolymph volume Disadvantages Limited control of blood flow distribution except at the arterial level Slow circulation/response times Body movements greatly influence blood pressure & flow Open vs closed circulatory systems in invertebrates