Circulatory systems – general questions

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 x2

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 moleculesrapidly 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? • To carry gases (O2, CO2 and others) to and from tissues • To carry nutrients, wastes & hormones between organs • To provide structural support & locomotion • 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 +suspendednutrients

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

16. Bulk Flow

17. Bulk Flow

18. Invertebrate circulatory fluids • 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 • Red blood cell hemoglobins (Fe): Some molluscs, annelids, echinoderms • Pink blood cell hemerythrins (amino acids): Some marine worms: annelids, sipunculids • Extracellular hemoglobins & chlorocruorin (Fe): Some annelids; bivalve molluscs, arthropods • Molluscan extracellular hemocyanin (Cu): Cephalopods, gastropods & some bivalves • Arthropod extracellular hemocyanin (Cu): Decapod crustaceans

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 theheart chamber, drawing hemolymphfrom the sinus via the ostia into theheart • 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 • (neurogenicheart) • 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. Open vs closed circulatory systems in invertebrates • 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