Circulation

1. Circulation Chapter 3

2. Circulatory System Function • Move circulatory fluid (blood) around body • Gas Transport • Nutrient Transport • Excretory Product Transport • Cell Signal Transport • Hydraulic Force • Heat Conductance • Immunity

3. Types of Circulation • Sponges • intracellular spaces • allows water to flow through • Nematodes, Platyhelminths, etc • gut cavity, coelomic fluid • Arthropods, annelids, chordates, etc • distinct circulatory system • pumps and channel system

4. Types of Pumps (Hearts) • Peristaltic • waves of muscular contraction along tubes drives blood flow • Chamber • muscular pump divided into chambers which contract • Pressure • contraction of muscles external to the circulatory system drives flow

5. Types of Channel Systems • Closed circulatory systems • blood carried in tubes (blood vessels) • arteries, capillaries and veins • vertebrates, cephalopods, echinoderms, annelids • Open circulatory systems • blood (hemolymph) passes from heart through short arteries into open sinuses surrounding the tissues • most mollusks and arthropods

6. Invertebrate Circulation:Annelids • Closed circulatory system • Dense capillary network at integument (respiration) • Peristaltic dorsal blood vessel drives blood flow

7. Invertebrate Circulation:Bivalves and Gastropods • Open circulatory system • (hemolymph) circulated in an open space (hemocoel) divided into lacunae • Two- or three-chambered heart • Hydraulic force used to control movement of the foot in bivalves

8. Invertebrate Circulation:Cephalopods • Closed circulatory system • pair of branchial hearts (drive blood to gills) • single chambered systemic heart (ventricle) • similar to system in higher vertebrates • separate pulmonary and systemic circuits Fig. 23.19

9. Invertebrate Circulation:Insects • Open circulatory system • Minimal gas transport • Large dorsal vessel w/peristaltic heart in posterior segment • hemolymph runs anteriorly to head, then ends in hemocoel • flow directed through hemocoel by longitudinal membranes • flows back to posterior dorsal vessel • Auxillary pumps supply wings limbs, and antennae Box 23.3

10. Invertebrate Circulation:Arachnids • Similar to insect design • Hemolymph contains higher [hemocyanin] • O2 transport • More extensive arterial systems in arachnids with books lungs • Specific arteries supply hydraulic pressure to legs for locomotion • legs of spiders lack extensor muscles

11. Invertebrate Circulation:Crustaceans • Some small or sessile spp. lack heart or blood vessels • Larger spp possess open system similar to insects • Extensive circulation in gills • heart receives oxygenated hemolymph from the gills then pumps it to the rest of the body Fig. 23.22

12. Vertebrate Circulation: General Patterns • Single passage through heart during circuit (e.g., fish) • Single circuit • Double passage through heart during circuit (e.g., mammals) • Separate pulmonary and systemic circuits Figs. 23.14 & 23.10

13. Vertebrate Circulation:Cyclostomes • Partially open system • large blood sinuses • Multiple “hearts” • branchial (regular) heart • two chambered • cardinal heart • portal heart • caudal hearts • gills (drive arterial blood)

14. Vertebrate Circulation:Teleosts and Elasmobranchs • Two-chambered heart • atrium + ventricle • Atrial contraction (systole) pushes blood into ventricle • valves prevent flow into sinus venosus • Ventricular systole forces blood into bulbus arteriosus • Backflow upon relaxation (diastole) prevented by valves • elastic recoil of bulbus arteriosus drives blood through blood vessels Fig. 23.14

15. Vertebrate Circulation:Dipnoi (Lungfish) • Three-chambered heart • Two-chambered atrium • Partially divided ventricle & bulbus cordis (conus arteriosis) • Separates oxygenated (left) and deoxygenated (right) blood • Can shunt blood to lungs or gill lamellae Fig. 23.16

16. Vertebrate Circulation:Amphibians • Three chambered heart • Two chambered atrium • Undivided ventricle • Spiral valve - separates blood flow in conus arteriosus • Right side (pulmonary) • Receives blood from tissues and skin • Pumps to skin and lungs • Left side (systemic) • Receives blood from lungs • Pumps to tissues

17. Vertebrate Circulation:Non-Archosaur Reptiles • Three chambered heart • Two chambered atrium • partly divided ventricle • Ventricle contains three sub-chambers • divided upon contraction • “five-chambered” heart • allows heart to redirect blood flow btw pulmonary and systemic circuits • “cardiac shunting”

18. Vertebrate Circulation:Crocodilians • Four-chambered heart • Left aortic arch and pulmonary artery arise from right ventricle • L and R arches connected by foramen of Panizza • Allows cardiac shunting • blood directed to lungs during air breathing • blood directed to tissues during diving Fig. 23.18

19. Vertebrate Circulation:Mammals and Birds • Four-chambered heart • Complete separation into right and left halves • Blood pressure can differ between pulmonary and systemic circuits • systemic BP = 95 mmHg • pulmonary BP = 14 mmHg Figs. 23.1 & 23.10; Table 23.1

20. Vertebrate Circulation:Mammals and Birds • Atria • Thin walled, support ventricular filling • Ventricles • Primary pumps for driving blood through circulation • One-way valves • Atrioventricular valves • Arterial (semilunar) valves • ensure unidirectional flow • veins → atria → ventricles → arteries Fig. 23.1

21. Mammalian/AvianCardiac Cycle • Systole (contraction) • Muscular walls of the ventricles contract • Elevation of blood pressure in the ventricles • Closure of atrioventricular valves • Blood pushes through arterial valves • Blood flows into arteries Fig. 23.2

22. Mammalian/AvianCardiac Cycle • Diastole (relaxation) • Muscular walls of the ventricles relax • Blood pressure in the ventricles falls below arterial pressure • Closure of arterial valves • Pressure falls below atrial pressure • Blood pushes through atrioventricular valves • Ventricular volume increases Fig. 23.2

23. Cardiac Output • amount of blood pumped by the heart per min. Qh = h * Vh • h = heart rate • frequency of contraction • Vh = stroke volume • volume of blood pumped by heart per contraction

24. Cardiac Output • Adjusted to meet metabolic demands of an organism •  activity,  cardiac output • Modify cardiac output by changing either heart rate or stroke volume

25. Heart Excitation:Myogenic (Vertebrates) • Heart excitation and contraction can occur in absence of external stimulation • Presence of internal “pacemakers” (modified muscle cells) form conduction system • Sinoatrial node • Atrioventricular node • Atrioventricular bundle • Purkinje fibers Fig. 23.4

26. Heart Excitation:Neurogenic (Arthropods) • Signals received from neurons directly responsible for muscle contraction • Posterior cells act as pacemakers • Anterior cells stimulate muscle contraction Fig. 23.5

27. Regulation of Cardiac Output (Mammals) • Heart rate (modify pacemaker activity): • The autonomic nervous system: • Parasympathetic nervous system (vagus nerve) • acetylcholine slows HR • Sympathetic nervous system (accelerans nerve) • norepinephrine increases HR • Hormones • Epinephrine (released from adrenal glands) • increased HR

28. Regulation of Cardiac Output (Mammals) • Stroke volume (modify force of contraction): • neural/hormonal • epinephrine and norepinephrine • increases force of muscle contraction • autoregulation • Frank-Starling Law • increased venous return increases stretch on the heart • increased stretch leads to stronger contractions

29. Oxygen Delivery During Exercise •  activity, O2 requirements and CO2 production • Three mechanisms of obtaining more O2 •  O2 extraction from the blood • only 25% of O2 removed from blood at rest • increase to 80-90% during exercise •  Heart Rate •  Stroke Volume

30. Animal Size and Cardiac Output • Smaller animals have relatively higher metabolic rates (b ~ 0.75) • Smaller animals have relatively higher cardiac outputs (b ~ 0.75) • Higher cardiac output due to higher heart rates, not larger stroke volumes

31. Blood Vessels • Arteries - large, elastic tubes, multiple layers of muscles • Arterioles - smaller diameter, less elastic, fewer muscle layers • Capillaries - thin diameter, thin walls, low diffusion resistance • Venules - larger diameter, thin walled, no muscle • Veins - large diameter, elastic walls, little muscle, may possess valves

32. Blood Vessels • Structural Patterns •  diameter,  number,  cross-sectional area • Functional Patterns • Blood volume: largest in veins, smallest in capillaries • Blood pressure: with  distance passed • Blood flow velocity:  with  diameter and  cross-sectional area Fig. 23.12

33. Blood Flow • Blood flows from an area of high total fluid energy to low total fluid energy • Bernoulli’s Theorem E = pv + mgh + 1/2mu2 • E = total fluid energy • pv = potential energy of pressure generated by the heart • mgh = gravitational potential energy • 1/2mu2 = kinetic energy Fig. 23.8

34. Overview of Blood Flow • Reasonable assumptions that will help simplify things… • Kinetic Energy varies little from one location to another within the system being analyzed • Flow is horizontal (gravitational potential energy is constant)

35. Blood Flow:Poiseuille’s Law • For the laminar flow of a fluid through a straight, rigid tube: Q = (pr4) / (8L) • Q = blood flow (volume per unit time) • p = difference in pressure between both ends • r = radius of the tube • L = length of the tube • = viscosity Fig. 23.9

36. Blood Flow:Poiseuille’s Law • Q  p • as pressure gradient increases, flow increases • Q  r4 • increased radius, large increase in flow • decreased radius, large decrease in flow • Q  1/L • flow decreases with increased tube length • Q  1/  • increased viscosity decreases flow

37. Gravity Effects on Blood Pressure • As height ’s, gravitational potential energy ’s, pressure ’s • Venous return • blood pressure in lower body greater than upper body due to gravity • pressure in veins exceeds arterial pressure • blood pools in leg veins • returned by venous pressure pumps Fig. 23.7

38. Gravity Effects on Blood Pressure • Head perfusion • arterial blood pressure must be high enough for blood to reach head • giraffes - long vertical neck • high arterial BP • venous values prevent backflow when head brought to ground level

39. Capillaries • Enormous number of capillaries • overall large cross-sectional area • Extremely thin diameter • slow blood flow • high SA/V ratio • Thin walls (simple squamous endothelium) • low diffusion distance

40. Ultrafiltration • Small molecules can diffuse into and out of capillaries • Additional amounts of fluid driven out by hydraulic pressure inside the capillaries = ultrafiltration. • Small particles driven out with water • large molecules (e.g. plasma proteins) remain in blood Fig. 23.13

41. Ultrafiltration • Loss of water with retention of proteins increases the colloid osmotic pressure of the blood • generates tendency for water to flow back into the blood as pressure in the capillaries decreases Fig. 23.13

42. Lymphatic System • Generally water loss by ultrafiltration exceeds water uptake by colloid osmotic movement of water • lost fluid enters lymphatic system • returned to the blood