1. CIRCULATION
Chapter 25

2. 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, most animals use circulatory systems to move fluid through their bodies by bulk flow (convective transport)

3. 1. Components of Circulatory Systems
Blood: A fluid that circulates through the system
Pump (Heart) or propulsive structures
Vasculature: A system of tubes, channels, or spaces
Not all animals have cardiovascular systems, e.g., sponge
This is a sample first topic page.

4. Circulatory System
food, water intake
oxygen intake
DIGESTIVE
SYSTEM
RESPIRATORY
SYSTEM
elimination
of carbon
dioxide
oxygen
nutrients,
water,
salts
carbon
dioxide
CIRCULATORY
SYSTEM
URINARY
SYSTEM
water,
solutes
Elimination of food residues
rapid transport to and from all cells
elimination of excess water, salts, wastes
Accepts oxygen, nutrients, and other substances, immune cells, signaling cells, from the respiratory, digestive, immune, and endocrine systems and delivers them to cells
Accepts carbon dioxide and wastes from cells and delivers them to respiratory and urinary systems for disposal

5. Figure 25.1 The Mammalian Heart
Four chambers: two atria, and two ventricles
One-way valves: prevent backflow
Left side has higher pressure and thicker walls
Flow (next slide)

6. Systemic aorta Pulmonary trunk Pulmonary valve Pulmonary artery
Figure The human heart
Systemic aorta
Pulmonary trunk
Pulmonary valve
Pulmonary artery
To lung
To lung
Pulmonary veins
Superior vena cava
From lung
From lung
Blood that has been oxygenated in the lungs travels to the heart in the pulmonary veins and enters the left atrium.
The strongly muscular left ventricle pumps the oxygenated blood through the aortic valve into the systemic aorta, from which it flows to the entire systemic circuit.
Right atrium
Blood flows through the left atrioventricular valve to enter the left ventricle.
After passing through the systemic circuit, the blood—now partly deoxygenated—flows into the venae cavae, then into the right atrium.
Blood flows through the right atrioventricular valve to enter the right ventricle.
Left ventricle
Inferior vena cava
Aortic valve
The right ventricle pumps the deoxygen-ated blood through the pulmonary valve into the pulmonary trunk, from which it flows to the lungs in the pulmonary circuit.
Myocardium

7. Pressure patterns in the Heart
Each single heart beat has two phases
Systole
Contraction of the ventricles creates the highest pressure
In humans, normally 120 mm Hg in the brachial artery
moves blood elsewhere
Diastole
Relaxation of the atria and ventricles yields the lowest pressure (80 mm Hg in the brachial artery)

8. Cardiac Output
Cardiac output (CO or Q) – amount of blood the heart pumps per unit time (mL/min)
Stroke volume (SV) – amount of blood the heart pumps with each beat (mL/beat)
Heart rate (HR): rate of contraction (beats/min)
CO = HR X SV
Bradycardia – decrease in HR
Tachycardia – increase in HR

9. If the heart rate is 60 beats per minute and the stroke volume is 80 ml, what is the cardiac output?
60 beats/min * 80 ml/beat
4800 ml/min = 4.8 l/min

10. Less ventricular pressure is needed to pump blood through this circuit
Right side of the heart
Resistance in the pulmonary circuit is low due to high capillary density in parallel
Less ventricular pressure is needed to pump blood through this circuit
The low pressure also protects the delicate blood vessels of the lungs
Figure 9.19

11. Electrocardiogram (discussed later)
Fig The synchronous changes in the dynamics of the left side of the human heart
Electrocardiogram (discussed later)
Blood pressure of the left ventricle, left atrium, and aorta
Closing and opening of valves (for one way flow)
Ventricular volume
Ventricular outflow
anphys2e-fig jpg

12. Figure 25.2 The heart as a pump: The dynamics of the left side of the human heart (Part 1)
The heart cycle is divided into five phases shown at the top and demarcated by vertical lines.
Atrial Systole
Isovolumetric Contraction
Ventricular Ejection
Isovolumetric Relaxation
Ventricular Filling
anphys2e-fig r.jpg
The arrow at the bottom indicates the start of ventricular systole (phases 2 and 3).

13. After the previous heart cycle, the atria contract
1: ATRIAL SYSTOLE
After the previous heart cycle, the atria contract
Contraction pumps more blood into the relaxed ventricles.
End diastolic volume (EDV).
Maximum volume of blood in the ventricles (end of ventricular relaxation) occurs at the end of atrial systole
EDV = 140 ml per ventricle in humans
anphys2e-fig r.jpg

14. 2: ISOVOLUMETRIC CONTRACTION
Ventricles start contracting
beginning of Systole,
Ventricular pressure (VP) > Atrial pressure (AP)
A-V valves cose (“lub”).
Aortic (& pulmonary artery) pressure > VP
Semilunar valves to arteries remain shut
No change in volume
Ventricles do not eject blood
anphys2e-fig r.jpg

15. 3: VENTRICULAR EJECTION
Ventricular pressure exceeds arterial pressure
Semilunar valves open
Ventricular contraction forces blood out into the arteries (decreasing ventricular volume).
The ventricles continue to contract and build pressure during the first half of the ejection phase (maximum pressure = systolic blood pressure).
anphys2e-fig r.jpg

16. 4: ISOVOLUMETRIC RELAXATION
Ventricles relax but do not fill
VP < aorta, semilunar valves close (second sound: “dup”), flow is momentarily reversed.
Ventricles are at end systolic volume (minimum volume.
Ventricles continue to relax, but the A-V valves are still closed, so there is no change in volume.
anphys2e-fig r.jpg
Aorta

17. Blood flows into relaxed ventricle
5: VENTRICULAR FILLING
Blood flows into relaxed ventricle
During ventricular systole the atria have been filling with blood returning from its body-wide journey.
When the ventricular pressure drops below that of the atria, the ventricles will begin filling passively.
anphys2e-fig r.jpg

18. The solid line indicates blood pressure in the
Left ventricle.
Right ventricle
Left atrium
Right atrium
Aorta
Pulmonary artery

19. Ventricular Filling and Emptying
In birds and mammals the ventricles fill passively during diastole.
atrial contraction is not necessary for ventricular filling (in humans atrial contraction usually adds < 20% to the ventricular volume).
The two ventricles contract simultaneously, but the left ventricle contracts more forcefully and develops higher pressure

20. Sound patterns in the Heart
Figure 25.2
Lub (or lubb)
closing of AV valves - start of ventricular systole (contraction of ventricles) then
Dub (or dupp)
closing of semilunar valves , beginning of ventricular diastole (relaxation of ventricles).
heart murmur: valve does not close properly, blood flows backward
lub
dub

21. The Aortic valve closes atB C D E

22. The Myogenic conducting system
Vertebrate hearts are myogenic
Heart cells beat (contract) on own when separated from nervous system
Cardiomyocytes (derived from cardiac muscle cells) do not contract, but produce spontaneous rhythmic depolarizations that cause cardiac muscle contraction
Neurogenic hearts in arthropods require nervous stimulation

23. Cardiomyocytes are cells with elongated, pale appearance
Figure The conducting system and the process of conduction in the mammalian heart
Cardiomyocytes are cells with elongated, pale appearance
Sinoatrial (S-A) node in the upper right atrium
Atrioventricular node between the atria and ventricles
Bundle branches in the walls of the ventricles
anphys2e-fig jpg

24. Initiation and Spread of Depolarization During a Heartbeat, 1
Depolarization begins in the Sinoatrial (S-A) node and spreads outward
SA node is the PACEMAKER
Rapid cycle of depolarizations
inherent rhythm of contraction
fire 70/80 times per minute, fastest rhythm of myogenic cells and therefore controls heart rate
anphys-fig jpg

25. (a) The conducting system and sinoatrial node
Figure The conducting system and the process of conduction in the mammalian heart
(a) The conducting system and sinoatrial node
Sinoatrial (S-A) node
Left atrium
Right atrium
Fibrous connective tissue
Atrioventricular (A-V) node
Atrioventricular bundle
Left bundle branch
Right bundle branch
Right ventricle
Left ventricle
Interventricular septum

26. (b) The initiation and spread of depolarization during a heartbeat
Figure The conducting system and the process of conduction in the mammalian heart
(b) The initiation and spread of depolarization during a heartbeat
A-V node
S-A node
Depolarized
Not polarized
KEY
Once the A-V node becomes depolarized, the depolarization spreads very rapidly into the ventricles along the conducting system. Atrial muscle starts to repolarize.
Bundle
branches
Although depolarization spreads rapidly throughout the atrial muscle, its spread into the A-V node is delayed. The depolarized atria start to contract.
Depolarization begins in the S-A node and spreads outward through atrial muscle.
The nearly simultaneous depolarization of cells throughout the ventricular myocardium leads to forceful ventricular contraction.

27. Initiation and Spread of Depolarization During a Heartbeat, 2
internodal pathways
connect the SA node to the atrioventricular (A-V) node
Although depolarization spreads rapidly throughout the atrial muscle, its spread into the A-V node is delayed. The depolarized atria start to contract.
anphys-fig jpg

28. Initiation and Spread of Depolarization During a Heartbeat, 3
The A-V node depolarizes
Depolarization spreads rapidly down into the ventricles along the conducting system (Bundles of His). Purkinje fibers convey signals across ventricles.
Atrial muscles start to repolarize.
anphys-fig jpg

29. Initiation and Spread of Depolarization During a Heartbeat, 4
The depolarization spreads rapidly upward through the ventricles
The nearly simultaneous depolarization leads to forceful ventricular contraction.
anphys-fig jpg

30. The Cardiac Cycle
Cardiac Cycle Animation

31. 0.1 liters/beat 0.36 liters/beat 1 liter/beat 3.6 liters/beat
If your cardiac output is 6 liters/minute and your resting heart rate is 60 beats/minute, what is your stroke volume.
0.1 liters/beat
0.36 liters/beat
1 liter/beat
3.6 liters/beat
10 liters/beat
6 liters / min
___________
60 beats / min

32. 5.25 L/min 7.20 L/min 12.0 L/min 17.2 L/min 47.4 L/min
What is the cardiac output of a patient who has the following cardiac function values? End Systolic Volume: 60 mL End Diastolic Volume: 160 mL Heart Rate: 1 beat every 0.5 seconds
5.25 L/min
7.20 L/min
12.0 L/min
17.2 L/min
47.4 L/min
160 – 60 ml/beat
100 ml/beat
100 ml/beat * 120 beats/min
12000 ml/min
12 L/min

33. Figure 25.6 Electrocardiography (Part 1)
anphys2e-fig r.jpg
The figure shows the spread of the negativity wave in the extracellular fluids as heart muscle depolarizes (goes from -90 mV to + 20 mV as Na+ enters myocytes) during contraction.

34. Fig. 25.6 Electrocardiogram – EKG/ECG
Measures electrical currents produced by depolarization (wave of contraction) of cardiac muscle
recorded with surface electrodes on chest
abnormalities: disorders of rhythm - heart block; may require pacemaker
ular
filling

35. Electrocardiogram (ECG or EKG)
P wave
Spread of impulse for Atrial depolarization and contraction.
QRS complex:
Impulse for Ventricular depolarization and contraction
Atrial repolarization (signal is masked by QRS).
T wave:
Impulse for Ventricular repolarization (recovery) at the end of systole, in preparation for the next contraction

36. The QRS complex of the electrocardiogram immediately precedes
atrial diastole.
the second heart sound (S2 or "dupp")
ventricular systole.
ventricular diastole.
atrial systole

37. Regulation of Stroke Volume Frank-Starling Law of the Heart
What comes in goes out
increase in end-diastolic volume results in a more forceful contraction of the ventricle and an increase in Stroke Volume
Increased venous return
in exercise, contracting limb and abdominal muscles squeeze limb and abdominal veins
Which causes increase stretch of cardiac muscle fiber
Which causes increase force of contraction

38. Animals must compensate for positional effects Gravity Effects
Hydrostatic pressure – pressure of a vertical column of fluid due to gravity
In vertical tubes, pressure is higher at bottom than top due to gravitational pull on fluid
Animals must compensate for positional effects
Gravity Effects
Figure Fluid-column effects on blood pressure in the arterial vascular system

39. Fig. 25.7b Positional Effects & Gravity
Higher pressure at tissues below heart & lower pressures at tissues above heart
Blood pressure varies when standing or prone
in humans, pressure at feet is 2X at heart and 3X at brain
makes it easy to pass out and get varicose veins

40. Gravitational effects on blood flow and pooling
Part of the reason we are asked to lay flat when we feel dizzy or why our sprained ankles “throb” and become swollen only when we are standing up.
If the brain has no pressure, there is no blood being delivered!

41. Positional Effects & Gravity
Remember: +/ mmHg pressure for each inch of elevation or depression.
How long would your neck have to be before your brain would not receive any blood if systolic pressure = 100 mm Hg? (use whole numbers)

42. Giraffe has very high BP to perfuse brain several feet away
Species differences
Giraffe has very high BP to perfuse brain several feet away
In a standing human, it takes an extra mm of Hg pressure to move blood from the heart to the brain.
In a giraffe, extra force is about 175 mm Hg (for a total of 250 mm Hg).
Special check valves and sinuses, as well as feedback mechanisms that reduce cardiac output, prevent this high pressure from damaging the giraffe’s brain when it puts its head down

43. Open Circulatory Systems
Circulatory fluid (hemolymph) comes in direct contact with the tissues in spaces called sinuses (Arthropods, most mollusks)

44. Closed Circulatory Systems
Circulatory fluid (blood) remains within the blood vessels and does not come in direct contact with the tissues (vertebrates, cephalopods, some annelids)

45. The conduits: blood vessels
Arteries and Veins have elastic walls and smooth muscle
arteries have thick, strongly muscled walls (except in pulmonary system)
veins have thinner walls than arteries. They have valves
capillaries have very thin walls with no muscle or elastic

47. Four chambered heart: two atria and two ventricles
Birds and Mammals
Four chambered heart: two atria and two ventricles
Systemic and pulmonary circuits are completely divided
Allows pressure to be different in the two circuits
Oxygenated and deoxygenated blood are completely separate
Figure 25.10

48. Fig 25.10 The circulatory plan in mammals and birds
In effect there are two hearts, a left heart for the systemic circuit, a right heart for the pulmonary circuit
anphys2e-fig jpg

49. Fig 25.12a Blood flow in the human systemic vasculature
Progressive increase in total cross-sectional area from the aorta (0.8 cm2) to the capillaries (600 cm2)
Decrease from capillaries to vena cava (1 cm2)
Cross-sectional area of venous system is larger than that of arterial system
veins have the greatest volume
75% of blood is in venous system
Fig 25.12a Blood flow in the human systemic vasculature

50. F = V ⋅ A 
F = flow in cm3/sec
V = mean velocity in cm/sec
A = cross-sectional area of the blood vessel in cm2
Volume of blood flowing through vessels always has to equal heart’s output
What happens to the velocity?

51. Cross-sectional Area and velocity
flow velocity
is highest in large-diameter transport vessels
is slowest in capillary beds; blood spreads out into many vessels with greater total cross-sectional area
increases after passing through the capillaries
Cross-sectional Area and velocity

52. Fig. 25.12 b Average Blood Pressure
Blood pressure is highest and varies most in the left ventricle
Blood pressure decreases away from heart as x-sectional area increases.
Blood pressure drops rapidly in arterioles due to high resistance
Pressure drops on whole journey from about 100 mm Hg in arteries to 20 mm in capillaries to 2 mm in veins

53. Figure Fluid exchange across mammalian systemic capillary walls: The Starling-Landis hypothesis
colloid osmotic pressure is not equivalent to the total osmotic pressure in a capillary. It is simply a measure of the osmotic pressure created by the proteins
anphys2e-fig jpg

54. Capillary Filtration
Interstitial fluid: extracellular fluid that directly bathes the tissues
fluid exchange between capillaries and interstitial fluid space
small molecules can diffuse across wall
Net Filtration Pressure (NFP)
Blood pressure forces fluid out of capillaries (hydrostatic pressure)

55. Fluid Exchange, cont.
colloidal osmotic pressure (plasma proteins)
plasma proteins are necessary to retain fluid in the vascular system >70,000 weight molecules do not pass through
this creates a 25 mm Hg osmotic pressure that draws water back into the capillaries

56. Exchange of Material From the Plasma to the Interstitial Fluid of Surrounding Cells
So, depending on blood pressure fluid moves in or out of capillaries (usually out near arterial side, and in on venous side
Usually outflow exceeds inflow. This creates lymph which travels through lymphatic system which eventually dump the fluid back into larger veins
Different animal groups have different osmotic pressures in their capillaries (mammals high, others low, birds surprisingly low)

57. The Lymphatic System
The lymphatic system collects the filtered fluid and returns it to the circulatory system
Lymphatic veins and ducts contain valves to prevent backflow

58. Moving Blood Back to the Heart
Blood in veins is under low pressure
Two major pumps assist in moving blood back to the heart
Skeletal muscle
Respiratory pumps
Inhalation: pressure in thoracic cage drops and draws blood into veins
Exhalation: pressure increases in the thoracic cage and pushes the blood towards the heart; blood does not move backwards because of valves

59. 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

60. Fig Typical circulatory plans of the major vertebrate groups, plotted on a phylogenetic tree of the groups
anphys2e-fig jpg

61. Figure 25.14 The circulatory plan in gill-breathing fish
Single circuit in fish
Some have accessory hearts in the tail
The teleost heart has four chambers in series (but only one atrium and one ventricle)
Heart  ventral aorta  gill capillaries  dorsal aorta  systemic circuit
Gill circulation is under higher pressure than the systemic circulation.
anphys2e-fig jpg

62. Amphibian Circulation
Like lungfish, the heart is only partially divided; two atria and one ventricle
Oxygenated and deoxygenated blood can mix in the ventricle, but
Septa and folds direct the oxygenated blood from the lungs to the systemic capillaries and not the pulmonary system.

63. Reptile Circulation
Non-crocodilian reptiles have a partially divided ventricle, which leads to a small amount of blood mixing.
Crocodilians have a completely separated four chambered heart, but do not have completely divided circulation outside of the heart.

64. Crocodilian Blood Shunt
Flap valve is opened to shunt blood from the pulmonary to systemic circuit during diving
anphys2e-fig jpg
Figure Blood flow in the heart ventricles and the systemic and pulmonary arteries of crocodilian reptiles

65. All have hearts and some blood vessels Most have open systems.
Molluscs
All have hearts and some blood vessels
Most have open systems.
Hemolymph = blood in open systems i
Only cephalopods have closed systems
Figure 25.21

66. All have one or more hearts and some blood vessels
Arthropods
All have one or more hearts and some blood vessels
All have open systems
Figure 25.24

67. However, insects use a tracheal system for most gas transport
Arthropods, Cont.
Insects have a relatively simple open circulatory system, but high metabolic rates
However, insects use a tracheal system for most gas transport