1. Circulation in Animals
Chapter 42.
Circulation in Animals

3. What are the issues
Animal cells exchange material across the cell membrane
nutrients
fuels for energy
oxygen
waste (urea, CO2)
If you are a 1-cell organism that’s easy!
If you are many-celled that’s harder

4. What are the issues?
Diffusion is not adequate for moving material across more than 1 cell barrier
NH3 CH
CO2 O2 aa
CO2
NH3
NH3
CO2 O2
CHO
NH3 CH
CO2
CO2 aa
CO2
NH3
NH3
NH3 O2
CO2
CO2
CHO
CO2 aa
NH3 CH
NH3
NH3
CHO O2
CO2
CO2 aa O2 aa

5. Simple diffusion Cnidarians Hydra Body cavity 2-cell layers think
all cells within easy reach of fluid
use gastrovascular cavity for exchange
Cnidarians
Hydra

6. What are the solutions? Circulatory system solves this problem
carries fluids & dissolved material throughout body
cells are never far from body fluid
only a few cells away from blood
overcoming the limitations of diffusion

7. In circulation… What needs to be transported nutritive respiratory
nutrients fuels from digestive system
respiratory
O2 & CO2 from & to gas exchange systems: lungs, gills
excretory
waste products from cells
water, salts, nitrogenous wastes (urea)
protection
blood clotting
immune defenses
white blood cells & others patrolling body
regulation
hormones

8. Circulatory systems All animals have: circulatory fluid = blood
tubes = blood vessels
muscular pump = heart
open
closed

9. Open circulatory system
Taxonomy
invertebrates
insects, arthropods, mollusks
Structure
no distinction between blood & extracellular (interstitial) fluid
hemolymph
The fact that open and closed circulatory systems are each widespread among animals suggests that both offer advantages. For example, the lower hydrostatic pressures associated with open circulatory systems make them less costly than closed systems in terms of energy expenditure. Furthermore, because they lack an extensive system of blood vessels, open systems require less energy to build and maintain. And in some invertebrates, open circulatory systems serve a variety of other functions. For example, in molluscs and freshly molted aquatic arthropods, the open circulatory system functions as a hydrostatic skeleton in supporting the body.

10. Closed circulatory system
Taxonomy
invertebrates
earthworms, squid, octopuses
vertebrates
Structure
blood confined to vessels & separate from interstitial fluid
1 or more hearts
large vessels to smaller vessels
material diffuses between vessels & interstitial fluid
What advantages might be associated with closed circulatory systems? Closed systems, with their higher blood pressure, are more effective at transporting circulatory fluids to meet the high metabolic demands of the tissues and cells of larger and more active animals. For instance, among the molluscs, only the large and active squids and octopuses have closed circulatory systems. And although all arthropods have open circulatory systems, the larger crustaceans, such as the lobsters and crabs, have a more developed system of arteries and veins as well as an accessory pumping organ that helps maintain blood pressure. Closed circulatory systems are most highly developed in the vertebrates.

11. Vertebrate circulatory system
Closed system
number of heart chambers differs
What’s the adaptive value of a 4 chamber heart?
4 chamber heart is double pump = separates oxygen-rich & oxygen-poor blood

12. Evolution of vertebrate circulatory system
heart structure & increasing body size
fish
amphibian
reptiles
birds & mammals
2 chamber
3 chamber
3 chamber
4 chamber
A powerful four–chambered heart was an essential adaptation in support of the endothermic way of life characteristic of mammals and birds. Endotherms use about ten times as much energy as equal–sized ectotherms; therefore, their circulatory systems need to deliver about ten times as much fuel and O2 to their tissues (and remove ten times as much CO2 and other wastes). This large traffic of substances is made possible by separate and independent systemic and pulmonary circulations and by large, powerful hearts that pump the necessary volume of blood. Mammals and birds descended from different reptilian ancestors, and their four–chambered hearts evolved independently—an example of convergent evolution.
Why is it an advantage to get big?
Herbivore: can eat more with bigger gut.
lowers predation
(but will push predators to get bigger as well, although no one east elephant s.) V A A A A A A A V V V V V

13. Driving evolution of CV systems
Metabolic rate
endothermy = higher metabolic rate
greater need for energy, fuels, O2, waste removal
more complex circulatory system
more powerful hearts

14. Evolution of 4 chambered heart
Double circulation
increase pressure to systemic (body) circuit
prevents mixing of oxygen-rich & oxygen-poor blood
Powerful 4-chambered heart
essential adaptation to support endothermy (warm-blooded)
endothermic animals need 10x energy
need to deliver 10x fuel & O2
convergent evolution in birds & mammals

15. Vertebrate cardiovascular system
Chambered heart
atria (atrium) = receive blood
ventricles = pump blood out
Blood vessels
arteries = carry blood away from heart
arterioles
veins = return blood to heart
venules
capillaries = point of exchange, thin wall
capillary beds = networks of capillaries
Arteries, veins, and capillaries are the three main kinds of blood vessels, which in the human body have a total length of about 100,000 km.
Notice that arteries and veins are distinguished by the direction in which they carry blood, not by the characteristics of the blood they contain. All arteries carry blood from the heart toward capillaries, and veins return blood to the heart from capillaries. A significant exception is the hepatic portal vein that carries blood from capillary beds in the digestive system to capillary beds in the liver. Blood flowing from the liver passes into the hepatic vein, which conducts blood to the heart.

16. Blood vessels
arteries
arterioles
capillaries
venules
veins

17. Mammalian circulation
Pulmonary circuit
vs.
Systemic circuit

18. Mammalian circulation
2 circulations
pulmonary = lungs
systemic = body
operate simultaneously
4 chambered heart
2 atria = thin-walled collection chambers
2 ventricles = thick-walled pumps
ventricles pump almost in unison
Vessels
veins carry blood to heart
arteries carry blood away from heart

19. Mammalian heart
to neck & head & arms
Coronary arteries

20. Heart valves 4 valves in the heart Atrioventricular (AV) valve
flaps of connective tissue
prevent backflow & keep blood moving in the correct direction
Atrioventricular (AV) valve
between atrium & ventricle
keeps blood from flowing back into atria when ventricles contract
Semilunar valves
between ventricle & arteries
prevent backflow from vessels into ventricles while they are relaxing SL AV AV
The heart sounds heard with a stethoscope are caused by the closing of the valves. (Even without a stethoscope, you can hear these sounds by pressing your ear tightly against the chest of a friend—a close friend.) The sound pattern is “lub–dup, lub–dup, lub–dup.” The first heart sound (“lub”) is created by the recoil of blood against the closed AV valves. The second sound (“dup”) is the recoil of blood against the semilunar valves.

21. Cardiac cycle 1 complete sequence of pumping heart contracts & pumps
heart relaxes & chambers fill
contraction phase
systole
ventricles pumps blood out
relaxation phase
diastole
atria refill with blood

22. Cardiac Cycle How is this reflected in blood pressure measurements?
ventricles fill
How is this reflected in blood pressure measurements?
systolic
________
diastolic
The cardiac cycle. For an adult human at rest with a pulse of about 75 beats per minute, one complete cardiac cycle takes about 0.8 second.
During a relaxation phase (atria and ventricles in diastole), blood returning from the large veins flows into the atria and ventricles.
A brief period of atrial systole then forces all remaining blood out of the atria into the ventricles.
During the remainder of the cycle, ventricular systole pumps blood into the large arteries. Note that 7/8 of the time—all but 0.1 second of the cardiac cycle—the atria are relaxed and are filling with blood returning via the veins.
chambers fill
pump
________
fill
ventricles pump

23. Measurement of blood pressure

24. Lub-dup, lub-dup Heart sounds Heart murmur closing of valves “Lub”
recoil of blood against closed AV valves
“Dup”
recoil of blood against semilunar valves
Heart murmur
defect in valves causes hissing sound when stream of blood squirts backward through valve SL AV AV

25. Form follows function Arteries thicker middle & outer layers
thicker walls provide strength for high pressure pumping of blood
elasticity (elastic recoil) helps maintain blood pressure even when heart relaxes

26. Form follows function Veins thinner-walled
blood travels back to heart at low velocity & pressure
blood flows due to skeletal muscle contractions when we move
squeeze blood in veins
in larger veins one-way valves allow blood to flow only toward heart

27. Form follows function Capillaries lack 2 outer wall layers
very thin walls = only endothelium
enhancing exchange

28. pre-capillary sphincters regulate flow into capillary beds
Blood flow
at any given time, only ~5-10% of body’s capillaries have blood flowing through them
capillaries in brain, heart, kidneys & liver usually filled to capacity
for other sites, blood supply varies over times as blood is needed
after a meal blood supply to digestive tract increases
during strenuous exercise, blood is diverted from digestive tract to skeletal muscles
At any given time, only about 5–10% of the body’s capillaries have blood flowing through them. However, each tissue has many capillaries, so every part of the body is supplied with blood at all times. Capillaries in the brain, heart, kidneys, and liver are usually filled to capacity, but in many other sites, the blood supply varies over time as blood is diverted from one destination to another. After a meal, for instance, blood supply to the digestive tract increases. During strenuous exercise, blood is diverted from the digestive tract and supplied more generously to skeletal muscles and skin. This is one reason that exercising heavily immediately after eating a big meal may cause indigestion.
pre-capillary sphincters regulate flow into capillary beds

29. Exchange across capillary walls
arteriole side
venule side
BP > OP
BP < OP
85% fluid return
15% from lymph
About 85% of the fluid that leaves the blood at the arterial end of a capillary bed reenters from the interstitial fluid at the venous end, and the remaining 15% is eventually returned to the blood by the vessels of the lymphatic system.
Direction of movement of fluid between blood & interstitial fluids depends on blood pressure & osmotic pressure

30. Exchange across capillary walls
Diffusion
bulk flow transport due to fluid pressure
blood pressure within capillary pushes fluid – water & small solutes – through capillary wall
causes net loss of fluid at upstream end of capillary
Endocytosis & exocytosis
larger molecules
Left behind
blood cells & most proteins in blood are too large to pass through, so remain in capillaries
The exchange of substances between the blood and the interstitial fluid that bathes the cells takes place across the thin endothelial walls of the capillaries.
Some substances are carried across endothelial cells in vesicles that form by endocytosis on one side and then release their contents by exocytosis on the other side.
Others simply diffuse between the blood and the interstitial fluid across cells or through the clefts between adjoining cells.
At any given time, only ~5-10% of body’s capillaries have blood flowing through them
capillaries in brain, heart, kidneys & liver are usually filled to capacity,
for other sites, blood supply varies over times as blood is needed
after a meal blood supply to digestive tract increases
during strenuous exercise, blood is diverted from digestive tract to skeletal muscles

31. Lymphatic system Parallel circulatory system transports WBC
defending against infection
collects interstitial fluid & returns to blood
maintains volume & protein concentration of blood
drains into circulatory system near junction of venae cavae with right atrium
transports fats from digestive to circulatory system

32. Lymph System

33. Control of heart Timely delivery of O2 to body’s organs is critical
mechanisms evolved to assure continuity & control of heartbeat
cells of cardiac muscle are “self-excitable”
contract without any signal from nervous system
each cell has its own contraction rhythm
cells are synchronized by the sinoatrial (SA) node, or pacemaker
sets rate & timing of cardiac muscle cell contraction
located in wall of right atrium

34. Electrical signals
Cardiac cycle regulated by electrical impulses that radiate across heart
transmitted to skin = EKG

35. Coordinated contraction
SA node generates electrical impulses
coordinates atrial contraction
impulse delayed by 0.1 sec at AV node
relay point to ventricle
allows atria to empty completely before ventricles contract
specialized muscle fibers conduct signals to apex of heart & throughout ventricular walls
stimulates ventricles to contract from apex toward atria, driving blood into arteries
The impulses generated during the heart cycle produce electrical currents that are conducted through body fluids to the skin.
Here, the currents can be detected by electrodes and recorded as an electrocardiogram (ECG or EKG).

36. Effects on heart rate Physiological cues affect heart rate
nervous system
speed up pacemaker
slow down pacemaker
heart rate is compromise regulated by opposing actions of these 2 sets of nerves
hormones
epinephrine from adrenal glands increases heart rate
body temperature
activity
exercise, etc.
In large land animals, blood pressure is also affected by gravity. In addition to the peripheral resistance, additional pressure is necessary to push blood to the level of the heart.
In a standing human, it takes an extra 27 mm of Hg pressure to move blood from the heart to the brain.
In an organism like a giraffe, this extra force is about 190 mm Hg (for a total of 250 mm Hg).
Special check valves & 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.

37. Blood & blood cells Blood is a mixture of fluid & cells
plasma = fluid (55% of volume)
ions (electrolytes), plasma proteins, nutrients, waste products, gases, hormones
cells (45% of volume)
RBC = erythrocytes
transport gases
WBC = leukocytes
defense
platelets
blood clotting
Dissolved in the plasma are a variety of ions, sometimes referred to as blood electrolytes,
These are important in maintaining osmotic balance of the blood and help buffer the blood.
Also, proper functioning of muscles and nerves depends on the concentrations of key ions in the interstitial fluid, which reflects concentrations in the plasma.

38. Constituents of blood

39. Plasma proteins Synthesized in liver & lymph system fibrinogen
clotting factor
blood plasma with clotting factors removed = serum
albumins
buffer against pH changes, help maintain osmotic balance & blood’s viscosity
globulins
immune response
immunoglobins = antibodies
help combat foreign invaders

40. Cell production Development from stem cells
ribs, vertebrae, breastbone & pelvis
Development from stem cells
Differentiation of blood cells in bone marrow & lymph tisssues
Recently, researchers succeeded in isolating pluripotent stem cells and growing these cells in laboratory cultures. Purified pluripotent stem cells may soon provide an effective treatment for a number of human diseases, including leukemia. A person with leukemia has a cancerous line of the stem cells that produce leukocytes. The cancerous stem cells crowd out cells that make erythrocytes and produce an unusually high number of leukocytes, many of which are abnormal. One experimental treatment for leukemia involves removing pluripotent stem cells from a patient, destroying the bone marrow, and restocking it with noncancerous stem cells. As few as 30 of these cells can completely repopulate the bone marrow.

41. Red blood cells O2 transport Small biconcave disks large surface area
produced in marrow of long bones
lack nuclei & mitochondria
more space for hemoglobin
iron-containing protein that transports O2
generate ATP by anaerobic respiration
last 3-4 months (120 days)
ingested by phagocytic cells in liver & spleen
~3 million RBC destroyed each second
Enucleated RBC
The nucleus is squeezed out of the cell and is ingested by the macrophage.
Cellular Life Expectancy
Red blood cells usually circulate for only about 3 to 4 months and are then destroyed by phagocytic cells in liver & spleen.
Enzymes digest the old cell’s macromolecules, and the monomers are recycled.
Many of the iron atoms derived from hemoglobin in old red blood cells are built into new hemoglobin molecules. But some are reused in digestive bile.
As adults, we make more than 2 million red blood cells in our bone marrow every second to replace those lost through normal attrition.

42. Red blood cell production
5-6 million RBC in 1µL of human blood
5 L of blood in body = 25 trillion RBC
produce ~3 million RBC every second in bone marrow to replace cells lost through attrition
each RBC 250,000 molecules hemoglobin
each Hb molecule carries 4 O2
each RBC carries 1 million O2
A negative–feedback mechanism, sensitive to the amount of O2 reaching the body’s tissues via the blood, controls erythrocyte production. If the tissues do not receive enough O2, the kidney synthesizes and secretes a hormone called erythropoietin (EPO), which stimulates production of erythrocytes. If blood is delivering more O2 than the tissues can use, the level of EPO falls and erythrocyte production slows.
Physicians use synthetic erythropoietin to treat people with health problems such as anemia, a condition of lower–than–normal hemoglobin levels. However, some athletes abuse EPO by injecting themselves with the drug to increase their erythrocyte levels. This practice, known as blood doping, is banned by the International Olympic Committee and other sports federations. In 2002, several athletes competing in the winter Olympics in Salt Lake City tested positive for EPO–like chemicals and as a result were stripped of some of their medals.

43. Hemoglobin
Protein with 4° structure
O2 carrier molecule

44. Blood clotting Cascade reaction self-sealing material
Powerful evolutionary adaptation
emergency repair of circulatory system
prevent excessive blood loss
Inherited defect in any step of the clotting process causes hemophilia, characterized by excessive bleeding from even minor cuts & bruises

45. Cardiovascular disease
Leading cause of death in U.S.
plaques develop in inner wall of arteries, narrowing channel
stroke, heart attack, atherosclerosis, arteriosclerosis, hypertension
tendency inherited, but other risk factors: smoking, lack of exercise, diet rich in fat

46. Cardiovascular health (U.S. 2001)
Heart Disease
696,947
Cancer
557,271
Stroke
162,672
Chronic lower respiratory diseases
124,816
Accidents (unintentional injuries)
106,742
Diabetes
73,249
Influenza/Pneumonia
65,681
Alzheimer's disease
58,866
Nephritis, nephrotic syndrome & nephrosis
40,974
Septicemia
33,865

47. Stroke Fact Sheet