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29 CIRCULATION
CHAPTER OUTLINE
LEARNING OBJECTIVES
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Describe the differences between open and closed circulatory systems.
List the functions provided by the circulatory system.
Describe the characteristics of arteries and arterioles.
Explain how capillaries are designed for exchange of substances between the blood and tissue cells.
List the features of veins.
Know the functions of the lymphatic system.
Discuss the components of blood and their functions.
List the functions of plasma, and explain how plasma helps the blood retain water.
Describe the circulatory systems of fish, reptiles, and amphibians.
Trace the path of blood flow through the mammalian and bird heart.
Describe how a wave of depolarization travels through the heart.
Explain how the performance of the heart can be monitored.
List several diseases of the circulatory system.
Circulation (p. 556)
29.1
29.2
Open and Closed Circulatory Systems (p. 556; Figs. 29.1, 29.2)
A. Circulatory systems may be open or closed.
B. In open circulatory systems, there is no distinction between the circulating fluid (blood) and
the extracellular fluid of the body tissues.
C. In closed circulatory systems, the circulating fluid (blood) is enclosed within blood vessels
that transport blood to and from a muscular heart.
D. Arteries carry blood away from the heart, exchange of gases and nutrients occurs through
thin-walled tiny capillaries, and veins return blood to the heart.
E. As blood plasma passes through capillaries, hydrostatic pressure forces fluid through the
capillary into the tissues cells; lymph vessels drain away excess tissue fluid.
F. The Functions of Vertebrate Circulatory Systems
1. The circulatory system transports gases and nutrients to body cells, and removes wastes
from cells.
2. The cardiovascular system transports hormones and functions in temperature regulation.
3. The circulatory system protects against injury and foreign microbes or toxins introduced
into the body.
Architecture of the Vertebrate Circulatory System (p. 558; Figs. 29.3, 29.4, 29.5, 29.6, 29.7)
A. The human circulatory system is made up of a muscular heart that provides the push to get the
blood flowing, a network of blood vessels to carry the blood, and the blood itself.
B. The circulatory system is often referred to as the cardiovascular system.
C. Blood flows away from the heart in muscular, thick-walled arteries.
D. The further the blood flows from the heart, the smaller the arteries become until they reach
the size of arterioles that lead to microscopic capillaries.
E. Through the walls of capillaries, the exchange of nutrients and gases between the blood and
the tissues occurs.
F. Capillaries merge to form venules that eventually increase in size to become veins as blood is
returned to the heart.
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29.3
29.4
G. Arteries: Highways from the Heart
1. Arterial walls have three layers: the innermost layer is smooth endothelium against which
the blood must flow; next is a layer of muscle; and the outermost layer is connective
tissue.
2. Arteries are both flexible and strong in order to carry high-pressure blood to all portions
of the body.
3. Arterioles are much smaller than arteries, and their muscular layer is greatly reduced.
4. Muscle cells in arteriole walls are in contact with the nervous system which can tell them
when to contract, limiting blood flow to certain areas.
H. Capillaries: Where Exchange Takes Place
1. Through the walls of capillaries, exchanges take place.
2. Capillaries are one cell thick with very narrow diameters, just wide enough to allow red
blood cells to pass through; this design ensures that the gases transported in the blood are
carried close to the tissue cells that need them.
I. Veins: Returning Blood to the Heart
1. Veins return blood to the heart.
2. They have the same three layers as arteries with less muscle.
3. Veins have valves inside that prevent the backflow of low-pressure blood as it returns to
the heart.
The Lymphatic System: Recovering Lost Fluid (p. 561; Figs. 29.8, 29.9)
A. When fluids are forced out of the blood through capillary walls, excess fluid remains in the
tissues.
B. Another system of vessels, the lymphatic system, drains off excess tissue fluid and eventually
returns it to the bloodstream.
C. Lymphatic capillaries are blind-end tubes with openings that permit tissue fluid, damaged
cells, debris, and bacteria to enter them.
D. Tissue fluid is called lymph once it is inside lymphatic vessels.
E. As lymph travels through the lymphatic vessels, it is filtered through lymph nodes that house
macrophages and lymphocytes, ready to attack any pathogens present.
F. Lymph also functions to return proteins to the bloodstream, and transport fats from the
intestines.
Blood (p. 562; Figs. 29.10, 29.11)
A. Blood Plasma: The Blood’s Fluid
1. Blood flows through the vessels of the circulatory system, carrying with it oxygen and
nutrients.
2. The fluid portion of the blood is called the plasma and it carries with it metabolites and
waste products, salts and ions, and plasma proteins.
3. These plasma proteins, such as serum albumin, help to maintain the osmotic pressure of
the blood so it does not lose too much water to the tissues.
4. Starving people often show edema as their blood gives up its water.
5. In the latter stages of starvation, even the plasma proteins are used as a source of
nutrition.
B. Blood Cells: Cells That Circulate Through the Body
1. Three types of cells make up almost half the volume of blood.
2. Erythrocytes, also known as red blood cells, carry oxygen to the cells of the body.
3. A protein called hemoglobin takes up most of the space inside a red blood cell.
4. Hemoglobin binds oxygen in areas where oxygen is plentiful, such as in the lungs, and
gives it up in tissues where oxygen is needed.
5. White blood cells, or leukocytes, help in the control of disease.
6. Some types of leukocytes are able to migrate out into tissues to attack pathogens.
7. The third type of cell exists as cell fragments; these platelets play a role in stopping
blood loss.
8. Along with platelet plugs, a plasma protein turns into fibrin, a stringy mesh of protein
fibers that cause blood clotting.
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Evolution of Vertebrate Circulatory Systems (p. 564)
29.5
29.6
29.7
Fish Circulation (p. 564; Fig. 29.12)
A. A fish heart is a modified tube consisting of a series of four chambers.
B. The first two chambers, the sinus venosus and atrium, are the collecting chambers.
C. The second two chambers, the ventricle and the conus arteriosus, are pumping chambers.
D. Blood enters the heart at the sinus venosus, where the wavelike contraction of the heart
begins.
Amphibian and Reptile Circulation (p. 565; Fig. 29.13)
A. Amphibians and reptiles overcame the problems of living on land in part with the evolution
of the lung, and a simultaneous change in circulation.
B. Amphibians and reptiles thus have a pulmonary and a systemic circulation that deliver blood
to the lungs and to the rest of the body, respectively.
Mammalian and Bird Circulation (p. 566; Figs. 29.14, 29.15, 29.16)
A. Mammals, birds, and crocodiles have a four-chambered heart that is two separate pumps
working together.
B. The increased efficiency of this double circulatory system allowed for endothermy and the
subsequent higher metabolic rate.
C. Circulation Through the Heart
1. Humans have four-chambered hearts like all mammals and birds.
2. One side of the heart pumps blood to the lungs to pick up oxygen, while the other side
distributes oxygenated blood to the rest of the body.
3. Oxygen-rich blood returns from the lungs through pulmonary veins to the left atrium of
the heart and flows mostly passively through the mitral valve into the left ventricle.
4. The thick-walled left ventricle contracts, sending oxygenated blood through a large
artery called the aorta and out to the body.
5. Backflow of blood from the aorta is prevented by an aortic valve.
6. Blood travels through the body's arteries and arterioles to capillaries.
7. Blood is returned to the heart through venules and veins that merge to form the vena
cava, which drains into the right atrium.
8. Blood flows from the right atrium through the tricuspid valve to the right ventricle.
9. The right ventricle contracts, pushing blood through the pulmonary valve into pulmonary
arteries that lead to the lungs.
D. How the Heart Contracts
1. The contraction of heart muscle is carefully controlled.
2. First the atria contract together, then there is a pause, then the ventricles contract
together.
3. A longer pause occurs before the cycle resumes.
4. Contraction is initiated by a cluster of self-exciting cells called the sinoatrial (SA) node
located in the upper wall of the right atrium.
5. A wave of depolarization is initiated there and rapidly spreads throughout the atria,
followed by their contraction.
6. The depolarization wave travels to the ventricles through an atrioventricular (AV) node
and rapidly spreads from there to Purkinje fibers and to the ventricles, and the ventricles
contract.
E. Monitoring the Heart’s Performance
1. The performance of the heart can be monitored by several methods.
2. Listening to its sounds using a stethoscope can determine the presence of an
incompletely closing valve, a condition called a murmur.
3. Arterial blood pressure can be measured.
4. The greatest pressure, systolic pressure, occurs when the ventricles contract.
5. When the atria are filling, pressure is at its lowest in the arteries, and is called diastolic
pressure.
6. The electrical impulses of the heart can also be measured using a recording instrument
that produces an electrocardiogram.
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29.8
Cardiovascular Diseases (p. 569; Fig. 29.17)
A. Humans are subject to a variety of cardiovascular diseases, many of them associated with the
accumulation of fatty materials on the inner surfaces of arteries.
B. Heart attacks result from an insufficient supply of oxygen to the heart muscle.
C. Angina pectoris is chest pain that occurs because of the same reasons as those that cause
heart attack, although the condition is less severe.
D. Strokes are caused by an interference with the blood supply to the brain.
E. Atherosclerosis is an accumulation of fatty materials and cellular debris within the lumen of
arteries that may block the flow of blood through the artery.
F. Arteriosclerosis is hardening of the arteries and occurs when calcium is deposited in arterial
walls.
KEY TERMS
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open circulatory system (p. 556) In an open circulatory system, there is no distinction between the
blood and the interstitial fluid or lymph.
closed circulatory system (p. 556) In a closed circulatory system, the blood is enclosed within vessels
that transport it to and from a heart.
arteries (p. 559) Arteries carry high-pressure blood away from the heart.
capillaries (p. 559) It is through these tiniest of the blood vessels that gas and nutrient exchange with
tissue cells occurs.
veins (p. 560) Veins collect circulating blood and return it to the heart.
lymphatic system (p. 561) The lymphatic system consists of a system of vessels, similar in structure to
veins, that drain excess tissue fluid. Portions of the lymphatic system house cells of immunity.
plasma (p. 562) The fluid portion of blood.
erythrocytes (p. 562) Red blood cells; carry oxygen in association with hemoglobin.
leukocytes (p. 563) White blood cells; fight against infection.
platelets (p. 563) Fragments of cells that function in hemostasis.
atrium (p. 564) The collecting chambers of the heart.
ventricle (p. 564) The pumping chambers of the heart.
pulmonary circulation (p. 565) The system of blood vessels leading from the heart to the lungs and
back.
systemic circulation (p. 565) The system of blood vessels leading from the heart to the body and back.
sinoatrial (SA) node (p. 567) The pacemaker of the heart.
atherosclerosis (p. 569) This is a medical condition in which the inner walls of arteries become
clogged with fatty deposits, elevating systolic blood pressure.
LECTURE SUGGESTIONS AND ENRICHMENT TIPS
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Heart Structure. As a demonstration, dissect a fresh beef or pork heart in class. You can frequently
obtain fresh materials from butchers at little or no cost. Ask them to leave the major blood vessels
intact. Show students the exterior features of the heart, including coronary vessels, auricles, and the
major arteries and veins leading to and from the heart. Then cut the heart in half lengthwise. Show
students the chordae tendinae (heart strings), atrioventricular valves, and aortic semilunar valve.
Discuss the thickness of the muscle in the walls of individual heart chambers as it relates to the
function of the chamber.
Factors That Influence Blood Pressure. A variety of factors influence blood pressure. Certainly as
individuals are more active, their blood pressure increases. As they return to rest, or go to sleep, their
blood pressure falls. Under stress, peripheral blood vessels constrict, increasing blood pressure. The
factors that influence blood pressure are heart action, blood volume, the thickness or viscosity of blood,
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and its resistance to flow. Divide your class into groups. Show students from each group how to
measure arterial blood pressure using sphygmomanometers. Also show them how to measure heart rate
in beats per minute. Have a volunteer or two from each group have their blood pressure and heart rate
measured. Then ask these volunteers to run in place or perform jumping jacks until they feel slightly
winded. Measure blood pressure and heart rate once again. Tabulate results on the chalkboard.
CRITICAL THINKING QUESTION
1.
Explain how the structure of the heart helps to reduce blood pressure in alveolar capillaries, thus
helping to keep lung tissue from filling with fluid.
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