circulation and cardiovascular systems
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Chapter 29Circulation and
Cardiovascular
Systems
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A Circulatory System Helps
Maintain Homeostasis
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29.1 A circulatory system
serves the needs of cells The circulatory system transports oxygen and
nutrients, such as glucose and amino acids, to
the cells It picks up wastes, which are later excreted from the
body by the lungs or kidneys
Both gas exchange and nutrient-for-wasteexchange occur across the walls of the smallest
blood vessels, capillaries No cell in the body of an animal is far from a capillary
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Figure 29.1 Exchanges of gases, nutrients, and wastes takes place
across capillary walls
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29.2 Some invertebrates do not
have a circulatory system Cnidarians, such as hydras, and flatworms, such as
planarians, do not have a circulatory system
In a hydra
The cells are either part of an external layer, or they linethe gastrovascular cavity
In either case, each cell is exposed to water and canindependently exchange gases and get rid of wastes
In a planarian
Trilobed gastrovascular cavity branches throughout thesmall, flattened body
No cell is very far from one of the three digestivebranches, so nutrient molecules can diffuse from cell tocell
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Figure 29.2 Invertebrates with a gastrovascular cavity
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29.3 Other invertebrates have an
open or a closed circulatory system
There are two types of circulatory fluid: Blood - always contained within blood vessels
Hemolymph - a mixture of blood and tissue fluid that flows into a bodycavity
Open circulatory system - found in arthropods and molluscs
Heart pumps hemolymph via vessels into tissue spaces and eventuallyhemolymph drains back to the heart
Slow delivery of oxygen and nutrients is sufficient for a sluggish animal(clam)
A grasshopper has colorless blood and doesn¶t depend on its opencirculatory system to deliver oxygen to its muscles
Tracheae open to outside and take oxygen directly to flight muscles
Closed circulatory system - found in annelids (earthworms) Heart pumps blood, which usually consists of cells and plasma, into a
system of blood vessels and valves prevent the backward flow of blood
Blood moves into capillaries, for exchanges with tissue fluid
Blood then moves from small veins into the dorsal blood vessel (a vein)
This dorsal blood vessel returns blood to the heart for repumping
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Figure 29.3A
Open circulatory
system in agrasshopper
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Figure 29.3B
Closed circulatory
system in an
earthworm
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29.4 All vertebrates have a
closed circulatory system Two different circulatory pathways in vertebrates Single-loop: heart only pumps blood to gills
Two-circuit: systemic circuit - heart pumps blood to all parts of thebody except for the lungs; the pulmonary circuit - heart pumps bloodto the lungs
Fishes - heart has a single atrium and a single ventricle Blood is fully enriched with oxygen when it leaves gills, the respiratory
organ for aquatic organisms
Amphibians and Reptiles - single ventricle pumps blood in thepulmonary circuit to the lungs Also pumps blood in the systemic circuit to the rest of the body
Although both O2 -rich and O2 -poor blood enter the single ventricle, it is
kept separate O2 -poor blood is pumped out of the ventricle to the lungs before O2-rich
blood enters and is pumped to the systemic circuit
Birds and Mammals Two atria and two ventricles in the heart and the complete separation of
the pulmonary and systemic circuits
Right ventricle pumps blood under pressure to the lungs, and the larger left ventricle pumps blood under pressure to the rest of the body 29-10
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Figure 29.4A
Single-loop
circulatorypathway in fishes
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Figure 29.4B Two-
circuit pathway in
amphibians and
most reptiles
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Figure 29.4C Complete
separation of pulmonary
and systemic circuits in
birds, mammals, and
some reptiles
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The Mammalian Cardiovascular
System Consists of the Heartand Blood Vessels
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29.5 The mammalian heart
has four chambers All vertebrates have a closed circulatory system,
called a cardiovascular system because it
consists of a heart (cardio) and a system of
blood vessels (vascular ) Septum divides the heart into left and right sides
Right side of heart pumps O2-poor blood to lungs, and the left
side pumps O2-rich blood to tissues
Each side has two chambers Upper, thin-walled chambers are atria (sing., atrium)
Lower chambers are thick-walled ventricles
Atria receive blood; ventricles pump blood away from heart
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Heart Valves
Atrioventricular valves - between the atria andventricles
Semilunar valves - between the ventricles and their attached vessels
After the blood passes through the right atrioventricular valve, the right ventricle pumps it through the pulmonary semilunar valve into the pulmonary trunk andpulmonary arteries that take it to the lungs Pulmonary veins bring O2-rich blood back to the left atrium
After the blood passes through the left atrioventricular valve, the left ventricle pumps it through the aorticsemilunar valve into the aorta, which takes it to thetissues Heart murmur is often due to leaky atrioventricular valves,
which allow blood to pass back into the atria after they haveclosed 29
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Figure 29.5 Structure of the heart
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29.6 The heartbeat is rhythmic
The average human heart contracts, or beats, about 70 timesa minute, or 2.5 billion times in a lifetime Each heartbeat, called the cardiac cycle, can be divided into
three phases The atria contract (while the ventricles relax)
The ventricles contract (while the atria relax)
All chambers rest
Systole refers to contraction of the heart chambers, and theword diastole refers to relaxation of these chambers
When the heart beats, the familiar ³lub-dub ´ sound is heardas the valves of the heart close Pulse - wave effect that passes down walls of arterial blood
vessels following ventricular systole Rhythmic contraction of heart is due to cardiac conduction
system The SA (sinoatrial) node initiates the heartbeat every 0.85
seconds and is called the cardiac pacemaker
An electrocardiogram (ECG) is a recording of the electrical
changes that occur in the heart during a cardiac cycle29
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Figure 29.6A
The phases of
a heartbeat
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Figure 29.6B
Conduction
system of the
heart
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29.7 Blood vessel structure
is suited to its function Arteries (and arterioles) - carry blood away from the heart
to the capillaries Arteries have a much thick wall with elastic tissue that allows
arteries to expand and accommodate the sudden increase in bloodvolume that results after each heartbeat
Smaller arteries branch into a number of arterioles
Capillaries - permit exchange of material with tissues Extremely narrow (8±10 mm wide) and have thin walls composed
of single layer of epithelium with basement membrane
The thin walls of a capillary facilitate capillary exchange
Veins (and venules) - return blood from the capillaries tothe heart Venules (small veins) - drain blood from the capillaries; then join to
form a vein
Veins often have valves that allow blood to flow only toward theheart when open and prevent the backward flow of blood when
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Figure 29.7A
Types of
blood vessels
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Figure 29.7B Anatomy of a capillary bed
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29.8 Blood vessels form
two circuits in mammals The Pulmonary Circuit
O2-poor blood from all regions of body collects in right atrium andthen passes into right ventricle, which pumps it into the pulmonarytrunk
Pulmonary trunk divides into the right and left pulmonary arteries,
which carry blood to the lungs As blood passes through pulmonary capillaries, carbon dioxide is
given off and oxygen is picked up
O2-rich blood returns to left atrium of through pulmonary veins
The Systemic Circuit Aorta and the venae cavae (sing., vena cava ) are the major blood
vessels To trace the path of blood to any organ in the body, start with the
left ventricle, then go the aorta, then the proper branch of the aorta,the organ, and the vein returning blood to the vena cava, whichenters the right atrium
Portal systems begin and end in capillaries
Hepatic portal system takes blood from the intestines to the liver 29
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Figure 29.8
Path of blood
in the body
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29.9 Blood pressure is essential to
the flow of blood in each circuit Blood pressure is normally measured on the brachial
artery of the upper arm A blood pressure reading consists of two numbers that represent
systolic and diastolic pressures, respectively Systolic pressure results from blood being forced into the arteries
during ventricular systole Diastolic pressure is the pressure in the arteries during ventricular
diastole
Blood pressure accounts for the flow of blood from theheart to the capillaries As blood flows from the aorta into the various arteries and
arterioles, blood pressure falls Blood pressure in the veins is low and cannot move blood back
to the heart, especially from the limbs
Venous return depends upon three factors: Skeletal muscle contraction, presence of valves in veins, and
respiratory movements29-26
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Figure 29.9A Velocity and blood pressure are related to the cross-
sectional area of the blood vessels
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Figure 29.9B How a valve affects the movement of blood in a vein
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APPLYING THE CONCEPTS²HOW BIOLOG Y IMPACTS OUR LIVES
29.10 Blood vessel deterioration
results in cardiovascular disease In U.S., about 20% of population suffers from
hypertension, high blood pressure Heredity and lifestyle contribute to hypertension
Hypertension is often seen in individuals who have atherosclerosis,which occurs when plaque protrudes into the lumen of a vessel andinterferes with the flow of blood
Plaque can cause a clot to form on the irregular arterial wall As long as the clot remains stationary, it is called a thrombus, but
when and if it dislodges and moves along with the blood, it is calledan embolus
A stroke often occurs when a small cranial arteriole burstsor is blocked by an embolus
Heart attack - when a coronary artery is completelyblocked, a portion of the heart muscle dies due to lack of oxygen
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APPLYING THE CONCEPTS²HOW BIOLOG Y IMPACTS OUR LIVES
29.11 Cardiovascular disease
can often be prevented The Don¶ts Smoking - When a person smokes, nicotine enters the
bloodstream and causes the arterioles to constrict and the bloodpressure to rise
Drug Abuse - Stimulants, such as cocaine and amphetamines,
can cause an irregular heartbeat and lead to heart attacks andstrokes
Weight Gain - in persons who are more than 20% above therecommended weight more tissues require servicing, and theheart sends the extra blood out under greater pressure
The Dos
HealthyD
iet - Physicians advise people to replace harmfulsaturated fats and trans fats with healthier ones, such asmonounsaturated fats (olive and canola oils) andpolyunsaturated fats (corn, safflower, and soybean oils)
Cholesterol Profile - Starting at age 20, all adults are advised tohave their cholesterol levels tested at least every five years
Exercise - People who exercise are less apt to have
cardiovascular disease29-30
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Figure 29.11 Plaque buildup in a coronary artery
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Blood Has Vital Functions
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29.12 Blood is a liquid tissue
Blood¶s numerous functions include the following: Transports substances to and from the capillaries, where
exchanges with tissue fluid take place
Helps defend the body against invasion by pathogens
(e.g., disease-causing viruses and bacteria) Helps regulate body temperature
Forms clots, preventing a potentially life-threatening loss of blood
Blood has two main portions Plasma - composed mostly of water (90±92%) and
proteins (7±8%) Also contains smaller quantities of many types of molecules,
including nutrients, wastes, and salts
Formed elements - red blood cells, white blood cells, andplatelets
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Types of Blood Cells
Red blood cells (erythrocytes) - transport oxygen usinghemoglobin, which contains iron, and combines looselywith oxygen
White blood cells (leukocytes) - help fight infections
Neutrophils, which are amoeboid, squeeze through the capillarywall and enter the tissue fluid, where they engulf foreign material
Monocytes appear and are transformed into macrophages,large phagocytizing cells that release white blood cell growthfactors
Lymphocytes play important role in fighting infection T cells attack infected cells that contain viruses
B cells - produce antibodies Each B cell produces just one type of antibody, which is specific for one
type of antigen
An antigen, which is most often a protein but sometimes apolysaccharide, causes the body to produce an antibody to combinewith the antigen
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Figure 29.12 Composition of blood
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29.13 Blood clotting
involves platelets Platelets result from fragmentation of large cells in the bone marrow
called megakaryocytes Blood contains 150,000±300,000 platelets per mm3
When a blood vessel in the body is damaged platelets clump at the siteof the puncture and partially seal the leak
Platelets and the injured tissues release a clotting factor called prothrombinactivator that converts prothrombin to thrombin
Thrombin acts as an enzyme that severs two short amino acid chains fromeach fibrinogen molecule
These activated fragments then join forming long threads of fibrin that windaround the platelet plug in the damaged area of the blood vessel andprovide the framework for the clot
If blood is allowed to clot in a test tube, a yellowish fluid develops abovethe clotted material, called serum Contains all the components of plasma, except fibrinogen
Hemophilia is a well-known, inherited clotting disorder Due to the absence of a particular clotting factor, the slightest bump can
cause internal bleeding29-36
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Figure 29.13 Blood clotting
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APPLYING THE CONCEPTS²HOW SCIENCE PROGRESSES
29.14 Adult stem cells
include blood stem cells A stem cell is a cell that is capable of becoming different
types of cells While embryonic stem cells possess the ability to become
virtually any cell type, adult stem cells are not quite as versatile
because they can become only certain other types of cell
Adult stem cells have been identified in many tissues,including the liver, skin, muscle, and even within thebrain, but the richest source is in the red bone marrow Adult stem cells from bone marrow are used to treat many white
blood cell and immune system disorders, including leukemia,certain blood cancers, and anemia
Like any organ transplant, a bone marrow transplant poses therisk of rejection
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Figure 29.14 Hematopoietic cells (adult stem cells in red bone
marrow) produce cells that become the various types of blood
cells.
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29.15 Capillary exchange
is vital to cells Capillary exchange occurs between a systemic capillary and
tissue fluid, the fluid between the body¶s cells Two forces control movement of fluid through capillary wall
Blood pressure, which tends to cause water to move out of a capillary intothe tissue fluid
Osmotic pressure, which tends to cause water to move from the tissue
fluid into a capillary Red blood cells and almost all plasma proteins remain in the
capillaries Fluid and other substances that leave a capillary contribute to the
tissue fluid
At the venous end of a capillary, blood pressure has fallen so
osmotic pressure is greater than blood pressure, and water tends to move into the capillary Some excess tissue fluid is always collected by the lymphatic
capillaries
Tissue fluid contained within lymphatic vessels is called lymph Lymph is returned to the systemic venous blood when the major lymphatic
vessels enter the subclavian veins in the shoulder region29-40
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Figure 29.15A Capillary exchange
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Figure 29.15B A lymphatic capillary bed lies near a blood capillary
bed
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29.16 Blood types must be
matched for transfusions
ABO System
Presence or absence of type A and type B
antigens on red blood cells determines aperson¶s blood type
In the ABO system, there are four types of blood:
A, B, AB, and O
Type O blood has no antigens on the red blood cells andis sometimes called the universal donor
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Rh System and
Erythroblastosis Fetalis Rh System
Another important antigen in matching blood types is theRh factor
85% of the U.S. population have this particular antigen on
red blood cells and are called Rh-positive Erythroblastosis Fetalis
During pregnancy, if the mother is Rh-negative and thefather is Rh-positive, the child may be Rh-positive
Rh-positive red blood cells may begin leaking across theplacenta into the mother¶s cardiovascular system, sinceplacental tissues normally break down before and at birth
The mother produces anti-Rh antibodies, which may crossthe placenta and destroy the child¶s red blood cells duringa subsequent pregnancy
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Figure 29.16A No agglutination occurs when the donor and
recipient have the same type blood
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Figure 29.16B Agglutination occurs because blood typeB has
anti-A antibodies in the plasma
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Connecting the Concepts:
Chapter 29 It is possible to relate the type of cardiovascular system
to the lifestyle of an animal Some small, aquatic animals have no cardiovascular system²
external water passing in and out of a gastrovascular cavity issufficient to meet the needs of their cells
Grasshoppers have an open circulatory system, but they utilizetracheae to deliver oxygen directly to their muscles
We traced the evolution of the two-circuit circulatorypathway in vertebrates and saw that a two-circuitpathway allows blood to pass to the lungs and to thetissues under pressure This is particularly useful in birds and mammals, which maintain
a warm body and an active way of life
Body fluids make ideal culture media for the growth of infectiousparasites, and these fluids often have ways to ward off aninvasion. You already know that white blood cells are involved inthese endeavors
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